SDDM February 2015

STRUCTURES DESIGN AND DETAILING MANUAL

FEBRUARY 2015

UDOT Structures Design and Detailing Manual February 2015

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FOREWORD

The UDOT Structures Design and Detailing Manual (SDDM) has been developed to provide the Structures Design Division staff and consultants with UDOT policies, procedures, practices and technical criteria. The SDDM consists of the written manual, working standards, structures design drawings, sample sheets, checklists and design memoranda. The information presented in the SDDM is expected to help fulfill UDOT’s mission of providing a safe and efficient transportation system. The SDDM has two major segments: • Administrative. The chapters present in house responsibilities, requirements,

procedures and practices. • Technical. The chapters provide structural engineers with the Department’s typical

structural design criteria, guidelines, policies and practices on all structural elements. Structural engineers are expected to meet all criteria presented in the SDDM. Exercise sound engineering judgment when conditions arise that are not specifically covered in the SDDM. The SDDM has been prepared based on the 6th Edition of the AASHTO LRFD Bridge Design Specifications.

ACKNOWLEDGEMENTS The Structures Design and Detailing Manual was developed by the Structures Design Division with assistance from the consulting firms of Roy Jorgensen Associates, Inc., and H. Boyle Engineering, Inc., and Professor Dennis Mertz of the University of Delaware. The SDDM Review Committee included: Carmen Swanwick Chief Structural Engineer Cheryl Hersh Simmons Structures Design Manager Joshua Sletten Bridge Management Engineer

In addition, representatives from the Structures Design Division and consultants provided review and comment on the SDDM and the structures design drawings, working standard sheets and sample sheets.


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REVISION PROCESS

The SDDM provides current policies and procedures for use in structural design projects. To ensure that the SDDM remains up to date and appropriately reflects changes in UDOT’s needs and requirements, the contents will be updated on a periodic basis.

The Structures Design Division is responsible for evaluating changes in the structural engineering literature (e.g., updates to the AASHTO LRFD Specifications, the issuance of new relevant publications, revisions to federal regulations) and for ensuring that the changes are appropriately addressed through the issuance of revisions to the SDDM. It is important that users of the SDDM inform UDOT of any inconsistencies, errors, need for clarification or new ideas to support the goal of providing the best and most up to date information practical. Send comments and proposed revisions to the Structures Design Manager using the Structural Review Comment Resolution Form.

To propose a revision to the Structures Design and Detailing Manual, complete and return the Structural Review Comment Resolution Form to:

Structures Design Manager Utah Department of Transportation 4501 South 2700 West PO Box 148470 Salt Lake City, UT 84114-8470 E-mail: [email protected] (include “Structures Design and Detailing Manual” in subject line)

Ensure that the submission addresses the following (attach additional sheets as necessary): • Applicable SDDM section number(s) • Proposed revision • Justification for revision


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TABLE OF CONTENTS Chapter 1 ........................ ORGANIZATION, TERMINOLOGY AND REFERENCE DOCUMENTS Chapter 2 ................. ADMINISTRATIVE GUIDELINES, REQUIREMENTS AND PROCEDURES Chapter 3 ...................................................................... DESIGN MEMORANDA AND REPORTS Chapter 4 ................ CONTRACT DOCUMENTS, PLANS, SPECIFICATIONS AND ESTIMATES Chapter 5 .......................................................................................................... DESIGN QUALITY Chapter 6 ......................................................................................... CONSTRUCTION SUPPORT Chapter 7 .................................................................................................................... RESERVED Chapter 8 .................................................................................................................... RESERVED Chapter 9 .................................................................................................................... RESERVED Chapter 10 ............................................................................................... PRELIMINARY DESIGN Chapter 11 .................................................................................... LOADS AND LOAD FACTORS Chapter 12 ........................................................... STRUCTURAL ANALYSIS AND EVALUATION Chapter 13 ....................................................................................................................... SEISMIC Chapter 14 ........................................................................................ CONCRETE STRUCTURES Chapter 15 ................................................................................................. STEEL STRUCTURES Chapter 16 ........................................................................................................... BRIDGE DECKS Chapter 17 ............................................................................................................ FOUNDATIONS Chapter 18 ...................................................................................................... SUBSTRUCTURES Chapter 19 ....................................................................... EXPANSION JOINTS AND BEARINGS Chapter 20 ............................................................... ACCELERATED BRIDGE CONSTRUCTION Chapter 21 .......................... BRIDGE PRESERVATION AND REHABILITATION OR WIDENING Chapter 22 .............................................................................. MISCELLANEOUS STRUCTURES


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FEBRUARY 2015

ORGANIZATION, TERMINOLOGYAND REFERENCE DOCUMENTS



Organization, Terminology and Reference Documents 1-i

TABLE OF CONTENTS

1.1 RESPONSIBILITIES .................................................................................................... 1-1

1.1.1 Division Vision/Mission ..................................................................................... 1-2 1.1.1.1 Vision .............................................................................................. 1-2 1.1.1.2 Mission ............................................................................................ 1-2

1.1.2 Chief Structural Engineer ................................................................................. 1-2 1.1.3 Bridge Management Division............................................................................ 1-3 1.1.4 Project Delivery Division ................................................................................... 1-3

1.1.4.1 Structures Design Division .............................................................. 1-3 1.1.4.2 Geotechnical Design Division ......................................................... 1-6

1.2 DEFINITIONS AND ACRONYMS ................................................................................ 1-8

1.2.1 Definitions ......................................................................................................... 1-8 1.2.2 Acronyms ......................................................................................................... 1-16

1.3 STRUCTURAL DESIGN LITERATURE (NATIONAL) ................................................ 1-20

1.3.1 AASHTO LRFD Bridge Design Specifications.................................................. 1-20

1.3.1.1 Description ...................................................................................... 1-20 1.3.1.2 Application ...................................................................................... 1-21

1.3.2 AASHTO Guide Specifications for LRFD Seismic Bridge Design .................... 1-21


1.3.3 AASHTO Standard Specifications for Highway Bridges ................................... 1-22


1.3.4 FHWA Seismic Retrofitting Manual for Highway Bridges ................................. 1-22


1.3.5 AASHTO Guide Specifications for Seismic Isolation Design ............................ 1-23


1.3.6 AASHTO/American Welding Society D1.5M/D1.5 Bridge Welding Code ......... 1-23


1-ii Organization, Terminology and Reference Documents


1.3.7 AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges .......... 1-23


1.3.8 AASHTO Guide Specifications for Distribution of Loads for Highway Bridges . 1-24


1.3.9 AASHTO LRFD Bridge Construction Specifications ......................................... 1-24


1.3.10 AASHTO Guide Specifications for Bridge Temporary Works ........................... 1-24


1.3.11 AASHTO LRFD Movable Highway Bridge Design Specifications .................... 1-25


1.3.12 AASHTO Standard Specifications for Structural Supports for Highway

Signs, Luminaires and Traffic Signals .............................................................. 1-25 1.3.12.1 Description ...................................................................................... 1-25 1.3.12.2 Application ...................................................................................... 1-25

1.3.13 AASHTO Guide Specification and Commentary for Vessel Collision

Design of Highway Bridges .............................................................................. 1-25 1.3.13.1 Description ...................................................................................... 1-25 1.3.13.2 Application ...................................................................................... 1-26

1.3.14 American Institute of Steel Construction Steel Construction Manual ............... 1-26


1.3.15 American Railway Engineering and Maintenance of Way Association

Manual for Railway Engineering ....................................................................... 1-26 1.3.15.1 Description ...................................................................................... 1-26 1.3.15.2 Application ...................................................................................... 1-26

1.3.16 Additional Structural Design Publications ......................................................... 1-27


Organization, Terminology and Reference Documents 1-iii

1.4 UDOT DOCUMENTS ................................................................................................... 1-28 1.4.1 UDOT Geotechnical Manual of Instruction ....................................................... 1-28 1.4.2 UDOT Roadway Design Manual of Instruction ................................................. 1-29 1.4.3 UDOT Roadway Drainage Manual of Instruction ............................................. 1-29 1.4.4 UDOT Environmental Process Manual of Instruction ....................................... 1-29 1.4.5 Specifications ................................................................................................... 1-30 1.4.6 Materials ........................................................................................................... 1-30 1.4.7 UDOT Steel and Concrete Construction Manual .............................................. 1-30 1.4.8 UDOT Construction Manual of Instruction ........................................................ 1-31

LIST OF FIGURES

Figure 1.1 — ORGANIZATION CHART ................................................................................ 1-1


1-iv Organization, Terminology and Reference Documents


Organization, Terminology and Reference Documents 1-1

Chapter 1 ORGANIZATION, TERMINOLOGY AND REFERENCE DOCUMENTS

This chapter presents an overview of the responsibilities of the Structures Division, and presents acronyms and definitions of key words commonly used throughout the UDOT Structures Design and Detailing Manual (SDDM).

1.1 RESPONSIBILITIES

In general, the Structures Division focuses on project delivery and the responsible management of the in service bridge inventory. Figure 1.1 presents the organization of the Structures Division.

Figure 1.1 — ORGANIZATION CHART


1-2 Organization, Terminology and Reference Documents

1.1.1 Division Vision/Mission

1.1.1.1 Vision

The Project Delivery Division produces safe, high quality and economical structural designs for preservation, rehabilitation and replacement projects through efficient, timely communication, innovation, technical expertise and professionalism.

The Bridge Management Division provides data to support structure project prioritization for preservation, rehabilitation and replacement, and emergency services to ensure the safety of the traveling public.

1.1.1.2 Mission

The Project Delivery Division provides structural engineering services, manages structure design and construction, and establishes and maintains structural design criteria and standards to ensure a safe, economical and reliable transportation system.

The Bridge Management Division inspects, monitors, reports and effectively manages the structure inventory for a safe, reliable transportation system.

1.1.2 Chief Structural Engineer

The Chief Structural Engineer establishes overall Department practices, and supervises the activities, schedules, quality, deliverables, etc., of the Bridge Management Division and Project Delivery Division. The responsibilities of the Chief Structural Engineer are to:

• Report to the Director on the Structures Division’s progress in meeting the Department’s Strategic Direction and Performance Measures

• Develop work programs for bridge projects for inclusion in the Statewide Transportation Improvement Program (STIP) of projects

• Ensure compliance with all federal polices, regulations, requirements, etc., related to structures and geotechnical engineering

• Monitor and evaluate the Division’s bridge inspection program, load rating program and emergency response plan

• Coordinate with the Systems Planning and Programming Division on the STIP process and Bridge Management System (BMS)

• Chair the Bridge Management Team (BMT) to develop the bridge program of projects for the in service bridge inventory

• Monitor and evaluate the Division’s coordination with the Regions to perform routine, safety and preservation maintenance activities

• Monitor and evaluate the Division’s coordination with the local governments on structure related activities (e.g., bridge inspection, project delivery, emergency maintenance)

• Participate in professional organizations related to bridge design, including the American Association of State Highway and Transportation Officials (AASHTO) and Transportation Research Board (TRB), to represent UDOT’s interests and concerns



• Oversee the development of: ○ New and revised structure drawings (sample sheets, working standards,

structure design drawings) ○ Revisions to the SDDM ○ Structural specifications (in a participation role) for the UDOT Standard

Specifications • Represent the Department in all litigation related to structural issues • Determine the Division’s appropriate participation in public hearings and public

informational meetings for projects with significant structural designs • Remain abreast of the key issues on individual bridge projects • Determine the Division’s course of action for any special studies, reports, etc., upon

request from the Director’s office, Federal Highway Administration (FHWA), AASHTO, etc.

• Serve as the Division’s focal point for coordination with FHWA, the Director’s office, etc. • Participate in the consultant selection process

1.1.3 Bridge Management Division

The UDOT Bridge Management Manual (BMM) presents the responsibilities of the Bridge Management Division.

1.1.4 Project Delivery Division

The Project Delivery Division is the Structures Division’s focal point for the preparation of all in house structural designs. The Project Delivery Division has the day to day responsibility to develop structural projects from project inception to advertisement. The Project Delivery Division performs the designs, conducts structural analyses of the proposed structures, prepares the bridge plans and computes quantities and cost estimates for bridge projects.

The Project Delivery Division also supervises all designs performed by consultants for structures and geotechnical work and enforces the QC/QA Procedures in Chapter 5.

1.1.4.1 Structures Design Division

The Structures Design Division is responsible for developing structure design criteria for all structures within projects.

1.1.4.1.1 Structures Design Manager

The Structures Design Manager is responsible for the overall administrative/management/ engineering activities associated with design activities. The Structures Design Manager establishes overall Department structural policies, practices and criteria, and manages the Structures Design Division’s coordination with other divisions.



The responsibilities of the Structures Design Manager are to:

• Manage the development of all in house structural designs • Monitor consultant designed projects, and review and approve project deliverables • Develop and revise all Structures Design Division forms used in project development • Coordinate with the Project Development Division to update, when needed, the Project

Delivery Network • Update and enforce the Structures Division Quality Control/Quality Assurance (QC/QA)

procedures • Review and approve all QC/QA documents • Review and approve all Division reports generated during project development • Serve on the BMT to develop the bridge program of projects for the in service bridge

inventory • Assign the structures design lead, designers and drafters to advance the project through

the project delivery process • Coordinate with the Bridge Management Division staff to update the bridge record for all

projects • Coordinate with the Regions during project development • Approve any deviations from structural design policies, practices or criteria • Approve manhour and cost estimates for in house and consultant designs • Provide technical support and approval for structural designs for projects on local

government facilities that are funded by state and/or federal funds • Sign structural design plans before advertisement • Manage the Division's manuals, specifications, special provisions and drawings • Review and approve permit projects • Participate in structure related research projects • Manage the Division’s activities in the field construction of structural elements, including:

○ Reviewing and approving construction working drawings ○ Performing periodic field construction inspections ○ Reviewing and commenting on construction change orders when requested

Refer to Section 6.2.2.1 for the Structures Design Manager responsibilities during construction.

1.1.4.1.2 Structures Project Engineer

The Structures Project Engineer coordinates with the Project Manager on projects with structures when the design is performed by consultants. The responsibilities of the Structures Project Engineer are to:

• Ensure that project development meets the requirements of the Project Delivery Network • Work with the Structures Design Team to meet all project requirements related to project

development, schedules, budgets, QC/QA, structural design, permits, coordination with other divisions, etc.

• Serve as the interface between the Project Manager, Structures Design Manager and Structures Design Team during project development



• Provide technical support for structural designs for bridge projects on local government facilities that are funded by state and/or federal dollars

• Perform and manage for design and oversight reviews • Participate in consultant selection process Refer to Section 6.2.2.3 for the Structures Project Engineer responsibilities during construction.

1.1.4.1.3 Structures Construction Engineer

The Structures Construction Engineer serves as the Structures Division’s focal point to ensure that the Division fulfills the responsibilities during the construction of structural elements (e.g., working drawings, construction inspections, change orders, value engineering (VE) proposals). The responsibilities of the Structures Construction Engineer are to: • Coordinate with the Bridge Management Division to ensure that all construction related

data is recorded in the bridge record • Review and comment on special provisions • Coordinate with the Construction Division and Region construction staff during project

development and construction • Review construction submittals • Coordinate with the Standards and Specifications Section to make revisions to the

UDOT Standard Specifications for structural items • Support maintenance • Participate as a panel member on the new product evaluation committee • Perform peer reviews of atypical designs • Perform constructability reviews as requested • Provide project specific training and develop construction checklists as requested • Attend District Engineers and Materials meetings Refer to Section 6.2.2.2 for the Structures Construction Engineer responsibilities during construction.

1.1.4.1.4 Structures Design Team

The Structures Design Team includes the:

• Lead Design Engineer • Senior Design Engineer • Design Engineer • Engineering Technician The specific responsibilities of the Structures Design Team are to prepare in house structural designs for highway bridge projects to:



• Determine applicable loads to the bridge • Design all structural elements (e.g., superstructures, substructures, foundations) based

on policies, practices, criteria, etc. • Design all structural elements to meet the Department’s seismic performance criteria • Coordinate with other divisions to develop the geometric design, hydraulic design and

geotechnical design of the structure • Attend field reviews • Attend project meetings • Meet the project schedule and manhour estimates • Prepare the contract documents for structural items, special provisions, construction

quantities and cost estimates for structural items • Remain abreast of the state of the art in bridge design through review of AASHTO, TRB,

FHWA, etc., publications, and investigate the use of new bridge design techniques • Provide technical support for structural designs for bridge projects on local government

facilities that are funded by state and/or federal dollars • In coordination with the Construction Division, review construction working drawings • In coordination with the Construction Division, review VE proposals from contractors • Review and comment on construction change orders when requested by the

Construction Division

1.1.4.2 Geotechnical Design Division

The Geotechnical Design Division is responsible for all geotechnical requirements for both roadway and bridge projects. For structural items, the Division’s responsibilities are to:

• Develop a subsurface exploration plan • Identify the proposed boring locations and recommended foundation type • Conduct the field exploration to gather the geotechnical data • Prepare and/or review the Geotechnical Report (based on the geotechnical subsurface

exploration data, preliminary bridge plans, and loads computed by the structural engineer), which provides the necessary geotechnical parameters for the structural engineer to perform the detailed foundation design

• Perform the laboratory testing for soils and rock (e.g., classification, moisture content) • In coordination with the structural engineer, select and design retaining walls (e.g.,

estimate of settlement, global stability) • Perform design reviews and/or oversight reviews • Assist the Construction Division to:

○ Prepare pile driving criteria ○ Review pile and drilled shaft installation plans ○ Determine acceptance of as built drilled shafts and piles

For roadway projects, the Geotechnical Design Division’s responsibilities are to:

• Perform site surveys as needed in the project area • Conduct field investigations (i.e., insitu field tests, gathering samples for laboratory

analysis)



• Identify geotechnical properties and parameters for embankment design • Recommend subgrade treatments for pavement section support • Gather geotechnical data to determine the stability of fill and cut earth slopes and of rock

cuts • Recommend slope stabilization methods • Work with the Construction Division and the Region construction staff to address

geotechnical issues that arise during construction • Perform design reviews and/or oversight reviews

1.1.4.2.1 Geotechnical Design Manager

The Geotechnical Design Manager is responsible for the overall administrative/management/ engineering activities of the Geotechnical Design Division. The Geotechnical Design Manager establishes overall Department geotechnical policies, practices and criteria, and manages the Division’s coordination with other divisions.

The responsibilities of the Geotechnical Design Manager are to:

• Develop work programs for geotechnical activities based on project schedules • Direct the use of the available manpower within the Geotechnical Design Division • Participate in professional organizations related to geotechnical engineering (AASHTO,

TRB) to represent the Department’s interests and concerns • Oversee the development and maintenance of:

○ Standard specifications related to geotechnical items ○ Special provisions related to geotechnical items ○ Geotechnical engineering criteria ○ The UDOT Geotechnical Manual of Instruction

• Represent the Department in all litigation related to geotechnical issues • Remain abreast of the key geotechnical issues on individual projects • Approve Geotechnical Reports • Approve geotechnical designs • Determine the need for geotechnical contractors and consultants, and review and

approve project deliverables • Direct and oversee the implementation of various design, consultant review, research

and development and related projects • Manage project budgets, timelines and procedures • Manage consultant geotechnical contracts

1.1.4.2.2 Geotechnical Design Team

The Geotechnical Design Team serves as the focal point for all project specific activities performed by the Geotechnical Design Division. The responsibilities of the Geotechnical Design Team are to:

• Plan the geotechnical work to meet specific project needs • Direct the field investigation unit in the subsurface investigations



• Attend and monitor on site the work of the drilling crews • Direct and monitor the work of Geotechnical Testing • Perform design reviews and/or oversight reviews • Perform the geotechnical engineering evaluation, analysis and design based on the

UDOT Geotechnical Manual of Instruction for the following: ○ Bridge foundations ○ Earth retaining systems ○ Seismic design ○ Pavement subgrade ○ Roadway slopes and embankments ○ Geosynthetics

In addition to the above geotechnical responsibilities in preconstruction, the Geotechnical Design Team is the primary point of contact between the Region field construction personnel and the Geotechnical Design Division. In this capacity, the Team serves as technical advisors to the Resident Engineer (RE) on geotechnical issues related to the:

• Review of plans and specifications • Interpretation of special provisions • Response to requests for information (RFI) • Review of change orders • Preparation of reports/documentation • Development and interpretation of instrumentation • Verification of deep and shallow foundation capacity • Construction problems/issues 1.1.4.2.3 Geotechnical Testing

Geotechnical Testing is responsible for conducting all necessary laboratory tests to identify the engineering properties needed by the project geotechnical engineers to conduct the engineering analyses and design. Chapter 4, Geotechnical Testing, of the UDOT Geotechnical Manual of Instruction discusses the lab testing responsibilities for Geotechnical Testing.

The drilling crews are responsible for all in house subsurface geotechnical investigations.

1.2 DEFINITIONS AND ACRONYMS

1.2.1 Definitions

1. Accelerated Bridge Construction Communication Plan. A plan to maintain contact between all parties involved during a bridge move.

2. Anchored Walls (Soil Nails or Rock Anchors). Retaining walls consisting of horizontal soil reinforcing elements drilled into an existing fill to stabilize the soil and connected to a



facing material to retain the soil. Anchored walls are typically constructed from the top down.

3. Auxiliary Waterway Openings. Relief openings provided for streams in floodplains through the roadway embankment in addition to the primary bridge waterway openings.

4. Average Annual Daily Traffic. The total volume of traffic passing a point or segment of a highway facility in both directions for one year, divided by the number of days in the year.

5. Average Daily Traffic. The total volume of traffic during a given time period, greater than one day and less than one year, divided by the number of days in that time period.

6. Average Daily Truck Traffic. The total number of trucks passing a point or segment of a highway facility in both directions during a given time period divided by the number of days in that time period.

7. Base Flood. The flood having a 1% chance of being exceeded in any given year (i.e., the 100 year event) or a 63% chance of being exceeded over a 100 year period.

8. Base Floodplain. The area subject to flooding by the base flood.

9. Bridge. A structure including supports erected over a depression or an obstruction, such as water, highway or railway, and having a track or passageway for carrying traffic or other moving loads, and having a bridge length of more than 20 ft.

10. Bridge Backwater. The incremental increase in water surface elevation upstream of a highway facility.

11. Bridge Components. A segregation of the bridge into three primary components — deck, superstructure and substructure.

12. Bridge Elements. A further segregation of the bridge components into discrete elements (e.g., prestressed concrete girders, expansion joints, bents, piles).

13. Bridge File. Electronic directory of all bridge records located on an independent server. Informally known as the bridge inventory.

14. Bridge Folder. A tangible folder containing hard copies of inspection reports, plan sets, sketches and other pertinent bridge information.

15. Bridge Inventory. Database of inspection information specifically used in the bridge management system. Does not contain plans, etc.

16. Bridge Management Software. Interface for database of bridge inventory and condition data specifically used in the bridge management system. Does not contain plans, etc.

17. Bridge Move Plan. A plan indicating a timeline for all bridge movement activities, itemizing potential threats to the movement schedule and identifying actions needed if an event disrupts the schedule of the bridge move.



18. Bridge Preservation. Actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend bridge life. Preservation actions can be preventive or condition driven.

19. Bridge Record. Electronic file of all bridge documents for a single bridge.

20. Bridge Rehabilitation. Major work required to restore the structural integrity of a bridge and work necessary to correct major safety deficiencies.

21. Bridge Replacement. Total replacement of a bridge with a new facility constructed in the same general traffic corridor. The replacement structure must meet the current geometric, material and structural standards required for the types and volume of projected traffic on the facility over the design life.

22. Bridge Roadway Width. The clear width measured at right angles to the longitudinal centerline of the bridge between the bottom of curbs or, for multiple heights of curbs, between the bottoms of the lower risers or, if curbs are not present, between the inner faces of parapet or railing.

23. Bridge Staging Area. Area in which a new bridge is constructed.

24. Bridge Temporary Works. Any structure used to provide temporary support to a bridge or bridge component.

25. Bridge Waterway Openings. The openings beneath the bridge intended to pass the stream flow under the design conditions.

26. Check Flood. A flood used to check the bridge waterway opening to accommodate a lesser design flood to judge whether a significant flood hazard, due to a flood larger than the proposed design discharge, has been overlooked.

27. Clearance Sign. A sign either attached to the structure or on the roadway before the structure warning vehicles of the allowable vertical clearance under the structure.

28. Condition Rating. An overall assessment of the physical condition of the deck, the superstructure and the substructure of a bridge or culvert. General condition (NBI) ratings range from 0 (failed condition) to 9 (excellent condition).

29. Construction Manager/General Contractor. A modified design build process in which the owner holds the contract for both the design consultant and the contractor.

30. Cross Slope. The slope in the cross section view of the travel lanes, expressed as a percent or ratio, based on the change in horizontal compared to the change in vertical.

31. Crossing Angle. The angle measured to the right while looking station ahead between the survey or control line of the structure alignment and the survey or control line of the feature crossed; if the alignment involves a horizontal curve, the angle is measured to a line tangent to the curve at the point of intersection.



32. Deck. The riding surface of the bridge.

33. Design Flood Frequency. The flood frequency selected for determining the necessary size of the bridge waterway opening.

34. Design Hourly Volume. Typically, the 30th highest hourly volume for the future year used for design, expressed in vehicles per hour.

35. Design Speed. The maximum safe speed that can be maintained over a specified section of highway.

36. Design Bid Build. The traditional contracting method in which UDOT develops a complete plan set before soliciting bids.

37. Design Build. A contracting method in which UDOT hires a contractor to develop and execute all project plans.

38. Engineer of Record. The licensed professional engineer who develops the overall structural design and the structural design criteria for the structure, and is responsible for the preparation of the structural engineering documents and who prepares and submits stamped drawings as required.

39. Federal Aid Highway. Highways on the federal aid highway system (the National Highway System and the Dwight D. Eisenhower National System of Interstate and Defense Highways) and all other public roads not classified as local roads or rural minor collectors.

40. Flood Frequency. The number of times a flood of a given magnitude can be expected to occur on average over a long period of time.

41. Foundation. The supporting rock or soil and bridge elements that are in direct contact with, and transmit loads to, the supporting rock or soil; includes piles, drilled shafts, spread footings and pile caps.

42. Fracture Critical Bridge. A bridge containing a fracture critical member. A bridge that does not contain redundant supporting elements.

43. Fracture Critical Member. A steel member in tension, or with a tension element, whose failure would likely result in a total or partial bridge collapse.

44. Freeboard. The clearance between the water surface elevation based on the design flood and the low chord of the superstructure.

45. Heavy Lifter. The firm employed by the contractor to provide heavy lifting equipment, operation and engineering.

46. I-Drive. Contains the bridge file and the bridge management system files.



47. Inventory Level Rating (LRFR). Generally corresponds to the rating at the design level of reliability for new bridges in the LRFD Specifications, but reflects the existing bridge and material conditions with regard to deterioration and loss of section.

48. Inventory Rating (LFR). Load ratings based on the inventory level allow comparisons with the capacity for new structures and, therefore, results in a live load that can safely utilize an existing structure for an indefinite period of time.

49. K-Values for Vertical Curves. The horizontal distance needed to produce a 1% change in longitudinal gradient.

50. Legal Level Rating (LRFR). This second level rating provides a single safe load capacity (for a given truck configuration) applicable to AASHTO and state legal loads. Live load factors are selected based on the truck traffic conditions at the site. Strength is the primary limit state for load rating; service limit states are selectively applied. Use the results of the load rating for legal loads as a basis for decision making related to load posting or bridge strengthening.

51. Load Rating. The determination of the live load carrying capacity of a bridge. Bridges are rated at two different stress levels referred to as Inventory Rating and Operating Rating.

52. Longitudinal Grade. The rate of roadway slope expressed as a percent between two adjacent vertical points of intersection (VPI). Upgrades in the direction of stationing are identified as positive (+). Downgrades are identified as negative (–).

53. Maximum Allowable Backwater. The maximum amount of backwater that is acceptable based on state and federal laws and on UDOT policies.

54. Mechanically Stabilized Earth Wall. Retaining walls consisting of horizontal soil reinforcing elements connected to a facing material to retain the soil, constructed from the bottom up.

55. Median. On a multilane facility, the area (or distance) between the inside edges of the two traveled ways. Note that the median width includes the two inside (or left) shoulders.

56. Micropiles. Small diameter reinforced piles that are drilled and grouted to support structures.

57. National Highway System. Consists of roadways important to the nation’s economy, defense and mobility. The National Highway System includes the following subsystem of roadways — interstate, other principal arterials, strategic highway network, major strategic highway network connectors and intermodal connectors.

58. Normal Crown. The typical cross section on a tangent section of roadway (i.e., no superelevation).



59. 100 Year Flood. A flood volume (or discharge) level that has a 1% chance of being exceeded in any given year or a 63% chance of being exceeded over a 100 year period.

60. Operating (In Service) Load Ratings. Routine load rating completed after design and incorporating any changes in condition noted in the inspection reports.

61. Operating Level Rating (LRFR). Maximum load level to which a structure may be subjected. Generally corresponds to the rating at the operating level of reliability in past load rating practice.

62. Operating Rating (LFR). Load ratings based on the operating level generally describe the maximum permissible live load to which the structure may be subjected. Allowing unlimited numbers of vehicles to use the bridge at operating level may shorten the life of the bridge.

63. Overpass. A grade separation where a highway passes over an intersecting highway or railroad.

64. Overtopping Flood. The flood event that will overtop the elevation of the bridge or roadway approaches.

65. Peak Discharge (or Peak Flow). The maximum rate of water flow passing a given point during or after a rainfall event or snow melt. The peak discharge for a 100 year flood is expressed as Q100.

66. Permit Level Rating (LRFR). Permit load rating checks the safety and serviceability of bridges in the review of permit applications for the passage of vehicles above the legally established weight limitations.

67. Permit Load Ratings. Special request load rating of an existing bridge for a permit load and incorporating any changes in condition noted in the inspection reports.

68. Plans. Approved contract drawings showing the location, type, dimensions and details of the specified work.

69. Prebid Meeting. A meeting held to show contractors the proposed project details and solicit input before bidding.

70. Preconstruction Meeting. A meeting held with the selected contractor to coordinate contract items necessary for the successful completion of the project.

71. Profile Grade Point (Finished Grade). The line at which the profile grade is measured on the pavement.

72. Recurrence Interval (Return Period). For a given discharge, the number of years between occurrences of that discharge. For example, the recurrence interval for a 100 year flood discharge is 100 years.

73. Regulatory Floodway. The floodplain area that is reserved in an open manner by federal, state or local requirements (i.e., unconfined or unobstructed either horizontally



or vertically) to provide for the discharge of the base flood so that the cumulative increase in water surface elevation is no more than a designated amount as established by the Federal Emergency Management Agency for administering the National Flood Insurance Program.

74. Roadway. The portion of a highway, including shoulders, for vehicular use. A divided highway includes two roadways.

75. Scour Critical. A bridge with a foundation element that has been determined to be unstable for the observed or evaluated scour conditions; that threatens substructure elements; and that places one or more elements in danger of failure.

76. Scour. Erosion of streambed or bank material due to flowing water; often considered as being localized around bents and abutments of bridges.

77. Self Propelled Modular Transporter. Self propelled multi-axle platform vehicle with self leveling capabilities, able to move in any direction and place loads within millimeters.

78. Self Propelled Modular Transporter Axle Line. A row of paired wheels (4 wheels or 2 axles) positioned along a line across the narrowest dimension of an individual SPMT unit.

79. Self Propelled Modular Transporter Axle Load. The amount of force exerted by each axle (2 wheels) of the SPMTs.

80. Self Propelled Modular Transporter Blocking. The apparatus between the top platform of the SPMTs and the bottom of the new bridge.

81. Self Propelled Modular Transporter Carrier Beam. Part of the SPMT blocking; the carrier beam is positioned perpendicular to the girders if the SPMTs are positioned parallel to the girders.

82. Self Propelled Modular Transporter Support Point. Point where the SPMT blocking supports the new bridge.

83. Skew Angle. The acute angle between a line normal to the structure control line and the centerline of support of the structure as measured at the intersection of the control line and centerline of support.

84. Special Provisions. A unique specification or a modification or revision to the UDOT Standard Specifications applicable to an individual contract.

85. Specifications. The compilation of provisions and requirements for the performance of the prescribed work.

86. Standard Drawings. Detailed drawings approved for repetitive use.

87. Standard Specifications. Specifications approved for general application and repetitive use.



88. State Highway. A public road owned by a state agency.

89. Structure Length. The overall length of a bridge measured along the line of survey stationing back to back of backwalls of abutments, if present; otherwise, end to end of the bridge floor. In no case, less than the total clear opening of the structure.

90. Substructure. The system of elements that support the superstructure. The substructure transfers the loads to the earth and retains material behind the supports. Substructure elements include abutments, bents, footings, piles, wingwalls, backwalls, etc.

91. Superelevation. The amount of cross slope provided on a horizontal curve to counterbalance, in combination with the side friction, the centrifugal force of a vehicle traversing the curve.

92. Superelevation Transition Length. The distance needed to transition the roadway from a normal crown section to the design superelevation rate. Superelevation transition length is the sum of the tangent runout and superelevation runoff distances.

93. Superstructure. The system of elements that spans the feature being crossed. The superstructure rests on the substructure. The superstructure includes the deck, parapets and girders or other support elements (e.g., trusses, arches, box girders).

94. Supplemental Specifications. Approved additions and revisions to the UDOT Standard Specifications.

95. Thalweg. The path of deepest flow in a waterway.

96. Traveled Way. The portion of the roadway for the movement of vehicles, exclusive of shoulders and auxiliary lanes.

97. Truck Percentage. The percentage of trucks in the total traffic volume on a facility.

98. Truck. A heavy vehicle engaged primarily in the transport of goods and materials, or in the delivery of services other than public transportation. For geometric design and capacity analyses, trucks are defined as vehicles with six or more tires.

99. Tunnel. An enclosed roadway with vehicle access that is restricted to portals regardless of type of structure or the method of tunnel construction.

100. Twenty Year Average Daily Traffic. For new construction and reconstruction projects, the projected future traffic volume most often used in project design.

101. Underpass. A grade separation where a highway passes under an intersecting highway or railroad.

102. Value Engineering. A function oriented technique that can be an effective management tool for achieving improved design, construction and cost effectiveness in various project elements.



1.2.2 Acronyms

A&D UDOT Acceptance and Documentation Guide AADT Average Annual Daily Traffic AASHTO American Association of State Highway and Transportation Officials ABC Accelerated Bridge Construction ABET Accreditation Board for Engineering and Technology ACI American Concrete Institute ADA Americans with Disabilities Act ADT Average Daily Traffic ADTT Average Daily Truck Traffic AISC American Institute of Steel Construction AISI American Iron and Steel Institute AITC American Institute of Timber Construction ANSI American National Standards Institute API American Petroleum Institute AREMA American Railway Engineering and Maintenance of Way Association ASCE American Society of Civil Engineers ASD Allowable Stress Design ASTM American Society for Testing and Materials ATC Alternate Technical Concept AWS American Welding Society BL Blast Load BMM UDOT Bridge Management Manual BMS Bridge Management System BMT Bridge Management Team BNFS Burlington Northern and Santa Fe Railroad BR Braking Force BSA Bridge Staging Area CADD Computer Aided Drafting Design CAPWAP Case Pile Wave Analysis Program CE Centrifugal Force CFR Code of Federal Regulations CG Center of Gravity CID Charge Identification Number CIP Cast-in-Place CMGC Construction Manager/General Contractor CPT Cone Penetration Test CR Creep CRSI Concrete Reinforcing Steel Institute CT Truck Collision CV Vessel Collision DB Design Build DBB Design Bid Build DBE Disadvantaged Business Enterprise DBFM Design Build Finance Maintain DC Component Dead Load DD Downdrag



DE District Engineer DHV Design Hourly Volume DL Dead Load DP Dye Penetrant Testing DW Dead Weight EDA Elastic Dynamic Analysis EEO Equal Employment Opportunity EH Horizontal Earth Pressure EIT Engineer in Training EL Locked in Forces EOR Engineer of Record (or designee) ePM electronic Project Manager ESA Equivalent Static Analysis EQ Earthquake Load ERE Earthquake Resisting Elements ERFC Early Release for Construction ERS Earthquake Resisting Systems ES Earth Surcharge ET Eddy Current Testing EV Vertical Earth Pressure FCM Fracture Critical Member FDC Field Design Change FE Field Engineer FEM Finite Element Method FEMA Federal Emergency Management Agency FHWA Federal Highway Administration FR Friction FRC Fiber Reinforced Concrete FRP Fiber Reinforced Polymer FTA Federal Transit Administration FWS Future Wearing Surface FY Fiscal Year GPR Ground Penetrating Radar GRAMA Government Records Access Management Act GRS Geosynthetic Reinforced Soil HDPE High Density Polyethylene HLMR High Load Multirotational HMWM High Molecular Weight Methacrylate HPS High Performance Steel IC Ice Load ICBO International Conference of Building Officials ICE Independent Cost Estimate IF Induction Field IM Dynamic Load Allowance IMDL Dead Load Dynamic Load Factor IR Impulse Response L Superelevation Runoff Length LFD Load Factor Design



LFR Load Factor Rating LL Live Load LMC Latex Modified Concrete LRFD Load and Resistance Factor Design LRFD Specifications AASHTO LRFD Bridge Design Specifications LRFR Load and Resistance Factor Rating LS Live Load Surcharge LSDC Low Slump High Density Concrete M&P Measurement and Payment MAP-21 Moving Ahead for Progress in the 21st Century Act MASH AASHTO Manual for Assessing Safety Hardware MCFT Modified Compression Field Theory MMC Microsilica Modified Concrete MOI Manual of Instruction MOT Maintenance of Traffic MSE Mechanically Stabilized Earth MT Magnetic Particle Testing MUTCD Manual on Uniform Traffic Control Devices NC Normal Crown NCEES National Council of Examiners for Engineering and Surveying NCHRP National Cooperative Highway Research Program NDC Notice of Design Change NDT Nondestructive Testing NEPA National Environmental Policy Act NFIP National Flood Insurance Program NHI National Highway Institute NHS National Highway System NICET National Institute for Certification in Engineering Technologies NSBA National Steel Bridge Alliance NTP Notice to Proceed P3 Public/Private Partnerships PCA Portland Cement Association PCI Prestressed/Precast Concrete Institute PDA Pile Driving Analyzer PDBS Project Development Business System PE Professional Engineer PIM Public Involvement Manager PIN Project Identification Number PL Pedestrian Load PPC Polyester Polymer Concrete PS Secondary Forces from Post-Tensioning PS&E Plans, Specifications and Estimate PT Dye Penetrant Testing PTFE Polytetrafluoroethylene PTI Post-Tensioning Institute PVC Polyvinyl Chloride QC/QA Quality Control/Quality Assurance RE Resident Engineer



RFC Released for Construction RFI Request for Information RFP Request for Proposals RFQ Request for Qualifications ROW Right of Way RT Radiographic Testing S&E Scope and Estimate S&L Situation and Layout SD Structure Design Drawings SDC Seismic Design Category SDDM UDOT Structures Design and Detailing Manual SDSR Seismic Design Strategy Report SE Differential Settlement SH Shrinkage SHRP Strategic Highway Research Program SHV Specialized Hauling Vehicle SI Systeme International d’unites SPMT Self Propelled Modular Transporter SRM FHWA Seismic Retrofitting Manual for Highway Bridges SS Sample Sheets SSR Seismic Strategy Report STIP Statewide Transportation Improvement Program STP Surface Transportation Program STRAHNET Strategic Highway Network SUE Subsurface Utility Exploration SW Structures and Walls TG Temperature Gradient TOC Traffic Operations Center TP Travel Path TR Tangent Runout TRB Transportation Research Board TS&L Type, Selection and Layout TSR Type Selection Report TU Uniform Temperature UDOT Utah Department of Transportation UIT Ultrasonic Impact Treatment UPRR United Pacific Railroad US Ultraseismic USDA United States Department of Agriculture USGS United States Geological Survey UT Ultrasonic Testing VE Value Engineering VECP Value Engineering Change Proposal VMS Variable Message Sign VPI Vertical Points of Intersection WA Water Load WL Wind on Live Load WS Wind Load on Structure



WSDOT Washington State Department of Transportation WWR Welded Wire Reinforcement

1.3 STRUCTURAL DESIGN LITERATURE (National)

This section discusses selected major national publications available in the structural design literature. It provides 1) a brief discussion on each publication and 2) the UDOT application of the publication. Use the latest edition of the publication, including all interim revisions.

1.3.1 AASHTO LRFD Bridge Design Specifications

1.3.1.1 Description

1.3.1.1.1 General

The LRFD Specifications serve as the national standard for bridge design. The LRFD Specifications establish minimum requirements consistent with current nationwide practices that apply to common bridges and other structures such as retaining walls and culverts; long span structures can require additional design provisions.

1.3.1.1.2 LRFD Methodology

The LRFD Specifications present a load and resistance factor design (LRFD) methodology for the structural design, which replaces the load factor design and allowable stress methodologies of the previous AASHTO Standard Specifications for Highway Bridges. Basically, the LRFD methodology requires that bridge components be designed to satisfy four sets of limit states: strength, service, fatigue and fracture, and extreme event. Through load and resistance factors derived through the use of statistical analyses, the strength provisions of the LRFD Specifications now reflect a uniform level of safety for all structural elements, components and systems.

1.3.1.1.3 Status

The information in the LRFD Specifications supersedes, partially or completely, several former AASHTO structural design publications, which AASHTO no longer maintains:

• AASHTO Guide Specifications for Horizontally Curved Highway Bridges • AASHTO Division 1A, Seismic Design of the Standard Specifications for Highway

Bridges • AASHTO Guide Specifications for Fracture Critical Nonredundant Steel Bridge Members • AASHTO Guide Specifications — Thermal Effects in Concrete Bridge Superstructures • AASHTO Guide Specifications for Design and Construction of Segmental Concrete

Bridges



• AASHTO Guide Specifications for Fatigue Design of Steel Bridges • AASHTO Standard Specifications for Alternate Load Factor Design Procedures for Steel

Beam Bridges Using Braced Compact Sections • AASHTO Guide Specifications for Strength Design of Truss Bridges • AASHTO Guide Specifications for Structural Design of Sound Barriers Although superseded, some of the publications contain background information or other presentations that are useful to a structural engineer.

1.3.1.2 Application

Use the LRFD Specifications as amended by the SDDM as the mandatory document for the structural design of bridges and other structures. The SDDM is based upon the 6th Edition of the LRFD Specifications. Exceptions to this policy are appropriate for:

• Existing elements for bridge widening and bridge rehabilitation projects (including seismic retrofits) where strengthening is not involved

• Structural elements for which no LRFD provisions are available (e.g., signs, signals, lighting)

• Other applications as approved by the Structures Design Manager The SDDM presents UDOT’s application of the LRFD Specifications to structural design.

1.3.2 AASHTO Guide Specifications for LRFD Seismic Bridge Design

1.3.2.1 Description

The AASHTO Guide Specifications for LRFD Seismic Bridge Design are an alternative set of provisions for the seismic design of bridges. The major difference between the seismic provisions in the LRFD Specifications is the methodology used for examining seismic demands. Because the methodology focuses on displacement, the AASHTO Guide Specifications for LRFD Seismic Bridge Design are often referred to as displacement based. By contrast, the seismic provisions in the LRFD Specifications are force based.

1.3.2.2 Application

Use the AASHTO Guide Specifications for LRFD Seismic Bridge Design for the seismic design of bridges as discussed in Chapter 13 of the SDDM. Do not use the seismic design guidelines in the LRFD Specifications for the seismic design of bridges.



1.3.3 AASHTO Standard Specifications for Highway Bridges

1.3.3.1 Description

AASHTO first published the AASHTO Standard Specifications for Highway Bridges in the late 1920s with annual interim revisions and, until the adoption of the LRFD Specifications, served as the national standard for the design of bridges. The final version of the AASHTO Standard Specifications for Highway Bridges is based on the ASD and LFD methodologies. AASHTO maintained the AASHTO Standard Specifications for Highway Bridges through 2000 and published the final comprehensive 17th edition in 2002.

1.3.3.2 Application

See Chapter 21 for the use of the AASHTO Standard Specifications for Highway Bridges on bridge widening and rehabilitation projects.

1.3.4 FHWA Seismic Retrofitting Manual for Highway Bridges

1.3.4.1 Description

The FHWA Seismic Retrofitting Manual for Highway Bridges (SRM) is based primarily on research conducted during the development of the 1983 FHWA guidelines by the Applied Technology Council, current Caltrans Bridge Design Aids and research conducted at the University of California at San Diego and elsewhere. The SRM offers procedures for evaluating and upgrading the seismic resistance of existing bridges. Specifically, the SRM contains:

• A preliminary screening process to identify and prioritize bridges that need to be evaluated for seismic retrofitting

• A methodology for quantitatively evaluating the seismic capacity of an existing bridge and determining the overall effectiveness of alternative seismic retrofitting measures

• Retrofit measures and design requirements for increasing the seismic resistance of existing bridges

The SRM does not prescribe requirements dictating when and how bridges require a retrofit.

1.3.4.2 Application

Use the FHWA Seismic Retrofitting Manual for Highway Bridges for retrofitting bridges when required by the Structures Design Manager.



1.3.5 AASHTO Guide Specifications for Seismic Isolation Design

1.3.5.1 Description

AASHTO published the AASHTO Guide Specifications for Seismic Isolation Design as a supplement to the AASHTO Standard Specifications for Seismic Design of Highway Bridges. The AASHTO Guide Specifications for Seismic Isolation Design present specifications for the design of bearings to seismically isolate the superstructure from the substructure of bridges.

1.3.5.2 Application

Use the current edition of the AASHTO Guide Specifications for Seismic Isolation Design, where applicable, in conjunction with the current AASHTO Guide Specifications for LRFD Seismic Bridge Design.

1.3.6 AASHTO/American Welding Society D1.5M/D1.5 Bridge Welding Code

1.3.6.1 Description

The AASHTO/AWS D1.5M/D1.5 Bridge Welding Code presents current criteria for the welding of structural steel in bridges. The Code supersedes the AASHTO Standard Specifications for Welding of Structural Steel Highway Bridges.

1.3.6.2 Application

Use the AASHTO/AWS D1.5M/D1.5 Bridge Welding Code for the design and construction of structural steel highway bridges. However, for items not specifically addressed in D1.5, such as welding on existing structures, welding on reinforcing steel and welding for tubular structures, refer to the current edition of AWS D1.1 and AWS D1.4.

1.3.7 AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges

1.3.7.1 Description

The AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges apply to bridges intended to carry primarily pedestrian traffic and/or bicycle traffic. The document is based on the LRFD design methodology.

1.3.7.2 Application

Use the AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges for the design of pedestrian bridges in conjunction with the LRFD Specifications.



1.3.8 AASHTO Guide Specifications for Distribution of Loads for Highway Bridges

1.3.8.1 Description

The AASHTO Guide Specifications for Distribution of Loads for Highway Bridges provide more refined live load distribution factors than the S-over factors of the AASHTO Standard Specifications for Highway Bridges. Although the refined equations appear similar, the equations are not the same as the equations provided in the LRFD Specifications.

1.3.8.2 Application

The use of the AASHTO Guide Specifications for Distribution of Loads for Highway Bridges is permitted for non LRFD applications. Do not use the publication with the LRFD Specifications. Only use the publication when refined live load distribution factors are required for load rating using the AASHTO Standard Specifications for Highway Bridges.

1.3.9 AASHTO LRFD Bridge Construction Specifications

1.3.9.1 Description

The AASHTO LRFD Bridge Construction Specifications are a companion document to the LRFD Specifications. The publication presents testing and acceptance criteria, material references and recommended guidelines for construction loads.

1.3.9.2 Application

The UDOT Standard Specifications reference the AASHTO LRFD Bridge Construction Specifications in many locations for the construction of structural elements. Use other provisions in the AASHTO LRFD Bridge Construction Specifications to supplement the UDOT Standard Specifications as appropriate.

1.3.10 AASHTO Guide Specifications for Bridge Temporary Works

1.3.10.1 Description

The AASHTO Guide Specifications for Bridge Temporary Works present recommended specifications for falsework, formwork and related temporary construction used to build bridge structures. The publication is useful to falsework designers, contractors, inspectors and structural engineers.



1.3.10.2 Application

Use the AASHTO Guide Specifications for Bridge Temporary Works to supplement the UDOT Standard Specifications for applicable bridge temporary works, except as superseded by the contract documents.

1.3.11 AASHTO LRFD Movable Highway Bridge Design Specifications


The AASHTO LRFD Movable Highway Bridge Design Specifications address the design of movable bridges using the LRFD Specifications. The document provides guidance for the structural design and machinery design of swing, bascule and vertical lift spans.


Use the AASHTO LRFD Movable Highway Bridge Design Specifications for the design of movable bridges.

1.3.12 AASHTO Standard Specifications for Structural Supports for Highway

Signs, Luminaires and Traffic Signals


The AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals present structural design criteria for the supports of various roadside appurtenances. The publication presents specific criteria and methodologies for evaluating dead load, live load, ice load and wind load.


Use the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires and Traffic Signals for the design of signs, luminaires and traffic signals.

1.3.13 AASHTO Guide Specification and Commentary for Vessel Collision

Design of Highway Bridges


The AASHTO Guide Specification and Commentary for Vessel Collision Design of Highway Bridges includes information relative to designing bridges to resist damage from vessel collisions. As feasible, the publication is based on probabilistic principles. The LRFD Specifications contain only the load section of the document. The AASHTO Guide Specification



and Commentary for Vessel Collision Design of Highway Bridges contains considerably more information.


Use the AASHTO Guide Specification and Commentary for Vessel Collision Design of Highway Bridges for the design of vulnerable bridges when required by the Structures Design Manager.

1.3.14 American Institute of Steel Construction Steel Construction Manual


The AISC Steel Construction Manual provides dimensions, properties and general design guidance for structural steel for various applications. The publication contains AISC allowable stress design and load and resistance factor design method criteria for steel buildings. However, the properties of the rolled structural shapes are useful for designing bridge structures.


Use the AISC Steel Construction Manual for dimensional properties of standard steel shapes. Use the specifications only where the publication addresses items not in the LRFD Specifications and with the approval of the Structures Design Manager.

1.3.15 American Railway Engineering and Maintenance of Way Association

Manual for Railway Engineering


The AREMA Manual for Railway Engineering provides detailed structural specifications for the design of railroad bridges. The AREMA specifications have approximately the same status for railroad bridges as the LRFD Specifications have for highway bridges; i.e., the structural design of railroad bridges must meet the AREMA requirements.


Occasionally, UDOT is responsible for the structural design of railroad bridges. Use the AREMA Manual for Railway Engineering for the design of structures carrying rail traffic; however, for seismic design of railroad bridges over UDOT roads, see Chapter 13 of the SDDM. In addition, the AREMA specifications contain requirements for the geometric design of railroad tracks passing beneath a bridge.



1.3.16 Additional Structural Design Publications

The structural design literature contains many additional publications that can be useful on a case by case basis. Verify the adequacy of any member proportions, details or practices in the publications to ensure consistency with the LRFD Specifications. The following briefly describes several of the structural design publications:

1. American Concrete Institute 318-05 Building Code Requirements for Structural Concrete. Addresses the proper design and construction of buildings of structural concrete. Although intended for building design, structural engineers find the document useful because the publication provides more detail on aspects of concrete design that are less typical in bridges.

2. American Concrete Institute Analysis and Design of Reinforced Concrete Bridge Structures. Contains information on various concrete bridge types, loads, load factors, service and ultimate load design, prestressed concrete, substructure and superstructure elements, precast concrete and reinforcing details.

3. American Institute of Timber Construction Timber Construction Manual. Provides criteria for the design of timber structures, including bridges, for both sawn and laminated timber.

4. Concrete Reinforcing Steel Institute Handbook. Meets the ACI Building Code Requirements for Reinforced Concrete.

5. Concrete Reinforcing Steel Institute Manual of Standard Practice. Explains generally accepted industry practices for estimating, detailing, fabricating and placing reinforcing bars and bar supports.

6. International Conference of Building Officials International Building Code. Provides criteria for the design of buildings.

7. National Cooperative Highway Research Program 343 Manuals for Design of Bridge Foundations. Provides additional information on the application of the LRFD Specifications to foundations.

8. National Steel Bridge Alliance “National Steel Bridge Alliance Collaboration Standards.” A series of documents addressing topics related to steel bridge design, including analysis, fabrication, plan presentation, shop drawing presentation, shop drawing review, constructability, quality control and standard details.

9. National Steel Bridge Alliance Steel Bridge Design Handbook. Addresses many aspects of structural steel materials, fabrication, economy and design and includes LRFD examples; the general computational procedure is helpful to structural engineers using the LRFD Specifications.

10. Portland Cement Association Notes on ACI 318-02 Building Code Requirements for Structural Concrete with Design Applications. Assists the structural engineer in the proper application of the ACI 318-02 design standard, which is the predecessor to ACI



318-05. Numerous design examples illustrate the application of the provisions of ACI 318-02.

11. Prestressed/Precast Concrete Institute Bridge Design Manual. Includes both preliminary and final design information for standard girders and precast, prestressed concrete products used for transportation structures. The document contains background, strategies for economy, fabrication techniques, evaluation of loads, load tables, design theory and numerous complete design examples. The publication explains and amplifies the application of both the AASHTO Standard Specifications for Highway Bridges and the LRFD Specifications.

12. Prestressed/Precast Concrete Institute Design Handbook. Includes information on the analysis and design of precast and/or prestressed concrete products in addition to a discussion on handling, connections and tolerances for prestressed products. The PCI Design Handbook contains general design information, specifications and standard practices.

13. Post-Tensioning Institute Post-Tensioned Box Girder Bridge Manual. Contains information on economics, design parameters, analysis and detailing, installation, prestressing steel specifications, post-tensioning tendons, systems and sources.

14. Post-Tensioning Institute Post-Tensioning Manual. Discusses the application of post-tensioning to many types of concrete structures, including concrete bridges. Also discusses types of post-tensioning systems, specifications and the analysis, design and construction of post-tensioned structures.

15. United States Department of Agriculture Forest Service Timber Bridge Manual. Addresses all aspects of traditional timber bridge construction plus the latest developments in laminated deck systems using adhesives or prestressing forces.

1.4 UDOT DOCUMENTS

UDOT publications in addition to the SDDM could apply to a structures design project.

1.4.1 UDOT Geotechnical Manual of Instruction

The UDOT Geotechnical Manual of Instruction presents criteria for geotechnical investigations and designs, including:

• Field investigations (e.g., subsurface exploration, soil sampling) • Geotechnical laboratory testing • Embankments/slopes (e.g., settlement, slope stability) • Foundations for structures • Retaining walls (e.g., global stability) and other earth retaining systems • Geotechnical support during construction



The purpose of the UDOT Geotechnical Manual of Instruction is to:

• Outline the roles and interaction of the Geotechnical Design Division and of consultant geotechnical engineers

• Identify standard procedures, practices, manuals, specifications, computer software, etc., for use in geotechnical work

• Establish standards for presentation of geotechnical information, including reports, test hole logs and laboratory test results

1.4.2 UDOT Roadway Design Manual of Instruction

The UDOT Roadway Design Manual of Instruction provides procedures and methods for developing and documenting improvements to the roadway network. The UDOT Roadway Design Manual of Instruction provides recommended values for critical roadway design dimensions, which includes values for the FHWA 13 controlling criteria (e.g., roadway width, horizontal alignment, stopping sight distance). The UDOT Roadway Design Manual of Instruction documents criteria for several bridge design elements, including:

• Bridge width • Vertical clearances • Horizontal and vertical alignment • Clear zones for bridge underpasses

1.4.3 UDOT Roadway Drainage Manual of Instruction

The UDOT Roadway Drainage Manual of Instruction documents practices and procedures for the hydraulic and hydrologic design of drainage appurtenances on the highway network, including hydrologic methods (e.g., Rational Method, United States Geological Survey (USGS), design flood frequency, culvert hydraulics, storm drainage systems and roadside channels. The UDOT Roadway Drainage Manual of Instruction documents drainage criteria for several hydraulic elements that impact bridges, including:

• Bridge waterway openings • Bridge scour • Bridge deck drainage • Streambank protection • Stream channels 1.4.4 UDOT Environmental Process Manual of Instruction

The UDOT Environmental Process Manual of Instruction provides guidance for the preparation of environmental analyses and documentation. The UDOT Environmental Process Manual of Instruction documents practices and procedures for compliance with the National Environmental Policy Act (NEPA) and many other federal and state environmental regulations. Several topics



in the UDOT Environmental Process Manual of Instruction relate to the development of bridge projects:

• Roles and responsibilities of Region and Central environmental staff • Environmental documentation (e.g., categorical exclusions, environmental assessments,

environmental impact statements) • Public/resource agency involvement • Environmental permits (e.g., Section 404, Section 401) • Mitigation commitments 1.4.5 Specifications

The specifications present the work methods, materials and acceptance of work for the construction of road, traffic and bridge projects. Refer to Section 4.3 for a description of various types of specifications.

1.4.6 Materials

The certification and quality control acceptance of construction materials is a critical element to ensure the performance and durability of the various highway elements. Several documents are available to ensure the use of quality materials in highway construction, including:

• UDOT Materials Manual for Instruction Part 8 • UDOT Minimum Sampling and Testing Requirements • UDOT Quality Management Plans • UDOT Standard Specifications • UDOT Steel and Concrete Construction Manual Verify that the bridge design and contract documents are consistent with the provisions in the listed documents.

1.4.7 UDOT Steel and Concrete Construction Manual

The UDOT Steel and Concrete Construction Manual is a mandatory part of the contract documents where the contractor furnishes or rehabilitates fabricated steel or concrete. The UDOT Steel and Concrete Construction Manual is an extension of the latest editions of the:

• AASHTO LRFD Bridge Construction Specifications • AASHTO/AWS D1.5 Bridge Welding Code • AWS D1.1 Structural Welding Code – Steel • AWS D1.2 Structural Welding Code – Aluminum • AWS D1.3 Structural Welding Code – Sheet Steel • AWS D1.4 Structural Welding Code – Reinforcing Steel • AWS D1.6 Structural Welding Code – Stainless Steel



The UDOT Steel and Concrete Construction Manual provides standard techniques and methods of inspection.

1.4.8 UDOT Construction Manual of Instruction

The UDOT Construction Manual of Instruction provides guidance to personnel that inspect and administer the contract provisions, and establishes specific responsibilities of the RE regarding contract administration and construction engineering management. The UDOT Construction Manual of Instruction is an administrative guide and reference describing acceptable methods and procedures for the preparation of records and reports in the administration and construction of projects under UDOT’s supervision.



FEBRUARY 2015

ADMINISTRATIVE GUIDELINES,REQUIREMENTS AND PROCEDURES



Administrative Guidelines, Requirements and Procedures 2-i

TABLE OF CONTENTS

2.1 SDDM SIGNIFICANCE AND APPLICATION .............................................................. 2-1

2.1.1 Document Priority ........................................................................................ 2-1 2.1.2 Approach ...................................................................................................... 2-1

2.2 POLICY ........................................................................................................................ 2-2

2.2.1 UDOT Structures Division Policies............................................................... 2-2 2.2.2 Administrative Rule R930-7-9 Utilities on Highway Structures .................... 2-3 2.2.3 Guide Signs on Bridges ............................................................................... 2-3 2.2.4 UDOT Aesthetics Policy ............................................................................... 2-3 2.2.5 UDOT Monument and City Logo Policy ....................................................... 2-3 2.2.6 UDOT Experimental Features and Evaluation of New Products Policy ....... 2-3 2.2.7 UDOT Standard Specifications .................................................................... 2-4 2.2.8 UDOT Standard Drawings ........................................................................... 2-4

2.3 DESIGN EXCEPTIONS/WAIVERS/DEVIATIONS ....................................................... 2-4

2.3.1 Design Exception/Waiver/Deviation from Standards ................................... 2-4 2.3.2 Structural Design Criteria Deviation ............................................................. 2-4

2.4 BRIDGE RECORD INFORMATION ............................................................................ 2-5 2.5 BUY AMERICA GUIDELINE ....................................................................................... 2-5 2.6 BRIDGE DESIGN LIFE ................................................................................................ 2-6 2.7 BRIDGE TREATMENT DESIGN DIRECTION ............................................................. 2-6

2.7.1 Bridge Treatments — Pavement Preservation Projects ............................... 2-6 2.7.2 Bridge Treatments – Pavement Rehabilitation Projects............................... 2-7 2.7.3 Asphalt Application Guidelines .................................................................... 2-8

2.8 UTILITY ATTACHMENT REQUIREMENTS ................................................................ 2-9 2.9 OVERHEAD SIGN STRUCTURE GUIDE SIGN REQUIREMENTS ............................ 2-11 2.10 CULVERT HEADWALL REQUIREMENTS ................................................................. 2-11 2.11 INSPECTION AND MAINTENANCE ACCESS REQUIREMENTS ............................. 2-11 2.12 PUBLIC ACCESS DESIGN REQUIREMENTS ........................................................... 2-12 2.13 PROJECT DEVELOPMENT TOOLS........................................................................... 2-12

2.13.1 Electronic Program Management................................................................. 2-12 2.13.2 ProjectWise .................................................................................................. 2-12


2-ii Administrative Guidelines, Requirements and Procedures

2.13.3 Project Delivery Network .............................................................................. 2-12 2.13.4 Digital Signature ........................................................................................... 2-13

2.14 STRUCTURE NUMBER .............................................................................................. 2-13

2.14.1 Structure Number Assignment ..................................................................... 2-13 2.14.2 Structure Number Placement ....................................................................... 2-15 2.14.3 Structure Drawing Number .......................................................................... 2-16

2.15 STRUCTURE NAME ................................................................................................... 2-18 2.16 STRUCTURES DIVISION ROLES AND RESPONSIBILITIES ................................... 2-18

2.16.1 Design Bid Build ........................................................................................... 2-18

2.16.1.1 Description ................................................................................. 2-18 2.16.1.2 Structures Division Involvement ................................................. 2-18

2.16.2 Design Build ................................................................................................. 2-18


2.16.3 Construction Manager/General Contractor .................................................. 2-20


2.16.4 Public/Private Partnerships .......................................................................... 2-21


2.16.5 Permit Project .............................................................................................. 2-21


2.16.6 Local Government Project – UDOT Advertisement ..................................... 2-23


2.16.7 Local Government Project – NonUDOT Advertisement ............................... 2-24


2.16.8 Emergency Project Delivery ......................................................................... 2-24

2.16.8.1 Description ................................................................................. 2-24


Administrative Guidelines, Requirements and Procedures 2-iii

2.16.8.2 Structures Division Involvement ................................................. 2-24

2.16.9 Maintenance Project Delivery ...................................................................... 2-24 2.16.9.1 Description ................................................................................. 2-24 2.16.9.2 Structures Division Involvement ................................................. 2-25

2.17 PROJECT DOCUMENT REQUIREMENTS................................................................. 2-25

2.17.1 Structure Plans ............................................................................................ 2-25 2.17.2 Structure Special Provisions ........................................................................ 2-25 2.17.3 Engineer's Estimate ..................................................................................... 2-26 2.17.4 Measurement and Payment ......................................................................... 2-26 2.17.5 Acceptance and Documentation .................................................................. 2-26 2.17.6 Structure Design Calculations ...................................................................... 2-26 2.17.7 Load Rating Package ................................................................................... 2-26 2.17.8 Structure Type Selection Report .................................................................. 2-26 2.17.9 Seismic Design Strategy Report .................................................................. 2-27 2.17.10 Geotechnical Report .................................................................................... 2-27 2.17.11 Hydraulics Report ........................................................................................ 2-27 2.17.12 Other Reports or Memoranda ...................................................................... 2-28 2.17.13 QC Cover Sheets ......................................................................................... 2-28 2.17.14 Project QA Audit .......................................................................................... 2-28 2.17.15 Structural Review Comment Resolution Form ............................................. 2-29 2.17.16 Milestone Review Comment Resolution Form ............................................. 2-29 2.17.17 Structural Review Completion – Plan in Hand (Stage 3) Review ................. 2-29 2.17.18 Structural Review Completion – PS&E (Stage 4) Review ............................ 2-29 2.17.19 Alternate QC/QA Procedures Acceptance ................................................... 2-30 2.17.20 Situation and Layout Acceptance ................................................................ 2-30 2.17.21 Final Structure Acceptance .......................................................................... 2-30 2.17.22 Structural Design Criteria Deviation ............................................................. 2-31 2.17.23 Structural Documentation Template ............................................................ 2-31

2.18 COMPUTER SOFTWARE ........................................................................................... 2-31 2.19 RAILROAD AGREEMENTS ........................................................................................ 2-31 2.20 RESEARCH ................................................................................................................. 2-32 2.21 MATERIALS ................................................................................................................ 2-32 2.22 CONSTRUCTION ........................................................................................................ 2-32 2.23 STRUCTURAL DESIGN AND MANAGEMENT SUPPORT SERVICES POOL ......... 2-33


2-iv Administrative Guidelines, Requirements and Procedures

LIST OF FIGURES

Figure 2.1 — STRUCTURE NUMBER ASSIGNMENT ...................................................... 2-14 Figure 2.2 — STRUCTURE NUMBER LOCATION ............................................................ 2-15 Figure 2.3 — STRUCTURE DRAWING NUMBER ............................................................. 2-17


Administrative Guidelines, Requirements and Procedures 2-1

Chapter 2 ADMINISTRATIVE GUIDELINES,

REQUIREMENTS AND PROCEDURES

The Structures Division establishes, oversees, enforces, adheres to and is responsible for a wide range of administrative policies, procedures, requirements and guidelines. This chapter discusses each of the administrative guidelines, requirements and procedures.

2.1 SDDM SIGNIFICANCE AND APPLICATION

The SDDM applies to all projects that include structures in which UDOT is involved. The projects include UDOT projects, local government projects using federal funds, state funded projects, maintenance projects and permit projects.

The SDDM establishes the structures design criteria and supplements the current LRFD Specifications.

2.1.1 Document Priority

Document priority is as follows:

• Design build (DB) project design criteria (where applicable) • Bridge design memoranda • SDDM • BMM • LRFD Specifications • All other reference publications

2.1.2 Approach

The following describes the basic approach for Part II of the SDDM:

1. Theory. The SDDM is not a structural design theory resource or a research document; the SDDM provides limited background information to describe the Structures Division structures design criteria and application.

2. Example Problems. Where beneficial to explain the intended application, the SDDM provides a few example problems or calculations demonstrating the proper procedure for selected design applications. For example, an example problem is useful where there has been a large variation in solutions contrary to expectations. The design examples or calculations illustrate the specific structural design criteria, practices and procedures for the indicated applications.


2-2 Administrative Guidelines, Requirements and Procedures

3. Details. Where beneficial, the SDDM provides design details for the various structural design elements.

4. AASHTO Coordination. The SDDM is a supplement to the LRFD Specifications that:

• Does not duplicate information in the LRFD Specifications, unless necessary for clarity

• Elaborates on specific articles of the LRFD Specifications • Presents interpretative information, where needed • Modifies sections from the LRFD Specifications where UDOT has adopted a

different practice • Indicates UDOT’s practice where the LRFD Specifications present multiple

options • Presents structures design applications used in Utah that are not included in the

LRFD Specifications

5. Structures Drawings. Where beneficial to explain typical details and requirements, the following are provided:

• Working standards (WS) sheets • Sample sheets (SS) • Structures design (SD) drawings

The structures drawings illustrate specific details, standard details, typical proportioning guidelines and structural design criteria. Although published separately, the structures drawings are considered part of the SDDM. See Section 4.2 for additional information.

2.2 POLICY

2.2.1 UDOT Structures Division Policies

The Structures Division is responsible for three UDOT policies:

1. UDOT Policy 08C-01 “Minimum Design Loads, Structures.” Defines the minimum design loads for the design of new state and local government bridges.

2. UDOT Policy 08C-02 “Structural Capacity of Existing Structures.” Provides guidance for the evaluation of the structural capacity of existing state and local government structures not designed to current standards or of structures that have deteriorated.

3. UDOT Policy 08C1-02 “Geotechnical Engineering.” Defines the design standards for geotechnical and geological engineering.

The policies are updated annually. Refer to the website for policy details and specifics.



2.2.2 Administrative Rule R930-7-9 Utilities on Highway Structures

The installation of utility facilities on highway structures can adversely impact the integrity and capacity of the structure, the safe operation of traffic, the maintenance efficiency and the aesthetic appeal of the structure. Do not install utility facilities on highway structures except in extreme cases. For extreme cases, refer to Section 2.8 for utility attachment requirements.

2.2.3 Guide Signs on Bridges

Guide signs cannot be attached to bridges. Guide signs require a stand alone cantilever or overhead sign structure. If proposed work on an existing bridge requires the removal of an existing guide sign, the replacement guide sign must be attached to a stand alone cantilever or overhead sign structure. If impractical due to extenuating circumstances and the guide sign cannot be attached to a stand alone cantilever or overhead sign structure, obtain approval from the Structures Design Manager following the procedures outlined in Section 2.9.

2.2.4 UDOT Aesthetics Policy

Reference: LRFD Article 2.5.5

See UDOT Policy 08C-03 “Project Aesthetics and Landscaping Plan Development and Review” for policies on aesthetics.

Projects involving structures are subject to an aesthetics review by the Aesthetics Committee. Coordinate with the Region Landscape Architect to determine the appropriate aesthetics requirements.

Refer to the aesthetics policy for requirements and guidelines on placing signs/logos/names on bridges that are requested by local agencies during the design stage of the project. See Section 2.2.5.

See Section 10.8.4 for more information on aesthetics.

2.2.5 UDOT Monument and City Logo Policy

See UDOT Policy 08A-02 “Placement of Monument Features and City Logo Panels on State Highways” for policies on the placement of monuments and logos on state highways.

2.2.6 UDOT Experimental Features and Evaluation of New Products Policy

See Sections 2.20 and 2.21 and refer to UDOT Policy 07B-03 “Experimental Features and Evaluation of New Products” for more information regarding experimental features and the new products evaluation process for inclusion in projects.



2.2.7 UDOT Standard Specifications

The Structures Design Division has responsibility or shares responsibility for over 30 standard specifications. The Geotechnical Design Division has responsibility or shares responsibility for over 30 standard specifications. Refer to the contact list for the current version of the UDOT Standard Specifications and UDOT Standard Drawings on the website for more information.

2.2.8 UDOT Standard Drawings

The Structures Division owns the structures and walls (SW) series standard drawings and supports other disciplines by providing structural design criteria, design and review as needed. Refer to the contact list for the current version of the UDOT Standard Specifications and UDOT Standard Drawings on the website for more information.

2.3 DESIGN EXCEPTIONS/WAIVERS/DEVIATIONS

2.3.1 Design Exception/Waiver/Deviation from Standards

All projects advertised through the UDOT system, whether funded with federal aid or other independent funding, must meet UDOT design standards. A request for a design exception and design waiver or a deviation from standards is appropriate when the request adds value to the project. Added value is subjective, but the request must be supported by and based on rational engineering principles. The Regions and the Central Preconstruction Engineer approve design exceptions, design waivers and deviations from standards on a case by case basis.

For structure related elements, the Central Preconstruction Engineer coordinates with the Structures Design Manager for input on design exceptions, waivers and deviations. The Design Exception and Design Waiver form and the Deviation from UDOT Standards form can be found on the website.

2.3.2 Structural Design Criteria Deviation

Request approval for structural design criteria deviations when approval from the Structures Design Manager is required or the structural design criteria or requirements in the SDDM or the LRFD Specifications are presented in one of the following contexts:

• Shall • Mandatory • Required

Use the following procedure to request a structural design criteria deviation:

1. Documentation. The structural engineer prepares the justification for the structural design criteria deviation at the earliest possible stage of the project. Use the Structural



Design Criteria Deviation Request template to document justification for the deviation request. Coordinate with the Structures Design Manger when developing the request. In the justification, identify the structural design criteria or requirements that are not met and discuss items such as the following:

• Site constraints • Safety considerations • Construction costs • Construction logistics • Product availability • Environmental impacts • Right of way impacts

2. Approval. Complete the Structural Design Criteria Deviation Acceptance form and

submit the form with the Structural Design Criteria Deviation Request to the Structures Design Manager for review. The Structures Design Manager approves all proposed deviations in writing.

The Structural Design Criteria Deviation Request template and Structural Design Criteria Deviation Acceptance form can be found on the website.

2.4 BRIDGE RECORD INFORMATION

Requests for bridge record information can be made through the UDOT website or through the Government Records and Access Management Act (GRAMA) process. Bridge record information includes any documents (e.g., calculations, reports, plans, photographs) related to a bridge. The individual requesting bridge record information assumes all responsibility and liability.

2.5 BUY AMERICA GUIDELINE

23 CFR Part 635.410 presents the Buy America provisions for federal aid projects. The provisions require that manufacturing processes for steel and iron products and any coatings occur in the United States. Use of a minimal amount of foreign material is permitted when the cost does not exceed 0.1% of the total contract price or $2500, whichever is greater. Refer to the UDOT Standard Specifications.

The structural engineer must determine if a proposed detail or material does not meet the Buy America provisions. A design waiver must be obtained from FHWA during the preconstruction stage and before advertising. The waiver process typically takes a minimum of six months.

The contractor is responsible for tracking where the exemption is used.



2.6 BRIDGE DESIGN LIFE

The 75 year design life defined in LRFD Article 1.2 is relevant only for the strength and fatigue limit states. The 75 year design life is not relevant to the service limit states, which are intended to address durability and longevity of the bridge.

The live load model for the strength limit states, including the notional load, load factors and multiple presence factors, represent the traffic distribution from 1992 (hence, HL-93) statistically projected over 75 years to produce safe bridges as quantified by the selected reliability index. Thus, if bridges are properly maintained, meaning no loss of resistance, bridges can safely carry loads for 75 years based upon the traffic of 1992. No traffic growth, either in volume or weight, was included in the development of the live load model. However, the assumption is that the HL-93 notional live load model is adequately safe today due to conservative assumptions in 1992.

The finite life resistance (the number of cycles due to truck traffic over the design life of the bridge) is also based on 75 years. Most bridges are designed for infinite life, but the few bridges with lower truck traffic volumes are designed for finite life based upon the average daily truck traffic (ADTT) summed over 75 years.

The service limit states are not calibrated to achieve uniform reliability as are the strength limit states. Deterioration data was not available to perform the calibration. Instead, the service limit states are calibrated to achieve member proportions based upon past successful practice.

Durability is a function of design, construction and maintenance. The use of superior materials (e.g., coated reinforcing, improved concrete mixes), additional cover and deck protection treatments can also improve bridge serviceability.

2.7 BRIDGE TREATMENT DESIGN DIRECTION

2.7.1 Bridge Treatments — Pavement Preservation Projects

The Structures Division participates in pavement preservation projects based on the scope of the project:

• Refer to the guidelines for pavement preservation projects if there is a bridge within the project limits.

• If the bridge does not have an existing asphalt overlay, do not perform any work on the bridge (i.e., skip bridge).

• If the bridge has an existing asphalt overlay: ○ Evaluate the integrity of the existing asphalt on bridge (cores recommended) ○ If substrate is in good condition as determined by the pavement engineer:

+ Rotomill and replace asphalt ≤ 1½ in. on deck and approach slab + Coordinate with the Structures Division + Provide taper on roadway, as necessary; profile and cross slope

adjustments could be required



+ Do not place any additional material weight on bridge; material placed cannot exceed material removed

○ If substrate is not adequate as determined by the pavement engineer, do not perform any work on the bridge or: + Remove asphalt to deck and approach slab, install waterproofing

membrane and replace asphalt 2-in. minimum and 3-in. maximum, provide taper on roadway, as necessary; profile and cross slope adjustments could be required

+ Coordinate with the Structures Division + Do not place any additional material weight on bridge; material placed

cannot exceed material removed

2.7.2 Bridge Treatments – Pavement Rehabilitation Projects

Refer to guidelines for pavement rehabilitation projects. Bridge preservation requirements within a rehabilitation project include:

• Bridge asphalt overlay (only applies to bridges with an existing asphalt overlay); allowable work based on the pavement evaluation is as follows: ○ Remove asphalt to deck and approach slab ○ Pothole patch concrete deck and approach slab ○ Install waterproofing membrane ○ Replace asphalt; 2-in. minimum and 3-in. maximum thickness ○ Provide taper on roadway, as necessary; profile and cross slope adjustments

could be required ○ Do not place any additional material weight on bridge; material placed cannot

exceed material removed • Bridge overlays (nonasphalt):

○ Sound concrete deck and approach slab ○ Pothole patch concrete deck and approach slab ○ Apply overlay system; for example, thin bonded polymer overlay or polyester

concrete overlay ○ Provide taper on roadway, as necessary; profile and cross slope adjustments

could be required ○ Bridge deck hydrodemolition and overlay ○ Bridge joint closure, repair or replacement ○ Bridge approach slab jacking ○ Concrete repair and sealing:

+ Superstructure - Parapet concrete repair and sealing - Beam end repair - End diaphragm placement

+ Substructure - Abutment concrete repair and sealing - Bent concrete repair and sealing



• Miscellaneous items ○ Spot painting structural steel ○ Bearing replacement

The Structures Division supplements funding for work items beyond deck and approach slab treatments.

2.7.3 Asphalt Application Guidelines

The Bridge Management Division inspects and maintains nearly 2000 bridges on the state highway system. Most of the bridges have a reinforced concrete deck. Approximately 1030 currently have an asphalt overlay on top of the concrete deck. An asphalt overlay on a bridge deck is not a preferred treatment for the following reasons:

1. Trapping Water. Asphalt traps moisture between the overlay and the surface of the concrete. Asphalt is a pervious material. Water penetrates the asphalt and traps the water on top of the membrane. Combined with salt, the presence of water rapidly increases the rate of deterioration and corrosion in the reinforcing in the bridge deck.

2. Membranes. Waterproofing membranes do not always perform as intended. A properly installed waterproofing membrane can block the chloride and water infusion into the bridge deck. However, once the overlay is installed, the membrane cannot be inspected or repaired. Instead of protecting the bridge deck, a failed membrane actually serves as a catalyst for rapid deterioration of the bridge deck.

3. Dead Load. Asphalt adds load to the bridge. Bridges typically carry 3 in. of asphalt. Installing more than 3 in. of asphalt reduces the capacity to carry live load (trucks). In some cases, the reduction in capacity requires that the bridge be posted for loads less than the legal amount.

4. Inspection. Asphalt prevents proper visual inspection of the bridge deck. Bridge deck condition is inspected and assessed every two years. However, a bridge deck overlaid with asphalt cannot be visually assessed and, therefore, timely rehabilitation of the deck cannot be planned. Improper inspection often leads to a reduced service life for the bridge and requires more expensive treatments to maintain the bridge.

5. Service Life. Asphalt does not provide a desirable service life. Asphalt is typically expected to last between 7 and 10 years. To properly maintain over 2000 bridges in the state, providing a treatment on a single bridge rarely occurs more often than once every 15 years.

6. Bridge Parapets. Asphalt greater than 3-in. thick can create an unsafe height for the bridge parapet. The height of the top of the parapet with respect to the driving surface is the most important factor in preventing vehicles from rolling over the parapet.

Do not apply an initial asphalt overlay to a new bridge. Older bridges, depending on the bridge condition, could be good candidates for an asphalt overlay and waterproofing membrane. Designed properly and installed correctly, an asphalt overlay and waterproofing membrane can



adequately protect the bridge deck, provide a smooth riding surface, help adjust profile irregularities and align the maintenance cycle of the bridge with that of the adjoining roadway.

Use the following recommendations when considering a bridge deck for an asphalt overlay and waterproofing membrane:

• Consider only bridge decks that have an existing asphalt overlay and where the adjoining roadway pavement is asphalt.

• Core the existing asphalt to determine the thickness and integrity of the lower layers. • Evaluate the cores and the underside of the deck (assess if the membrane is

functioning). • Determine if a partial removal and replacement (mill and fill) of the asphalt is acceptable. • Do not add weight to the bridge. • Limit the maximum overlay thickness to 3 in. • Allow for proper drainage of the bridge deck (raise catch basins when necessary). • Allow for adequate movement and drainage at the bridge joints (provide an acceptable

joint) to maintain integrity and function of the original joint.

2.8 UTILITY ATTACHMENT REQUIREMENTS

Do not place utilities on structures unless no reasonable alternative exists. Utilities placed on structures require the approval of the Region Director and the Structures Design Manager. Attachment of natural gas utility lines will not be permitted to bridge structures that serve vehicular traffic or crosses over vehicular or pedestrian traffic.

When no other option is viable based on the requirements in Administrative Rule R930-7-9, approval must be obtained by the Structures Design Manager following the procedures outlined in Section 2.3. Submit the following items to the Structures Design Manager for review:

• Project memorandum: Provide and address the following: ○ Project scope of work ○ Map of project limits ○ Utility location ○ Structures impacted ○ Utility owner and stakeholders

• Structure design attachment details with situation and layout • Detailed cost estimate to attach the utility to the structure • Alternative utility layout for the option when not attached to the structure • Alternative cost estimate for the option when the utility is not attached to the structure • Geotechnical boring logs and geotechnical analyses to support costs if required

Providing the above information does not constitute approval. Do not proceed with any work until receiving formal approval.



If approved by the Structures Design Manager, attach utilities on the structure as follows:

• Coordinate with the utility owner and meet all utility owner requirements. • Provide individual sleeved casings, conduits or ducts as appropriate. • Typically, place utilities in the first interior bay; conceal utilities from view (locate above

girder bottom flange); attaching utilities to the visible exterior of the superstructure is not permitted.

• Lay out all utility pipes, etc., on a straight line for the full length of the bridge structure. • Place all utilities that carry liquids inside a casing that extends the entire length of the

structure for a distance of 10 ft beyond the ends of the approach slabs. When carrying pressurized utilities, design the casing to carry full service pressure to provide a satisfactory containment in case the utility is damaged or leaks.

• Accommodate pipes that pass through abutment walls, diaphragms and other structural members.

• Paint visible pipes and pipe sleeves to match the color of adjacent structural members. • Attach utility supports to girder webs. Use roller or cradle type supports that adequately

support the pipe, sleeve or conduit and that accommodate longitudinal thermal expansion and contraction.

• Do not allow manholes or access openings for utilities in bridge decks, webs, bottom slabs or abutment diaphragms.

• Do not use field welding on steel girders. Field drilling on concrete girders and steel girders at approved locations is permitted.

• Use attachments with permanent type, approved epoxy resin anchors. Attachment hardware must be galvanized or stainless steel. Some epoxies creep when subjected to permanent tension loads; therefore, use appropriate bonding materials.

• Do not allow a utility attachment that impairs inspection and maintenance activities. • Do not allow a utility attachment that reduces the vertical clearance or freeboard. • Do not locate attachments on the upstream side of the bridge because, during floods,

trees and other drift occasionally strike the girders. • Do not allow bolting through the deck. • For final approval authority for attachments to historic bridges, coordinate with the

Environmental Services Division and other stakeholders identified in the environmental document.

• Do not permit a utility installation that interferes with the contractor constructing the bridge.

• Do not allow a utility attachment design that discharges the pipe product into the stream or river in the event of a pipe failure.

• Do not allow the use of bridge members to resist forces caused by moving fluids. • Provide an expansion deflection device where the conduit or casing crosses a bridge

expansion joint. • Locate trenching in the vicinity of existing bents or abutments a sufficient distance from

footings to prevent undercutting of existing footings or to prevent disturbing foundation soils for future foundations.

The Structures Division must review the general layout and structure attachment details for acceptance. Refer to Administrative Rule R930-7-9 “Utilities on Highway Structures” for more information on attaching utilities to bridge structures.



2.9 OVERHEAD SIGN STRUCTURE GUIDE SIGN REQUIREMENTS

The Traffic and Safety Division manages the guide sign panels that are placed on the overhead sign structures. If a sign panel must be replaced on an existing overhead sign structure, provide a sign panel no larger than the existing sign panel with maximum height and width dimensions equal to the existing sign panel. Locate the centroid of the new sign panel in the exact location on the overhead sign structure as on the existing sign panel.

If the new sign panel does not meet the stated requirements, the existing overhead sign structure and foundation cannot be reused. Deviation from this requirement requires a structural design criteria deviation. See Section 2.3.2. Include a structural design analysis to validate the structural integrity due to the change in conditions with the request. Refer to Section 22.2 for overhead structure design requirements.

2.10 CULVERT HEADWALL REQUIREMENTS

Provide a concrete headwall on all culverts 36 in. or greater. Pipes less than 36 in. in diameter do not typically require concrete headwalls. Refer to Section 22.1.

2.11 INSPECTION AND MAINTENANCE ACCESS REQUIREMENTS

Make all bridge superstructures, expansion joints, backwalls, enclosed compartments and bearings accessible for long term inspection by arms length, direct viewing. Make expansion joints accessible for direct viewing from the underside of the joint. For expansion joints at abutments, provide inspector access between the end diaphragm and the backwall to allow inspection of the backwall and the underside of the expansion joint by arms length, direct viewing. Make open framed superstructures accessible with walkways and ladders or by use of a snooper truck.

Box girders with an inside depth of 5 ft or more require access through the box girder for interior inspection. In all box girders, provide an opening that is at least 3 ft by 3 ft, has a hinged metal door that swings out from the box girder and has a removal bolt for locking. Minimize the weight of the door to facilitate opening by inspection personnel. Where required, provide a method of ladder support for inspection access.

Consider providing lighting in box girders during the scoping stage of the project. Document the evaluation in the Structures Type Selection Report (TSR).

See Chapter 3 of the BMM for an in-depth discussion on bridge inspection.



2.12 PUBLIC ACCESS DESIGN REQUIREMENTS

Prevent public access to closed areas such as between full height concrete diaphragms and backwalls on seat type abutments. Use a chain link type fence between the exterior girders and wingwalls with an access gate that has a removal bolt for locking. Do not inhibit the normal expansion and contraction movement of the structure with the detail used.

2.13 PROJECT DEVELOPMENT TOOLS

2.13.1 Electronic Program Management

The ePM system allows employees, local government agencies and consultants to access information on planning, funding, scheduling and staffing of design projects. The ePM system is a tool to assist Project Managers through the project development process.

The Bridge Program Manager initiates a project through screen 300 in ePM, which assigns the project a Project Identification Number (PIN). This establishes initial funding, project location and project description. After the STIP process is completed, a project is funded and moved into scoping status within ePM. The Structures Design Manager works with the appropriate Region to establish a schedule in MS Project, which inputs the critical dates into ePM. At this point, the committed advertising date is set in ePM. As the project progresses through design and construction, ePM is used to enter staff time, to track expenditures and estimated costs and to monitor the status of the project.

On a programmatic level, ePM is used to track current program balances, project balances, history of funding adjustments and funding types.

Additionally, the location and date in ePM is used by the GIS Division to map projects at various stages, which allows planners to combine projects in close proximity and provide information to interested parties on current and future projects.

For additional guidance on the ePM system, refer to the website.

2.13.2 ProjectWise

Use ProjectWise as required by the Project Development Division. Refer to the website for more information regarding the document posting requirements, attributes and document naming conventions.

2.13.3 Project Delivery Network

The Project Delivery Network outlines the stages, activities and tasks necessary for developing projects for advertising. The Project Delivery Network describes the project development



sequence for the structure design process, identifies the deliverables from each activity and task and describes the coordination between the structural engineer and other design disciplines.

For additional information on the project development process, refer to the Project Delivery Network guidance on the website, the UDOT Project Manager Guide and the UDOT Local Government Guide.

2.13.4 Digital Signature

A digital signature is any electronic means that indicates that a person adopts the contents of an electronic document. All plan sets require a digital signature to validate acceptance. Refer to Section 4.2.10.

2.14 STRUCTURE NUMBER

2.14.1 Structure Number Assignment

The Structures Division assigns a unique structure number to each permanent structure for which plans are prepared. The structure number is the primary means of identification for the structure and never changes throughout the structure life.

Request a new structure number or drawing number through the website. Figure 2.1 describes the process for the structure number assignment.

When a structure is replaced, a new structure number is assigned to the new structure. The records of the demolished structure remain in the bridge inventory for historical purposes; therefore, the structure number of a demolished structure is never reused.

When a structure is repaired or modified, the structure retains the existing structure number, and a new structure drawing number is requested to differentiate the new plan set from the original plan set.

Refer to Section 3.4.4 of the BMM for structure type designations for both state owned structures and structures owned by local governments.

Obtain a structure number for retaining walls that meet the following requirements:

• Any retaining wall 3 ft or greater (maximum exposed face) • Any retaining wall regardless of height that could affect the integrity of a structure (e.g.,

retaining wall supporting an adjacent building) • Any retaining/noise wall that exceeds the parameters in the UDOT Standard Drawings

(SW series)



Structure Type

Description Letter

DesignationNotes

Bridge Timber superstructure A Does not include timber decks

Bridge Structural steel superstructure C Includes steel arches and trusses

Bridge CIP or precast concrete superstructure without prestressing

D Typically includes rigid frames and monolithic concrete T-beams

Bridge Prestressed (either pretensioned or post-tensioned) concrete superstructure

F Includes voided slabs and box beams with prestressing

Culvert Concrete three-sided or box culvert included in the scope of buried structures (LRFD Section 12)

E

• Typically carry water and have earth fill cover

• Includes concrete arch culverts and many pedestrian undercrossings

Overhead sign

Overhead span type (single or double mast), cantilever (including dual) or butterfly sign

G

• Does not include roadside signs • Includes overhead VMS

structures • Includes roadside VMS

structures

Headwall Concrete headwall H Only used for culverts that do not receive a structure number

Retaining wall Retaining wall R

Rockery sloped walls (0.4H:1.0V or steeper) are not assigned a structure number and are limited to 3 ft of exposed face

Miscellaneous Structures not characterized by any other description

V

• Includes flexible culverts (e.g., structural plate or corrugated metal pipe)

• Includes pipe arrays, vaults and various drainage structures

• Includes tunnels

Figure 2.1 — STRUCTURE NUMBER ASSIGNMENT

When a project includes several retaining walls, all retaining walls of the same type (e.g., concrete cantilever, mechanically stabilized earth (MSE) single stage, MSE two stage, MSE block) are grouped together to assign a structure number. The grouped retaining walls use the same general structure number (e.g., R-123) provided that a letter designation is added to the end of the structure number to distinguish each individual retaining wall (e.g., R-123A, R-123B). Use one plan set for all retaining walls grouped under a single structure number. Provide a location plan showing all retaining walls covered by the general structure number (e.g., R-123) on the first sheet of the plan set (e.g., general notes, quantities) followed by the details of each individual retaining wall.

Similarly, when a project includes several overhead sign structures, overhead sign structures of the same type (e.g., single cantilever, double cantilever, single mast span, double mast span, variable message sign (VMS) span, VMS cantilever) are grouped together to assign a structure number. The overhead sign structures use the same general structure number (e.g., G-123), provided that a letter designation is added to the end of the structure number to distinguish each



individual overhead sign structure (e.g., G-123A, G-123B). Organize overhead sign structure plans the same as retaining wall plans.

Any barrier that retains more pavement and earth than Standard Drawing BA 3A1 does not require a structure number, but design calculations and plans must be submitted for review.

2.14.2 Structure Number Placement

The structure number (not the drawing number, when different) is placed on the constructed structure either by permanently casting the number into a structural concrete member or by another method as detailed in the plans.

Place the structure number on the structure according to Figure 2.2.

Structure Type Location Attachment Comments

Bridge Right approach parapet

Cast into concrete

Two way bridges require structure number placement at two locations

Concrete drainage structure (includes three- sided precast structures)

Top and exposed face of headwall (two places, each headwall)

Cast into concrete Center on headwall facing away from box opening

Pedestrian bridge Support adjacent to outside shoulder

Cast into concrete

Overhead sign structure Near top of foundation

Cast into concrete

Retaining wall At the beginning of the wall and at 500-ft intervals

Cast into concrete

Visible to inspectors on the ground in front of the wall or on top of the coping

Concrete arch drainage Headwall or end beam

Cast into concrete Center on headwall facing away from drainage opening

Structural steel multiplate arch

Top of headwall or end beam/coping

Cast into concrete Center on headwall facing away from drainage opening

Note: Cast the structure number into the bridge element. Do not use the structure drawing number if different than structure number.

Figure 2.2 — STRUCTURE NUMBER LOCATION



Refer to WS sheets for the exact size and location of the structure number on a bridge. Use the WS sheets as a guide for the size of the structure number on other structure types.

Structural supports for high mast lighting, traffic signals, camera poles, etc., though designed as structures, are not given a structure number by the Structures Division. The structural supports are numbered and inventoried by the Traffic and Safety Division, which also applies to standardized structures constructed according to the UDOT Standard Drawings.

2.14.3 Structure Drawing Number

The Structures Division assigns to each structure plan set a unique structure drawing number. The structure drawing number is the primary means of identifying the structure plan set. The structural engineer requests the structure drawing number through the website.

For new structures, the structure drawing number is the structure number.

For a modification of an existing structure, the structure drawing number modifies the existing structure number:

• For bridge and box culvert widenings, the structure drawing number adds a W to the end of the existing structure number. (Examples: C-123W; E-1234W).

• For a bridge rehabilitation, the structure drawing number adds R to the end of the existing structure number. When a bridge is rehabilitated multiple times, the structure drawing number adds Rn to the end of the existing structure number, where n is the number of times the bridge has been rehabilitated. (Examples: Original plans = C-123; 1st rehabilitation project = C-123R; 2nd rehabilitation project = C-123R2; 3rd rehabilitation project = C-123R3).

• For the extension of an existing box culvert, the structure drawing number adds En before the structure type designation of the existing structure number, where n is the number of times the box culvert has been extended. (Examples E1E-1234. E2E-1234).

• For projects that include the rehabilitation or preservation of multiple bridges with similar details, details of all bridges can be combined into one multiple bridge plan set with one structure drawing number. In this case, the structure drawing number is M-nnn, where M denotes a plan set that includes details for multiple structures and nnn is a unique three digit number.

The use of a multiple bridge plan set is limited to bridges with work items that use generic details and limited bridge specific details. Work items that can be part of a multiple structure plan set include the following:

• Concrete repair and sealing (e.g., deck, parapets, girders, substructure elements, slope protection)

• Deck pothole patching and waterproofing membranes and overlays • Joint seals • Parapet modification or replacement • Expansion joint repair, closure or replacement • Structural steel painting



• Bearing maintenance • Diaphragm modification

Work items that must use a single structure plan set include the following:

• Structural member modification initiated to increase the load capacity (repairs initiated to address deterioration that could also increase capacity can be addressed in a multiple structure plan set)

• Structural member replacement (e.g., deck, girders) • Bridge widening

Include all structural work for a specific bridge in a single plan set. If there are structural work items for a bridge that require a single structure plan set and other work items for the same structure that could be part of a multiple structure plan set, include all work items in the single structure plan set.

Refer to the summary in Figure 2.3.

Type Structure Number

Structure Drawing Number

Comment Modification Example

New bridge C-123 N/A C-123

Bridge widening C-123 Add W after number

C-123W

Bridge rehabilitation

C-123 Add Rn after number

C-123R, C-123R2, C-123R3, etc.

n = the number of times rehabilitated

Box culvert widening

E-1234 Add W after number

E-1234W

Box culvert extension

E-1234 Add En before type designation

E1E-1234, E2E-1234, etc.

n = the number of times extended

Overhead sign structure

G-123A, G-123B, etc.

Combine individual signs of the same type on the same project into one plan set

G-123

Rehabilitation or preservation of multiple bridges in one plan set

Various M-nnn M-123 nnn = unique three digit number

Figure 2.3 — STRUCTURE DRAWING NUMBER



2.15 STRUCTURE NAME

The structure name is a description of the bridge crossing and includes the name of the feature carried and the feature crossed. A few examples of structure names include “US 40 over Silver Creek and UPRR,” “10600 South over I-15,” “I-70 over the Colorado River.” The structure name provides a clear description of the bridge. In some cases, the structure name must be abbreviated to fit within the title block of the plan sheets.

2.16 STRUCTURES DIVISION ROLES AND RESPONSIBILITIES

UDOT uses a variety of project delivery methods, depending upon the project type, local vs state, funding source, etc. This section discusses the roles and responsibilities of the Structures Division for each method of project delivery, where the project includes structural elements. For example, the discussion references the application of QC/QA to each project delivery method.

2.16.1 Design Bid Build


DBB is a project delivery method in which the agency or owner contracts with separate entities for the design and construction of a project. DBB has three main sequential stages — the design stage, the bidding stage and the construction stage.

2.16.1.2 Structures Division Involvement

All projects advertised through the UDOT system follow the Project Delivery Network.

The design reviewer and oversight reviewer roles are consistent with the design quality processes and procedures defined in Chapter 5.

2.16.2 Design Build


DB is a contracting method in which a single contract is awarded to provide design and construction services. In this method of project delivery, contractors and consultant design firms form an integrated team and assume the responsibility for design and construction. DB allows the overlap of design and construction activities, often resulting in faster project delivery. The project is often segregated into packages or segments, allowing construction to begin on portions of the project while other elements are still being designed.




The SDDM references several areas when approval from the Structures Design Manager is required. In a DB project, the Structures Design Manager is the Structures Division representative and not the Structures Design Manager for the design builder.

During the procurement stage, the Structures Division representative provides the structures baseline requirements and defines the structures project specific elements or use on the project and provides Requests for Proposals (RFP) document review. The lead structures engineer for the Program Manager is responsible for developing structure concept plans, specifications and estimates and for reviewing the RFP for compatibility within the project. Any changes to the RFP require approval from the Structures Division representative.

Design submittals depend on the approved quality management plan provided by the design builder. In most cases, design submittals occur at 30%, 60%, 100%, early released for construction (ERFC) and released for construction (RFC). The 60% design submittal can be either formal or informal. An informal submittal is treated as an over the shoulder review without formal comments.

The Structures Division provides or assigns design and oversight reviewers.

The design reviewer provides a detailed review of the submittal package for conformance with the contract requirements, the SDDM, the BMM and AASHTO requirements. The design reviewer also considers errors, omissions and constructability. The design reviewer works with the design builder and the Structures Division representative to verify that all comments are addressed and all end of project submittals are provided. The design reviewer attends project team meetings through the design stage of the project.

The design reviewer role can be performed by the Program Manager’s lead structural engineer, a structural engineer contract employee through a work task order or a consultant structural engineer selected using a direct select or a Structures Division representative. The difference in selection methods between the work task order and a direct select is based on anticipated contract value. The design reviewer cannot be part of the DB team.

The oversight reviewer provides a cursory review of the design submittal package for conformance with the contract requirements, the SDDM, the BMM and AASHTO requirements. The oversight review also considers errors, omissions and constructability. The oversight reviewer reviews the review comments provided by the design reviewer to ensure applicability and adherence to the project requirements. Attendance at project team meetings is determined on a project by project basis, depending on the scope of work.

The oversight reviewer role can be performed by a structural engineer contract employee through a work task order, a consultant structural engineer selected using a direct select or a Structures Division representative. The difference in selection methods between the work task order and a direct select is based on anticipated contract value.

The design reviewer and oversight reviewer roles are consistent with the design quality processes and procedures defined for a DBB project. Refer to Chapter 5.



The Structures Division representative attends project team meetings including all review comment resolution meetings and provides a Department perspective on the applicability of review comments. The Structures Division representative notifies the Program Manager, Project Manager and RE that the structure plans are approved to be released for construction and provides technical support during construction.

2.16.3 Construction Manager/General Contractor


CMGC is a modified DB process in which the owner holds the contract for both the design consultant and the contractor. The option is available to select bid-build at the end of the design stage if the negotiated price for construction is not acceptable to the owner. The option places the owner in charge of project decisions and keeps the cost savings with the owner.

CMGC goals are to deliver projects quicker than the traditional method, to provide better budget controls and to develop a close partnership between the owner, the designer and the contractor. CMGC can be a suitable method for projects that are complicated and can benefit from a collaborative effort during the project scoping stage.

CMGC allows identification and mitigation of high risk elements in the design stage. The risk sharing approach reduces contractor risk and results in lower bid prices. The design consultant develops partial design plans and specifications to advertise for the CMGC services. The contractor submits a guaranteed maximum price to provide construction input into design, manage the construction contract and construct the project. The contractor works with the design consultant to ensure innovation, cost savings and reduced delivery time.


The SDDM references several areas where approval from the Structures Design Manager is required for certain aspects of structures design. A CMGC project is consistent with a DBB project, which follows the Project Delivery Network. The Structures Design Manager is the UDOT Structures Design Manager.

During the project scoping stage, a Structures Division representative participates in scoping the project, provides the structures design criteria, helps develop the RFP and participates in selecting the design consultant (if not an internal design) and the contractor.

The design submittals and review process for a CMGC project are consistent with the design quality processes and procedures for a DBB project. Refer to Chapter 5. The major difference is the ability to tailor a design to the contractor’s approach and divide the plan set into early procurement and phasing packages.



2.16.4 Public/Private Partnerships


P3 is a type of project that includes financing and/or maintenance provided by private entities. Although primarily awarded as DB projects, both CMGC and DBB contracts are permitted. DB P3 projects with maintenance are often referred to as design build finance maintain (DBFM). P3 projects create a contract between private entities (e.g., toll facilities, developers, contractors) to provide financing plus other elements identified in the contract. Other elements can include design, construction and maintenance for the project. Not all P3 projects provide both financing and maintenance. The financing repayment terms can be based on tolls or other measures defined in the project RFP. P3 is most often associated with construction and operation of toll roads, but P3 use has expanded into nontoll facilities.


The Structures Division involvement in a P3 project follows the same procedure as outlined for a DB project.

2.16.5 Permit Project


An encroachment permit allows certain time limited construction, installation and repair activities to occur within the state right of way in conformity with state and federal law.

A structural/geotechnical review is required before issuing a permit that authorizes any activity that:

• Could directly impact the function of a state bridge facility (e.g., bridge widening, culvert extension) (Activity 1)

• Could indirectly impact the function of a bridge facility (e.g., retaining walls supporting the roadway, culverts crossing beneath roadways) (Activity 2)

• Does not impact or permanently impact structures, but has structural components (e.g., a toe wall at the edge of a trail) (Activity 3)

• Impedes upon UDOT ROW (e.g., a new pedestrian bridge over a state roadway) (Activity 4)

If any permitting activity that requires a structural/geotechnical review occurs, the following requirements apply:

• The design must meet SDDM and BMM requirements including the Structures QC/QA Procedures in Chapter 5.

• The design must be reviewed by the Structures Division including the Geotechnical Design Division.



• For Activities 1 and 4: ○ The design must be performed by a designer prequalified on the Structural

Design and Management Support Services Pool. ○ Construction management and inspection services must follow the UDOT

construction management and inspection services procedures (e.g., sampling, testing, documentation, as built plans).

• For Activities 2 and 3: ○ Construction management and inspection services can be by permit inspectors

as appropriate.

Executed facility maintenance agreements are required between UDOT and the requester.


Structural permit project reviews are coordinated at a Region level. If a permit request involves designing, modifying or impacting a structure within or adjacent to the state ROW, the Region Permit Officer provides the Structures Project Engineer with the plans, shop drawings and other supporting documents to complete the review.

The Structures Project Engineer or designee reviews the documents for consistency with Department specification requirements and examines how the permit work affects state facilities. The documents are returned to the Region Permit Officer either approved or noted to revise and resubmit. If the review comments require revisions to the documents, the Region Permit Officer returns the documents to the requester stating to revise, update and resubmit for approval. When all comments have been addressed, the Structures Project Engineer sends a Structures Division memorandum to the Region Permit Officer granting approval to issue the permit.

Three types of impacts are typically encountered:

1. Installation of a New Facility Next to a Structure. The design reviewer reviews the plans to ensure that the permanent installation does not negatively impact the existing structure and that the construction does not threaten the structural integrity.

2. Modification of an Existing UDOT Structure. Modifications can range from modifying slope protection to culvert extensions and bridge widenings. The design reviewer ensures that the design is performed and checked according to UDOT design requirements, that the plans are complete and accurate relative to the work being performed and, when necessary, that a structure number has been requested.

3. Installation of a New Structure Over a State Roadway. The design reviewer ensures that the design is performed and checked according to UDOT design requirements, that the plans are complete and accurate relative to the work being performed and, when necessary, that a structure number has been requested.

Design reviews on permit projects are limited to internal Structures Division staff. The Structures Project Engineer tracks all permit project reviews performed by the Structures Division.



2.16.6 Local Government Project – UDOT Advertisement


Local government agencies implement planning and programming activities for improvements and maintenance activities for local streets and roads. The local government agency applies for funds through the appropriate programming authority when they need federal or state assistance. FHWA has authorized UDOT, through a stewardship agreement, to provide oversight on all local projects using federal aid.


The Structures Division performs design reviews and oversight reviews on local government agency projects with federal aid.

During the consultant selection process, the Structures Division representative helps develop the Request for Qualifications (RFQ) and assists in the selection process when requested by the Region.

The design review and oversight review roles used on a local government project are identical to the roles on DBB projects with minor differences. When setting up the project, the Project Manager can choose which network is used to deliver the project — the Project Delivery Network or the local government Project Delivery Network. If the local government network is chosen, the design review submittals are 30%, 60% and 90%. Typically, a 60% structure review is not required unless a unique project element exists. If the 60% review is required, only redlined plan comments are provided.

The design review and oversight review roles can be performed by a structural engineer contract employee through a work task order or a consultant structural engineer selected using a direct select, depending on the contract value, or a Structures Division representative. If a Structures Division representative is used in the design review role, the oversight review is not required.

The local government is responsible for any project costs that exceed the funded amount. To limit the project cost, the Structures Division’s first choice is to conduct the design review and/or oversight review role in house when work loads allow.

The Structures Division representative attends project team meetings and comment resolution meetings, provides a Department perspective on the applicability of comments and technical support during construction, and notifies the Structures Design Manager when all required documentation has been provided and the plan package is ready for final structure acceptance.

See Chapter 7 of the BMM for more discussion on local government projects.



2.16.7 Local Government Project – NonUDOT Advertisement


Local government agencies deliver structure projects on local routes that are agency funded or for which alternative funding is provided by grants, developers or other means. Federal funding requirements do not apply to the project delivery process.


The Structures Division has no ownership or oversight responsibilities for the project. However, the Bridge Management Division must inspect and report the bridge condition to FHWA. Therefore, the Structures Division encourages local government agencies to use the SDDM to establish structural design criteria, follow the plan development requirements and follow the Structures QC/QA Procedures to ensure quality within the design.

See Chapters 3 and 7 of the BMM for more information on bridge inspection requirements and local government coordination.

2.16.8 Emergency Project Delivery


An emergency project is the result of an unforeseen event that affects a structure. Examples include a bridge hit by an oversized vehicle, scour due to flooding or damage due to an earthquake.


The Structures Design Division develops the bid contract documents similar to a DBB project. Advertisement is based on the BMM and not the Project Delivery Network when the contract value is under $500,000.

See Section 2.4.6 of the BMM and Chapter 5 of the BMM for more information on emergency projects.

2.16.9 Maintenance Project Delivery


The Maintenance Division is responsible for completing routine maintenance and responsive maintenance activities. See Chapter 6 of the BMM. Depending on the complexity of the maintenance activity, the work can be performed by internal crews or through procurement of a contractor.




Routine maintenance tasks do not usually require the assistance of the Structures Division. However, responsive maintenance activities often require Structures Division support to evaluate and develop solutions that do not affect structural integrity.

An issue could be identified by bridge inspectors during bridge inspection or by the maintenance shed during routine site visits. When an issue is identified, the Structures Division works with the maintenance personnel to determine if the issue needs to be monitored or addressed. If the issue needs to be addressed, further discussions ensue regarding the timing of the repair and whether the repair is considered a permanent solution or a temporary solution.

If the repair is a permanent solution, the Structures Construction Engineer works with maintenance personnel to develop the repair and costs. Through the collaborative process, the repair approach is determined and the level of detail required is determined to clearly convey the concept. The work performed is documented and placed in the structure record. When the repair is performed through procurement of a contractor, the Structures Construction Engineer develops plans according to standard Structures Division practices and follows QC checking and audit procedures. The development of the plans often involves direct coordination with contractors. The project does not follow the Project Delivery Network.

If the repair is a temporary solution, the Structures Division works with the maintenance personnel to develop the temporary repair approach. In most cases, plans are not developed. A more permanent solution will be developed and addressed in a future project.

2.17 PROJECT DOCUMENT REQUIREMENTS

2.17.1 Structure Plans

Submit structure plans by structure drawing number.

Name the file:

PIN_Structure Dwg #_Plans_Adv_YYYYMMDD.pdf

Example:

11223_F-345_Plans_Adv_20141215.pdf

2.17.2 Structure Special Provisions

Provide a Word version and a .pdf for each structure related special provision within a project.

Name the file:

PIN_Structure Dwg #_Special Provision #_Special Provision Name_YYYYMMDD.pdf



Example:

11223_F-345_03139S_Concrete Bridge Deck Removal_20141215.pdf

2.17.3 Engineer's Estimate

Refer to the ProjectWise attributing on the website for the naming convention.

2.17.4 Measurement and Payment


2.17.5 Acceptance and Documentation


2.17.6 Structure Design Calculations

Organize the structure design calculations by element (e.g., deck, girder, diaphragm, seismic) from superstructure to substructure. Include the designer and checker initials on each page of the calculations and number the pages according to the section. Provide a calculation cover sheet at the beginning of each element section. Submit the structure design calculations as a single .pdf. Include all computer program input and output files to support the design calculations.

Name the file:

PIN_Structure Dwg #_Calcs_Adv_YYYYMMDD.pdf

Example:

11223_F-345_Calcs_Adv_20141215.pdf

2.17.7 Load Rating Package

Refer to Chapter 4 of the BMM. Use the electronic file naming convention for the load rating package, except add the PIN_ to the beginning of the file name.

2.17.8 Structure Type Selection Report

Use the Structure TSR template on the website to develop project alternatives. The Structures Design Manager signs the Structure TSR during the plan in hand stage.



Name the file:

PIN_Structure Dwg #_Report_Report Name_YYYYMMDD.pdf

Example:

11223_F-345_Report_TSR_20141215.pdf

2.17.9 Seismic Design Strategy Report

Use the SDSR template on the website to develop the preliminary and final structure design seismic strategy. The Structures Design Manager signs the SDSR during the plans, specifications and estimate (PS&E) stage.

Name the file:

PIN_Structure Dwg #_Report_Report Name_Stage_YYYYMMDD.pdf

Example:

11223_F-345_Report_SDSR_PIH_20141215.pdf

2.17.10 Geotechnical Report

The Geotechnical Report is a required structure deliverable. Refer to the UDOT Geotechnical Manual of Instruction for layout and report requirements.

If the Geotechnical Report addresses a single structure, name the file:

PIN_Structure Dwg #_Report_Geotech_Final_YYYYMMDD.pdf.

Example:

11223_F-345_Report_Geotech_Final_20141215.pdf

If the Geotechnical Report addresses several structures on a project, name the file:

PIN_Project Name_Report_Geotech_Final_YYYYMMDD.pdf.

Example:

112233_I-215_4700South_to_SR-201_Report_Geotech_Final_20141215.pdf

2.17.11 Hydraulics Report

The Hydraulics Report is a required structure deliverable. Refer to the UDOT Drainage Manual of Instruction for layout and report requirements.



If the Hydraulics Report addresses a single structure, name the file:

PIN_Structure Dwg #_Report_Hydraulics_Final_YYYYMMDD.pdf.

Example:

11223_F-345_Report_Hydraulics_Final_20141215.pdf

If the Hydraulics Report addresses several structures on a project, name the file:

PIN_Project Name_Report_Hydraulics_Final_YYYYMMDD.pdf.

Example:

112233_I-215_4700South_to_SR-201_Report_Hydraulics_Final_20141215.pdf

2.17.12 Other Reports or Memoranda

Projects often require additional reports or memoranda to address specific issues.

Name the file:

PIN_Structure Dwg #_Memo_Subject_Stage_YYYYMMDD.pdf

Example:

11223_F-345_Memo_Bearing Stiffener_PS&E_20141215.pdf

2.17.13 QC Cover Sheets

Combine all QC cover sheets into one file and organize the sheets by date which, preferably, corresponds to the design stages.

Name the file: PIN_Structure Dwg #_Review_QC_YYYYMMDD.pdf Example: 11223_F-345_Review_QC_20141215.pdf 2.17.14 Project QA Audit

Combine all Project QA Audit forms into one file and organize the form by date which, preferably, corresponds to the design stages.



Name the file: PIN_Review_QA_YYYYMMDD.pdf Example: 11223_Review_QA_20141215.pdf 2.17.15 Structural Review Comment Resolution Form

Complete and submit the Structural Review Comment Resolution Form to document structural reviews.

Name the file:

PIN_Project Name_Review_Form Name_YYYYMMDD.pdf.

Example:

112233_I-215_4700South_to_SR-201_Review_STR_CRF_20141215.pdf

2.17.16 Milestone Review Comment Resolution Form


2.17.17 Structural Review Completion – Plan in Hand (Stage 3) Review

Complete and submit the Structural Review Completion – Plan in Hand (Stage 3) Review form to document completion of the structural review.

Name the file: PIN_Review_Form Name_YYYYMMDD.pdf Example: 11223_Review_PIH_REV_20121215.pdf 2.17.18 Structural Review Completion – PS&E (Stage 4) Review

Complete and submit the Structural Review Completion – PS&E (Stage 4) Review form to document completion of the structural review.



Name the file: PIN_Review_Form Name_YYYYMMDD.pdf Example: 11223_Review_PSE_REV_20121215.pdf 2.17.19 Alternate QC/QA Procedures Acceptance

The Structures Division prefers that all designs be performed following the Structures Division QC/QA Procedures. If an alternative QC/QA procedure is requested, complete and submit the Alternate QC/QA Procedures Acceptance form during the scoping stage of the project.

Name the file:

PIN_Acceptance_Form Name_YYYYMMDD.pdf

Example:

11223_Acceptance_ALT_ACC_20141215.pdf

2.17.20 Situation and Layout Acceptance

The Structures Design Manager accepts the structures design approach and situation and layout at the plan in hand stage of the project.

Name the file:

PIN_Acceptance_Structure Dwg #_Form Name_YYYYMMDD.pdf

Example:

11223_Acceptance_F-345_S&L_ACC_20141215.pdf

2.17.21 Final Structure Acceptance

The Structures Design Manager accepts the final structure design before advertising the project.

Name the file:

PIN_Acceptance_Structure Dwg #_Form Name_YYYYMMDD.pdf

Example:

11223_Acceptance_F-345_Final_ACC_20141215.pdf



2.17.22 Structural Design Criteria Deviation

A structural design criteria deviation is required for all deviations from defined structures design criteria and procedures. See Section 2.3.2. Requests for approval must be submitted at the scoping stage of the project.

Name the file:

PIN_Structure Dwg #_Form Name_YYYYMMDD.pdf

Example:

11223_F-345_DEV_ACC_20141215.pdf

2.17.23 Structural Documentation Template

Refer to the Structural Documentation Email (3S6) template on the website for the submittal outline and requirements.

Refer to the Structural Documentation Email (5S1) template on the website for the submittal outline and requirements.

2.18 COMPUTER SOFTWARE

Document the program name and version number used in all designs.

Document any errors in the software identified during the design and checking process. If an error is discovered, submit a brief memorandum to UDOT describing the error, the significance of the error, the program name and the program version.

UDOT evaluates the memorandum, confirms the findings and, where necessary, initiates remedial action to correct any design deficiencies in previously designed and constructed structures that used the software.

Designers are responsible for the accuracy of all computer software used for design.

2.19 RAILROAD AGREEMENTS

Where construction of a project requires the use of Railroad properties or adjustments to Railroad facilities, an agreement is necessary between UDOT and the Railroad. The Region Utility and Railroad Coordinator prepares the agreement with the Railroad.

Refer to the Project Delivery Network for required exhibits and information to support the agreement process. Include the Railroad Notes and Clearance sheet in all structure plan sets that involve Railroads.



To prevent a project involving the Railroad from becoming unduly delayed, anticipate a minimum six month review period from the Railroad.

2.20 RESEARCH

The Structures Division strives to be innovative in finding solutions to structures related challenges. The Structures Design Division and the Geotechnical Design Division actively participate in the local and national research efforts.

If the Department does not have a specification for a product and the Structures Division desires to evaluate a new product for use on structures, the Structures Division coordinates with the Research Division to evaluate the product. The Research Division performs a background evaluation, executes a research project, and helps implement the product into a project. Refer to UDOT “Policy 07B-03 Experimental Features and Evaluation of New Products” for more information.

The Structures Design Manager, Bridge Management Engineer, Geotechnical Design Manager or designee participates in research projects.

2.21 MATERIALS

Product acceptance is performed on a project basis according to the acceptance criteria defined in the project specifications.

If the Department has a specification for a particular product, a supplier for that product may submit the product to the Materials Division for evaluation. The product is evaluated against the specification and by a new product evaluation panel. If the product is approved, the product is added to the approved product list. The Materials Division maintains the approved product list. Inclusion on the approved product list constitutes acknowledgment that the material meets specification criteria, streamlining the documentation that is submitted for that item during construction; the acknowledgement is not an indication of performance.

The Structures Construction Engineer participates on the new product evaluation panel.

2.22 CONSTRUCTION

The Structures Division supports projects through construction. On consultant designed projects, construction support services are included in the contract and tracked through the Project Delivery Network. The Engineer of Record (EOR) attends the project prebid meeting if part of the project and the preconstruction meeting, and addresses structure questions and requests throughout construction.



The Structures Construction Engineer, Structures Design Manager or EOR performs just in time training on structure projects that have unique or new features.

Refer to Chapter 6 for more discussion.

2.23 STRUCTURAL DESIGN AND MANAGEMENT SUPPORT SERVICES POOL

The Structural Design and Management Support Services Pool is for as needed services, based on the intermittent needs of the Structures Division for support. The Structures Design Manager directs the services and establishes the duration based on the support need. Selection can be made through an on-call work task order or a pool direct select.



3

FEBRUARY 2015

DESIGN MEMORANDA AND REPORTS



Design Memoranda and Reports 3-i

TABLE OF CONTENTS

3.1 STRUCTURES DIVISION MEMORANDA ................................................................... 3-1

3.1.1 Concept Report ................................................................................................ 3-1 3.1.2 Site Visit ........................................................................................................... 3-2

3.2 STRUCTURE SCOPE AND ESTIMATE REPORT ...................................................... 3-2 3.3 STRUCTURE TYPE SELECTION REPORT ............................................................... 3-2 3.4 SEISMIC DESIGN STRATEGY REPORT ................................................................... 3-3 3.5 GEOTECHNICAL REPORT ........................................................................................ 3-3 3.6 HYDRAULICS REPORT .............................................................................................. 3-3

LIST OF FIGURES


Design Memoranda and Reports 3-ii


Design Memoranda and Reports 3-1

Chapter 3 DESIGN MEMORANDA AND REPORTS

Design memoranda and reports document decisions made during the planning and design process. Use the templates provided on the website as guidance in developing the design reports; deviations from the templates require approval of the Structures Design Manager. Comply with the requirements defined in Chapter 5 and the Structures QC/QA Procedures for the documents before distribution.

3.1 STRUCTURES DIVISION MEMORANDA

Structures Division memoranda are used as a tool to clarify, convey and document information more formally than an email but, for example, with less detail than a Structure Scope and Estimate (S&E) Report. A memorandum is never used to pursue funding. Funding requests require a Structure S&E Report.

Use a memorandum to document issues or concerns in the project file or structures record as a response to a Region request or to document a site visit. When a memorandum is used to summarize structure specific recommendations resulting from requests initiated by the Region or other divisions, summarize the request, recommendations, options, costs and any assumptions within the memorandum. Copy the Bridge Management Engineer on all structure specific memoranda. Place a copy of the memorandum in the structures project folder in ProjectWise or in the structures record as appropriate.

The following sections identify two specific uses of Structures Division memoranda.

3.1.1 Concept Report

During the Region’s project concept stage, the Structures Division uses a Structures Division memorandum to communicate structure design concepts for inclusion by the Project Manager in the structures summary in the Region’s Concept Report. Document project objectives, existing information, assumptions and structure recommendations for all structures (e.g., bridges, box culverts, walls, sign structures) within the project limits. Include a cost estimate; see Section 4.4. Coordinate with the Geotechnical Design Division during development of recommendations and include costs associated with the geotechnical investigation. Coordinate with the Hydraulics Section, as necessary, during development of recommendations and include costs associated with additional studies or permit requirements.

If the Concept Report affects an existing structure, place a copy of the memorandum in the structure record and include the Bridge Management Engineer when the memorandum is sent to the Region.



3.1.2 Site Visit

Document observations from field visits in a memorandum to the project file or in the structure record, as appropriate. Include information to convey the purpose of the visit, suggested actions, recommendations and conclusions.

3.2 STRUCTURE SCOPE AND ESTIMATE REPORT

The Structure S&E Report is used for planning purposes and to identify funding needs for the Structures Division bridge rehabilitation/replacement program and bridge preservation program. See Chapter 2 of the BMM for a thorough discussion on Structures Division planning and programming. The Structure S&E Report defines the project objective and provides relevant background information for the structure. Develop an assessment and recommendations based on the bridge deficiencies and needs relative to the defined objective. Note special considerations to identify critical unknowns and potential project challenges.

Focus the cost estimate on the quantifiable items for each discipline and on the costs associated with design engineering, construction engineering and contingencies. Refer to Section 4.4 to develop the cost estimate. Determine reasonable construction sequencing to identify proposed activities, durations of activities, feasible work windows to perform work and traffic control phasing. Construction sequencing can impact the unit costs or need for an increased contingency percentage. Document all assumptions to support the scope, schedule and budget refinements that must be considered when the project progresses into the design stage.

The Bridge Management Team (BMT) approves the Structure S&E Report before inclusion in the program. See Chapter 2 of the BMM for additional details.

3.3 STRUCTURE TYPE SELECTION REPORT

The Structure Type Selection Report (TSR) presents the results of a feasibility type study and the selection evaluation criteria. The Structure TSR expands upon the information developed in the Structure S&E Report. Describe the existing structure and determine bridge layout and geometry for new bridge/widening design. Determine treatments for rehabilitation and preservation projects. Discuss the proposed work alternatives and refine the cost estimate based on the available information. Identify the recommended alternative and include a justification and total cost for the preferred alternative.

The Structures Design Manager approves the Structure TSR at the plan in hand stage of the Project Delivery Network.



3.4 SEISMIC DESIGN STRATEGY REPORT

The Seismic Design Strategy Report (SDSR) documents the structure seismic design approach. Provide a brief description of the basis for the seismic criteria and design specifications. Provide a general structure description and define the seismic level of performance. Describe the structure design seismic behavior including the global design strategy, the earthquake resisting system (ERS) and the earthquake resisting elements (ERE). Provide the seismic results and expected performance.

The Structures Design Manager reviews the Seismic Design Strategy Report (Preliminary) at the plan in hand stage of the Project Delivery Network for conformance. Once the bridge design is complete, the Seismic Design Strategy Report is updated with the seismic results. The Structures Design Manager approves the Seismic Design Strategy Report (Final) when approving the final structures documentation package.

Chapter 13 discusses seismic design in detail.

3.5 GEOTECHNICAL REPORT

The Geotechnical Report provides the general purpose of the geotechnical investigation and describes the scope of work. Refer to all pertinent reports and previous investigations. Describe any existing facilities and document all findings including site conditions, surface drainage, geology, faulting and seismicity, soil materials, geohydrologic conditions and climatic conditions. Summarize all laboratory and field testing and the physical relationship to the plan and profile of the planned work. Describe the proposed structures and recommendations for foundation design and analysis.

The geotechnical engineer completes the analysis and prepares the report. Refer to the UDOT Geotechnical Manual of Instruction for report requirements.

Refer to Section 10.7 for design interaction between disciplines for developing the Geotechnical Report.

3.6 HYDRAULICS REPORT

The Hydraulics Report summarizes the hydrologic and hydraulic design. The Hydraulics Report provides the following structure related information:

• Water surface elevation for the design and base flood • Suggested low chord elevation • Necessary structure waterway opening dimensions, skew angle and bottom of channel

elevation • Hydraulic scour analysis results • Flow velocities



• Any necessary channel and abutment protection measures The hydraulics engineer performs the analysis and prepares the Hydraulics Report. Refer to the UDOT Drainage Manual of Instruction for additional details and required content.

Refer to Section 10.6 for design interaction between disciplines for developing the Hydraulics Report.

FEBRUARY 2015

CONTRACT DOCUMENTS, PLANS,SPECIFICATIONS AND ESTIMATES



Contract Documents, Plans, Specifications and Estimates 4-i

TABLE OF CONTENTS

4.1 CONTRACT DOCUMENTS ......................................................................................... 4-1 4.2 PLANS ....................................................................................................................... 4-2

4.2.1 CADD Standards ........................................................................................... 4-2 4.2.2 Plan Sheet Requirements .............................................................................. 4-3

4.2.2.1 Sample Sheets ............................................................................ 4-3 4.2.2.2 Working Standards ...................................................................... 4-4 4.2.2.3 Checklists .................................................................................... 4-4

4.2.3 Plan Sheet Numbering .................................................................................. 4-4 4.2.4 Plan Sheet Sequence .................................................................................... 4-4 4.2.5 Reinforcing Callouts ...................................................................................... 4-4 4.2.6 Dimensioning ................................................................................................. 4-6 4.2.7 Units of Measurement ................................................................................... 4-7 4.2.8 Scales ..................................................................................................... 4-7 4.2.9 Plan Sheet Abbreviations .............................................................................. 4-7 4.2.10 Digital Signature ............................................................................................ 4-7 4.2.11 Structure Design Drawings ............................................................................ 4-8 4.2.12 Existing Structures Plans ............................................................................... 4-8 4.2.13 As Built Drawings .......................................................................................... 4-8

4.3 SPECIFICATIONS ....................................................................................................... 4-8

4.3.1 UDOT Standard Specifications ...................................................................... 4-8 4.3.2 Supplemental Specifications ......................................................................... 4-9 4.3.3 Special Provisions ......................................................................................... 4-9

4.3.3.1 Types of Special Provisions ......................................................... 4-9 4.3.3.2 Preparing Special Provisions ....................................................... 4-10

4.4 ESTIMATE ................................................................................................................... 4-11

4.4.1 Engineer’s Estimates ..................................................................................... 4-11

4.4.1.1 Concept or Scoping Estimate ...................................................... 4-11 4.4.1.2 Preliminary Estimate .................................................................... 4-11 4.4.1.3 PS&E Estimate ............................................................................ 4-11

4.4.2 Contingencies ................................................................................................ 4-11

4.4.2.1 Mobilization .................................................................................. 4-12 4.4.2.2 Traffic Control .............................................................................. 4-12 4.4.2.3 Preconstruction Engineering ........................................................ 4-12 4.4.2.4 Construction Engineering............................................................. 4-12

4.4.3 Quantities ..................................................................................................... 4-12


4-ii Contract Documents, Plans, Specifications and Estimates

4.4.3.1 Units of Measurement .................................................................. 4-12 4.4.3.2 Rounding ..................................................................................... 4-13 4.4.3.3 Significant Digits .......................................................................... 4-13

4.5 MEASUREMENT AND PAYMENT DOCUMENT ........................................................ 4-14

4.5.1 Item Numbers ................................................................................................ 4-14 4.5.2 Plan Quantity ................................................................................................. 4-15 4.5.3 Lump Sum ..................................................................................................... 4-15 4.5.4 As Constructed Quantity (Unit Measurement) ............................................... 4-16 4.5.5 Variable Quantity Items ................................................................................. 4-16 4.5.6 Multiple Funding Sources .............................................................................. 4-16

4.6 ACCEPTANCE AND DOCUMENTATION ................................................................... 4-16 4.7 ESTIMATING UNIT PRICES ....................................................................................... 4-17

4.7.1 Cost Basis 4-17 4.7.2 Cost Adjustments .......................................................................................... 4-17

APPENDIX 4A ABBREVIATION LIST .................................................................................. 4-19 APPENDIX 4B UNITS OF MEASUREMENT IN SUMMARY TABLE ................................... 4-26

LIST OF FIGURES

Figure 4.1 — REINFORCING FOR MAJOR CALLOUTS ......................................................... 4-5


Contract Documents, Plans, Specifications and Estimates 4-1

Chapter 4 CONTRACT DOCUMENTS, PLANS, SPECIFICATIONS AND ESTIMATES

The contract documents must clearly communicate to prospective bidders the details of the project to allow the submission of a responsive proposal from bidders. Contractors, material suppliers and construction inspection personnel must clearly understand how to execute their responsibilities and to meet expectations.

This chapter discusses contract documents, plans, specifications and engineer’s estimates. Appendix 4A includes the abbreviation list, and Appendix 4B has a summary table for units of measurement that apply to structure design projects. The conventions in this chapter for the contract document elements are intended to achieve uniformity in content and presentation.

4.1 CONTRACT DOCUMENTS

The contract documents are the written, legally binding documents that define the roles, responsibilities and work under the contract. The individual documents that constitute the contract documents are defined in the UDOT Standard Specifications.

An advertising package containing bid documents is advertised to bid or as a RFP for DB projects. The contractor prepares a bid based on the contract documents. Key components of the advertising package include:

1. Plans. Plans are graphic and pictorial portions of the contract documents showing the design, location and dimensions of the work, generally including plan views, elevation views, sections and design details.

2. Specifications. Specifications are the portion of the contract documents consisting of the written requirements for materials, equipment, systems, standards and workmanship for the work, and acceptance requirements for work performed under the contract.

3. Engineer’s Estimate. The engineer’s estimate provides quantities of items to bid and provides the anticipated construction costs used for programming and funding purposes.

4. Measurement and Payment (M&P) Document. The M&P defines how items are measured, the basis for payment, what the payment includes and what the payment does not include.

Once the project is awarded, and all bonds, insurance certificates and contract documents have been signed, the Department issues a notice to proceed (NTP) authorizing the contractor to proceed with the work. The contract includes the plans, specifications and measurement and payment documents. The following sections discuss the contract documents in more detail.


4-2 Contract Documents, Plans, Specifications and Estimates

DBB projects also require documentation to advertise the project that is not included in the contract documents. The advertising checklist for DBB projects defines most of the requirements and must be completed before advertising. Refer to the website for information on the advertising checklist. Also, in association with the M&P is the UDOT Acceptance and Documentation Guide (A&D). The A&D is provided for information only. The A&D summarizes the submittal, testing and acceptance requirements defined in the specifications and is used as a tool by the RE during construction.

4.2 PLANS

Project plans are a collection of plan sheets that detail items requiring construction. Structure plan sheets grouped under a structure drawing number represent a structures plan set. Include all information required to construct the structure in the structures plan set with the exception of information contained in the project specifications.

The following sections are intended to improve the consistency and effectiveness of structure plan sheets by simplifying the plan sheets and providing a uniform appearance and content.

Deviations from the following sections require approval from the Structures Design Manager. The Structures Division does not enforce rigid rules but does demand consistency. Structural engineers and detailers are responsible for implementing the guidelines. The Project Manager or Structures Design Manager has the option of requesting a CADD standards check to ensure that the CADD standards are met.

4.2.1 CADD Standards

UDOT has consolidated the CADD procedures across all disciplines. Follow the UDOT CADD Standards Manual except as noted in this section. The UDOT CADD Standards Manual is available on the website.

Use one of the two standard Structures Division borders (StructBorder.dgn or StructBorder_LG-DB.dgn). Use the StructBorder_LG-DB.dgn for local government and DB projects. The signature block for the border requires an approval signature from the project specific Structures Design Manager. Use the StructBorder.dgn for all other structure projects. The signature block for the border requires approval signature from the UDOT Structures Design Manager. Complete the title blocks according to the UDOT CADD Standards Manual. Include the responsible consulting firms’ name under the words Structures Division in the title block.

List the structure number and the drawing number on each plan sheet. The structure number is the permanent identification number assigned to the structure. The drawing number identifies the plan sets associated with the structure number. For a new bridge, the structure number and drawing number are the same. For a rehabilitation/widening or other project on a previously constructed structure, the drawing number consists of the structure number with additional identifiers indicating the nature of the project. The structure number does not change. Section 2.14 provides additional information on structure numbers and drawing numbers.



4.2.2 Plan Sheet Requirements

The plan sheets included in the bid package are PDFs scaled to print on 11″ × 17″ sheets. Use line weights, scales and fonts as defined in the UDOT CADD Standards Manual except as modified in the following sections. Refer to the UDOT CADD Standards Manual for specific CADD requirements. Do not repeat project specification requirements in the plan set. Do not list proprietary materials unless required by local governments or owners or approved by FHWA. Match bid item names in the plan sets with names used in project specifications and in the M&P.

Use the following conventions:

• Draw all details at 1:1. Draw all plan views in the real world coordinate system using the proper seed file and coordinate system to ensure compatibility with other discipline drawings. The practice allows referencing of structures files, roadway files, survey files, etc., and ensures that the structure plans can use Inroads files to verify stations and offsets.

• Use 3D layout and details when required. • Avoid overcrowding. If all details that normally appear on a specific sheet result in

overcrowding, use an additional sheet. When placing a view or section on another sheet, add a note or notes with references to the related sheets. For example: ○ SEE “APPROACH SLAB DETAILS” FOR SECTIONS A-A AND B-B. ○ SEE “APPROACH SLAB PLAN” FOR LOCATIONS OF SECTIONS A-A AND

B-B. • Avoid oversized details. Too many plan sheets make plans difficult to read. Do not

oversize details and spread details over numerous sheets. • Place a North arrow on all plan views, including plan views of details. • Place the quantity block in the lower right hand corner of the sheet. • Place sheet notes above the quantity block. • When details or structural elements are complex, use two drawings — one for

dimensions and the second for reinforcing details. • Only show a detail once within a set of plans. If required on another sheet, cross

reference the detail. • Use 100-ft stations. Show stationing to the one hundredth of a foot. Label stationing at

100-ft intervals, and provide tick marks at 20-ft intervals. For short structures or details, label the station of the intermediate tick to establish direction of stationing and scale.

The primary tools provided by the Structures Division to promote consistency are sample sheets and working standards. The Structures Division also supplies checklists outlining typical sheet content. Available sample sheets, working standards and checklists are listed, and available for download, on the website.

4.2.2.1 Sample Sheets

Sample sheets (SS) are examples of typical structure plan sheets. Use the sheets as a guide when preparing structure plan sets. Sample sheets depict typical layouts and information provided on structure drawings. Sample sheets guide users in developing plan sets and



encourage consistency in presentation. Sample sheets do not depict specific requirements. For specific requirements, refer to the SDDM, plan sheet checklists, working standards (WS) and structure design (SD) drawings.

4.2.2.2 Working Standards

Working standards (WS) define the form, function and requirements of commonly used plan sheets. The WS sheets identify areas requiring the input of the structural engineer with a blue note. Replace the border with the project border, and update the sheet where indicated by the blue notes. Ensure that the WS sheet is compatible with the design and details of a specific structure. The WS sheet becomes part of the sealed plan set, and the EOR is responsible for all information on the WS sheet. Review the WS sheets, identify any areas of concern and inform the Structures Division of proposed changes in addition to the changes indicated by the blue notes. The Structures Design Manager must approve changes to the WS sheets in areas not indicated by the blue notes.

4.2.2.3 Checklists

Plan sheet checklists provide direction on content to include on plan sheets. However, checklists are not all inclusive, and structural engineers must review the plans and include all information required to construct the structure and reflect the designer’s intent.

4.2.3 Plan Sheet Numbering

Number each plan sheet of a drawing number sequentially from one to the total number of sheets required for the plan set. The only exception is that geotechnical sheets have the same number but a letter is added. The convention permits adding geotechnical sheets without changing the sheet numbering for plan sheets following the geotechnical sheets.

4.2.4 Plan Sheet Sequence

The sequence of the plan sheets is the Situation and Layout (S&L) sheet(s) followed by the geotechnical sheets and structure detail sheets. Present the structure detail sheets in the order of construction with the reinforcing schedule at the end of the structures plan set.

4.2.5 Reinforcing Callouts

List major callouts in the form: A-BMC AT X, where A is the number of reinforcing bars, B is the reinforcing size, M is the reinforcing location code and C is the reinforcing bar mark. For example, 122-5S1 AT 6″ indicates that there are 122 #5 bars spaced at 6 in. in the deck and that the bar dimension is listed in the reinforcing schedule under the reinforcing bar mark, S1. See Figure 4.1. Minor callouts use the form BMC, where B is the reinforcing size, M is the



reinforcing location code and C is the reinforcing bar mark. Always list reinforcing spacing in inches. The SS sheets include examples of reinforcing callouts.

Figure 4.1 — REINFORCING FOR MAJOR CALLOUTS Below is a list of bridge reinforcing location codes:

• Abutment A • Wingwall W • Girder G • Footing F • Column C • Bent cap B • Diaphragms D • Deck slab S • Approach slab AS • Sleeper slab SS • Parapet P • Catch basin CB Below is a list of miscellaneous structure reinforcing location codes:

• Apron A • Barrel B • Headwall H • Retaining wall R Include pile, prestressed girder and drilled shaft reinforcing in the pile or drilled shaft pay item; do not include the reinforcing in the reinforcing schedule. Do not provide a bar mark on the pile or drilled shaft sheet.



Number reinforcing consecutively for each type — A1, A2, A3, B1, B2, B3.

When construction is phased, structural engineers can indicate in which phase the reinforcing is installed by using a three digit number, where the first digit indicates the phase. For example, bar A101 is in phase 1 and bar A201 is in phase 2. Reinforcing crossing the phase line is included in the phase placed first. Reinforcing in a closure pour is included in the phase placed second. Where appropriate, use a single reinforcing callout to identify reinforcing across both phases. Detail the reinforcing crossing the phase line to show the required lap at the phase line or the required mechanical splice type.

Specify reinforcing cover on details when the required cover is different from the cover listed in the general notes.

Include reinforcing in precast elements in the reinforcing schedule. Reinforcing in precast elements does not require a special reinforcing code.

4.2.6 Dimensioning

Provide sufficient dimensions to define the structure. Dimension so that the reader need not add or subtract dimensions to determine the length, width or height of an element. Refer to the sample sheets for examples of accepted dimensioning. Do not use stacked fractions.

All dimensions are to ⅛ in. except structural steel dimensions, which are to 1/16 in. All elevations are to 0.01 ft. Provide a (+) or (-) symbol with the dimension when the dimension is not a multiple of ⅛ in. State the dimension as follows when placing a string of identical dimensions: 10 spaces at 8′-0⅛″(-) = 80′-1″.

Provide dimension strings along a single line. Do not offset dimension lines in a continuous string of dimensions.

Avoid duplicate dimensions, which create problems if a dimension is changed on one detail and not another. Ensure that dimensions are consistent from one detail to another when placing duplicate dimensions. An acceptable use of duplicate dimensions is to duplicate a single dimension in a detail view to assist in identifying the orientation of the detail.

Do not provide point callouts that do not agree with a dimension string or could disagree with a dimension string. For example, do not provide elevations at the top and bottom of a wall plus a dimension from the top to bottom of the wall. Do not provide a station and offset at the end of the wall plus a dimension from the abutment to the end of the wall.

Verify that multiple dimension strings on a single detail add to the same value.

Place dimensioning horizontally or vertically. Place vertical dimensioning so that the dimensioning is read from the right. If practical, place the dimension above or to the right of a detail.

A dot in lieu of arrows is acceptable at intermediate dimension points.



List dimensions greater than 12 in. as feet and inches. List dimensions less than 12 in. as only inches. List dimensions equal to 12 in. as either 1 ft or 12 in., with 1 ft preferred.

Existing dimensions that are not exactly known are listed with a (+/-) after the dimension.

4.2.7 Units of Measurement

Use US customary units — feet, inches, pounds, yards, etc.

4.2.8 Scales

Use the scales defined in the UDOT CADD Standards Manual. Use the following scales to supplement the scales listed in the UDOT CADD Standards Manual. Do not use other scales and do not use the scales listed below in nonstructure plan sets:

• 2:1 • 3:1 • 4:1 • 5:1 • 6:1 • 8:1 • 15:1 4.2.9 Plan Sheet Abbreviations

Where practical, avoid using abbreviations except as noted in the abbreviation list. See Appendix 4A. Do not use abbreviations in titles of details or in title blocks.

Do not use periods in abbreviations in structure plan sets. The omission is recommended by the International Committee on Weights and Measures for SI units and is advocated by the American Standards Association Sectional Committee for scientific symbols and abbreviations that are not complete English words. For example, use 60 cu ft rather than 60 cu. ft. The omission of periods saves time, labor and space and does not reduce readability.

Do not use apostrophes. Do not use the plural in abbreviations. The abbreviation of the plural is the same as the singular. For example: 22 lb, 40 cu yd, 25 in., 30 ft, 70 gal.

4.2.10 Digital Signature

UDOT requires digital signatures. Refer to the website for information on the digital signature process.

Provide a PE stamp on the first sheet of a plan set. The signature of the EOR in the signature block on the border on all following sheets on the Senior Design Engineer line serves as an effective stamp. The EOR is responsible for all sheets in the structures plan set. The first



geotechnical sheet in the plan set is stamped by the geotechnical engineer, and the geotechnical engineer is responsible for the geotechnical recommendations, but the EOR must ensure that the geotechnical sheets and recommendations are appropriate for the structure presented in the plans.

4.2.11 Structure Design Drawings

SD drawings identify specific engineering requirements. SD drawings are a design aid and list specific design requirements or details, but are not plan sheets and are not included in plan sets.

4.2.12 Existing Structures Plans

Mark the existing structure plans as “FOR INFORMATION ONLY” on each existing structure plan sheet. On bridge replacement or widening projects, include the entire existing structure plan set, and include in the structures drawings table on the index to sheets in the roadway plan set. On bridge rehabilitation or preservation projects, include the applicable existing structure plan sheets and provide an index for the information only sheets on sheet 1 of the S&L.

4.2.13 As Built Drawings

See Section 6.6.5.

4.3 SPECIFICATIONS

Specifications present the written requirements for work methods, materials and acceptance for the work performed under the contract. UDOT maintains standard and supplemental specifications.

During design, evaluate the review periods in the specifications for compatibility with the project. Extremely large or complex projects with multiple submittals could require more review time than the specifications provide. Coordinate with the Structures Design Manager, and prepare a modification to the specification when additional review time is required. The specification modification must explicitly define the number of days needed for review and approval and any requirements for scheduling multiple submittals for large projects with several structures.

4.3.1 UDOT Standard Specifications

The UDOT Standard Specifications are included in all Department construction contracts. The specifications are written to the contractor and define the contractor’s responsibility, the items of work the contractor is expected to provide and the Department’s expectations.



The UDOT Standard Specifications reference the AASHTO LRFD Bridge Construction Specifications and AASHTO Guide Specifications for Bridge Temporary Works in applicable locations.

Ensure that the structure design and the contract documents are consistent with the UDOT Standard Specifications. Where design intent and the UDOT Standard Specifications conflict, coordinate with the Structures Design Manager and either modify the design to conform with the specification requirements or provide a special provision that defines the project specific requirements.

4.3.2 Supplemental Specifications

Supplemental specifications are additions, deletions and/or revisions to the UDOT Standard Specifications that have been adopted since the last printing. The majority of the supplemental specifications will be incorporated into the UDOT Standard Specifications at the next revision. Supplemental specifications are updated when needed and included as part of the contract documents. Use supplemental specifications only if the project requires that section. Supplemental specifications do not apply for all projects. See the website for supplemental specifications to be included in contracts.

4.3.3 Special Provisions

Use special provisions when the plans, UDOT Standard Specifications or supplemental specifications do not adequately define the work or material requirements. Clearly define the required work, submittals, type of materials, equipment required, construction methods or details, how the item of work is measured and the basis of payment. Special provisions are developed and incorporated as either project specific provisions or standard special provisions.

Department special provisions, division special provisions and region special provisions have been developed to uniformly address unique features, processes or changes to the specifications for situations frequently encountered and are available on the website.

4.3.3.1 Types of Special Provisions

Two types of special provisions are available:

1. M Designation (00000M). The M designation indicates a project specific special provision that modifies an existing standard specification. The special provision may require new or modified bid items.

2. S Designation (00000S). The S designation indicates a project specific special provision that is new or entirely replaces an existing standard specification. The special provision could require new or modified bid items.

Use the following procedure to determine the section number for a project specific unique special provision.



Examine the list of bid items to determine if a bid item has already been set up. The first five numbers of a bid item refer to the section number of the standard specification or the special provision that defines the item.

Examine the unique numbers list in the Project Development Business System (PDBS) or on the website for the UDOT Standard Specifications. Choose a number identified as a structures number in the same CSI division as a standard item with similar work.

For example, for a unique special provision for a specific repair on a steel girder, the first step is to determine the appropriate CSI division based on the primary work performed. The work is on a steel girder and applies to Division 05, Metals, of the CSI specifications. The first 2 numbers of the specification represent the CSI division. Many numbers starting with 05 are identified as structure specific in the special provision unique numbers list. Because the main item of work is similar to structural steel, select a number close to 05120. For the example, the title for a unique special provision is:

SECTION 05131S – REPAIR STRUCTURAL STEEL

The letter S at the end of a section number indicates a project specific special provision that is new or entirely replaces a standard specification. Assigning section numbers to special provisions organizes the special provisions into the appropriate divisions. Supplemental specifications are numbered in the same manner.

4.3.3.2 Preparing Special Provisions

When writing special provisions, follow the UDOT Specifications Writer’s Guide and provide special attention to the following items:

• Ensure that the special provision is written to the contractor. All actions are to be performed by the contractor unless otherwise noted.

• Ensure that each paragraph of the special provision is clear to the reader. Do not attempt to cover up omissions or unknowns by using the term “as directed by the Engineer.” Write a special provision in clear, concise and easy to understand language.

• Provide technical definitions. • Provide reasonable and effective meaning to all language in the contract. Tailor the

special provision to the job and language of the contract. • Emphasize the end result. Specify by objective; defined objectives eliminate the

problem of unreasonable tolerances and reduce the cost. Review the special provision and search for content that could be misinterpreted. Words or phrases can have more than one meaning. Eliminate potential conflicts.

• Eliminate conflicts between the plans and the special provision. The special provisions govern if discrepancies arise between the two documents.



4.4 ESTIMATE

The engineer's estimate is an important element of the overall design process. Estimates are used at various stages from planning through advertising to determine project construction costs to align scope and funding. Preparing the estimate requires knowledge of construction methods, fabrication processes and construction costs based on the measurement and payment for each item. The estimate uses item numbers to identify pay items. The following sections discuss the engineer’s estimate at various stages and provide guidance on quantity calculations and contingencies.

4.4.1 Engineer’s Estimates

4.4.1.1 Concept or Scoping Estimate

Before a structure project is assigned a project number, the Structures Division prepares a construction cost estimate. The following applies to developing an initial construction cost estimate:

1. Responsibility. The structural engineer prepares the construction cost estimate, which is submitted to the Project Manager.

2. Basis for Estimate. Base the construction cost estimate on historical data, the anticipated structure type and foundation, right of way, approaches, inflation, estimated square footage of the structure and appropriate contingency.

4.4.1.2 Preliminary Estimate

The structural engineer prepares a preliminary estimate for plan in hand by updating structural costs from the scoping stage construction cost estimate. At this stage, make a reasonable estimate of the major structure quantities and use the appropriate contingency.

4.4.1.3 PS&E Estimate

After the final design is complete, the structural engineer prepares the engineer’s estimate and enters all required data into the PDBS system. Determine the final cost estimate using the calculated quantities and unit prices. Section 4.7 provides guidance for determining unit prices. Refer to the following sections for information on item numbers, item prices, contingencies, etc.

4.4.2 Contingencies

For anticipated but undetermined costs, add a contingency factor based on the sum of the estimated construction costs and preliminary engineering costs. The contingency factor usually decreases as the project progresses and more project specific details are available (e.g., 25%



at concept or scoping stage, 15% at the preliminary design stage and 10% at PS&E). Note that project funding must exceed the engineer’s estimate by 10% to proceed to advertising.

4.4.2.1 Mobilization

Add 10% of the estimated construction cost for the contractor’s mobilization, which is the cost incurred by the contractor to mobilize the labor and equipment necessary for construction. Consider increasing mobilization costs for accelerated bridge construction (ABC) projects with significant equipment demands.

4.4.2.2 Traffic Control

Add 5% of the estimated construction cost for traffic control, which is an estimated amount required to maintain traffic during construction.

4.4.2.3 Preconstruction Engineering

Add 10% of the estimated construction cost for engineering.

4.4.2.4 Construction Engineering

Construction engineering refers to the cost of the construction project. Add 10% of the estimated construction cost for construction engineering and management.

4.4.3 Quantities

An accurate estimate of quantities is critical to prospective contractors interested in submitting a bid on the project. The first step in producing an estimate is to calculate the project quantities. Quantities are calculated using the design as shown on the plan sheets. The engineer’s estimate uses the computed quantities and estimated unit bid prices to estimate the total project cost.

4.4.3.1 Units of Measurement

Report the quantity estimates in the quantities table for all contract bid items consistent with the names and units of measurement presented in the M&P. Appendix 4B illustrates typical units of measurement used in the summary tables. Refer to Section 4.5 for three basic methods of measuring contract items for payment — plan quantity, lump sum, and as constructed quantity (unit measurement).



4.4.3.2 Rounding

Round quantities provided in the engineer’s estimate according to the criteria in the rounding accuracy column in Appendix 4B. For all calculations, carry one more decimal place than that noted in Appendix 4B. Document any required rounding of raw estimates in the calculations. Do not round the calculations until the value is incorporated into the engineer’s estimate. All values can be conservatively rounded up, but either up or down rounding is permitted.

4.4.3.3 Significant Digits

Perform quantity calculations considering the implied correspondence between the accuracy of the data and the given number of digits. In all calculations, retain the number of significant digits so that the accuracy is neither sacrificed nor exaggerated. Use the following rules to determine the appropriate number of significant digits:

1. Number of Digits. Any digit that is necessary to define the specific value or quantity is considered significant. For example, when a measurement is taken, the measurement can be recorded as 157, which has three significant digits. If the measurement had been made to the nearest 0.1, the measurement could have been 157.4, which has four significant digits.

Zero can be used to indicate either a specific value, like any other digit, or a number’s order of magnitude. A measurement rounded to thousands can be 120,000. The three left hand digits of the number are significant; each measures a value. The three right hand digits are zeroes and only indicate the order of magnitude of the number rounded to the nearest thousand. The identification of significant digits is only possible through knowledge of the circumstances. For example, the number 1000 can be rounded from 965, in which case only one zero is significant, or it can be rounded from 999.7, in which case all three zeroes are significant.

2. Addition and Subtraction. When adding and subtracting quantities, do not express the significant digits of the answer any further to the right than occurs in the least precise number. The following illustrates the rule:

Consider the addition of three numbers drawn from three sources, the first of which reported data in millions, the second in thousands and the third in units:

163,000,000 217,885,000 + 95,432,768 476,317,768

Round the total to 476,000,000 (e.g., in millions).

3. Multiplication and Division. Do not express the product or quotient for multiplication and division calculations with any more significant digits than used in the calculations. The following illustrates the rule:



a. Multiplication. The following applies:

113.2 × 1.43 = 161.876; round to 161.9

b. Division. The following applies:

113.2 ÷ 1.43 = 79.16; round to 79.2

4.5 MEASUREMENT AND PAYMENT DOCUMENT

The M&P specifies how each bid item in the contract is measured and paid. A sample M&P containing all typical bid items is available for review on the website. The website also provides directions on creating a project specific M&P.

The M&P provides the item number, the item title, method of measurement, basis of payment and any special instructions to the contractor with respect to the pay item. The M&P is used in conjunction with the specifications to substantiate acceptance of materials and work items for both quality and quantity. For each item, the M&P can include information on:

• Measurement procedures • Additional work included in the price of the item • Incidental items included in the price of the item • How quantity changes or quantity estimate errors affect the price The M&P is typically created during the PS&E stage after the quantities listed on the plan sheet summary table are entered into PDBS. The M&P program reads the PDBS item list and automatically populates the M&P. The structural engineer must review standard and nonstandard item descriptions in the M&P to verify that plan and specification requirements are adequately addressed, modify the document to meet specific project requirements and ensure that the modifications are incorporated into the overall project M&P.

4.5.1 Item Numbers

A nine digit number, title and description identify each item listed in the M&P. The first five digits of the item number correspond to the applicable specification. Use digits 6 to 9 to identify standard items. An X in any of the locations in the summary table indicates that the user must define the number. The last character can be a number or one of the following characters:

• * as the last character indicates a special provision is required. An asterisk used in a bid item number collects no history in the PDBS.

• P as the last character indicates that the specific bid item cannot be found, but is covered in the UDOT Standard Specifications or by a supplemental specification. Using a P allows the user to change the title, unit of measurement or description. A P used in a bid item number collects no history in the PDBS.

• D as the last character indicates a dimension must be added or changed. The D is part of the number and not added by the user.



• U as the last character indicates that the item price is the same for every project. • X in any of the last 3 digits in Appendix 4B indicates a variable number. For example,

Appendix 4B item 0222100XD, could be 02221001D for parcel 1, 02221002D for parcel 2, etc.

Appendix 4B lists typical structure item numbers.

4.5.2 Plan Quantity

A plan quantity is the accepted estimated quantity in the bid proposal and is the final quantity for which payment is made unless the RE revises the plan dimensions through an approved change order. For example, granular backfill borrow is measured based on the plan set, which shows vertical fill limits adjacent to the structure. In reality, excavations are sloped next to structures so that the volume of granular backfill borrow placed always exceeds the amount measured for payment. Because contractors bid the item as a plan quantity, UDOT only pays for the quantity needed according to the design plan quantity rather than the quantity that is actually placed by the contractor. In addition, the contractor can elect to over excavate and place additional backfill. The additional quantity is documented for testing frequency but not for payment. Therefore, if the M&P references plan quantity, do not estimate how much will actually be placed; only calculate the quantity based on the dimensions provided in the plans.

4.5.3 Lump Sum

Use lump sum bid items where the scope of work for the item is clearly defined, and the amount of work has a minimal chance of changing during construction. Lump sum payment is considered full compensation to the contractor for all resources necessary to complete the work. The M&P defines which quantities can be estimated as lump sum. The structural engineer notes any special circumstances or relevant information in the M&P. If there is a significant chance of quantity changes, bid the work by the unit and not lump sum. The quantities for the following lump sum items are required as part of the item name in the M&P:

1. Structural Concrete. Note the estimated cubic yards of structural concrete.

2. Structural Steel. Include the approximate steel weight, in pounds, of all steel components within the project.

3. Damp Proofing. Provide the area requiring damp proofing in square feet.

4. Concrete Coating. Identify the square feet of concrete coating required.

5. Specialty/Nonstandard Items. Modify the M&P when the standard description does not accurately define the bid item or the work included in the bid item.



4.5.4 As Constructed Quantity (Unit Measurement)

An as constructed quantity is based on a unit measurement such as length, area, volume or weight. Actual work performed is verified, measured, computed and paid.

4.5.5 Variable Quantity Items

For some items, the exact quantity or element cannot be defined until the contractor begins work (e.g., parapet surface repair, concrete bridge deck repair). Use engineering judgment when entering the item quantity. For the variable quantity items, the contractor provides a unit bid price. The contractor is paid on the amount of work completed. Complete the M&P work description to incorporate all work included in the unit price.

4.5.6 Multiple Funding Sources

Some projects require two or more funding sources for work conducted under various financing arrangements. For projects requiring quantity divisions, segregate the quantities according to the applicable funding source.

4.6 ACCEPTANCE AND DOCUMENTATION

The A&D is used by the RE and construction inspectors to identify required submittals, testing and acceptance criteria for each bid item in the project. The A&D is structured similar to the M&P and includes the item number, item title and pay unit. For each item, the A&D can include information on:

• Contractor submittals • Testing and sampling • Inspection element • Documentation The A&D is typically created after the PS&E stage and after the quantities listed on the plan sheet summary table are entered into PDBS. The A&D program reads the PDBS item list and automatically populates the A&D. The structural engineer must review standard and nonstandard item descriptions in the A&D to verify that plan and specification requirements are adequately addressed, modify the document to meet specific project requirements and ensure that the modifications are incorporated into the overall project A&D. The A&D is provided for information only in the advertising package.



4.7 ESTIMATING UNIT PRICES

Determine unit prices from the following sources:

• PDBS • RS Means Heavy Construction Cost Data, an industry publication • Local contractors • Industry sources (especially for elements with little or no known information) 4.7.1 Cost Basis

The Construction Division maintains a log of past structure construction bid costs, the Bid Tabulations, on a computer spreadsheet. Use the information from the spreadsheet as a starting point for estimating the construction costs. The Construction Division also maintains a page on the website, Estimator’s Corner, that provides additional information on cost estimating. The basic procedure is:

• Find a similar type structure relative to foundation type, crossing type and superstructure type.

• Compare the quantities for the similar type structure to the estimated quantities for the proposed structure.

• Compare the low bid, second and/or third low bid and engineer’s estimate for the similar type structure.

• Develop a reasonable bid estimate with consideration for inflation or other project specific factors.

• Compute an estimated unit cost based on the historical data. • Compute an estimated cost according to the square footage of the structure. • Use the estimated per square foot of structure for scoping estimates and as a check to

verify that current quantities are within historical averages. • Identify elements that could cause the project structure to vary from historical averages.

4.7.2 Cost Adjustments

The structural engineer adjusts the estimated construction costs to reflect the actual conditions (known or anticipated) at the structure. Adjustment factors can include:

• Geographic location • Availability of materials • Time of year • Bidding environment • Reliability of recent construction cost data (e.g., presence of unbalanced bids) • Recent trends in availability and cost of materials (e.g., shortages) • Extent of falsework required • Anticipated difficulty of construction



• Size of project relative to size of previous projects for which cost data is available • Known foundation problems at the bridge site • Specialty equipment • Risk to contractor • Anticipated construction logistics (e.g., traffic control during construction) • Construction schedule • Construction techniques • Any other factors appropriate for the structure • Judgment and experience of the estimator



Appendix 4A

ABBREVIATION LIST Agency Abbreviations Notes BNSF BNSF Railroad FHWA Federal Highway Administration RMP Rocky Mountain Power

UDOT Utah Department of Transportation

UPRR Union Pacific Railroad UTA Utah Transit Authority Descriptive Abbreviations ABND Abandoned ABUT Abutment AHD Ahead APPR Approach APPROX Approximate ARCH Architectural BK Back BENT Bent No abbreviation allowed BNT PL Bent Plate CIP Cast-in-Place CG Center of Gravity C TO C Center to Center

Centerline CLR Clearance COL Column CONC Concrete CNSTR Construction CJ or CNSTR JT or CNSTR JOINT Construction Joint

CL Control Line CC Crash Cushion CF Cross frame C&G Curb and Gutter DIA or Ø Diameter DIAPH Diaphragm EOD Edge of Deck EOSW Edge of Sidewalk EST Estimate, Estimated

L C



Descriptive Abbreviations (Continued) EXIST Existing EXP Expansion FENCE Fence No abbreviation allowed FS Field Splice FIX Fixed FTG Footing GALV Galvanize GA Gauge GDR Girder GRIND Grind No abbreviation allowed

GRND Ground For use in abbreviations for existing ground or ground line

HH Heavy Hex

HOV/T High Occupancy Vehicle and Toll Lane

HOV High Occupancy Vehicle Lane HW High Water HORZ Horizontal ID Inside Diameter

INT Integral or Interior or Intermediate

INV Invert JT Joint LN Lane LW Lightweight MVC Minimum Vertical Clearance NOM Nominal NTS Not to Scale # Number OC On Center OPT Optional OCJ or OPT CNSTR JT Optional Construction Joint O-O Out to Out OD Outside Diameter PHZ Plastic Hinge Zone PL Plate PT Point

PTMVC Point of Minimum Vertical Clearance

QTY Quantity



Descriptive Abbreviations (Continued) ROW Right of way RDWY Roadway RD Round SHLD Shoulder SW Sidewalk SLAB Slab No abbreviation allowed SP Slope Protection SQ Square STD Standard STIFF Stiffener STR # Structure Number SYM Symmetrical TBC Top Back of Curb VERT Vertical VC Vertical Clearance

Dimensional or Quantity Abbreviations CU Cubic CU FT Cubic Feet CFS Cubic Feet Per Second CY OR CU YD Cubic Yards FT Feet FPS Feet Per Second INCH Inch No abbreviation allowed KLF Kips Per Linear Foot KSF Kips Per Square Foot KSI Kips Per Square Inch LIN Linear LF or LIN FT Linear Feet MPH Miles Per Hour LB Pound PLF Pounds Per Linear Foot PSF Pounds Per Square Foot PSI Pounds Per Square Inch SQ Square SQ FT Square Feet SY or SQ YD Square Yards YD Yard



Direction and Geometry Abbreviations (Continued) BRG Bearing CP Control Point E East EB Eastbound EL Elevation LT Left N North NB Northbound OFF Offset PC Point of Curvature PI Point of Intersection PT Point of Tangent PVC Point of Vertical Curve PVI Point of Vertical Intersection PVT Point of Vertical Tangent PGL Profile Grade Line R Radius RT Right S South SB Southbound STA Station SE Superelevation TAN Tangent TC Tangent to Curve W West WB Westbound WP Working Point

Miscellaneous Abbreviations & and APPROX Approximate ADT Average Daily Traffic ADTT Average Daily Truck Traffic MISC Miscellaneous YR Year ME Manhole Electric MG Manhole Gas



Miscellaneous Symbol Abbreviations (Continued) MSC Manhole Storm Drain MSS Manhole Sanitary Sewer MT Manhole Telephone MW Manhole Water UP Utility Pole

Rating Table Abbreviations F Flexure INV Inventory OPER Operating S Shear

Reinforcing Abbreviations ADJ Adjust ALT Alternate A.S. As Shown BF Back Face BAY Bay No abbreviation allowed BTWN Between BOT Bottom CTR Center CLR Cover EA Each EF Each Face EMBED Embedment EQ Equal FF Front Face INC Increment LAP Lap MAX Maximum MIN Minimum REINF Reinforcing or Reinforcement REQ'D Required SPA Spaces STAGGER Stagger No abbreviation allowed TOP Top No abbreviation allowed TYP Typical Do not use parentheses



Right of Way Line Abbreviations ¼ Quarter Section Line 40 40-Acre Line

FRTG R/W Frontage Road Right of Way Line

L/A Highway Limited Access Line N/A Highway No Access Line PE Perpetual Easement Line PL Property Line RR Railroad Right of Way Line

R/W L/A Highway Right of Way and Limited Access Line

R/W N/A Highway Right of Way and No Access Line

R/W Highway Right of Way Line SEC Section Line TE Temporary Easement Line

Signal Line Abbreviations DET Detection Circuit FUT Future Conduit LTG Lighting Circuit PEDC Pedestrian Circuit PEM Pre-Emption Circuit PSH Push Button Circuit PWR Power Source Circuit RAD Radar Detection Circuit SIG Signal Circuit VID Video Detection Circuit

Utility Line Abbreviations

ATMS Automated Traffic Management System

Always use ATMS; never write out

BCTV Buried Cable CTV Overhead Cable PC Pipe Culvert E Overhead Electrical BE Buried Electrical FO Fiber Optic



Utility Line Abbreviations (Continued)

G Gas Identify as High Pressure Gas Line or gas line in callout

IR Irrigation PETRO Petroleum SWR Sanitary Sewer SD Storm Drain BTEL Buried Telephone TEL Overhead Telephone WTR Water



Appendix 4B UNITS OF MEASUREMENT IN SUMMARY TABLE

Item Number Item Estimate

Unit Bid Unit Rounding Accuracy

020560015 Granular Borrow (Plan Quantity) Cubic Yard 1 020560025 Granular Backfill Borrow (Plan Quantity) Cubic Yard 1

020560060 Free Draining Granular Backfill (Plan Quantity) Cubic Yard 1

020750030 Geotextiles – Drainage Square Yard 1

0222100XD Remove Building, Basement, and Foundation Parcel # Parcel 1

022210015 Remove Bridge Each 1 022210020 Remove Box Culvert Each 1 022250010 Asphalt Surfacing Removal (Structures) Square Yard 1 024550010 Pile Driving Equipment Lump 1 024550020 Driven Piles, 12 inch Foot 1 02455003D Driven Piles, inch Foot 1 02455004D Driven Piles, HP × Foot 1 0246600XX Drilled Shafts, inch Foot 1 0262200XX Underdrain, inch Foot 1 026250010 Approach Slab Drain Frame Modification Each 1 026260010 Deck Drain Modification Each 1 026260020 Deck Drain Closure Each 1

02633001D Concrete Drainage Structure, ft wide × ft deep Each 1

026330010 Concrete Drainage Structure Cubic Yard 0.5 026330015 Concrete Drainage Box – Precast Each 1 026450010 Precast Concrete Box Culvert Lump 1 026450020 Precast Concrete Three-Sided Culvert Lump 1 027550010 Concrete Slab Jacking Cubic Yard 1 0282100XX ft Chain Link Fence, Type Foot 1 0289300XX inch Overhead Sign Foundation Each 1

028930XXX inch Overhead (type) Sign Structure Each 1

029820010 Bridge Concrete Grinding Square Yard 1

03056001D Self-Consolidating Concrete (SCC) (est. qty __ yd3) Cubic Yard Lump 1

031390010 Concrete Bridge Deck Removal Lump 1

032110010 Reinforcing Steel – Coated (Plan Quantity) Pound 1

032110015 Reinforcing Steel – Coated Pound 1 032110020 Reinforcing Steel Pound 1 032110025 Reinforcing Steel (Plan Quantity) Pound 1

032110030 Reinforcing Steel – Galvanized (Plan Quantity) Pound 1




Unit Bid Unit Round Accuracy

032110030 Reinforcing Steel – Stainless (Plan Quantity) Pound 1

033100011 Structural Concrete Cubic Yard 1 03310001D Structural Concrete (Est. Qty yd3) Cubic Yard Lump 1 033100020 Concrete – Small Structure Cubic Yard 0.5 033100030 Concrete Slope Protection Square Yard 1 033110010 Joint Closure Square Foot 1 033380010 Precast Substructure Elements Lump 1 033390010 Precast Concrete Deck Panel Square Foot 1 034000010 Precast Approach Slab, __ ft × __ ft Square Foot 1 033720010 Thin Bonded Polymer Overlay, Type I Square Foot 1 033720020 Thin Bonded Polymer Overlay, Type II Square Foot 1 033920010 Penetrating Concrete Sealer Square Foot 1 033930010 Concrete Healer/Sealer Square Foot 1

0341200XD Prestressed Concrete Member, __ ft __ inch Type Each 1

035750010 Flowable Fill Cubic Yard 1 036050010 Approach Slab Jacking Cubic Yard 1 039240010 Column Repair Each 1 039240015 Column Sealing Each 1 039240020 Pedestal Repair Each 1 039240030 Bent Cap Repair Each 1 039240050 Diaphragm Repair Each 1 039240060 Wingwall Repair Each 1 039240070 Abutment Backwall Repair Each 1 039240080 Beam End Repair Each 1 039240085 Parapet Surface Repair Foot 1 039240090 Parapet Sealing Foot 1 039240100 Deck Edge Repair Foot 1 039320010 Concrete Slope Protection Repair Square Foot 1 039330010 Parapet Modification Foot 1 039330020 Parapet End Modification Each 1 039340010 Structural Pothole Patching Square Foot 1 05120001D Structural Steel (Est. Qty lb.) Pound Lump 1 051200020 Structural Steel Pound 10 051250010 Prefabricated Steel Truss Bridge Lump 1 058320010 Expansion Joint Foot 0.1 058320020 Expansion Joint Modification Foot 0.1 058350010 Modular Expansion Joint Foot 0.1 058350020 Modular Expansion Joint Modification Foot 0.1 071050010 Waterproofing Membrane Square Foot 1 071110010 Dampproofing (Est. Qty. sq ft) Square Foot Lump 1




Unit Bid Unit Round Accuracy

079210010 Sealing Existing Concrete Slope Protection Joints Foot 1

079220010 Relief Joint Crack Sealing Foot 1 099810010 Concrete Coating (Est. Qty. sq ft) Square Foot Lump 1

099920010 Cleaning and Overcoating Structural Steel Lump 1

165260010 Electrical Work Bridges Lump 1

FEBRUARY 2015

DESIGN QUALITY



Design Quality 5-i

TABLE OF CONTENTS

5.1 QUALITY PROGRAM .................................................................................................. 5-1

5.1.1 Alternative Quality Procedures ......................................................................... 5-1 5.1.2 Responsibilities ................................................................................................ 5-2 5.1.3 Documentation ................................................................................................. 5-2

5.2 QUALITY CONTROL CHECK ..................................................................................... 5-2

5.2.1 Request for Proposal Check – Design Build Projects ...................................... 5-2 5.2.2 Structure Type Selection Report and Situation and Layout Check .................. 5-2 5.2.3 CADD Standards Check ................................................................................... 5-4 5.2.4 Independent Technical Analysis ....................................................................... 5-4 5.2.5 Plans, Specifications and Estimate Check ....................................................... 5-5

5.3 QUALITY ASSURANCE AUDIT .................................................................................. 5-5 5.4 STRUCTURAL REVIEWS ........................................................................................... 5-5

5.4.1 Request for Proposal Review – Design Build Projects ..................................... 5-7 5.4.2 Geometry (Stage 2) Review ............................................................................. 5-7 5.4.3 Plan in Hand (Stage 3) Review ........................................................................ 5-7 5.4.4 Intermediate Design (Stage 4) Review ............................................................. 5-9 5.4.5 Plans, Specifications and Estimate (Stage 4) Review ...................................... 5-12

5.5 ACCEPTANCE ............................................................................................................ 5-14

5.5.1 Request for Proposals Acceptance — Design Build ........................................ 5-14 5.5.2 Structure Type Selection Report ...................................................................... 5-14 5.5.3 Situation and Layout ......................................................................................... 5-14 5.5.4 Seismic Design Strategy Report (Final) ........................................................... 5-15 5.5.5 Final Structure Acceptance .............................................................................. 5-15

5.6 CONSTRUCTION SUBMITTALS AND REVISIONS ................................................... 5-16

LIST OF FIGURES

Figure 5.1 — DOCUMENTATION OF QUALITY PROCEDURES ............................................ 5-3 Figure 5.2 — STRUCTURAL REVIEWS ................................................................................... 5-6 Figure 5.3 — PLAN IN HAND STRUCTURAL REVIEW TASKS ............................................... 5-8 Figure 5.4 — PLAN IN HAND STRUCTURAL REVIEW TIME .................................................. 5-9 Figure 5.5 — PS&E STRUCTURAL REVIEW TASKS ............................................................ 5-13 Figure 5.6 — PS&E STRUCTURAL REVIEW TIME ............................................................... 5-12 Figure 5.7 — SITUATION AND LAYOUT REVIEW TIME ....................................................... 5-15 Figure 5.8 — FINAL STRUCTURE ACCEPTANCE REVIEW TIME ....................................... 5-16


5-ii Design Quality


Design Quality 5-1

Chapter 5 DESIGN QUALITY

Design quality is an essential element in project development. When properly executed, quality control reduces costs, minimizes errors and enables the project to meet schedules. This chapter presents design requirements for design quality, and discusses the procedures to ensure the quality of all structure deliverables as required by the Project Delivery Network.

5.1 QUALITY PROGRAM

The Structures Division quality program for projects consists of:

1. Project QC/QA. The project structures team follows the procedures as outlined in the Structures QC/QA Procedures. The project structures team designs, checks and audits the structures project documents.

2. Structural Reviews. The Structures Division can assign an independent design reviewer and oversight reviewer to evaluate the structures project documents for adherence to the Structures Division design requirements, consistency and constructability. Structural reviews are performed before the milestone reviews at the plan in hand stage and at the PS&E stage. The structural engineer responds to and addresses the structural review comments as outlined in the Structures QC/QA Procedures.

The structural reviews and the milestone reviews can occur concurrently on a case by case basis depending on the project. The Project Manager works with the Structures Design Manager as necessary on schedule revisions.

3. Milestone Reviews. The project team completes project milestone reviews at the end of

each stage of the Project Delivery Network. The project team responds to and addresses the milestone review comments as outlined in the Structures QC/QA Procedures.

4. Structures Division Acceptance. After the project team addresses comments from the structural reviews and the milestone reviews, the Structures Division accepts the design at the plan in hand stage and at the advertising stage.

The Structures QC/QA Procedures and all forms associated with project QC/QA, milestone reviews, structural reviews and the Structures Division acceptance are available on the website.

5.1.1 Alternative Quality Procedures

The Structures QC/QA Procedures allow alternative procedures. Complete and submit alternative QC/QA procedures or requested modifications in writing to the Structures Design Manager for approval using the Alternate QC/QA Procedures Acceptance form during the


5-2 Design Quality

scoping stage of the project. Place a copy of the approved form in the structures project folder in ProjectWise.

5.1.2 Responsibilities

Refer to the Structures QC/QA Procedures for roles and responsibilities.

5.1.3 Documentation

Document the completion of all quality procedures required in the Project Delivery Network, the Structures QC/QA Procedures and this chapter.

Figure 5.1 summarizes the documentation requirements for all quality procedures.

5.2 QUALITY CONTROL CHECK

All structure deliverables required by the Project Delivery Network (i.e., drawings, calculations, reports) must be checked according to the Structures QC/QA Procedures before distribution for review (whether structural review or milestone review), including documents prepared for inclusion in DB projects.

5.2.1 Request for Proposal Check – Design Build Projects

The RFP for a DB project is typically developed by a Program Manager (consultant firm) hired by UDOT to manage that specific project. The structural engineer for the Program Manager is responsible for developing the specific structures performance requirements and structures related documents for the project. The structural engineer cross references project specific design requirements with other disciplines for consistency, compatibility and constructability. The Program Manager prepares, checks and audits the structures performance requirements and structures related documents (i.e., concept drawings, special provisions, reports) following the Structures QC/QA Procedures. For RFP development, the project document cover sheet is required. Specify on the form all related documents (i.e., calculations, concept plans, special provisions) that were designed and checked during the RFP development. Perform an audit according to Section 5.3.

5.2.2 Structure Type Selection Report and Situation and Layout Check

The Structure TSR provides the project objective and a description of the structural recommendations, and summarizes the existing conditions and the basis of structural evaluation. The S&L drawings define the general concept and geometry of the structure.


Design Quality 5-3

Procedure Required Documentation Form

Quality Control (QC)

QC check Check prints* N/A

Independent Technical Analysis Cover Sheet ITA_COV

QC cover sheet

Calculation Cover Sheet CAL_COV

Computer Program Input Cover Sheet COM_COV

Drawing Cover Sheet DWG_COV

Project Document Cover Sheet DOC_COV

Quality Assurance (QA)

QA audit Project QA Audit AUD_QA

Reviews

Structural review

Structural Review Comment Resolution Form STR_CRF

Design reviewer/ oversight review

Structural Review Completion – RFP Preparation and Review (Design Build)

RFP_REV

Structural Review Completion – Plan in Hand (stage 3) Review

PIH_REV

Structural Review Completion – PS&E (stage 4) Review

PSE_REV

Milestone review

Milestone Review Comment Resolution Form F1

Acceptance

Structures Division acceptance

Structural RFP Acceptance (Design Build) RFP_ACC

S&L Acceptance (3S6) S&L_ACC

Final Structural Acceptance (5S1) PSE_ACC

Structural Design Criteria Deviation Acceptance DEV_ACC

Alternate QC/QA Procedures Acceptance ALT_ACC

* Check prints are not required to be uploaded to ProjectWise. At a minimum, keep check prints for

two years after the project construction completion.

All other required documentation is to be uploaded to the structures project folder in ProjectWise.

Refer to Section 2.17 for the document naming convention.

Figure 5.1 — DOCUMENTATION OF QUALITY PROCEDURES


5-4 Design Quality

The checker performs the QC check on the Structure TSR and confirms that all supporting documents (i.e., calculations, reports) have been checked before beginning the check of the S&L drawings.

The structural engineer completes the S&L checklist and submits the checklist as part of the S&L deliverable as defined in the Project Delivery Network. In addition to the S&L checklist, the checker evaluates the conceptual design of the structure in conjunction with the Structure TSR including the following:

• Geometric layout • Structure type • Structure width • Span length • Support locations • Girder type and spacing • Horizontal and vertical clearances • Expansion joint locations • Aesthetic requirements • Potential utility conflicts • Context sensitivity • Environmental requirements • Seismic Design Strategy Report (Preliminary) • Constructability • Agreement with the roadway drawings • Other items appropriate for the structure Resolve all questions and concerns before finalizing the Structure TSR and S&L drawings.

5.2.3 CADD Standards Check

A formal external review to verify compliance with CADD requirements is typically not performed. The structural engineer ensures that drawings meet the Structures Division CADD requirements identified in Section 4.2.1. The Structures Design Manager can request a formal review if the drawings appear to disregard or vary from the established CADD requirements. The review verifies the appropriate level usage, reference file use, scales, etc.

5.2.4 Independent Technical Analysis

The Structures Design Manager or the RFP DB documents identify projects that require an independent technical analysis. Reasons for an independent technical analysis include, but are not limited to, a complex or unusual structure, an inexperienced structural engineer or inexperience with the structure type.

Initiate the independent technical analysis during the PS&E stage. Adjust the design schedule to allow for completion of the independent technical analysis and incorporation of the independent technical analysis comments before the PS&E review.


Design Quality 5-5

Verify that the independent technical analysis comments are addressed in the design documents before submitting the PS&E deliverables.

5.2.5 Plans, Specifications and Estimate Check

Check all drawings as a complete package.

Use the structures plan sheet checklists as tools to ensure consistency in content and format of structure plan sheets. The checklists, with the exception of the S&L checklist, can be included in the QC/QA documentation but are not a required deliverable.

Recheck the S&L to ensure compliance with the most recent roadway drawings and any changes within the design. Confirm with the roadway designer that the most current roadway drawings are being used. Verify that the information and details not available at the plan in hand stage are included. Update and QC check the S&L checklist.

Check the entire set of design documents (e.g., drawings, calculations, specifications, engineer’s estimate). Complete all checking and resolve all questions and concerns before submitting for PS&E review.

Resolve all questions and concerns before finalizing the PS&E documents for advertising.

5.3 QUALITY ASSURANCE AUDIT

Complete a project QA audit on all structure deliverables according to the Structures QC/QA Procedures before submitting deliverables for structural reviews and milestone reviews. Use the Project QA Audit form to document the QA audit.

5.4 STRUCTURAL REVIEWS

All deliverables are subject to reviews by a UDOT structural engineer or a structural engineer appointed by UDOT before the milestone reviews. The Structures Design Manager determines if a structural design review is required, the scope of the design review and whether an oversight review is required. Refer to Figure 5.2 for a summary of the types of reviews, the stage the reviews typically occur, and the section that discusses review expectations.

QC/QA must be complete before submitting documents for a structural review.


5-6 Design Quality

Review Type Design Stage

Completion Section

RFP review (design build)

During RFP development

Before submitting for structural RFP acceptance (design build)

5.4.1

Plan in hand (Stage 3) review

Stage 3 Before submitting for S&L acceptance (3S6)

5.4.3

Intermediate design (Stage 4) review

Stage 4 During PS&E, when required 5.4.4

PS&E (Stage 4) review Stage 4 Before preparing/compiling PS&E review package

5.4.5

Figure 5.2 — STRUCTURAL REVIEWS

The intent of the structural reviews is to verify completeness, accuracy and compliance with design requirements and industry standards. General instructions to reviewers are as follows:

• Conduct all reviews with professionalism and tact. • Review projects advertised through the UDOT bidding system for compliance with

SDDM requirements, including plan presentation. For additional roles and responsibilities on local government projects, see Section 2.16.6.

• Focus the structural reviews of local government projects that do not advertise through the UDOT bidding system on plan content, not format, unless directed otherwise by the Structures Design Manager; local government projects are encouraged to but not required to follow UDOT structure plan presentation. See Section 2.16.7.

• Review permit projects similar to local government projects that do not advertise through the UDOT bidding system. See Section 2.16.5.

The following provides an overview of the general procedures for design reviews and oversight reviews including performing the review, addressing the review comments and completing the review procedure as detailed in the Structures QC/QA Procedures.

1. Perform Review:

• The Structures Design Manager assigns a design reviewer and an oversight reviewer to each project with structures, when required.

• The design reviewer reviews the design deliverables and prepares comments on the Structural Review Comment Resolution Form as described in the Structures QC/QA Procedures.

• The design reviewer submits the review comments to the oversight reviewer. • The oversight reviewer examines the review comments for consensus, provides

additional comments if necessary, and returns the Structures Review Comment Resolution Form to the reviewer.

• The design reviewer returns the completed Structural Review Comment Resolution Form to the structural engineer for the project or posts the document in ProjectWise and notifies the structural engineer.


Design Quality 5-7

2. Address Review Comments:

• The structural engineer for the project responds to the review comments as defined in the Structures QC/QA Procedures and returns the form to the design reviewer.

• The structural engineer and design reviewer discuss comments and responses and agree upon a final disposition.

3. Complete Review Procedure:

• The structural engineer provides the final deliverables, which address or incorporate the review comments, to the design reviewer and oversight reviewer for comment disposition and resolution verification.

• The design reviewer verifies the final dispositions and responses are complete. • The design reviewer and oversight reviewer complete the appropriate Structural

Review Completion form for the stage of the project, post the form in ProjectWise, and notify the Structures Design Manager that the review is complete and all comments are resolved to the design reviewer’s and oversight reviewer’s satisfaction.

5.4.1 Request for Proposal Review – Design Build Projects

After the Program Manager completes the QC check and QA audit, the Program Manager prepares the Structural Review Completion – RFP Preparation and Review (Design Build) form and submits the form to the Structures Division. The Structures Division’s assigned structural engineer and geotechnical engineer review the geotechnical performance requirements, structures performance requirements and related documents (i.e., concept drawings, special provisions, reports), verifies that the Structures QC/QA Procedures were followed, and verifies that the project document cover sheet and the Project QA Audit form are complete for the RFP development. The assigned structural engineer and geotechnical engineer complete and sign the Structural Review Completion – RFP Preparation and Review (Design Build) form and place the form in the structures project folder in ProjectWise as part of the project QC/QA documentation.

5.4.2 Geometry (Stage 2) Review

A formal review is not required at the geometry stage.

5.4.3 Plan in Hand (Stage 3) Review

The structural engineer prepares the deliverables listed below from the structural documentation package and submits the deliverables to the design reviewer for comments. Refer to Figure 5.3 for the Structures Division expectations of the design reviewer and oversight reviewer.


5-8 Design Quality

Deliverable Task

Structure Type Selection Report (TSR) • Verify inclusion in package • Review content for reasonableness and

correctness

Seismic Design Strategy Report (Preliminary)

• Verify inclusion in package • Review document and compare

description with design drawings

S&L drawings

• Verify that drawings meet all requirements of the S&L checklist

• Verify appearance of the S&L drawings; request a formal CADD review if the drawings appear to not follow the Structures Division CADD requirements (Chapter 4)

• Verify that structures are constructable using proven construction methods

• Spot check, cross reference and look through nonstructural sheets to validate that the information shown and impacts from nonstructural items are addressed

• Confirm that drawings represent acceptable design practices and presentation

S&L checklist • Verify inclusion in package • Review in conjunction with the S&L

drawings

Structural Design Criteria Deviation Acceptance

• Verify inclusion in package (if applicable) • Review information as it applies to the

drawings

QC/QA documentation (QC cover sheets for all deliverables and Project QA Audit form)

• Verify inclusion in package • Review content for completeness

Structural Review Completion – Plan in Hand (Stage 3) Review form

• Complete and submit form

Figure 5.3 — PLAN IN HAND STRUCTURAL REVIEW TASKS


Design Quality 5-9

The design reviewer also performs the following:

• Verifies that comments on the Milestone Review Comment Resolution Form (Task 2V1, Geometry Review Meeting) have been addressed

• Verifies that the S&L meets the requirements of the Structure Foundation Type Memo • Verifies that the S&L meets the requirements of the Draft Hydraulics Report • Provides written comments on the Structural Review Comment Resolution Form • Posts the form directly to ProjectWise • Verifies that QC/QA documentation for all deliverables is complete • Coordinates with the oversight reviewer to finalize comments • Resolves all comments with the structural engineer according to the structural review

comment resolution procedures in the Structures QC/QA Procedures • Verifies that all comments are addressed in the deliverables • Completes the Structural Review Completion – Plan in Hand (Stage 3) Review form and

places with the QC/QA documentation in ProjectWise • Notifies the Structures Design Manager that the review is complete and provides a link

to the Structural Review Completion – Plan in Hand form in ProjectWise The review time requirement is 3 to 5 weeks before submitting to the Structures Design Manager for acceptance, distributed as shown in Figure 5.4.

Task Time Allowance

Perform review 1 to 2 weeks

Address review comments 1 to 2 weeks

Finalize review documentation 1 week

Figure 5.4 — PLAN IN HAND STRUCTURAL REVIEW TIME

5.4.4 Intermediate Design (Stage 4) Review

An intermediate design review is not required for all projects, but is occasionally requested on complex projects, projects using new materials or procedures and projects requiring significant coordination with other disciplines or the contractor. The Structures Design Manager identifies projects requiring an intermediate design review. The Structures Design Manager also lists specific areas of concern when applicable.

An intermediate design review is an over the shoulder review. Structure drawings are reviewed to verify concept and scope and to identify design issues that significantly affect the design. The intermediate design review is not a detailed design or drawing check, but a review to validate compliance with the design direction and verify that the design meets scope, intent and all project design criteria and requirements.

The objective of the intermediate design review varies from project to project but, in general, allows evaluation of the design during the design procedure to avoid any significant redesign


5-10 Design Quality

efforts and schedule impacts that could occur if identified at the PS&E review. The tasks that can be included in the intermediate review are to:

• Identify and resolve design issues associated with new types of construction • Identify and resolve design issues associated with new methods of design • Verify constructability • Improve constructability • Allow suppliers to comment on use of new materials • Allow other disciplines to review the design and identify areas of concern • Allow contractors to review the design to improve constructability or reduce cost • Verify that specific design requirements are checked • Verify and plan construction schedules Schedule the intermediate design review early in the design procedure to improve the opportunity to incorporate quality, efficiency and economics into the design without significant redesign.

The structural engineer compiles the intermediate design review materials (unchecked) and submits the package to the design reviewer. The package can include some or all of the following:

• A set of drawings • Calculations • Memos • Specifications • Quantity estimates • Proposed construction scheme The submittal must provide adequate information to allow review and evaluation of the design concept. The design reviewer evaluates the material submitted and requests additional material, if needed. The intermediate design review is not a detailed design or drawing check. The unchecked drawings often contain errors or inaccurate information. Coordination with the structural engineer is often required to clarify the drawings.

The intermediate design review submittal must include adequate information required to evaluate any specific concerns identified by the Structures Design Manager. The intermediate design review submittal for projects without specific concerns typically includes all materials in the S&L submittal and the unchecked drawings as follows:

• S&L drawings • Soil data drawings • Pile or drilled shaft drawings • Foundation drawings • Abutment drawings • Bent drawings • Framing drawings • Girder detail drawings


Design Quality 5-11

• Post-tensioning or prestressing drawings • Deck detail drawings Ideally, the structural engineer submits all created drawings. Due to the preliminary and unchecked nature of the drawings, the structural engineer has the option to not submit created drawings that add no value for the design reviewer. The drawings are reviewed from a conceptual perspective. The design reviewer submits comments either by marking up a set of drawings or providing written comments on the Structural Review Comment Resolution Form. The design reviewer must provide written comments when requested by the Structures Design Manager.

The structural engineer schedules a meeting to review the comments, if needed. Formal responses to comments on a set of marked up drawings is not required; however, the structural engineer responds to all comments provided on the Structural Review Comment Resolution Form according to the procedures in the Structures QC/QA Procedures to document resolution of all written comments. The structural engineer scans the final form and places the scanned copy in the structures project folder in ProjectWise.

In general, the design reviewer does the following:

• Verifies that the specific concerns identified by the Structures Design Manager are addressed

• Verifies that the seismic strategy is appropriate for the structure and is consistent with the structure performance goals; verifies that details and geometry identified in the Seismic Design Strategy Report (Preliminary) are applied or can be applied to the drawings

• Reviews major structure elements; identifies elements that are beyond typical maximum and minimum values

• Verifies that typical details are appropriate; ensures that any nonstandard details are appropriate

• Verifies the constructability of the design; identifies constructability concerns; identifies difficult or impossible to construct details; evaluates the construction sequence; evaluates pick weights, stability of materials lifted, potential crane locations, crane size requirements and overhead utility conflicts; evaluates construction time lines for time critical projects

• Verifies inspection access • Identifies issues that impact bridge maintenance; for example, verifies that the deck

drains will not soak the girders or substructure; identifies avoidable erosion or snow removal problems

• Verifies compliance with project aesthetics, environmental requirements and project specific design requirements

• Identifies concerns with design methods


5-12 Design Quality

5.4.5 Plans, Specifications and Estimate (Stage 4) Review

The structural engineer prepares the following deliverables and submits the package to the design reviewer and oversight reviewer for comments. See Figure 5.5 for review tasks for project submittals.

The design reviewer completes the following:

• Verifies that the Geotechnical Report is complete and reflected properly in the structures design

• Verifies that the Hydraulics Report (if applicable) is complete and reflected properly in the structures design

• Notifies the Structures Project Engineer if final reports are not complete • Verifies consistency of items and quantities among the plans, specifications, special

provisions, engineer’s estimate, measurement and payment, and acceptance and documentation documents

• Provides written comments on the Structural Review Comment Resolution Form • Posts the form directly to ProjectWise • Verifies that QC/QA documentation for all deliverables is complete • Coordinates with oversight reviewer to finalize comments • Resolves all comments with the structural engineer according to the Structural Review

Comment Resolution Form procedures in the Structures QC/QA Procedures • Verifies that all comments are addressed in the deliverables • Completes the Structural Review Completion – PS&E (Stage 4) Review form and places

the form with the QC/QA documentation in ProjectWise • Notifies the Structures Design Manager that the review is complete and provides a link

to the Structural Review Completion – PS&E (Stage 4) Review form in ProjectWise The review time requirement is 5 to 8 weeks before the PS&E meeting, distributed as shown in Figure 5.6.

Task Time Allowance

Perform review 1 to 2 weeks

Address review comments 1 to 2 weeks

Finalize review documentation 1 week

Submit PS&E documents to project team for review 2 to 3 weeks (required)

Figure 5.6 — PS&E STRUCTURAL REVIEW TIME


Design Quality 5-13

Submittal Task

Structure plans

• Verify that drawings meet all requirements of the SDDM • Verify that applicable WS sheets have been used • Verify appearance of the S&L drawings; request a formal CADD

review if the drawings appear to not follow the Structures Division CADD requirements (Chapter 4)

• Verify that structures are constructable using proven construction methods

• Spot check, cross reference and look through nonstructural drawings to validate that information shown and impacts from nonstructural items are addressed

• Confirm that drawings represent acceptable design practices and presentation

• Verify that all appropriate structural details are included • Verify that dimensions and callouts are clear and complete • Verify that drawing notes use active voice and imperative mood • Verify that drawings clearly communicate the intended design • Verify that all structures are identified, reviewed and have a structure

number assigned

Specifications and special provisions

• Verify that active voice and imperative mood is used • Verify that construction schedule is appropriate • Verify that specifications and special provisions are clear and

understandable • Verify that all required structural special provisions are included • Verify that correlation among plans, specifications and special

provisions is complete

Engineer’s estimate (structure items)

• Verify that quantities and unit costs for structural items are reasonable • Verify that all items are included in the estimate • Verify that bid items reference appropriate specification or special

provision

Measurement and payment

• Verify that measurement and payment information for structural items are complete and acceptable

Acceptance and documentation

• Verify that structural items are complete

Calculations (upon request of reviewer)

• Compare design calculations with information in the drawings (if applicable)

Seismic Design Strategy Report (Final)

• Verify inclusion in package • Review document and compare description with design drawings

Structural design criteria deviation acceptance

• Verify inclusion in package (if applicable) • Review information as applicable to the calculations

Responses to all previous structures related review comments

• Verify that comments on the Milestone Review Comment Resolution Form (Task 3V1, Plan In Hand Review Meeting) have been addressed

• Verify that intermediate design review and independent technical analysis comments have been addressed, if applicable

QC/QA documentation (QC cover sheets for all deliverables and Project QA Audit form)

• Verify inclusion in package • Review content for completeness

Structural Review Completion – PS&E (Stage 4) Review form

• Complete and submit form

Figure 5.5 — PS&E STRUCTURAL REVIEW TASKS


5-14 Design Quality

5.5 ACCEPTANCE

All structure deliverables intended for use on UDOT projects and on local government projects with federal funding require formal acceptance by UDOT at various design stages. Acceptance means that the deliverables are ready for the next stage. Acceptance does not relieve the EOR of responsibility for the design of a bridge or structural component. The EOR retains the responsibility for errors, correctness of details and conformance to SDDM requirements. The Structures Design Manager accepts by signature the following structure deliverables.

5.5.1 Request for Proposals Acceptance — Design Build

Once the Structures Design Division and Geotechnical Design Division review has been completed on the RFP for DB projects, the Structures Design Manager or designee and the Geotechnical Design Manager accept all structural performance requirements, special provisions and concept/preliminary design drawings before advertising the RFP. The RFP acceptance submittal includes the RFP structural documents, the completed Structural Review Completion – RFP Preparation and Review (Design Build) form and the Structural RFP Acceptance (Design Build) form.

The Structures Design Manager completes and signs the Structural RFP Acceptance (Design Build) form and places the form in the structures project folder in ProjectWise as part of the project QC/QA documentation. Acceptance of concept/preliminary design plans is required before advertising the RFP.

5.5.2 Structure Type Selection Report

The Structures Design Manager or designee reviews and accepts the Structure TSR and the SDSR (Preliminary). Acceptance is typically concurrent with the S&L acceptance and is documented by signature on the reports.

5.5.3 Situation and Layout

Once the comments have been reviewed and addressed and the Structural Review Completion – Plan in Hand (Stage 3) Review form has been signed, the structural engineer prepares the structural documentation package and submits the package to the Structures Design Manager for acceptance. The package includes the deliverables identified in the Project Delivery Network and on the S&L Acceptance (3S6) form. The Structures Design Manager or designee provides acceptance of the submittal package by signing the S&L Acceptance (3S6) form. Place the completed form and the structural documentation package deliverables in the structures project folder in ProjectWise.

Allow the appropriate time to obtain S&L acceptance before beginning the Stage 4 design. Review time is distributed as shown in Figure 5.7.


Design Quality 5-15

Task Time Allowance

Submit S&L drawings and preliminary cost estimate to project team for review

2 to 3 weeks (required)

Accept structural documentation package (Structures Design Manager)

1 week

Figure 5.7 — SITUATION AND LAYOUT REVIEW TIME

Complete the S&L acceptance before submitting deliverables for the plan in hand meeting and before beginning the Stage 4 design.

5.5.4 Seismic Design Strategy Report (Final)

The Structures Design Manager reviews and accepts the SDSR (Final). Acceptance is typically at the same time as the Final Structural Acceptance (5S1) and is documented by signature on the report. No formal acceptance documentation is required.

5.5.5 Final Structure Acceptance

The Structures Design Manager or designee accepts the final design documents for all UDOT projects, local government projects with federal funding and permit projects that modify a structural element of an existing UDOT structure. Final structure acceptance occurs after the comment resolution meeting is completed and all review comments are addressed and before submitting for advertisement.

The structural engineer prepares the final structural documentation package and submits the package to the Structures Design Manager for acceptance with the completed Final Structural Acceptance (5S1) form, the signed Structural Review Completion – PS&E (Stage 4) Review form and any other documentation requested by the Structures Design Manager. Include the deliverables identified in the Project Delivery Network and on the Final Structure Acceptance (5S1) form.

The Structures Design Manager verifies that the final design documents are complete and the contract documents are ready for advertising. The final acceptance is not a detailed check, but a review to confirm that the design is complete and that the QC/QA documentation is complete.

The Structures Design Manager provides acceptance of the final project deliverables for advertising by signature on the Final Structural Acceptance (5S1) form and the final structure drawings (when applicable).

Complete the final structural acceptance before submitting for advertisement. The review time requirement for final structure acceptance is two weeks before submitting to the Region for advertising; see Figure 5.8.


5-16 Design Quality

Task Time Allowance

Review structural documentation package and provide acceptance for advertising

2 weeks (required)

Figure 5.8 — FINAL STRUCTURE ACCEPTANCE REVIEW TIME

5.6 CONSTRUCTION SUBMITTALS AND REVISIONS

See Chapter 6 for construction submittals and requirements for what and how to review. In general, revisions to design documents (e.g., drawings, specifications) generated after advertisement or release for construction must follow the Structures QC/QA Procedures.

FEBRUARY 2015

CONSTRUCTION SUPPORT



Construction Support 6-i

TABLE OF CONTENTS

6.1 INTRODUCTION .......................................................................................................... 6-1 6.2 ROLES AND RESPONSIBILITIES .............................................................................. 6-1

6.2.1 Central Construction, Materials and Civil Rights Divisions ............................... 6-1

6.2.1.1 District Engineer ............................................................................. 6-2 6.2.1.2 Resident Engineer .......................................................................... 6-2 6.2.1.3 Field Engineer, Inspectors and Technicians ................................... 6-2 6.2.1.4 Central and Region Materials Personnel ........................................ 6-3

6.2.2 Structures Division ........................................................................................... 6-3

6.2.2.1 Structures Design Manager ............................................................ 6-3 6.2.2.2 Structures Construction Engineer ................................................... 6-4 6.2.2.3 Structures Project Engineer ............................................................ 6-4 6.2.2.4 Bridge Management Engineer ........................................................ 6-4 6.2.2.5 Bridge Database Engineer .............................................................. 6-4 6.2.2.6 Engineer of Record ......................................................................... 6-5 6.2.2.7 Geotechnical Engineer ................................................................... 6-5

6.3 CONSTRUCTABILITY REVIEWS ............................................................................... 6-6 6.4 CONSTRUCTION SUBMITTALS ................................................................................ 6-6

6.4.1 Working Drawings ............................................................................................ 6-6

6.4.1.1 Distribution Process for Review ...................................................... 6-7 6.4.1.2 Review and Approval Requirements .............................................. 6-7 6.4.1.3 Tracking and Documentation .......................................................... 6-8 6.4.1.4 Working Drawing Checklists ........................................................... 6-9

6.4.2 Miscellaneous Construction Submittals ............................................................ 6-9

6.5 INSPECTION AND ON SITE SUPPORT ..................................................................... 6-10

6.5.1 Meetings and Site Visits ................................................................................... 6-10 6.5.2 Project Acceptance .......................................................................................... 6-10

6.5.2.1 Substantial Completion ................................................................... 6-10 6.5.2.2 Final Acceptance ............................................................................ 6-10

6.6 DESIGN CLARIFICATIONS AND CHANGES ............................................................ 6-11

6.6.1 Requests for Information .................................................................................. 6-11 6.6.2 Construction Change Orders ............................................................................ 6-11 6.6.3 Notice of Design Change and Field Design Change ........................................ 6-12


6-ii Construction Support

6.6.3.1 Initiation, Evaluation and Tracking Design Change Requests ........ 6-12 6.6.3.2 Documentation of Design Change Revisions ................................. 6-13 6.6.3.3 Distribution of Design Changes ...................................................... 6-13

6.6.4 Value Engineering Change Proposal ............................................................... 6-14 6.6.5 As Built Plans ................................................................................................... 6-14

LIST OF FIGURES

Figure 6.1 — REVIEW STAMP ............................................................................................. 6-8


Construction Support 6-1

Chapter 6 CONSTRUCTION SUPPORT

The responsibilities of the Structures Division extend beyond the preconstruction stage. For all structural items, the Structures Division must provide the necessary support to the RE to assist in construction. In many cases (e.g., for change orders), the Structures Division is best positioned to identify and evaluate any impacts on the long term functionality of the structural elements.

This chapter presents the Structures Division’s responsibilities for construction support and input. Examples include construction change orders, review of working drawings and RFIs and on site support.

6.1 INTRODUCTION

During construction, the EOR is responsible for structure specific support, and the Structures Division is responsible for statewide oversight and Region support for all structures in collaboration with the Construction Division and Materials Division. Support responsibilities include review of shop drawings, erection plans, requests for information, design changes, ABC planning activities, attendance at project meetings, site visits, and participation in substantial completion and final acceptance. The EOR has a unique perspective and knowledge of the structure design, and the knowledge is valuable during submittal reviews, when addressing questions that arise in construction, and in resolving discrepancies according to the design intent. Therefore, the EOR and Structures Division must be proactive, available and responsive in coordinating with the RE for the construction project.

6.2 ROLES AND RESPONSIBILITIES

Although project team members have specific roles during the design and construction stage, this chapter focuses primarily on roles and responsibilities during construction.

6.2.1 Central Construction, Materials and Civil Rights Divisions

The Construction, Materials and Civil Rights Divisions have responsibility for the administration of contracts during the construction stage. The Divisions assume the responsibility when the contract is advertised according to established Department procedures. The responsibility ceases when the Department has accepted the project and final payment has been issued to the contractor. The Materials Division is responsible for the overall management of the Department’s materials acceptance program and all Central Materials laboratory testing and inspection programs. The Civil Rights Division is responsible for administering the civil rights program as required by FHWA regulations, contract compliance and DBE programs.


6-2 Construction Support

6.2.1.1 District Engineer

The DE is assigned to construction contract administration and reports to the Region Director. The DE:

• Evaluates and approves change orders • Provides stewardship for federal participation • Participates in resolving disputes and potential claims that have been escalated • Coordinates construction activities with other Region operations

6.2.1.2 Resident Engineer

The RE is UDOT’s representative on the project and operates under the supervision of the DE. The RE coordinates activities with the Project Manager on issues that affect the project scope, schedule and budget. The RE:

• Assesses the compatibility of the design with site conditions during the design stage • Provides constructability reviews during the preconstruction stage • Conducts preconstruction conferences, the regularly scheduled team meetings, special

coordination meetings and the substantial and physical completion walk throughs • Administers the construction project according to established policies and procedures • Monitors the project to ensure compliance with the contract documents • Enforces specifications, controls inspection and testing, and ensures proper

documentation • Ensures that project staff have the required certifications and qualifications • Provides training to field personnel • Assigns qualified staff to conduct field inspections for structural items • Notifies the Structures Division of any issues related to structural items and coordinates

submittal reviews • Resolves issues and disputes with the contractor • Prepares contract change orders • Maintains a record of all FDCs • Submits the as built plans, which are an electronic copy of the as constructed (i.e.,

redlined) plans, to the Structures Division and EOR for review and concurrence that the changes, including FDCs, have been incorporated

• Submits the final as built plan set with all structure related FDCs to the Structures Division at completion of the project for incorporation into the structure record

6.2.1.3 Field Engineer, Inspectors and Technicians

The FE reports directly to the RE. The FE:

• Monitors work progress • Documents noncompliance issues



• Supervises or performs inspections and testing • Helps evaluate change orders The inspectors and technicians report directly to the RE. The inspectors and technicians:

• Provide sampling and testing according to minimum sampling and testing • Document sampling and testing activities and report test results • Confirm that all materials and work complies with the contract document materials

acceptance • Helps evaluate change orders 6.2.1.4 Central and Region Materials Personnel

Include Central Materials in all inspections related to structural precast elements and structural steel. Central Materials inspectors:

• Provide technical assistance to the RE on materials issues • Inspect and/or qualify fabrication facilities including temporary facilities used for project

site precast elements • Inspect precast elements for compliance with approved working drawings, standards

and specifications • Provide steel girder inspection/material verification during fabrication • Provide overhead sign structural steel inspection/material verification during fabrication • Monitor steel girder erection for compliance with approved erection plan and

specifications • Provide inspection of bolts, welds (shop and field) and shear stud installation • Conduct nondestructive testing of structural steel (i.e., ultrasonic testing, penetrant

testing, magnetic particle testing, radiographic testing) • Monitor and inspect structural steel girders during and after deck removal • Conduct structural steel coatings inspection and lead coating removal • Inspect bearings 6.2.2 Structures Division

6.2.2.1 Structures Design Manager

The Structures Design Manager:

• Determines if an independent constructability review is warranted during the design stage

• Assigns oversight reviewers as appropriate for review of construction submittals • Attends meetings and site visits as appropriate • Participates in resolving field questions that have been escalated • Oversees structural design support for construction



6.2.2.2 Structures Construction Engineer

The Structures Construction Engineer reports directly to the Structures Design Manager. The Structures Construction Engineer:

• Coordinates with the RE and EOR to ensure that construction submittals are reviewed in a timely and thorough manner

• Collaborates with the RE and EOR to develop solutions to construction problems or plan errors

• Provides an oversight review on all EOR responses to design clarifications and changes including RFIs and FDCs, unless reviewed by the Structures Project Engineer

• Attends meetings and site visits 6.2.2.3 Structures Project Engineer

The Structures Project Engineer reports directly to the Structures Design Manger. The Structures Project Engineer:

• Coordinates with the RE and EOR to ensure that construction submittals are reviewed in a timely and thorough manner

• Coordinates with the RE and EOR to develop solutions to construction problems or plan errors

• Coordinates with the RE and EOR to review change orders • Provides an oversight review on all EOR responses to design clarifications and changes

including RFIs and FDCs, unless reviewed by the Structures Construction Engineer • Attends meetings and site visits 6.2.2.4 Bridge Management Engineer

The Bridge Management Engineer:

• Assigns bridge inspectors to collect pertinent information for the inventory after substantial completion

• Participates in partial acceptance and/or the substantial completion inspection, as appropriate

6.2.2.5 Bridge Database Engineer

The Bridge Database Engineer reports directly to the Bridge Management Engineer. The Bridge Database Engineer:

• Manages the data collection and storage of information for each structure as part of asset management and planning

• Copies documentation provided by the RE into the structure record including as builts, approved shop drawings, and submittals and change orders involving structural items



6.2.2.6 Engineer of Record

The EOR is the individual that signed and stamped the plans and calculations for the work. The EOR can be an employee of the Department or a consultant working for the Department. The EOR:

• Must be licensed in the state of Utah as a professional civil or structural engineer • Provides technical assistance to the RE on construction questions • Participates in project meetings as necessary • Participates in field and shop inspections as requested • Reviews construction submittals, RFIs and FDC requests • Limits comments and responses to technical requirements of submittals, interpretation of

the plan set and clarifications of comments on construction submittals • Directly communicates with suppliers and fabricators to discuss technical issues with the

approval of the RE • Does not discuss issues related to measurement, payment or potential resolutions to

problems with the contractor unless the RE is present and has requested the discussion • Must be responsive to the RE and give priority to contract related questions, requests for

information and submittal reviews; delays caused by an untimely review can result in contractor claims for time and/or compensation

• Submits all responses to the Structures Division for approval before sending to the RE and contractor

6.2.2.7 Geotechnical Engineer

The project geotechnical engineer’s roles and responsibilities are the same as the EOR for elements specific to geotechnical design. The geotechnical engineer:

• Provides technical assistance to the RE on construction questions • Participates in project meetings, as necessary • Reviews construction submittals, RFIs and FDC requests as necessary including:

○ Review and acceptance of contractor ground improvement proposals ○ Review and acceptance of hammer data sheets ○ Review and acceptance of MSE wall submittals and other geotechnical

structures ○ Verification of PDA pile capacity

• Provides vibration monitoring • Provides interpretation of instrumentation (e.g., settlement, inclinometers) • Provides inspector training for pile driving and drilled shaft installation • Must be licensed in the state of Utah as a PE, professional structural engineer or

professional geologist



6.3 CONSTRUCTABILITY REVIEWS

During the preconstruction stage, construction support includes reviewing plans and specifications to verify that the structural elements can be reasonably constructed and that there is a feasible phasing scheme. The Project Delivery Network details the timing for constructability reviews. The project team identifies the need for separate constructability reviews and the scope, and if the review is to be performed by a specialist or third party. The Structures Construction Engineer, when assigned, and the RE perform constructability reviews during the milestone reviews. Depending on the complexity of the project, the Structures Design Manager can request that an independent constructability review be performed as an intermediate design review (refer to Section 5.4.4). The design schedule is developed to reflect the appropriate frequency and timing of all reviews.

6.4 CONSTRUCTION SUBMITTALS

The Structures Division and EOR assist the Construction Division by reviewing and responding to structure related construction submittals. Types of construction submittals include but are not limited to:

• Working drawings ○ Shop drawings ○ Erection drawings ○ Shipping drawings ○ Temporary works drawings

• Methods and procedures as defined within applicable standards (e.g., AASHTO, American Society for Testing and Materials (ASTM), American Institute of Steel Construction (AISC))

• Material submittals • RFIs • FDCs • Nonconformance requests The UDOT Standard Specifications and project special provisions identify the required construction submittals for each bid item, the requirements for the submittal content and the schedule allowance for review and approval.

6.4.1 Working Drawings

Working drawings are drawings produced by the contractor that supplement the contract drawings to provide information not included in the contract documents but required to fabricate, erect, transport or temporarily support the structure or structural elements in completion of the work. Working drawings do not supersede the contract drawings.



Working drawings for fabricator designed structures (e.g., MSE wall drawings, prefabricated steel truss pedestrian superstructures, three-sided precast culvert structures) must be stored with the project plan set and become part of the structure record.

6.4.1.1 Distribution Process for Review

Lines of communication, and the specific individuals involved in the specified role, are established at the project preconstruction meeting. The process for review is:

• Fabricators and subcontractors submit to the contractor. • The contractor submits the construction submittal according to the specification

requirements to the RE. When permitted by the contractor, the fabricator can submit the construction submittal instead of the contractor.

• The RE distributes the submittal to the EOR with a copy to the Structures Design Manager. The Structures Design Manager assigns oversight as appropriate to either the Structures Project Engineer or Structures Construction Engineer.

• The EOR reviews and approves the submittal according to the specifications. • The EOR is responsible for ensuring that all disciplines (e.g., geotechnical, hydraulics)

and the Structures Division review the construction submittal, if applicable. For example, a retaining wall working drawing requires a review stamp by the structural engineer and the geotechnical engineer responsible for the design.

• Upon completion of the review and concurrence on the response from the Structures Division, the EOR returns the construction submittal to the RE and copies the: ○ Contractor ○ Fabricator ○ Structures Design Manager ○ Engineer for Materials (material submittals only) ○ Materials Engineer for Concrete and Steel ○ Testing Program Coordinator (steel material submittals and steel working

drawings only) The RE is responsible for verifying compliance with the specifications.

Depending on the outcome of the review, several iterations of the process may occur.

6.4.1.2 Review and Approval Requirements

The allowable time for review and approval of working drawings is according to the project specifications. The EOR reviews and returns the working drawings as quickly as possible. The EOR must complete reviews within the allowable review period.

The contractor is responsible for obtaining Railroad approval. Typically, the Railroad only reviews working drawings that have been reviewed and approved by the Structures Division.

In general, the RE has the overall responsibility for verifying that the fabricator of structural components is supplying the items as specified by the construction contract and initiating



coordination with other divisions as needed for approval. The contractor must ensure that all structural items are fabricated or constructed to the correct dimensions and materials, and conforms to the construction contract documents.

The EOR is responsible for:

• Reviewing working drawings for general conformance with the design concept and compliance with the contract documents including, but not limited to, reviewing: ○ Girder working drawings ○ Joint working drawings ○ Bearing working drawings ○ Precast element working drawings ○ Forming plans ○ Deck overhang forming plans

• Reviewing requests for revisions and reviewing plans detailing revisions including, but not limited to, revised: ○ Deck pour sequence and screed deflections ○ Closure pour locations

• Returning the working drawings within the allotted review period • Documenting the working drawing submittal receipt, review and return The Structures Division provides oversight on all responses during the construction stage.

Review and approval do not relieve the contractor from responsibility for errors, correctness of details, conformance to the contract and the successful completion of the work.

6.4.1.3 Tracking and Documentation

The EOR reviews the construction submittals for compliance with the drawings and specifications, and marks comments and discrepancies in red on the submittal/drawing. Upon completion, the EOR stamps each drawing with the review stamp and signs or initials the response as appropriate. See Figure 6.1.

Figure 6.1 — REVIEW STAMP



The EOR checks structural steel shop drawings in accordance with AASHTO/NSBA G.1.1 – 2000 Shop Detail Drawing Review/Approval Guidelines.

The EOR must track reviews by maintaining a record of shop drawing reviews. At a minimum, include the following information in the record:

• Submittal identification number • Structure number • Project name and number • Submitted by fabricator/vendor/designer • Contractor • Fabricator job number • Receipt date of submittal document • Date sent to reviewer/EOR • Name of reviewer/EOR • Date received back from reviewer/EOR • Status/action or decision of review/remarks (e.g., no exception taken, rejected, revise

and resubmit) • Date returned to designer The Structures Division maintains an overall record of shop drawing reviews. To maintain the record, the Structures Division must be copied on all submittals as discussed in the distribution process for reviews.

6.4.1.4 Working Drawing Checklists

Use the structures working drawing checklists applicable to the project. The checklists are provided as guidelines on minimum items to check. Do not include the checklists in the returned set. See the website for checklists.

6.4.2 Miscellaneous Construction Submittals

The Structures Division and EOR support the RE with review of various other submittals and requests, as appropriate, including:

• Methods and procedures as defined within applicable standards (e.g., AASHTO, ASTM, AISC)

• Material submittals • RFIs • FDCs • Nonconformance requests Upon completion of the review, the EOR returns the construction submittal to the RE and other individuals as defined at the preconstruction meeting.



6.5 INSPECTION AND ON SITE SUPPORT

6.5.1 Meetings and Site Visits

The EOR and Structures Project Engineer, Structures Construction Engineer or designee:

• Attend prebid meeting • Attend preconstruction and post-construction meetings • Support the RE as requested, such as:

○ Attending prepour conferences before planned major concrete pours ○ Attending pre-activity meetings as needed ○ Observing concrete placement on major pours ○ Accompanying the geotechnical engineer to observe foundation subgrade

preparation and foundation construction activities ○ Making routine field visits ○ Providing technical support for processing change orders and resolving claims

and disputes ○ Providing project specific training ○ Observing the placement or erection of precast concrete elements, precast

concrete girders and structural steel girders ○ Observing stressing and grouting operations

Notify the RE of planned visits or any issues or problems observed.

6.5.2 Project Acceptance

6.5.2.1 Substantial Completion

The EOR and Structures Project Engineer or Structures Construction Engineer are expected to participate in partial acceptance and/or the substantial completion inspection and provide the RE with a list of items of work that have not been completed according to the contract requirements.

The Bridge Management Engineer can attend or assign bridge inspectors to attend the substantial completion inspection to collect pertinent information for the inventory. Often, the attendance provides a good opportunity to access the structure while the structure is closed to traffic.

6.5.2.2 Final Acceptance

After physical completion, the RE provides the Bridge Database Engineer with an electronic copy of all necessary documentation to update the structure record, including:



• Approved as builts • Approved shop drawings and submittals • Approved change orders involving structural items

6.6 DESIGN CLARIFICATIONS AND CHANGES

Sometimes, after a project has been awarded (DBB or CMGC) or plans have been released for construction (DB), design clarifications and/or changes are required to maintain or improve quality, for constructability or for modifying the design to reflect unexpected or changed conditions in the field. Whether initiated by the contractor, UDOT or the EOR, the RE is responsible for coordinating with the Structures Division and EOR to determine if the request materially affects the design intent. The EOR is responsible for evaluating the request to ensure that the intent of the design is not compromised and that the EOR or contractor’s engineer makes necessary plan changes. The Structures Division provides oversight on all requests and responses. The procedures for design clarifications and changes during construction are described in the following subsections.

6.6.1 Requests for Information

During the advertisement period, prospective bidders can seek clarification on provisions, design details, etc., in the contract documents through RFIs. Usually, the requests are addressed to the Project Manager who seeks input from the appropriate party for response. If related to structural items, the requests are forwarded to the Structures Division for a response. If changes to the contract documents are necessary, the EOR coordinates with the Project Manager to prepare an addendum. The Project Manager submits the addendum to the Construction Division. The Construction Division posts the addendum to the UDOT advertisement website and notifies prospective bidders that the addendum was posted.

During construction, RFIs can be initiated by the contractor or the RE. RFIs initiated by the contractor must go through the RE. Suppliers and fabricators submit questions on contract documents through the contractor. The process allows both the RE and contractor to remain informed on contract document questions. The RE is responsible for forwarding any RFIs related to structural items to the Structures Division and EOR. All RFIs must be reviewed and responded to in a timely manner. All responses to RFIs must be sent to the Structures Division for approval before being returned to the contractor. Sometimes, a RFI can result in a construction change order, NDC or FDC.

6.6.2 Construction Change Orders

Change orders modify the contract and are required for plan or specification changes or additions, differing site conditions or significant changes in the character of work, changes or extensions of contract time, extra work required that is not within an original bid item and acceptance of a value engineering change proposal (VECP). Either UDOT or the contractor can initiate a change order, but both parties must be in agreement before the work is performed.



The RE is responsible for preparing, coordinating and documenting the change order. If the change order is related to or impacts structural items, the RE is responsible for including the Structures Division and the EOR in the development of the change order. The Structures Division supports the RE during the change order preparation and review process to:

• Determine agreement with and acceptance of the change order • Verify that the proposed change is consistent with the original design intent • Verify that the change does not adversely impact the structural elements • Calculate and verify the quantities and costs 6.6.3 Notice of Design Change and Field Design Change

Once plans and specifications have been released for construction, proposed design changes and field design changes must go through a design review process. The following presents the process for initiating, notifying, evaluating and responding to changes made through a NDC or FDC. In some cases, depending on the impacts, a NDC and/or FDC can result in a construction change order.

DB projects often require an approved project specific quality management plan defining the processes and procedures for initiating, tracking, checking, reviewing, quality assurance, distributing and releasing the changes.

6.6.3.1 Initiation, Evaluation and Tracking Design Change Requests

A design change can be initiated in one of the following processes:

• The EOR can determine that a previously signed and stamped plan sheet or specification requires a change to maintain the overall quality of the design. The EOR coordinates with the Structures Design Manager and, with concurrence, initiates the request for a design change by preparing a NDC. The NDC is a memorandum to the Structures Design Manager and RE, which serves as notification of a revision and re-release of impacted plan sheets and specifications. The memorandum must contain information on the anticipated change, the affected plans and/or specifications, work that could be delayed, completion of the revisions and when the revisions will be distributed. Plans and specifications are revised according to Section 6.6.3.2.

• The contractor or RE can request a FDC to improve constructability, to address differing field conditions, to increase cost effectiveness or to address errors or ambiguities in the plans. A FDC may or may not require a re-release of the plans and specifications. In some cases, the change can be reflected on the as built plans in lieu of re-releasing. The EOR must evaluate the request and confirm that the integrity of the original design is maintained. All design changes to plans, sketches, memoranda, specifications, calculations and reports are signed, stamped and dated by a PE in responsible charge licensed in Utah and, preferably, by the EOR. Plans and specifications are revised according to Section 6.6.3.2.



The EOR must ensure that all disciplines (e.g., geotechnical, hydraulics) review the proposed change, as applicable. The Structures Division provides an oversight review on all proposed design changes.

The RE is responsible for tracking all requests for design changes.

6.6.3.2 Documentation of Design Change Revisions

Document all plan revisions due to NDCs or FDCs using the following procedure:

• Place a revision number in a triangle and cloud the revision to indicate the revision to the plan sheet.

• Number the revisions consecutively starting at one for the first revision. • Cloud the revision and place the revision number in a triangle near the revision cloud. • Place the revision number in a triangle in the title block area for revisions and provide a

brief description of the revision. Start at the bottom line and work up with subsequent revisions. When more than three revisions are required, place the revision information in the sheet area. Remove the cloud and number in a triangle from the sheet, indicating a previous revision, and only cloud the new revision.

If additional calculations or changes to the original calculations are required as a result of the proposed change, development of and revisions to calculations follow the same process as during the design stage.

All changes (e.g., drawings, calculations, documents) undergo the same QC/QA procedure as the original. See Chapter 5.

The EOR or contractor’s engineer signs and stamps all design change plans, sketches, memoranda, specifications, calculations and reports.

When design changes can be conveyed clearly by memorandum and without a re-release of drawings, the RE verifies that the changes are incorporated into the as built drawings.

6.6.3.3 Distribution of Design Changes

Upon completion of the QC/QA procedures and concurrence from the Structures Division, the EOR prepares a memorandum summarizing the reason for the change and the documents impacted. The EOR sends the memorandum and revised documents to the RE and copies, at a minimum, the following individuals:

• Structures Design Manager • Bridge Database Engineer • Engineer for Materials, as appropriate • Materials Engineer for Concrete and Steel, as appropriate



The RE distributes the revised documents and ensures that all field personnel (e.g., contractor personnel, inspectors) are using the revised documents for construction.

6.6.4 Value Engineering Change Proposal

In accordance with the UDOT Standard Specifications, contractors can submit VECPs for modifications to the plans and specifications that result in savings and preserve essential functions and characteristics of the facility including but not limited to service life, economy of operation, ease of maintenance, desired capacity and safety. The process for submitting VECPs is detailed in the UDOT Standard Specifications. The RE obtains input from the Structures Division for any VECPs related to structural items. In general, the EOR reviews the proposal to determine that the proposed design is at least equal to the functionality, durability and longevity of the design presented in the contract documents.

6.6.5 As Built Plans

In accordance with the UDOT Standard Specifications, after project completion, the contractor provides the RE with all surveying and design data and a redlined hard copy plan set showing as constructed features denoting changes from the original design. However, to verify accuracy and completeness, the RE must have a systematic method for identifying, documenting and tracking field changes to facilitate the review of the contractor’s submitted drawings for acceptance. The RE submits an electronic copy of the redlined, as constructed plans (which become the as built plans) to the Structures Division and EOR for review and concurrence that changes, including FDCs, have been incorporated.

For final acceptance, the RE sends a PDF file or the ProjectWise link for the electronic copy of the as builts to the Bridge Database Engineer. All as builts are copied to the structure record.

FEBRUARY 2015

RESERVED



Reserved 7-1

Chapter 7 RESERVED


7-2 Reserved

FEBRUARY 2015

RESERVED



Reserved 8-1

Chapter 8 RESERVED


8-2 Reserved

FEBRUARY 2015

RESERVED



Reserved 9-1

Chapter 9 RESERVED


9-2 Reserved

FEBRUARY 2015

PRELIMINARY DESIGN



Preliminary Design 10-i

TABLE OF CONTENTS

10.1 PROCESS .................................................................................................................. 10-1

10.1.1 Evaluate the Site ......................................................................................... 10-1 10.1.2 Evaluate the Project Geometry .................................................................... 10-2 10.1.3 Evaluate Costs ............................................................................................ 10-3 10.1.4 Select a Preferred Option ............................................................................ 10-3

10.2 STRUCTURAL REQUIREMENTS ............................................................................. 10-4

10.2.1 Structural Requirements .............................................................................. 10-4 10.2.2 Live Load Deflection Criteria ....................................................................... 10-4 10.2.3 Span to Depth Criteria ................................................................................. 10-4 10.2.4 Continuous vs Simple Spans ....................................................................... 10-4 10.2.5 Composite Action ........................................................................................ 10-4 10.2.6 Number of Girders ....................................................................................... 10-5 10.2.7 Approach Slabs ........................................................................................... 10-5

10.3 STRUCTURAL GUIDANCE ...................................................................................... 10-6

10.3.1 Span Arrangement ...................................................................................... 10-6 10.3.2 Span Length Ranges ................................................................................... 10-6 10.3.3 Typical Girder Spacing and Overhang Dimensions ..................................... 10-7 10.3.4 Seismic ........................................................................................................ 10-8

10.4 GEOMETRIC GUIDANCE ......................................................................................... 10-9

10.4.1 Cross Section .............................................................................................. 10-9 10.4.2 Sidewalks on Bridges .................................................................................. 10-10 10.4.3 Bridge Undercrossing Geometry ................................................................. 10-10 10.4.4 Horizontal Clearances ................................................................................. 10-10 10.4.5 Vertical Clearances ..................................................................................... 10-10 10.4.6 Skew ............................................................................................................ 10-11 10.4.7 Straight Girders on Horizontal Curve Alignment .......................................... 10-12

10.5 ROADWAY GEOMETRIC GUIDANCE ..................................................................... 10-12

10.5.1 Vertical Alignment ........................................................................................ 10-12 10.5.2 Horizontal Alignment ................................................................................... 10-13 10.5.3 Superelevation Transitions .......................................................................... 10-13 10.5.4 Variable Width Structures ............................................................................ 10-13 10.5.5 Future Widening of Road Crossed .............................................................. 10-14 10.5.6 Future Structure Widening ........................................................................... 10-14

10.6 HYDRAULIC GUIDANCE .......................................................................................... 10-14


10-ii Preliminary Design

10.6.1 Hydraulic Design Coordination .................................................................... 10-14 10.6.2 Hydraulic Design Criteria ............................................................................. 10-15 10.6.3 Abutment Hydraulic Design Factors ............................................................ 10-15 10.6.4 Bent Hydraulic Design Factors .................................................................... 10-15 10.6.5 Foundation Hydraulic Design Factors ......................................................... 10-16

10.7 GEOTECHNICAL GUIDANCE .................................................................................. 10-16 10.8 OTHER PRELIMINARY DESIGN CONSIDERATIONS ............................................. 10-17

10.8.1 Right of Way ................................................................................................ 10-17 10.8.2 Utilities ......................................................................................................... 10-17 10.8.3 Railroads ..................................................................................................... 10-17

10.8.3.1 Highway Bridges Over Railroads ............................................... 10-17 10.8.3.2 Railroad Bridges Over Highways ............................................... 10-18

10.8.4 Aesthetics .................................................................................................... 10-18

10.8.4.1 Preliminary Design Considerations ............................................ 10-18 10.8.4.2 References ................................................................................ 10-19

10.8.5 Environmental .............................................................................................. 10-19 10.8.6 Construction and Maintenance of Traffic ..................................................... 10-19

10.8.6.1 Access and Time Restrictions.................................................... 10-19 10.8.6.2 Phased Construction ................................................................. 10-20 10.8.6.3 Falsework .................................................................................. 10-20

10.8.7 Maintenance and Inspection ........................................................................ 10-21

10.9 SUPERSTRUCTURE SELECTION GUIDANCE ....................................................... 10-21

10.9.1 Traditional Superstructure Types ................................................................ 10-21

10.9.1.1 Precast Prestressed Concrete I-Girders .................................... 10-21 10.9.1.2 Composite Steel Girders ............................................................ 10-22

10.9.2 Alternative Superstructure Types ................................................................ 10-23

10.9.2.1 Composite Steel Box Girders..................................................... 10-24 10.9.2.2 Cast-in-Place or Precast Concrete Slab, Conventionally

Reinforced Concrete Slab .......................................................... 10-25 10.9.2.3 Segmental Concrete Box Girders .............................................. 10-25

10.9.3 Additional Superstructure Types ................................................................. 10-26

10.10 SUBSTRUCTURE AND FOUNDATION SELECTION GUIDE .................................. 10-27


Preliminary Design 10-iii

10.10.1 Abutments ................................................................................................... 10-27 10.10.1.1 Integral Abutments ..................................................................... 10-28 10.10.1.2 Semi-Integral Abutments ........................................................... 10-29 10.10.1.3 Seat Abutments ......................................................................... 10-30

10.10.2 Bents ........................................................................................................... 10-30

10.10.2.1 Drop Bent ................................................................................... 10-31 10.10.2.2 Internal Bent .............................................................................. 10-31 10.10.2.3 Straddle Bent ............................................................................. 10-31 10.10.2.4 Capless Bent ............................................................................. 10-32 10.10.2.5 Wall Bent ................................................................................... 10-32 10.10.2.6 Extended Pile Bents .................................................................. 10-33 10.10.2.7 Columns ..................................................................................... 10-33

10.10.3 Foundations ................................................................................................. 10-33

10.10.3.1 Piles ........................................................................................... 10-34 10.10.3.2 Drilled Shafts ............................................................................. 10-34 10.10.3.3 Spread Footings ........................................................................ 10-35

10.11 RETAINING WALLS .................................................................................................. 10-35 10.12 CULVERTS ................................................................................................................ 10-36

10.12.1 Cast-in-Place or Precast Concrete Box Culverts ......................................... 10-36

10.12.1.1 Description ................................................................................. 10-36 10.12.1.2 Advantages/Disadvantages ....................................................... 10-36

10.12.2 Cast-in-Place or Precast Three-Sided Culvert Structures ........................... 10-39

10.12.2.1 Description ................................................................................. 10-39 10.12.2.2 Advantages/Disadvantages ....................................................... 10-39

LIST OF FIGURES

Figure 10.1 — TYPICAL SPAN LENGTH .............................................................................. 10-7 Figure 10.2 — TYPICAL GIRDER SPACINGS ...................................................................... 10-8 Figure 10.3 — SKEW MEASUREMENT ................................................................................ 10-12 Figure 10.4 — RETAINING WALLS CONSTRUCTED FROM THE TOP DOWN ................. 10-37 Figure 10.5 — RETAINING WALLS CONSTRUCTED FROM THE BOTTOM UP ................ 10-38


10-iv Preliminary Design


Preliminary Design 10-1

Chapter 10 PRELIMINARY DESIGN

The LRFD Specifications do not specifically address preliminary design considerations. The LRFD Specifications do address the topics in Section 10.2 of this chapter, and Section 2 of the LRFD Specifications discusses many of the nonstructural topics (e.g., geometrics, hydraulics) that are involved in the preliminary design process.

Preliminary design requires close coordination with other design disciplines. Adjustments in alignment or geometry can result in simplified construction, improved durability, construction time savings and cost savings. The preliminary design stage allows examination of various scenarios to identify the most effective project solution.

The preliminary design stage requires a project wide approach. Minimizing individual element costs does not always result in minimizing project costs. For example, the minimum cost of pavement for a road between two points is a straight line with minimal profile change. The straight line, minimal profile change option can add significant right of way (ROW) and structure costs. In the preliminary design stage, structural engineers, roadway designers, geotechnical engineers and hydraulics engineers must coordinate and balance cost and time elements to determine the optimum project wide approach.

Although minor adjustments can be made during final design, requests for adjustments often encounter resistance because late changes result in increased design costs and delayed advertising. The project team must, as practical, identify potential problems early in the design process.

10.1 PROCESS

The following presents an overview of the process for preliminary design. The process is presented as a list of tasks and questions for team members during preliminary design. The process applies to all structure types, bridges, culverts, walls, sign structures, rehabilitations or other miscellaneous structures, although some items are linked to specific structure types. Also note that, although the process is presented as a linear list, preliminary design is not linear. The process is iterative, requiring significant coordination and collaboration.

10.1.1 Evaluate the Site

• Review the preliminary scope and estimate. • Visit the site. • Identify obstacles or constraints:

o Are there utility conflicts? o Are there future widening plans? o Is there evidence of scour or bank erosion?


10-2 Preliminary Design

o Is settlement a constraint? o Will there be significant construction time limitations? o What are the environmental limitations?

• Identify opportunities for improvement: o Would realignment benefit the project? o Does the location lend itself to an enhanced aesthetic concept or plan? o Does the location lend itself to specific ABC approaches? o Can the structure be eliminated? o Can curves and other complex geometry be located so that the elements are

outside of the bridge limits (including approach slabs)? • Evaluate the rehabilitation scope:

o Does the scope address structure deficiencies? o Does the scope meet the budget limitations? o Can significant performance improvements be made with minor increases in

project scope or cost?

10.1.2 Evaluate the Project Geometry

• Coordinate with the roadway designer and geotechnical and hydraulics engineers: o Identify and understand roadway constraints. o Identify and understand geotechnical constraints. o Identify and understand hydraulic constraints.

• Review the concept geometry: o Does the concept geometry reflect the project goals? o Does the concept geometry avoid identified obstacles or constraints? o Would an alternative geometry benefit the project? o Does the geometry limit structure types? o Is the horizontal curvature excessive? o Is the vertical curvature excessive? o Have the bridge deck elevation contours been evaluated to prevent low spots? o Is the concept compatible with roadway constraints? o Is the concept compatible with geotechnical constraints? o Is the concept compatible with hydraulic constraints? o Is the concept compatible with environmental constraints? o Are curves and other complex geometry located outside the bridge limits

(including approach slabs)? o Are superelevation transitions within the bridge limits such that the entire cross

section rotates as a unit? If not, can a longitudinal construction joint be provided at the point of rotation?

• Identify potential structure types and layouts: o Minimize the bridge skew to provide simpler and more efficient design and

construction. o Avoid skewed supports on horizontally curved bridges. Design horizontally

curved bridges with radial supports. o Evaluate multispan bridges with steep profile grades that cross multiple

alignments to balance substructure stiffness.



o Coordinate with the roadway designer on the preliminary structure type options and geometry: + Bridge requirements — structure depths, span lengths, section width + Culvert requirements — types, lengths, widths, cover + Wall requirements — potential types + Sign structures — potential types

o Coordinate with the geotechnical engineer on preliminary structure type options and foundation options: + Bridge requirements — geometry, preliminary foundation reactions + Culvert requirements — types, lengths, widths, cover + Wall requirements — potential types and location + Sign structure requirements — potential types and location

o Coordinate with the hydraulics engineer on preliminary structure type options and hydraulic requirements: + Bridge requirements — span arrangements, preliminary substructure

widths, foundation element types, elevations o Review the environmental constraints.

10.1.3 Evaluate Costs

• Perform a system wide cost analysis: o Are quantity estimates reasonable? o Are item prices reasonable? o Do prices reflect trends in construction costs? o Are major items identified? o Are contingencies included?

• Identify high cost items: o Can adjustments be made to reduce or eliminate high cost items? o What factors drive the selection of the high cost item? o Can the factors that dictate the high cost items be altered?

• Re-evaluate options with an emphasis on reducing high cost items using a project wide approach.

10.1.4 Select a Preferred Option

• Justify the selection. • Document the selection and provide deliverables as defined in the Project Delivery

Network. • Re-evaluate the selection as project variables change. • Re-evaluate the geometry:

o Verify that the alignment profiles provide adequate vertical clearance and structure depth for the selected bridge type.

o Evaluate bridge deck elevation contours to prevent low spots.



The following sections elaborate on various design considerations that impact preliminary design.

10.2 STRUCTURAL REQUIREMENTS

10.2.1 Structural Requirements

Meet the LRFD Specifications requirements except as modified by the SDDM. Chapters 11 through 22 discuss specific elements and element requirements. The following sections provide generic requirements not specifically addressed in other SDDM chapters that impact preliminary and final design.

10.2.2 Live Load Deflection Criteria

Reference: LRFD Article 2.5.2.6.2

Limit the live load deflections to the span length based criteria in LRFD Article 2.5.2.6.2.

10.2.3 Span to Depth Criteria


The LRFD Specifications provide optional depth to span ratios for typical bridge types. The depth to span ratios provide good guidance for efficient girder and/or structure design. Strict conformance to the depth to span ratios is not necessary. Use of a structure depth less than required in LRFD Article 2.5.2.6.3 is permitted where overall project costs are reduced through the use of a shallower girder.

10.2.4 Continuous vs Simple Spans

Use continuous structures. Add expansion joints between continuous frames when a single continuous frame results in integral abutment movements exceeding the limits defined in Section 18.1.3.1. Simple span girder systems made continuous for live loads are considered continuous structures.

Continuous structures provide superior structural performance when compared to bridges with simple spans and joints.

It is appropriate to use simple spans when widening existing bridges consisting of simple spans.

10.2.5 Composite Action

Reference: LRFD Articles 4.5.2.2 and 9.4.1



Composite action enhances the stiffness and economy of girder bridges by using the bridge deck as an integral part of the girder cross section. Make all bridge decks and girders fully composite throughout the entire length of the bridge, in both the positive and negative moment regions. Design the shear connectors or other connections between decks and girders to develop full composite action. Shear connectors are not required on splice plates.

Base the stiffness characteristics of composite girders on full participation of the effective width of the concrete deck in the positive moment regions. Consider composite concrete bridge decks uncracked throughout the span for the determination of moments and shears for service and strength limit states in structural analysis.

Do not use noncomposite bridge decks.

10.2.6 Number of Girders


Typical highway bridges require a minimum of four girders per span to provide redundancy. Exceptions are appropriate for narrow bridges or single lane bridges where a minimum of three girders can be used. Do not use two girder systems on highway bridges.

Pedestrian bridges are typically narrow structures where two girder systems or single girder systems are appropriate.

Design and fabricate two girder systems with fracture critical provisions. Apply the ηr factor defined in Chapter 11 to both two and three girder systems. The maximum girder spacing for a three girder system is 13′-0″.

The cost of a girder bridge increases with the number of girders in the cross section. Conversely, structure redundancy increases with the number of girders. The basic objective is to identify a girder spacing and corresponding number of girders that optimizes the superstructure design by providing sufficient redundancy with minimal cost.

10.2.7 Approach Slabs

Provide approach slabs that are at least 25-ft long (measured along the control line of the bridge), are the same width as the bridge deck and extend over the abutment wingwalls. Make allowance for settlement between the approach slab and wingwall by providing a minimum 5-in. gap between the top of the wingwall and the approach slab. Use the approach slab design defined in the WS sheets.

Coordinate with the Structures Design Manager when the use of the standard 25-ft approach slabs present additional project complications. Obtain approval from the Structures Design Manager when 25-ft approach slabs are not used.



10.3 STRUCTURAL GUIDANCE

10.3.1 Span Arrangement

The required length of a bridge is typically easy to determine. Determining the optimum number of spans is more difficult, which depends on:

• Roadway profile • Vertical clearance • Construction requirements • Environmental factors • Allowable depth of structure • Allowable locations of bents • Foundation conditions • Waterway opening requirements • Safety of underpassing traffic • Flood debris considerations Consider single span bridges for all locations. Single span bridges are typically the most cost effective structures for structural steel girder spans up to 225 ft and for prestressed concrete girder spans up to 150 ft. Limitations on permissible structure depth can make single span bridges impractical.

Single span bridges typically require the least maintenance and usually perform better in extreme events. Use caution when selecting single span bridges on high skews and/or curved alignments because typical cost estimates, quantity estimates and expected performance is not always applicable.

10.3.2 Span Length Ranges

Figure 10.1 presents the typical span length ranges for the traditional and alternative superstructure types. The upper limit of the span ranges suggests a boundary above which other superstructure types or span arrangements are usually more cost effective. The lower limit of the range suggests a boundary below which other superstructure types are usually more cost effective. The limits represent typical structures and can be exceeded for atypical locations and project requirements. Use caution when exceeding the limits.



Structure Type Typical Span Length Ranges

Simple Spans Continuous

Spans

Tra

ditio

nal

Sup

erst

ruct

ures

Precast, prestressed concrete I-girders 50 ft to 150 ft 50 ft to 160 ft

Composite steel Plate I-girders 40 ft to 225 ft 90 ft to 250 ft

Rolled beams 30 ft to 90 ft

Alte

rnat

ive

Sup

erst

ruct

ures

Composite steel box girders 120 ft to 250 ft 120 ft to 400 ft

CIP or precast, conventionally reinforced concrete slab

20 ft to 40 ft

CIP or precast, post-tensioned concrete slab 30 ft to 65 ft

Segmental concrete box girders

Span by span 100 ft to 150 ft

Balanced cantilever

100 ft to 400 ft

B

urie

d S

truc

ture

s Box culverts, precast or CIP 4 ft to 20 ft per cell

Three-sided culvert or precast arch 8 ft to 80 ft

Figure 10.1 — TYPICAL SPAN LENGTH 10.3.3 Typical Girder Spacing and Overhang Dimensions

Figure 10.2 presents the typical girder spacings for the traditional and alternative superstructure types. Generally, wider girder spacing results in a lower cost superstructure. However, wider girder spacings reduce redundancy and require thicker decks, deeper girders, larger cross frames and higher concrete strengths for concrete girders.

Proportion the overhang to provide a minimum of 1 ft from the edge of flange to the edge of deck. The overhang width for a balanced design in a girder bridge is approximately 30% of the girder spacing. Typical overhang widths are less than 40% of the girder spacing for I-girders and 50% for box girders. The maximum overhang width is 5.5 ft.



Structure Type Typical

Girder Spacing T

radi

tiona

l S

uper

stru

ctur

es

Precast, prestressed concrete I-girders 6 ft to 12 ft

Composite steel Plate I-girders 8 ft to 14 ft

Rolled beams 6 ft to 12 ft

Alte

rnat

ive

S

uper

stru

ctur

es Composite steel box girders

Web to web spacing: 8 ft to 12 ft

CIP or precast, conventionally reinforced concrete slab

N/A

CIP or precast, post-tensioned concrete slab N/A

Segmental concrete box girders N/A

Figure 10.2 — TYPICAL GIRDER SPACINGS 10.3.4 Seismic

Chapter 13 discusses detailed seismic considerations.

Ideally, bridges have a regular configuration as defined in the AASHTO Guide Specifications for LRFD Seismic Design, which allows predictable seismic behavior and promotes plastic hinging in readily identifiable and repairable components. Selecting a structural form based solely on gravity type loading considerations and then adding seismic resistive elements and details is unlikely to provide the best solution. In general, consider the following when selecting the structure type:

1. Alignment. Curved bridges can lead to unpredictable seismic response.

2. Substructure Skew. Skewed supports can lead to unpredictable seismic response and cause rotational response with increased displacements.

3. Superstructure Weight. Increased superstructure weight increases seismic demands.

4. Joints. Expansion joints are weak links in the seismic response system.

5. Foundations. Liquefaction affects both shallow and deep foundations.

6. Substructure Stiffness. The substructure configuration must avoid large differences in the stiffness of the substructure units. Consider designing the structure to uniformly distribute seismic forces to substructure units by varying the column cross section between bents or strategically locating pinned versus fixed column ends.



7. Plastic Hinges. Plastic hinges are an effective method of damping and dissipating the seismic energy input to the structure. Locate plastic hinges where they are accessible for inspection and repair after an earthquake. Force plastic hinges to develop in the columns rather than the bent cap, superstructure or foundation elements.

10.4 GEOMETRIC GUIDANCE

Good bridge geometric design is intrinsic to the development of aesthetic, economic, safe, low maintenance and efficient structures. The alignment geometry defines the bridge geometry and appearance. No amount of aesthetic treatment can compensate for undesirable bridge geometry.

Coordinate with the roadway designer to obtain the preliminary roadway geometry. Evaluate the initial geometry and work with the roadway designer to mitigate impacts of roadway design decisions on the design of the structure. In some cases, the optimum roadway alignment significantly increases the cost of the structure. Although bridges can accommodate almost any given geometry, coordination between the roadway designer and structural engineer can result in a lower overall project cost by using an alignment that balances the structure cost with the additional roadway costs.

The roadway designer determines the roadway classification based upon AASHTO and UDOT standards. The DD series in the UDOT Standard Drawings specify bridge geometry requirements for the cross sections of the bridge, roadway and feature(s) crossed.

Use the requirements on the drawings when laying out bridges. Verify the correctness and consistency of the roadway information received and resolve any conflicts with the standards.

Roadway design factors that impact bridge location and structure type selection include:

• Horizontal alignment (e.g., tangent, curve, superelevation, skew) • Vertical clearances and alignment (e.g., longitudinal gradient, vertical curves) • Traffic volumes • Roadway and shoulder widths • Presence of medians and sidewalks • Clear zones through underpasses

10.4.1 Cross Section

The roadway classification and traffic volumes determine the minimum number of lanes and minimum shoulder widths of the bridge and the road crossed.

Design the bridge width to comply with the UDOT Standard Drawings. Add 2 ft to the roadway shoulder width for shy distance as defined in the UDOT Standard Drawings.



Where a bridge includes a median parapet, provide a longitudinal joint in the center of the median parapet and separate the cross section into two separate bridges. The typical space between median barriers is 2 in.

Use cross slopes on bridges in compliance with the UDOT Standard Drawings. The roadway designer provides the superelevation data to the structural engineer.

10.4.2 Sidewalks on Bridges

Refer to the DD series in the UDOT Standard Drawings for geometric and barrier requirements. Section 16.6.1 discusses the use of bridge parapets in combination with a sidewalk.

10.4.3 Bridge Undercrossing Geometry

Design the bridge undercrossing geometry in accordance with the UDOT Standard Drawings. In general, carry the approaching roadway cross section, including any auxiliary lanes, bicycle lanes, sidewalks, etc., through the underpass. Evaluate spanning the clear zone to eliminate barriers.

In addition, consider the potential for future development or traffic increases in the vicinity of the underpass that could significantly increase traffic or pedestrian volumes. If appropriate, an allowance for future widening can be provided to allow for sufficient lateral clearance for additional lanes. The need for accommodating future travel lanes is made on a case by case basis.

10.4.4 Horizontal Clearances

Provide horizontal clearances under bridges in accordance with the DD series in the UDOT Standard Drawings. Bridge underpass geometries must balance safety requirements with costs.

Eliminate intermediate supports from within the roadside clear zone where possible. When intermediate supports cannot be eliminated from the clear zone, provide a roadside barrier to protect the support in its entirety.

10.4.5 Vertical Clearances

Provide the following minimum vertical clearances:

• 16′-6″ for all highway grade separations; do not exceed a 17′-0″ minimum vertical clearance when the minimum vertical clearance over the highway is the controlling profile factor

• 23′-4″ for bridges over railroads; do not exceed a 24′-0″ minimum vertical clearance when the minimum vertical clearance over the railroad is the controlling profile factor



• 17′-6″ for stand alone pedestrian overpass structures crossing highways • 10′-0″ for structures over a walkway, sidewalk or trail • 17′-6″ for overhead sign structures; measure the clearance from the highest elevation of

the roadway section to the lowest point on the sign panel (or to the support if within the required clearance envelope)

• 18′-0″ for overhead variable message signs; measure the clearance from the highest elevation of the roadway section to the lowest point on the sign panel (or to the support if within the required clearance envelope)

Add an additional 1 ft to the minimum vertical clearance of all highway and railroad grade separations for nonredundant structural elements such as post-tensioned straddle bent caps.

When calculating the minimum vertical clearance for bridges with prestressed concrete girders, consider the bottom of the girder as a straight line between supports, because the girder is cast as a straight line. Some excess camber can remain in the girder, but too many variables exist to accurately predict girder camber during the design stage. Evaluate the potential for long term sag.

If the structure is expected to settle after initial construction, adjust the vertical clearance to allow for settlement. Show the anticipated settlement on the plans.

Where girders are haunched over the median strip and the median can accommodate additional traffic lanes, maintain 16′-6″ minimum vertical clearance between the girder haunch and the future lanes. In computing the clearance, assume that the superelevation of the road is continued through each of the future lanes provided through the adjacent shoulders. Also assume that shoulder widths remain unchanged for future construction.

10.4.6 Skew

The maximum permitted skew is 60°. Skews over 50° require prior approval from the Structures Design Manager. Avoid skews over 30° where feasible. See Figure 10.3 for skew measurement.

Most bridges use skewed supports. Skews of less than approximately 30° cause few problems for most bridge types. Structures with skews more than 30° are more difficult and expensive to construct. Construction and maintenance problems are common on bridges skewed over 45°. Bridges with skews over 30° can also have long term functionality problems (e.g., uplifting of girders in the acute corners, bridge bearings translating sideways).

Evaluate the impacts of minimizing the skew by extending the span. The impacts of skew on structural design are discussed in the respective locations throughout the SDDM. In general, skew angles of more than 30° affect the design of structural elements. Request that the roadway designer examine the roadway realignment to reduce the skew on skewed structures of more than 30°.

See Sections 12.5.4 and 12.5.5 for guidance on acceptable methods of analysis for skewed bridges.



Figure 10.3 — SKEW MEASUREMENT 10.4.7 Straight Girders on Horizontal Curve Alignment

Use the following criteria to determine when straight girders can be used on a bridge with a horizontally curved alignment:

• For curve offsets (between supports) equal to 12 in. or less — use straight girders and widen the bridge to eliminate a curved edge of deck.

• For curve offsets (between supports) greater than 12 in. and equal to or less than 24 in. — use straight girders and curved edges of deck. Consider curved steel plate girders.

• For curve offsets (between supports) greater than 24 in. — use curved girders and curved edges of deck.

In all cases, comply with minimum and maximum deck overhang requirements. Do not use a distance between the edge of deck and the girder top flange less than 1 ft.

10.5 ROADWAY GEOMETRIC GUIDANCE

10.5.1 Vertical Alignment

Vertical curvature on bridges can cause excessive haunch depths on precast, prestressed concrete I-girders, which can preclude the use of precast, prestressed concrete I-girders. If necessary, work with the roadway designer to balance the costs of decreasing the rate of the vertical curve to allow the use of precast, prestressed concrete I-girders.

Steel girders and CIP structures are fabricated to match the vertical curve, which eliminates large haunches.



10.5.2 Horizontal Alignment

Many bridges are constructed on horizontal curves. Horizontal curves complicate the design, geometry and construction of bridges and reduces the number of bridge types that are appropriate for the site. Bridges with a tight radius curve are difficult/expensive to construct and usually require additional maintenance. Bridges on larger radius curves often require lengthy spans to clear the undercrossing feature. Coordinate with the roadway designer when adjustments to the roadway curvature offer significant savings. In general, structural steel and CIP concrete are best suited for horizontally curved bridges.

See Sections 12.5.3 and 12.5.5 for guidance on acceptable methods of analysis for bridges on curved alignments.

10.5.3 Superelevation Transitions

Superelevation transitions do not create additional structural analysis; however, the geometry becomes more difficult to construct. Most bridges can be constructed with the transitions on a bridge if the transition is constant over the entire length of the bridge. Avoid superelevation transitions on only one side of a crown section.

Verify the required superelevation transition length with the roadway designer. Where practical, reduce or relocate the superelevation transition length to eliminate the transition over the bridge. Alternatively, suspend the transition on the bridge and resume the transition on the other side of the bridge, where practical.

10.5.4 Variable Width Structures

Most bridges are a constant width. However, ramps and roadway approaches sometimes extend onto or through a bridge. The variable width can create complex detailing and design challenges. The transitions in bridge width can be either linear or curved. Detailing and design can become very complex when the bridge is on a horizontal curve with a linear or curved width transition.

Evaluate eliminating the variable width by extending the required extra width across the structure. The reduction in design and construction costs often offsets the additional cost of the wider bridge deck. If the bridge is widened to accommodate the variable width, coordinate with the roadway designer to align barriers, roadway striping, etc., and verify that adequate ROW is available. Verify the required taper length with the roadway designer. Occasionally, the ramp geometry can be modified to eliminate the need for extra bridge width.

For bridges with tapers, begin and end tapers at a support (bent or abutment), or continue the taper across the entire length of the bridge.



10.5.5 Future Widening of Road Crossed

Locate abutments based on the requirements of the road beneath the bridge. The roadway width is typically based on 20 year traffic projections. However, the LRFD Specifications require a 75 year design life for bridges. Verify with the project design criteria if appropriate to consider potential future widening projects when laying out the structure.

Evaluate the use of abutments on fill slopes to eliminate retaining walls and to accommodate future widenings via fill slope removal combined with soil nail walls.

10.5.6 Future Structure Widening

Consider the possibility of future structure widening. Single web girder (steel or concrete) bridges are relatively easy to widen. Avoid single cell box girders or widely spaced box girders where single lane or smaller widenings are likely.

10.6 HYDRAULIC GUIDANCE

Design bridges crossing watercourses to reduce the effects of scour and channel instability over the life of the structure. Scour is a function of watercourse characteristics and bridge characteristics. Primary watercourse characteristics include stream flow, stream velocity and stream bed material. Primary bridge characteristics include span lengths, bent sizes, number of columns, column shape, support skew and vertical geometry. Channel instability can result in future impacts to roadways and bridges if not considered in design. Document potential impacts due to scour and channel instability in the Structure TSR; also include proposed measures to reduce scour and channel instability.

10.6.1 Hydraulic Design Coordination

Coordinate with the hydraulics engineer and provide the preliminary bridge opening geometry, sizes and locations of supports. The hydraulics engineer is responsible for conducting the hydraulic analysis and preparing the Hydraulics Report. The process can be iterative because the most cost effective bridge type and span lengths may not be compatible with the hydraulic requirements.

The hydraulics engineer provides the necessary hydraulic information for inclusion on the situation and layout sheets, including:

• Water surface elevations • Recommended low chord elevation • Recommended bridge waterway opening dimensions, skew angle and bottom of channel

elevation • Scour depth



• Flow volumes and velocities • Any necessary bridge scour and channel protection measures 10.6.2 Hydraulic Design Criteria

The hydraulic criteria for the design of bridge waterway openings is provided below:

1. Design Flood Frequency. The minimum design event is based on the roadway classification and ranges from the 25 year event to the 50 year event. Where the local community has adopted FEMA requirements, the 100 year event must be used.

2. Maximum Allowable Backwater. The hydraulics engineer determines the allowable backwater to minimize flooding of adjacent properties. On FEMA delineated floodways, no backwater can be introduced by the structure in the 100 year design event. On FEMA delineated floodplains, 1 ft of maximum backwater can be introduced by the structure in the 100 year design event. For all sites, the maximum allowable backwater is limited to an amount that will not result in unreasonable damage to upstream property or to the highway.

3. Freeboard. The amount of freeboard should be based on the ability of the watercourse to convey ice and debris and provide the level of protection desired by the Department. For navigable waters, the vertical clearance is typically based on normally expected flows during the navigation season and applicable federal requirements. Provide a minimum freeboard of 2 ft from the low chord of the bridge to the water surface based on the design event.

4. Scour. Design bridge foundations to withstand the worst case scour condition up to the 100 year flood event, and provide a minimum factor of safety of one against failure due to the worst case scour condition up to the 500 year flood event.

10.6.3 Abutment Hydraulic Design Factors

The hydraulic design factors for abutments include orientation and protection from scour. The hydraulics engineer identifies protective measures to minimize potential scour.

Where practical, locate bridge abutments beyond the water surface elevation for the design flood so that the bridge does not affect the backwater elevation. When the abutments are located in the design flood zone, consider locating abutments outside the ordinary high water elevation to minimize construction cost and risk associated with construction in the waterway.

10.6.4 Bent Hydraulic Design Factors

Design bent shapes, spacing and orientation to minimize flow disruption and local scour. Align bents with the flow direction at flood stage and minimize the number of columns to minimize the opportunity for debris to be caught and the possibility of debris dams forming at the bridge causing an increase in backwater and scour.



Locating bents in waterways is an interactive process between the structural engineer, geotechnical engineer and hydraulics engineer. Initially, the hydraulics engineer determines the required channel geometry to meet the hydraulic requirements. The structural engineer coordinates with the hydraulics engineer and estimates the number and length of spans, types of bents and low chord elevation. The hydraulics engineer evaluates the proposed bridge geometry to determine if the structure meets or exceeds the hydraulic requirements. Next, the structural engineer and geotechnical engineer evaluate potential foundation designs for the bent and provide preliminary design information to the hydraulics engineer for scour analysis. The structural engineer evaluates the impacts of scour and reduces the number of bents in the scour zone if appropriate.

Bents in water are expensive, difficult to construct, reduce the hydraulic opening and increase the contractor risk. Balance the cost of longer spans, deeper structures and increased superstructure costs with reductions in the number of bents and the number of columns per bent.

10.6.5 Foundation Hydraulic Design Factors

Stream and river crossings require deep foundations on all foundation elements unless the foundations are socketed into stable rock below the scour elevation.

The hydraulics engineer, geotechnical engineer and structural engineer evaluate the potential scour and the possibility of channel migration in designing foundations for bridges. The history of a watercourse and channel migration can help the designer make decisions on bridge type, bridge geometry and foundation type. Coordinate with the geotechnical engineer to determine foundation type and depth based on estimates of potential scour. The structural engineer must consider the effects of scour on the axial capacity and lateral stability of piles or drill shafts.

10.7 GEOTECHNICAL GUIDANCE

Coordination between the structural engineer and geotechnical engineer for foundation type selection and design is performed in two stages. During preliminary design, the structural engineer provides the geotechnical engineer with a structure layout and preliminary foundation vertical loads. The geotechnical engineer performs the drilling, sampling and testing and provides the preliminary foundation recommendations; i.e., either spread footings or deep foundations (with recommended pile type or shaft size). The preliminary foundation recommendations are documented in the Structures Foundation Type Memo. During final design, the loads are refined, foundation element capacities are refined and extreme event performance is evaluated.

The geotechnical engineer is also responsible for evaluating system global slope stability.

For waterway crossings, the design of bridge foundations involves an interdisciplinary team of hydraulic, geotechnical and structural engineers to provide a design that withstands the effects of estimated total scour.



Section 17.1 further discusses the coordination among the hydraulics, geotechnical and structural engineers for foundation selection and design.

10.8 OTHER PRELIMINARY DESIGN CONSIDERATIONS

10.8.1 Right of Way

Evaluate the impacts of structure types and wall requirements with respect to ROW requirements. Coordinate with the roadway designer to determine the impacts of increased structure depths on fill slope limits and ROW acquisition versus wall costs or increased span lengths to determine the minimum project costs or impacts.

10.8.2 Utilities

Work with the project utility coordinator early in project development to identify and mitigate utility impacts. The structure design must be consistent with UDOT utility accommodation policies. Section 2.8 discusses the policy for utility attachments to bridges. The UDOT Utility Coordination Manual of Instruction also discusses requirements.

10.8.3 Railroads

Work with the project railroad coordinator early in project development to identify impacts and determine Railroad requirements. Discuss the structure type, track configuration and clearances with the Railroad for highway/railroad grade separations. Also, see the UDOT Railroad Coordination Manual of Instruction for more detail on projects with highway bridges over railroads and the interaction with the Project Delivery Network. Refer to the WS sheets for the required railroad sheet for bridges crossing railroads. See Section 2.19 for more discussion.

10.8.3.1 Highway Bridges Over Railroads

Placement of any substructure elements in the Railroad ROW requires approval from the Railroad. For bridge replacements, the Railroad often requires removal of existing bents from the ROW.

Design highway bridges constructed over railroads to be consistent with the requirements from a variety of sources:

1. FHWA. The Code of Federal Regulations prescribe the FHWA policies, procedures and design criteria for preparing federal aid projects involving railroad facilities.

2. AREMA. AREMA provides recommended engineering practices for railroad design and construction throughout the United States. The AREMA Manual for Railway Engineering documents the practices, which contains the AREMA requirements for the geometric design of railroad tracks passing beneath a highway bridge. The AREMA Manual has



approximately the same status to railroad engineers as the LRFD Specifications has to highway bridge engineers.

3. LRFD Specifications. LRFD Article 3.6.5.1 presents criteria for the design of bridge abutments and bents over highways or railroads.

4. Union Pacific Railroad and Burlington Northern and Santa Fe Railroad. Use the UPRR/BNFS Guidelines for Railroad Grade Separation Projects for the design of highway bridges over railroads. Generally, UPRR requires that railroad tracks and maintenance roads be clear spanned.

5. Utah Transit Authority. The UDOT Railroad Coordination Manual of Instruction provides policies and practices for highway bridges over UTA railroad facilities.

10.8.3.2 Railroad Bridges Over Highways

Occasionally, UDOT is responsible for the structural design of railroad bridges. Use the specifications of the AREMA Manual for Railway Engineering; however, for seismic requirements, see Chapter 13 of the SDDM.

Provide reinforcement for shrinkage and temperature as specified in LRFD Article 5.10.8.

10.8.4 Aesthetics


See UDOT Policy 08C-03 “Project Aesthetics and Landscaping Plan Development and Review” for policies and procedures on aesthetics. Refer to the UDOT Aesthetics Guidelines for additional guidance.

Projects involving structures are subject to an aesthetics review by the Aesthetics Committee. Coordinate with the Region Landscape Architect to determine the appropriate aesthetics requirements.

Also, see Section 2.2.4.

10.8.4.1 Preliminary Design Considerations

Aesthetic design is an integral element of all bridge designs. Bridge aesthetics is inherent in the structure type, size and shape. The public expects transportation facilities that are economical, safe and durable, but that also have an attractive appearance. Aesthetic design cannot be an afterthought; aesthetics is not ornamentation. Aesthetic decisions during preliminary design cannot easily be changed later in project development because of schedule and budget requirements.



All bridges have an aesthetic impact. A bridge has a strong visual impact on any landscape and can become a central element in a community, even if the bridge is a simple crossing. Ensure that even the most basic structure complements, rather than detracts, from the surroundings. Once constructed, a bridge remains in place for 75 years or longer; all who view the bridge observe the results of the engineer’s design efforts.

The bridge must be consistent with other bridges in the vicinity. When designing a new bridge, consistency of bridge type and detail with existing bridge(s) is critical.

With proper attention to bridge aesthetics in preliminary design, an aesthetically pleasing bridge need not cost more than an unattractive bridge. Bridges that are well proportioned structurally using the least material possible are generally visually attractive.

10.8.4.2 References

Refer to the following documents for guidance and explanation of aesthetic principles:

• Frederick Gottemoeller, Bridgescape: The Art of Designing Bridges, John Wiley & Sons, Inc., 2004

• NRC, Bridge Aesthetics Around the World, Transportation Research Board, National Research Council, Washington, DC, 1991

• Maryland DOT, Aesthetic Bridges Users Guide, 2005 • Minnesota DOT, Aesthetic Guidelines for Bridge Design, 1995 • TRB Bridge Aesthetics Sourcebook, March 2009 • UDOT Aesthetics Guidelines, current version 10.8.5 Environmental

Ensure that the proposed structure type complies with and is compatible with commitments and requirements defined in the project environmental documents.

10.8.6 Construction and Maintenance of Traffic

Indicate a sequence of construction unless a single method of construction is obvious. Consider the impacts of construction requirements for the structure type selected. Confined job sites can limit construction options and make the historical low cost option less viable.

10.8.6.1 Access and Time Restrictions

Bridges over waterways typically have restrictions associated with construction, which can impact structure type selection. Regulations administered by various agencies can restrict the time period that the contractor is allowed to work within the waterway. Construction time limitations reduce the relative cost of longer spans and fewer bents compared to shorter spans with more bents.



Bridges with many bents can be cost effective when constructed sequentially with a single crew and reusing forms. Accelerated schedules often preclude the use of sequential construction and eliminate the associated cost savings.

10.8.6.2 Phased Construction

Project considerations can require phased construction to maintain traffic during construction. Evaluate the impacts of phasing requirements in preliminary design. The arrangement and sequencing of each phase of construction is unique to each project. Consider the requirements for adequate construction clearances and the requirements of the traveling public when determining the phasing requirements. Phased construction can increase the required number of girders and increase the required number of bent columns.

10.8.6.3 Falsework

Temporary falsework can be an expensive construction item. Precast elements can eliminate shoring costs. Consider precast elements when significant falsework is required.

The cost of the falsework can become prohibitive for elements over a waterway and/or with a high finished elevation. Consider alternative structural systems and construction methods.

Falsework in the clear zone must be protected by barriers.

Coordinate with the Railroad for falsework lateral and vertical clearances and protection requirements for bridges over railroads.

Consider the following when using a structure type requiring falsework:

1. Environmental. Some sites can be environmentally sensitive, and the use of falsework could be prohibited.

2. Hydraulics. For falsework over a waterway, coordinate with the hydraulics engineer to determine minimum falsework opening dimensions.

3. Traffic Impacts. Constructing falsework over traffic poses several risks. Installing and removing falsework requires extended lane closures or expensive traffic cross overs. Vehicular impacts to falsework can pose a hazard to the traveling public and construction workers.

4. Geotechnical. Settlement of falsework is a potential consideration. Coordinate with the geotechnical engineer to determine if falsework on simple, low cost footings is viable or if higher cost deep foundation elements are required to support the falsework.



10.8.7 Maintenance and Inspection

The structure type selection impacts maintenance costs. Where available, choose low maintenance elements. Evaluate and document the following maintenance considerations as appropriate:

1. Deck Expansion Joints. Open or inadequately sealed deck expansion joints lead to deterioration of structural elements by permitting the flow of waterborne deicing agents through the joints. Use jointless bridges with integral abutments, continuous decks and drainage control to eliminate deterioration associated with leaking joints, when possible.

2. Paint. Potential environmental issues associated with removing paint from steel structures makes the use of unpainted weathering steel preferable to painted steel from a maintenance perspective. However, weathering steel is not appropriate for all locations. Refer to Section 15.2.1 for weathering steel usage limitations.

3. Bearings. Use low maintenance bearings when viable. Refer to Section 19.2 for additional information.

4. Bridge Inspection. See Section 2.11.

10.9 SUPERSTRUCTURE SELECTION GUIDANCE

Numerous superstructure types are available and potentially viable for a particular location. Consider innovative and nontraditional or alternative superstructure types.

10.9.1 Traditional Superstructure Types

Traditional superstructure types, precast, prestressed concrete girders and structural steel plate girders, are appropriate and cost effective for the majority of bridges in Utah because the state has local precasters and steel fabricators. Additionally, the experience and equipment of the local contracting industry and the availability of materials favor the use of traditional superstructure types.

10.9.1.1 Precast Prestressed Concrete I-Girders

10.9.1.1.1 Description

A precast, prestressed concrete I-girder bridge is a girder and deck structure. The deck is replaceable by complete removal and replacement without the need for shoring. The structure type is efficient for multiple equal spans with a large number of girders, but does not adapt well to complex geometries.



See Chapter 14 for a detailed discussion on design practices for precast, prestressed concrete I-girders. Use the Utah bulb tee girder on new concrete girder bridges. Match existing girder type and stiffness on bridge widening projects. See Section 21.9.

Use precast, prestressed concrete I-girders when the cost of additional profile height is offset by a reduction in superstructure costs. Consider the transportation and erection of precast, prestressed concrete I-girders in selecting girder lengths.

Refer to Figures 10.1 and 10.2 for typical span lengths and girder spacings.

10.9.1.1.2 Advantages/Disadvantages

Advantages of this structure type are typically low construction cost, low maintenance cost, replaceable deck and simple construction.

Disadvantages include limited span lengths, higher depth/span ratios, difficulty in adapting to complex geometrics, difficulty in handling, shipping and erecting long spans, and aesthetic concerns on curved bridges and bridges on sharp vertical curves.

10.9.1.1.3 Concrete Strength

Concrete strengths up to 10 ksi can be produced in most precast plants. Higher strengths allow longer spans and/or increased girder spacing but increase cost and slow production. Typically, an upper limit for concrete strength of 8.5 ksi is appropriate.

10.9.1.2 Composite Steel Girders


A composite steel girder bridge is a girder and deck structure, using either steel plate I-girders or rolled beams. The deck is replaceable by complete removal and replacement without the need for shoring. Composite steel plate I-girders are efficient for spans over 160 ft and are adaptable to bridges with limited structure depth, complex geometries and/or horizontal curves. Consider composite steel rolled beams for spans up to approximately 90 ft. If a composite steel rolled beam design is proposed for a new bridge, allow the substitution of a composite steel plate I-girder with equivalent depth and plate dimensions equal to the rolled beam or as determined according to the LRFD Specifications. Do not use cover plates.

Inadequate design and detailing has a greater impact on composite steel I-girder bridges than on precast, prestressed concrete I-girder bridges. Poor design increases the required steel quantities. Good detailing practices significantly reduce the potential for fatigue cracking and brittle fracture.

Composite steel plate I-girders can have a constant or variable depth. Avoid abrupt depth changes for aesthetics. Continuous composite steel plate I-girders haunched at the supports are also an option. Use a parabolic variation in depth when haunching a girder at a support.



Consider structure erection issues, where to locate crane(s), how the girders are delivered to the site, can girders be erected in pairs, etc. Girder field sections can be easily transported in lengths up to approximately 120 ft. Coordinate with the fabricator when specifying longer field sections and allow the elimination or addition of field splices when appropriate documentation is supplied. Field splices can also be shown as optional on the plan set.

See Chapter 15 for a detailed discussion on design practices for structural steel superstructures.

Use composite steel girder superstructures at sites with limited structure depth, on bridges with longer spans and, occasionally, to minimize the structure weight and foundation demands.

Refer to Figures 10.1 and 10.2 for typical span lengths and girder spacings.


Advantages of composite steel plate I-girders and rolled beams include fast on site construction, simple details and formwork, good aesthetics, adaptable to complex geometrics, low dead weight and a replaceable deck. Composite steel plate I-girders also have long span capability.

Disadvantages of composite steel plate I-girders and rolled beams include higher girder costs, increased maintenance costs and dependence on good design and detailing practices.

10.9.1.2.3 Steel Strength

Use Grade 36 or Grade 50 steel for composite steel rolled beams. Use Grade 50 or Grade 70 for webs and flanges of composite steel plate I-girders. Higher grade steels are available. Obtain approval from the Structures Design Manager before specifying higher grade steels. Use of Grade 36 and Grade 50 steel is permitted for any secondary element.

10.9.2 Alternative Superstructure Types

Evaluate alternative superstructure types when traditional structure types are not suited to the project specific criteria and to the unique environment of the bridge location. The Structures Division promotes innovative and forward thinking solutions, which must meet the goals of low maintenance and long term durability.

To evaluate alternative superstructure types, provide information early in the preliminary design process that demonstrates the following:

• The superstructure type is accepted for general use by other transportation authorities. Include project contact information.

• If not in general use by other transportation authorities, identify any test projects or research that has been performed.



• The superstructure type and components perform well under the environmental conditions at the project site, including frequent freeze thaw cycles, heavy road salt use and high seismic events.

• The superstructure type allows for total deck removal and replacement with minimal impact to cross traffic and bridge traffic.

Also, provide justification that the proposed alternative superstructure type is a better solution for the project, and supply a life cycle cost analysis with a comparison to a traditional superstructure type.

Alternative superstructure types can be rejected without cause.

10.9.2.1 Composite Steel Box Girders


Composite steel box girders are structural steel plate girders with two webs and a common bottom flange. The webs are usually inclined to improve aesthetics and reduce the width of the bottom flange. Spans are economical up to approximately 250 ft. Composite steel box girders can have a variable depth, but variable depth significantly increases the cost of the bridge.

Consider composite steel box girders for tight radius curved structures and where a composite steel plate I-girder could be used but the appearance of a box girder is desired. Refer to Figures 10.1 and 10.2 for typical span lengths and girder spacings.


Advantages of composite steel box girder bridges include fast on site construction, low dead weight, adaptability to tight radius curves, replaceable deck and long span capability.

Disadvantages include high girder costs and increased maintenance costs; steel boxes are not readily adaptable to skewed or variable width bridges. Composite steel box girders are difficult to handle in the shop due to the size and weight and require significant bracing during fabrication and erection. In addition, the structure type is susceptible to thermal movements during erection and may require temporary or permanent external bracing between boxes. Composite steel box girders require a fabrication sequence that is less cost effective for fabricators in shops optimized to fabricate composite steel plate I-girders. The local fabricator shops are optimized for I-girders, and the use of composite steel box girders increases the relative cost of fabrication when compared to I-girders.

10.9.2.1.3 Steel Strength

Use Grade 50 or Grade 70 for webs and flanges of composite steel box girders. Higher grade steels are available. Obtain approval from the Structures Design Manager before specifying higher grade steels. Use of Grade 36 and Grade 50 steel is permitted for any secondary element.



10.9.2.2 Cast-in-Place or Precast Concrete Slab, Conventionally Reinforced Concrete Slab


CIP, conventionally reinforced concrete slabs (CIP concrete slabs) are suitable to short spans and low clearances and easily adapt to skewed alignments. Concrete slabs are the simplest superstructure system and easy to construct, and structural continuity is achieved without difficulty.

Use of prestressing or post-tensioning can extend the span range and improve durability.

Consider CIP concrete slabs for short bridge spans in areas that allow cost effective shoring.


The advantages of the structure type are low construction costs and low maintenance costs. Construction time is also fairly short. The appearance is neat and simple, especially for low, short spans.

The disadvantages are that CIP concrete slabs require falsework and have a limited span range.

10.9.2.2.3 Concrete Strength

Concrete strengths up to 10 ksi can be produced in most precast plants. Higher strengths allow longer spans and/or increased girder spacing but increase cost and slow production. Typically, an upper limit for concrete strength of 8.5 ksi is appropriate.

Coordinate with local suppliers to determine availability of high strength CIP concrete. CIP concrete strengths up to 6 ksi are readily available.

10.9.2.3 Segmental Concrete Box Girders


Most segmental concrete box girder bridges have a single cell superstructure with only two girder webs. The spacing of the web is based on the efficiency of the deck design. Segmental concrete box girders are either CIP or precast with longitudinal post-tensioning and transverse post-tensioning in the deck. The longitudinal post-tensioning can be placed internal to the webs as with conventional CIP, post-tensioned construction. The longitudinal post-tensioning can also be placed fully external to the web or a combination of internal and external. Internal post-tensioning has the same considerations as CIP, post-tensioned concrete box girders. Externally post-tensioned bridges usually have thinner webs because a wider web is not needed for the post-tensioning.



Segmental concrete box girder construction requires that the bridge be designed for a specified method of construction and included in the contract documents with assumed erection loads. In many cases, the construction of the bridge and not the permanent loads controls the design of the substructure.

The precast method is usually less expensive than the CIP method and is used primarily for shorter spans. Segments are match cast in a casting yard, transported to the site and connected in the erected position by temporary and permanent post-tensioning. The final section is typically CIP, and the entire structure is subsequently post-tensioned along the full length of span. Erection methods can be by balanced cantilever, temporarily supported by underslung trusses or by an overhead gantry.

CIP segmental concrete box girder construction uses a traveling form support. The traveling form is set to grade, rebar and ducts are placed, and the concrete is placed and cured. Once a segment reaches the design strength, the system is post-tensioned, the traveling form is advanced and the process is repeated. Erection methods include balanced cantilever, a gantry crane or a system of stays.

Consider segmental concrete box girder construction when the total deck area exceeds approximately 250,000 sq ft. Precast, segmental concrete box girder construction requires a significant investment in the casting facilities and erection equipment.

Precast, segmental concrete box girder segments differ from project to project, but the American Segmental Bridge Institute has established standard sections.

Refer to Figure 10.1 for typical span lengths.

An experienced contractor and construction engineer are necessary for segmental concrete box girders. Erection methods and equipment used to erect the segments vary from project to project. The contractor is required to verify the design based on the means and methods of construction.


Advantages include reduced traffic impacts when overhead construction techniques are used, low maintenance costs, fast onsite construction for the precast method and low depth/span ratios.

Disadvantages include the complexity of time dependent analysis and design, variable construction costs, limited number of qualified contractors, complex construction and construction engineering, lengthy construction time for the CIP method and decks cannot be replaced. Also, the construction method is only economical on large projects.

10.9.3 Additional Superstructure Types

Additional superstructure types that are beyond the scope of the SDDM but can be applicable to structures requiring spans over 350 ft include:



• Steel trusses • Steel or concrete arches • CIP multicell boxes • Cable supported concrete or steel bridges Selection of any of the above superstructure types require coordination with and approval from the Structures Design Manager.

10.10 SUBSTRUCTURE AND FOUNDATION SELECTION GUIDE

Use the following guidance to select the substructure and foundation type that is suitable at the site to economically satisfy the geometric and structural requirements of the bridge. Chapter 18 discusses the detailed design of substructure elements; Chapter 17 discusses the detailed design of foundations.

Substructure and foundation type selection occurs in conjunction with the superstructure type selection. Balance the foundation and substructure costs and characteristics when selecting the type of superstructure.

Consider the following:

• Foundation conditions influence the cost, size, number and spacing of the necessary substructure supports.

• Dead load has a major influence on foundation costs. Consider the economics of using lighter structural elements.

• Scour can have a significant impact on the foundation design which can, in turn, have a significant impact on the superstructure type selection.

• Seismic response, liquefaction, slope stability, etc., can have a significant impact on the substructure design which can, in turn, have a significant impact on the superstructure type selection.

10.10.1 Abutments

Reference: LRFD Article 10.6

Abutments are either spill through or wall type. Spill through abutments are placed at the top of the slope. Slopes are typically 1.5H:1V, which requires slope protection and good fill conditions. Slopes flatter than 2H:1V do not require slope protection. Slope stability requirements can also require shallow fill slopes to maintain the stability of the slope.

Spill through abutments require longer spans compared to wall type abutments, but eliminate retaining walls and/or full height abutments. Evaluate the overall cost of longer spans with spill through abutments compared to shorter spans with increased wall costs. Wall type abutments consisting of a stub integral abutment on a MSE wall are typically more cost effective. Spill through abutments are more aesthetic than wall type abutments and allow for future widening



with the future construction of CIP retaining walls or soil nail walls. Spill through abutments with 2H:1V fill slopes are often preferred for wildlife undercrossings because the slope provides a more natural setting.

Use wall type abutments to minimize span lengths if permitted by project specific criteria. Wall type abutments eliminate fill slopes under the bridge, but require extensive retaining walls. The retaining walls run either along the approaches to the bridge or parallel to the abutment. Wall type abutments can be either stub abutments on piles through a MSE wall or full height abutments.

An abutment can be one of the following basic types:

• Integral • Semi-integral • Seat

See the SD drawings for additional information on abutment types.

10.10.1.1 Integral Abutments


Integral abutments directly connect the superstructure to the substructure. There is no expansion joint in the bridge deck, and the abutment moves with the superstructure. Integral abutments require flexible foundation elements to allow superstructure rotation and thermal movement. Typically, a single row of piles provides the required flexibility. A single row of drilled shafts is also viable, but evaluate the movement demands and the axial load transmitted into the superstructure from the less flexible shafts.

Do not use integral abutments on spread footings.

Integral abutments are standard for typical structures. Add finwalls to increase lateral seismic resistance where required. Wingwalls and finwalls are typically cantilevered from the abutment and move with the structure. Orient wingwalls parallel to the bridge to avoid resisting passive earth pressures due to thermal movement. Support flared wingwalls or wingwalls parallel to the abutment on independent foundations.

Consider a semi-integral abutment when significant post construction differential settlement in piles along an integral abutment could be possible.

Integral abutments on bridges with flares, skewed supports or horizontal curvature is permitted. Evaluate the soil load imbalance from flares and curvature. Skew also results in unbalanced soil pressures because the lines of action of the soil pressures on the two abutments do not coincide. Additionally, the horizontal axis of rotation of a skewed abutment is not parallel to the bending axis of the superstructure girders, which produces torsion in the superstructure.

Evaluate the thermal movement of an integral abutment. Integral abutments are not appropriate if thermal movement exceeds the limits defined in Section 18.1.




Advantages include excellent performance in seismic events. Integral abutments mobilize passive pressure to resist and dampen seismic forces and do not contain any weak links between the superstructure and substructure. Additionally, integral abutments move the expansion joint at the end of the bridge to a point where joint leakage does not promote deterioration of bearings or abutment seats. The simple details of integral abutments also reduce the initial construction costs and subsequent maintenance costs on typical structures.

Disadvantages include bridge length limitations associated with pile or shaft displacement limits and the required increase in abutment and bridge resistance to handle the large passive pressure loads.

10.10.1.2 Semi-Integral Abutments


Semi-integral abutments allow the bridge to move over the abutment. The superstructure rests on expansion bearings that minimize horizontal loads and movements transferred to the substructure. Use shear keys to provide lateral resistance. Use bolsters or longitudinal shear keys to limit longitudinal movement. Because the superstructure rests on bearings, the superstructure can be raised and bearings replaced or shimmed to accommodate differential deflection.

Use semi-integral abutments:

• Where superstructure movements exceed the pile movement capacity • Where differential settlement along the abutment is anticipated • Where spread footings are applicable • On post-tensioned bridges to reduce losses into foundation elements due to creep and

shrinkage • On ABC bridges to eliminate closure pours and simplify construction and move details Semi-integral abutments on bridges with flares, skewed supports or horizontal curvature is permitted. Evaluate the soil load imbalance from flares and curvature. Skew also results in unbalanced soil pressures because the lines of action of the soil pressures on the two abutments do not coincide. Although the horizontal axis of rotation of a skewed abutment is not parallel to the bending axis of the superstructure girders, semi-integral abutments (when compared to integral abutments) reduce the effect of torsion in the superstructure through the use of bearings similar to a seat abutment.


Advantages include good performance in seismic events. Semi-integral abutments mobilize passive pressure to resist and dampen seismic forces. Additionally, semi-integral abutments move the expansion joint at the end of the bridge to a point where joint leakage does not



promote deterioration of bearings or abutment seats. Semi-integral abutments do not yield or damage piles due to temperature movements and are compatible with spread footings.

Disadvantages include more complex detailing and the slide plane is a weak link in a seismic event.

10.10.1.3 Seat Abutments


Seat abutments consist of a footing, stem wall, seat and backwall with an expansion joint between the approach slab and the superstructure deck. The footing can be pile, shaft or soil supported. Bearings support the superstructure on the abutment seat. The backwall retains the backfill above the abutment seat so that the backfill is not in contact with the superstructure. The approach slab extends over the top of the backwall.

Seat abutments are only permitted when an expansion joint is required at the abutment. The Structures Design Manager must approve the use of seat abutments.


Advantages include eliminating substructure movements and eliminating bridge displacement limits and foundation type limits.

Disadvantages include increased maintenance, higher cost and poor seismic event performance when compared to integral and semi-integral abutments.

10.10.2 Bents

Bents typically consist of a bent cap supported on columns or a bent wall. Occasionally, a bridge can be designed with a column under every girder eliminating the need for a bent cap, but this is often not cost effective.

A bent can be one of the following basic types:

• Drop bents • Internal bents • Straddle bents • Capless bents • Wall bents • Extended pile bents Bents can also be fixed or expansion. Fixed connections provide a more redundant load path for extreme event loads because the loads are dispersed to all bents. Expansion bents are used to control temperature movement loads and control loads to short or stiff bents.



Refer to the SD drawings for additional information on bent proportioning.

10.10.2.1 Drop Bent


Drop bents are the most common. In a drop bent, the girders rest on top of the bent cap. The bent cap is supported by columns.


Advantages include simple details, easy design, flexibility in locating columns and low cost.

Disadvantages include reduced vertical clearance under the cap and poor aesthetics associated with short columns and large caps.

10.10.2.2 Internal Bent


In an internal bent, the girders frame directly into the bent cap. Only use internal bents when no other viable option exists due to difficult and costly construction. In addition, internal concrete caps do not allow inspection of the top tension flanges after the bridge is placed into service. Do not use internal bents made of steel due to a lack of redundancy.

Internal bents are most often used to eliminate support skew in applications where a bent is required in the median, the crossing is skewed and the vertical clearance requirements do not permit drop caps.


Advantages include increased vertical clearance under the bent cap and the reduced visual impact of the cap.

Disadvantages include high cost, difficult details, reduced inspectability and reduced redundancy.

10.10.2.3 Straddle Bent


In a straddle bent, the column spacing is spread out to straddle an element passing under the cap. Straddle bents can also be drop bents or internal bents.



Typically, use straddle bents with pin connections at the top of the columns. Pin connections reduce the torsional shear forces in the straddle bents. Most straddle bents are concrete and use post-tensioning to reduce the depth, control cracking and enhance torsional resistance.


Advantages include increased options for locating bents because the cap can straddle elements that otherwise require spanning.

Disadvantages include high costs, poor aesthetics, difficult details, increased susceptibility to damage during seismic events and poor aesthetics.

10.10.2.4 Capless Bent


A capless bent eliminates the cap by placing a column under every girder. Capless bents are viable where girder spacings are large and on high skews where the addition of columns is offset by the elimination of the cap.


Advantages include simplified bent detailing and increased construction speed.

Disadvantages include complex bearing details, complex framing plans, reduced redundancy and higher costs for typical bridges.

10.10.2.5 Wall Bent


A wall bent uses a continuous wall extending to almost the outside edge of bridge to transfer girder loads to foundation elements. Wall bents are typically 2′-6″ wide with tied reinforcement. Wall bents are very stiff about the strong axis and flexible about the weak axis. Only use wall bents when no other viable option is available. Wall bents are an option for bridges over railroads to satisfy AREMA crash wall requirements where limited ROW is available to place the bent.


Advantages include a narrow footprint and longitudinal flexibility.

Disadvantages include poor aesthetics, increased cost and attraction of seismic loads in the stiff direction.



10.10.2.6 Extended Pile Bents


In an extended pile bent, the pile cap or footing is eliminated and the piles extend up to the bent cap. Do not use extended pile bents without approval from the Structures Design Manager.


Advantages include reduced cost.

Disadvantages include constructability problems due to misaligned piles, poor aesthetics, painting for steel piles, lower lateral capacity, large number of supports that can trap debris when located in waterways and reduced substructure stiffness.

10.10.2.7 Columns


Columns are substructure components that support the cap. Use either single or multiple columns, depending upon the width and skew of the bridge.

Column design requires coordination with adjacent structures and project specific aesthetic requirements. Typically, all column shapes use a circular reinforcing pattern with continuous spirals or welded hoops. The minimum width or diameter is 3 ft, which is typically increased in 6-in. increments.

Consider a single column bent for narrow bridges over waterways. Water hitting a bent at an angle greatly increases scour, which does not adversely affect a single round column. In addition, a single column traps less debris. However, in this case, single columns are usually at least 6 ft in diameter.

Separate the columns from railroad crash walls for improved seismic performance.

10.10.3 Foundations

Foundation selection and design requires close coordination with the geotechnical engineer. Evaluate the impacts of seismic loading and potential for liquefaction in the preliminary design stage.

The following foundation types are available:

• Driven piles • Drilled shafts • Spread footings



10.10.3.1 Piles


A pile is a long, slender deep foundation element drilled or driven into the ground. Concrete filled, steel pipe piles and H-piles are most common, but prestressed concrete piles are permitted. Determine the selected type of pile based on the required bearing capacity, length, soil conditions and economic considerations.

Micropiles are a type of pile that can be installed in locations with limited overhead space.

See Section 17.2 for design details.


Advantages include low cost, simple and fast construction, high degree of quality control, flexibility or high lateral displacement capacity, and capacity to tolerate moderate scour.

Disadvantages include potential instability due to significant scour, low stiffness, high noise and vibration during driving and corrosion potential of steel piles. Piles require a pile cap to distribute loads, and the pile cap can interfere with utilities.

10.10.3.2 Drilled Shafts



A drilled shaft (also called a caisson or cast-in-drilled-hole pile) is a long, slender deep foundation element constructed by excavating a hole with auger equipment and placing concrete, with reinforcing, in the excavation. Casing and/or drilling slurry could be necessary to keep the excavation stable. See Section 17.3 for design details.


Advantages include significant resistance to scour, a smaller foundation footprint, less noise and vibration during installation, significant lateral capacity and significant vertical capacity in some conditions.

Disadvantages include difficult quality control and lower lateral displacement capacity compared to steel piles. High mobilization costs for the equipment also reduce the cost effectiveness.



10.10.3.3 Spread Footings



A spread footing is a shallow foundation consisting of a reinforced concrete slab bearing directly on soil or rock. Structural requirements and the characteristics of supporting components, such as soil or rock, determine the spread footing geometry. Spread footings distribute the loads transmitted by bents or abutments to suitable soil strata or rock at relatively shallow depths.

Use spread footings where loads permit and where there are no scour issues.

Settlement criteria must be consistent with the function and type of structure, anticipated service life and consequences of unanticipated movements on service performance. Do not allow longitudinal angular distortions between adjacent spread footings greater than 0.008 radians in simple spans and 0.004 radians in continuous spans. Selection of Spread Footings on Soils to Support Highway Bridge Structures (FHWA Report Number FHWA-RC/TD-10-001, February 2010) provides guidance on the proper estimation of deformations to encourage the cost effective use of spread footings to support highway bridges.

Ground modification techniques can improve the soil allowing the use of spread footings. Geotechnical engineers typically recommend ground modification techniques to address differential settlement concerns or to avoid potential liquefaction problems. The techniques include the construction of columns of gravel in the ground (i.e., stone columns) or compaction grouting through the pressure injection of a slow flowing water/sand/cement mix into a granular soil or removal of low capacity soils and replacement with higher capacity soils.

See Section 17.4 for design details of spread footings.


Advantages of spread footings include low cost high speed construction and low noise levels. Spread footings eliminate vibration during construction.

Disadvantages include increased risk of settlement and the potentially large foundation footprints. Spread footings are often not a viable solution in locations subject to scour.

10.11 RETAINING WALLS

Retaining walls provide lateral support for a variety of applications:

• Cuts in slopes for roadway alignments • Roadway widening where ROW is limited • Grade separations



• Stabilization of slopes where instabilities have occurred • Protection of environmentally sensitive areas • Bridge abutments • Excavation support Retaining walls are grouped according to the construction method, top down construction or bottom up construction. Figure 10.4 lists typical top down retaining walls, typical cost effective wall height ranges and other pertinent information. Figure 10.5 lists typical bottom up retaining walls, typical cost effective wall height ranges and other pertinent information. Coordinate with the geotechnical engineer to determine preliminary wall type options. Section 22.4 discusses each wall type in more detail.

10.12 CULVERTS

See Section 22.1 for more discussion.

10.12.1 Cast-in-Place or Precast Concrete Box Culverts


A concrete box culvert is a structure that consists of a top, bottom and sides and is usually buried below the roadway but the top can be driven on. The box can be precast or CIP. A box culvert can have single or multiple openings allowing the passage of water, livestock, vehicles or wildlife under a roadway. Box culverts are typically embedded within the surrounding soil.

Use box culverts for small stream crossings, pedestrian undercrossings and other locations where cost effective.

10.12.1.2 Advantages/Disadvantages

Advantages include low construction costs, low maintenance costs and simple construction when water is not present.

Disadvantages include span length limitations, confining feel for wildlife or pedestrians and difficulty to adapting to complex geometry.



Figure 10.4 — RETAINING WALLS CONSTRUCTED FROM THE TOP DOWN



Figure 10.5 — RETAINING WALLS CONSTRUCTED FROM THE BOTTOM UP



10.12.2 Cast-in-Place or Precast Three-Sided Culvert Structures


The precast three-sided concrete culvert is available in two types — the flat top and the arched top. Three-sided culverts must be placed on CIP concrete footings. The flat top culvert requires no fill and can be driven on; the arch top culvert requires a minimum of 2 ft of fill. The arch top culvert has some dependence on proper backfill for its stability; the flat top culvert does not depend on backfill for stability.

Precast three-sided culvert structures are a viable solution for stream crossings where scour is not a concern, for pedestrian crossings and for wildlife undercrossings.

10.12.2.2 Advantages/Disadvantages

Advantages are low maintenance costs, simple construction, increased span lengths when compared to box culverts and improved aesthetics for arch top culverts.

Disadvantages include limited span lengths, foundations subject to scour, difficulty in adapting to complex geometry and difficulty in handling, shipping and erecting long spans. Longer span arches also require considerable rise.



FEBRUARY 2015

LOADS AND LOAD FACTORS



Loads and Load Factors 11-i

TABLE OF CONTENTS

11.1 LRFD DESIGN PHILOSOPHY .................................................................................. 11-1

11.1.1 Limit States .................................................................................................. 11-1 11.1.2 Basic LRFD Equation .................................................................................. 11-1 11.1.3 Load Modifier ............................................................................................... 11-2 11.1.4 Load Factors and Combinations .................................................................. 11-2

11.1.4.1 Strength Load Combinations ..................................................... 11-2 11.1.4.2 Service Load Combinations ....................................................... 11-3 11.1.4.3 Extreme Event Load Combinations ........................................... 11-4 11.1.4.4 Fatigue and Fracture Load Combinations .................................. 11-4 11.1.4.5 Application of Maximum and Minimum Load Factors ................ 11-4 11.1.4.6 Load Factors for Uniform Temperatures .................................... 11-5

11.2 PERMANENT LOADS ............................................................................................... 11-6

11.2.1 Wearing Surface Dead Load ....................................................................... 11-6 11.2.2 Future Wearing Surface .............................................................................. 11-6

11.3 TRANSIENT LOADS ................................................................................................. 11-6

11.3.1 Vehicular Live Load ..................................................................................... 11-7

11.3.1.1 General ...................................................................................... 11-7 11.3.1.2 The Nature of the Notional Load ................................................ 11-7 11.3.1.3 Multiple Presence Factors ......................................................... 11-8 11.3.1.4 Noncritical Axle Loads ............................................................... 11-8 11.3.1.5 Two Design Trucks in a Single Lane for Negative Moment

and Interior Reactions ................................................................ 11-8 11.3.1.6 Sidewalk Loading ....................................................................... 11-9 11.3.1.7 Application of Horizontal Superstructure Forces to the

Substructure .............................................................................. 11-9

11.3.2 Friction Forces ............................................................................................. 11-9 11.3.3 Thermal Loads ............................................................................................. 11-10 11.3.4 Earthquake Effects ...................................................................................... 11-10 11.3.5 Live Load Surcharge ................................................................................... 11-11 11.3.6 Ice Loads ..................................................................................................... 11-11 11.3.7 Self Propelled Modular Transporter Loads .................................................. 11-11

11.4 ACCELERATED BRIDGE CONSTRUCTION LOADS .............................................. 11-11


11-ii Loads and Load Factors

LIST OF FIGURES

Figure 11.1 — SPECIAL LOADING FOR NEGATIVE MOMENT AND INTERIOR REACTIONS OF CONTINUOUS SPANS.................................................... 11-9 Figure 11.2 — TRANSFER OF HORIZONTAL SUPERSTRUCTURE FORCE TO SUBSTRUCTURE THROUGH MOMENT CONNECTION .................... 11-10 Figure 11.3 — DEAD LOAD DYNAMIC LOAD FACTOR .................................................... 11-12 Figure 11.4 — DESIGN LIVE LOAD FOR BRIDGE MOVES .............................................. 11-12

ACRONYMS

BL Blast Load BR Braking Force CE Centrifugal Force CR Creep CT Truck Collision CV Vessel Collision DC Component Dead Load DD Downdrag DW Dead Weight EH Horizontal Earth Pressure EL Locked In Forces EQ Earthquake Load ES Earth Surcharge EV Vertical Earth Pressure FR Friction FWS Future Wearing Surface IC Ice Load IM Dynamic Load Allowance IMDL Dead Load Dynamic Load Factor LL Live Load LS Live Load Surcharge PL Pedestrian Load PS Secondary Forces from Post-Tensioning SE Differential Settlement SH Shrinkage TG Temperature Gradient TU Uniform Temperatures WA Water Load WL Wind on Live Load WS Wind Load on Structure


Loads and Load Factors 11-1

Chapter 11 LOADS AND LOAD FACTORS

Sections 1 and 3 of the LRFD Specifications present design requirements for loads and load factors. This chapter discusses the loads and load factor provisions in Sections 1 and 3 of the LRFD Specifications that require amplification, clarification and/or an enhanced application. This chapter also addresses load factors not defined in the specifications and defines requirements where the LRFD Specifications offer options, but the Structures Division requires the use of a specific option.

11.1 LRFD DESIGN PHILOSOPHY

11.1.1 Limit States


The LRFD Specifications categorize the design criteria within groups termed limit states. The limit states are service, strength and extreme event. The LRFD Specifications assign a series of load combinations to the various limit states. The limit states are intended to capture load effects for design calculations to provide a buildable, serviceable structure capable of safely carrying loads for the life of the structure.

11.1.2 Basic LRFD Equation

Components and connections of a bridge are designed to satisfy the basic LRFD equation for all limit states:

φ≤γη niii RQ (LRFD Eq. 1.3.2.1-1)

Where:

γi = load factor Qi = load or force effect ɸ = resistance factor Rn = nominal resistance ηi = load modifier as defined in LRFD Equations 1.3.2.1-2 and 1.3.2.1-3

The left hand side of LRFD Equation 1.3.2.1-1 is the sum of the factored load (force) effects acting on a component; the right hand side is the factored nominal resistance of the component for the effects. Consider all applicable limit state load combinations for the equation. Similarly, the equation is applicable to all structural components and foundations.


11-2 Loads and Load Factors

For the strength limit states, the LRFD Specifications are a hybrid design code in that the force effect on the left hand side of the LRFD equation is based upon elastic structural response, while resistance on the right hand side of the equation is determined predominantly by applying inelastic response principles; i.e., force effects such as moment and shear are determined using elastic methods while the expressions for resistance are beyond the elastic range at the ultimate state. The LRFD Specifications have adopted the hybrid nature of strength design on the assumption that the inelastic component of structural resistance remains relatively small because of noncritical redistribution of force effects and, therefore, an elastic structural response model is appropriate. Providing adequate redundancy and ductility in the structure ensures the noncritical redistribution of forces.

11.1.3 Load Modifier

The load modifier ηi relates the factors ηD, ηR and ηI to ductility, redundancy and operational importance. The location of ηi on the load side of the LRFD equation could appear counterintuitive because ηi appears to relate more to resistance than to load. ηi is on the load side for a logistical reason. When modifying a maximum load factor, ηi is the product of the factors as indicated in LRFD Equation 1.3.2.1-2; when modifying a minimum load factor, ηi is the reciprocal of the product as indicated in LRFD Equation 1.3.2.1-3. The factors are somewhat arbitrary and reflect the desire to promote redundant and ductile bridges.

In general, use ηi values of 1.00 for all limit states, because bridges designed according to the SDDM demonstrate traditional levels of redundancy and ductility. Coordinate with the Structures Design Manager to determine appropriate values of ηi for special cases. Do not apply the load modifier that accounts for operational importance in LRFD Article 1.3.5 to seismic loads. Refer to Chapter 13 for seismic design requirements for critical and essential bridges. For structural systems with only two longitudinal main members (e.g., two girder/truss/arch bridges), the factor of redundancy, ηR, is 1.20 for the girder/truss/arch. Use a ηR of 1.15 for three girder systems. The Structures Division prefers bridges with four or more girders.

11.1.4 Load Factors and Combinations


LRFD Table 3.4.1-1 provides the load factors for load combinations associated with the various limit states.

11.1.4.1 Strength Load Combinations

The LRFD Specifications have calibrated the load factors for the strength load combinations based upon structural reliability theory, which represents the uncertainty of the loads. The following simplifies the significance of the strength load combinations, and provides guidance on which strength limit states are applicable to the bridge:



1. Strength I Load Combination. Represents random traffic and the heaviest truck to cross the bridge in the 75 year design life. During the live load event, a significant wind is not considered probable and, thus, not included.

2. Strength II Load Combination. Represents an owner specified permit load model. The live load event has less uncertainty than random traffic and, thus, uses a lower live load factor than used in Strength I load combination. The Structures Division currently does not specify a design permit load. Therefore, the Strength II load combination is generally not considered.

3. Strength III Load Combination. Represents the most severe design wind event. The LRFD Specifications assume that no significant live load crosses the bridge during the event.

4. Strength IV Load Combination. Represents an extra safeguard for bridge superstructures and typically governs where the unfactored dead load exceeds seven times the unfactored live load. For additional safety, and based on engineering judgment, the LRFD Specifications have arbitrarily increased the load factor for DC to 1.5 in this case. The rationale for the increase is that the only significant load factor when DC significantly exceeds LL is the 1.25 load factor for DC.

5. Strength V Load Combination. Represents the simultaneous occurrence of a normal live load event and a 55-mph wind event with load factors of 1.35 and 0.4, respectively.

For components not governed by wind force effects, the Strength III and Strength V load combinations do not govern. Generally, the Strength I load combination governs for a typical multigirder highway overpass.

11.1.4.2 Service Load Combinations

Unlike the strength load combinations, the service load combinations are material dependent. The following applies:

1. Service I Load Combination. Applied to control cracking in reinforced concrete components and compressive stresses in prestressed concrete components. Also, use the load combination to calculate deflections and settlements of superstructure and substructure components.

2. Service II Load Combination. Applied to control permanent deformations of compact steel sections and the slip in slip critical (i.e., friction type) bolted steel connections.

3. Service III Load Combination. Applied to control tensile stresses in prestressed concrete superstructure components under vehicular traffic loads.

4. Service IV Load Combination. Applied to control tensile stresses in prestressed concrete substructure components under wind loads.



11.1.4.3 Extreme Event Load Combinations

The extreme event limit states differ from the strength limit states because the event for which the bridge and bridge components are designed has a greater return period than the 75 year design life of the bridge (or a much lower frequency of occurrence than the loads of the strength limit state). The following applies:

1. Extreme Event I Load Combination. Applied to earthquakes. Because of the high seismicity in specific regions of Utah, the load combination often governs design of substructure elements. Use a live load factor (γEQ) of 0.25 in the Extreme Event I load combination. The live load for the Extreme Event 1 load combination is the lane load only. Do not include the moving truck load in the live load for the Extreme Event 1 load combination. Apply the lane load from beginning to end of bridge. The number of lanes is the roadway width divided by 12 ft and rounded down to the nearest integer with no reduction for multiple lanes loaded.

An earthquake in conjunction with maximum scour is unlikely. Underwater inspections are completed in five year intervals, and scour holes are normally identified and flagged for repair during the inspection. Evaluate the structure response using both no scour and one half of the total design scour for the design frequency event listed in the Hydraulic Report.

2. Extreme Event II Load Combination. Applied to various vessel or vehicle collisions or ice applied individually.

11.1.4.4 Fatigue and Fracture Load Combinations

Reference: LRFD Articles 3.6.1.4.1 and 3.6.1.4.2

The fatigue and fracture load combination, although strictly applicable to all types of superstructures, only affects the steel elements, components and connections of a limited number of steel superstructures.

The LRFD Specifications define the fatigue load for a particular bridge component by specifying both a magnitude and a frequency. Use the Fatigue I load combination when designing for infinite life. Use the Fatigue II load combination when designing for a finite number of cycles during a 75 year life or the life required by the project documents. A design based on a finite number of cycles requires approval from the Structures Design Manager.

Section 15.4 discusses fatigue and fracture for steel.

11.1.4.5 Application of Maximum and Minimum Load Factors

In LRFD Table 3.4.1-1, the variable γP represents load factors for all permanent loads, shown in the first column of load factors. The variable γP acknowledges that a maximum load factor does not always determine the critical design loading. Maximum and minimum load factors are



defined to reflect the uncertainty in the actual loads. The actual loads could be more or less than the nominal specified design values.

LRFD Table 3.4.1-2 provides the two extreme values for the various permanent load factors. The maximum and minimum values do not represent a usable range of values for a single check. Use either the maximum or minimum load factor; do not use a load factor in between the maximum and minimum. Structural engineers must evaluate and, where uncertain, calculate all applicable load combinations using both the maximum and the minimum values for each load case when calculating the governing load combinations. Further, in a single load combination evaluation, γP is uniformly applied to a specific permanent load.

Select the appropriate maximum or minimum load factors to produce the more critical load effect. For example, in continuous superstructures with relatively short end spans, transient live load in the end span increases the bearing load, while transient live load in the second span decreases the bearing load and could result in uplift. To check the maximum compression force in the bearing, place the live load in the end span and use the maximum DC load factor of 1.25 for all spans. To check possible uplift of the bearing, place the live load in the second span and use the minimum DC load factor of 0.90 for all spans.

Superstructure design uses the maximum load factors almost exclusively; the most common exception is uplift of a bearing as discussed above. With the use of maximum and minimum load factors, the LRFD Specifications have generalized load situations such as uplift where a permanent load (in this case a dead load) reduces the overall force effect (in this case a reaction). Select the maximum or minimum load factor for each load combination to produce extreme force effects.

Substructure design routinely uses the maximum and minimum load factors from LRFD Table 3.4.1-2. An illustrative yet simple example is a spread footing supporting a cantilever retaining wall. When checking bearing, the weight of the soil, EV, over the heel is factored up by the maximum load factor, 1.35, because greater EV increases the bearing pressure, qult, making the limit state more critical. When checking sliding, EV is factored by the minimum load factor, 1.00, because lesser EV decreases the resistance to sliding, Qτ, again making the limit state more critical. Foundation and substructure design requires the application of both the maximum and minimum load factors; see Chapters 17 and 18.

11.1.4.6 Load Factors for Uniform Temperatures

The load factors for TU for the strength limit states have two specified values ⎯ a load factor of 0.5 for the calculation of stress and a load factor of 1.2 for the calculation of deformation. Use the greater value of 1.2 to calculate unrestrained deformations (e.g., a simple span expanding freely with rising temperature). The lower value of 0.5 for the elastic calculation of stress reflects the inelastic response of the structure due to restrained deformations. For example, one half of the temperature rise is used to elastically calculate the stresses in a constrained structure. Using 1.2 times the temperature rise in an elastic calculation overestimates the stresses in the structure. The structure resists the temperature inelastically through redistribution of the elastic stresses.



11.2 PERMANENT LOADS

Permanent loads listed in LRFD Article 3.3.2 are either primary loads due to gravity or loads associated with material properties or construction processes. Permanent gravity based loads are always present in or on the bridge and do not change in magnitude during the life of the bridge. Permanent gravity based loads are listed in LRFD Article 3.5.1 and include:

• Gravitational dead loads — DC, DW and EV • Earth pressures — EH, ES and DD Loads associated with material properties or construction processes include:

• Construction process loads — EL, PS • Material properties based loads — CR, SH The following sections present modifications or clarifications to the magnitude and application of permanent loads in the LRFD Specifications.

11.2.1 Wearing Surface Dead Load

Use an asphalt overlay (or bituminous wearing surface in the LRFD Specifications) unit weight of 0.160 kcf, which is greater than the asphalt overlay (bituminous wearing surface) unit weight of 0.140 kcf in the LRFD Specifications. The increase is intended to better reflect asphalt overlay materials used in Utah.

11.2.2 Future Wearing Surface

FWS is a type of DW load. Design new structures or rehabilitations for a FWS load of 0.04 ksf, which is based on a 3-in. FWS at 0.160 kcf.

11.3 TRANSIENT LOADS

Transient loads are not always present in or on the bridge or change in magnitude during the life of the bridge. Specific transient loads include:

• Live loads (LRFD Article 3.6) — LL, PL, IM, LS, BR and CE • Water loads (LRFD Article 3.7) — WA • Wind loads (LRFD Article 3.8) — WS and WL • Extreme events (LRFD Articles 3.6.5, 3.9, 3.10 and 3.14) — BL, EQ, CT, CV and IC • Superimposed deformations (LRFD Article 3.12) — TU, TG and SE • Friction forces (LRFD Article 3.13) — FR



Creep, shrinkage, settlement and temperature are superimposed deformations which, if restrained, result in force effects. For example, restrained strains due to a uniform temperature increase induce compression forces. Note that the LRFD Specifications list CR and SH as permanent loads. Because the loads vary over the life of the structure, CR and SH could be considered transient loads.

The following sections present modifications or clarifications to transient loads in the LRFD Specifications.

11.3.1 Vehicular Live Load

11.3.1.1 General

Reference: LRFD Articles 3.6.1.1, 3.6.1.2 and 3.6.1.3

Vehicular live load, designated HL-93, consists of the design truck or design tandem applied simultaneously with the lane load. For short and medium span bridges, which predominate in Utah, vehicular live load is the most significant component of the total load. Short span bridges can be categorized as bridges governed by the design tandem vehicle; medium span bridges can be categorized as bridges governed by the design truck vehicle. Dead loads become a more significant component of the total load on long span bridges. Long span bridges are defined as bridges governed by the design lane load and the Strength IV load combination where the dead load is seven times or more greater than the live load.

11.3.1.2 The Nature of the Notional Load

The HL-93 live load model is a notional load in that the model is not a physical representation of any specific truck. However, the force effects (i.e., the moments and shears) due to the superposition of vehicular and lane load within a single design lane of the notional load represent the maximum force effects due to vehicles permitted on highways, including exclusion vehicles. Exclusion vehicles are a group of vehicles that are over the legal limit, but permitted on the highways in various states by the grandfathering provision.

The components of the HL-93 notional load are:

• A 72-kip design truck or a 50-kip design tandem; formerly, the design truck was designated as the HS-20 truck and the design tandem as the alternate loading in the AASHTO Standard Specifications

• A 0.64 k/ft uniformly distributed lane load, similar to the lane load of the AASHTO Standard Specifications, but without any of the previous associated concentrated loads

A dynamic load allowance (IM) of 0.33 is applicable only to the design trucks and the design tandems, but not to the uniformly distributed lane load.

The force effects of the HS-20 truck alone are less than that of the vehicles permitted on highways. Thus, a heavier vehicle is appropriate for design, as characterized by the HL-93 live load model. AASHTO developed the concept of superimposing the design vehicle force effects



and the design lane force effects to yield moments and shears representative of real trucks on the highways. The moments and shears produced by the HL-93 load model are essentially equivalent to the moments and shears of a 57-ton truck.

11.3.1.3 Multiple Presence Factors

The multiple presence factor of 1.0 for two loaded lanes, as given in LRFD Table 3.6.1.1.2-1, is the result of the LRFD Specifications’ calibration for the notional load, which has been normalized relative to the occurrence of two side by side, fully correlated (or identical) vehicles. Use the multiple presence factor of 1.2 for one loaded lane where a single design tandem or single design truck governs, such as in overhangs, decks, etc. Do not apply the multiple presence factors to fatigue loads.

11.3.1.4 Noncritical Axle Loads

Neglect axles that do not contribute to the extreme force effect under consideration.

11.3.1.5 Two Design Trucks in a Single Lane for Negative Moment and Interior

Reactions


The combination of the lane load and a single vehicle (either a design truck or a design tandem) does not always adequately represent the real life loading of two heavy vehicles closely following one another, interspersed with other lighter traffic. At interior supports, the LRFD Specifications specify a special load case to calculate the maximum force effects for negative moment and load on continuous superstructures and supports. Two design trucks (with a fixed rear axle spacing of 14 ft and a clear distance not less than 50 ft between them, superimposed with the lane load, all within a single design lane and multiplied by a factor of 0.90) captures a statistically valid representation of negative moment and interior reactions due to closely spaced heavy trucks.

The LRFD Specifications specify the sequence of highway loading for negative moment and reactions at interior bents due to the shape of the influence lines for such force effects. The LRFD Specifications do not extend the special load case to other structures or portions of structures because the case is not expected to govern for other influence line shapes. Figure 11.1 illustrates the loading.

In positioning the two trucks to calculate negative moment or the reaction over an internal support of a continuous girder, spans over 90 ft in length allow positioning of the truck in each span’s governing position (over the peak of the influence line). If the spans are greater than 90 ft in length, the trucks remain in the governing positions but, if they are smaller than 90 ft, the maximum force effect can only be attained by trial and error with either one or both trucks in off positions (i.e., nongoverning positions for each individual span away from the peak of the influence line).



Figure 11.1 — SPECIAL LOADING FOR NEGATIVE MOMENT AND INTERIOR REACTIONS OF CONTINUOUS SPANS

11.3.1.6 Sidewalk Loading

Reference: LRFD Article 3.6.1.6

Where sidewalks are present on the bridge, design for the dead load and pedestrian live load on the sidewalk; however, also design the full width of the bridge, including sidewalks, for the traffic live load assuming that traffic can mount the sidewalk. Do not apply pedestrian and traffic loads concurrently. Design sidewalks and multi-use paths where separated from traffic lanes by parapets for vehicular loads to account for potential future widening.

11.3.1.7 Application of Horizontal Superstructure Forces to the Substructure

The transfer of horizontal superstructure forces to the substructure depends on the type of superstructure to substructure connection. Assume that CE, BR and WL act horizontally at a distance of 6 ft above the roadway. Connections can be fixed, pinned or free for both moment and shear.

If the horizontal superstructure force is applied to the substructure through a pinned connection, then no moment transfer occurs. Apply the superstructure force to the substructure at the connection.

For a fixed or moment connection, apply the superstructure horizontal force with an additional moment to the substructure as shown in Figure 11.2. The additional moment is equal to the horizontal force times the distance between the force’s line of action and the point of application.

11.3.2 Friction Forces


LRFD Article 3.13 discusses the determination of forces due to friction between the sliding surfaces.



Figure 11.2 — TRANSFER OF HORIZONTAL SUPERSTRUCTURE FORCE TO SUBSTRUCTURE THROUGH MOMENT CONNECTION

Use the AASHTO Guide Specifications for Seismic Isolation Design to determine the effects of degradation on the friction coefficient of PTFE sliding surfaces.

The AASHTO Guide Specifications for Seismic Isolation Design increase the coefficient of friction of the sliding surfaces to account for unintended additional friction forces due to the possibility of future degradation. Consider the horizontal force due to friction conservatively. Include friction forces where design loads increase, but neglect friction forces where design loads decrease.

11.3.3 Thermal Loads


Use Procedure B of LRFD Article 3.12.2.2 to determine the appropriate design thermal movement range.

11.3.4 Earthquake Effects

Apply the provisions of the UDOT Geotechnical Manual of Instruction in conjunction with the AASHTO Guide Specifications for LRFD Seismic Bridge Design to determine earthquake demands in Utah. Chapter 13 and other chapters in the SDDM present required seismic design and detailing practices. Refer to Section 11.1.4.3 for the required live load factor for the Extreme Event I load case.



11.3.5 Live Load Surcharge


Consider the approach slab reactions on the abutment due to the HL-93 live load on the approach slabs. The approach slab is a simple span. Conservatively, apply the maximum approach slab live load reaction with the maximum live load reaction from the first or last span. Do not apply the live load surcharge specified in LRFD Article 3.11.6.4 to abutment backwalls when a 25-ft long approach slab is used and the approach slab is supported on one end by the abutment and on the other end by the sleeper slab.

Retaining walls that retain soil supporting a roadway must be able to resist any lateral pressure due to the live load surcharge. See Section 22.4 for retaining walls.

11.3.6 Ice Loads


Apply ice loads as specified in LRFD Article 3.9, identify special situations in the design of bridges where historical ice loads have caused problems, and evaluate whether or not to place a bent in the water. Consider ice loads in the conceptual design of the bridge.

11.3.7 Self Propelled Modular Transporter Loads

Use a load factor of 1.3 when applying SPMT loads to existing bridges or temporary structures.

11.4 ACCELERATED BRIDGE CONSTRUCTION LOADS

ABC loads are a type of transient load effect that occurs when a preconstructed structure is moved into place. The LRFD Specifications do not specify ABC loads. ABC loads include:

• Jacking loads • Friction loads • Lifting loads • Acceleration and deceleration loads Bridge design for ABC bridges must meet all LRFD Specifications requirements. Evaluate all possible additional loading conditions on structural components related to ABC projects. When moving a bridge by sliding or launching or on SPMTs, check the structural components of the bridge for Strength I and Service I load cases using the loads and load factors defined in the LRFD Specifications, except as modified in the figures below. Apply the IMDL provided in Figure 11.3 to DC and DW loads (if present at time of move) or to horizontal friction loads based on DC and DW for all bridges moved into place.



Type of Move IMDL

Lateral bridge slides 1.00 (vertical); 1.5 (horizontal loads from jacking)

Longitudinal launches 1.15

SPMT moves 1.15

Figure 11.3 — DEAD LOAD DYNAMIC LOAD FACTOR

Figure 11.4 defines the design LL during different types of bridge moves.

Type of Move LL Factor LL

Lateral bridge slides 1.00 0.01 ksf* plus any equipment load over 10 kips

Longitudinal launches 1.00 0.01 ksf* plus any equipment load over 10 kips

SPMT moves 1.00 Any equipment load over 10 kips

* Reduction in the 0.01 ksf load is permitted on structures exceeding 7500 sq ft and where access to the bridge is controlled. Coordinate with the Structures Design Manager to determine the reduced loading requirements.

Figure 11.4 — DESIGN LIVE LOAD FOR BRIDGE MOVES

FEBRUARY 2015

STRUCTURAL ANALYSISAND EVALUATION



Structural Analysis and Evaluation 12-i

TABLE OF CONTENTS

12.1 DISTRIBUTION OF SUPERIMPOSED DEAD LOAD ............................................... 12-1 12.2 DISTRIBUTION OF LIVE LOAD ............................................................................... 12-1

12.2.1 Definition of Live Load Distribution .............................................................. 12-1 12.2.2 Approximate Methods for Determining the Distribution Factor .................... 12-1

12.2.2.1 Approximate Distribution Factors for Girder and Slab Bridges .... 12-2 12.2.2.2 Precast, Prestressed Concrete Girder Example ......................... 12-3

12.3 MODELING CONCRETE BRIDGE PARAPETS ....................................................... 12-6 12.4 INFLUENCE LINE ANALYSIS .................................................................................. 12-6 12.5 REFINED ANALYSIS ................................................................................................ 12-7

12.5.1 2D Analysis (Straight, Zero Skew Bridges) ................................................. 12-8 12.5.2 2D Analysis (Straight Bridges with Long Spans or Wide Girder Spacing) ... 12-8 12.5.3 2D Analysis (Horizontally Curved Bridges) .................................................. 12-8 12.5.4 2D Analysis (Skewed Bridges) .................................................................... 12-9 12.5.5 3D Analysis (Highly Skewed or Horizontally Curved Bridges or Bridges

Moved into Place) ........................................................................................ 12-9 12.6 WIND LOAD DISTRIBUTION .................................................................................... 12-9 12.7 MODELING AND ANALYSIS VERIFICATION.......................................................... 12-10

LIST OF FIGURES

Figure 12.1 — DESIGN LANE AND TRUCK PLACEMENT PRODUCING THE WORST CASE FOR AN INDIVIDUAL INTERIOR GIRDER, G4 ................. 12-2

Figure 12.2 — UTAH BULB TEE GIRDER (UBT42) ........................................................... 12-5


12-ii Structural Analysis and Evaluation


Structural Analysis and Evaluation 12-1

Chapter 12 STRUCTURAL ANALYSIS AND EVALUATION

Section 4 of the LRFD Specifications presents the methods of structural analysis for the design and evaluation of bridge superstructures, but analysis procedures for substructures are not specifically discussed. This chapter discusses the structural analysis and evaluation provisions of Section 4 of the LRFD Specifications that require amplification, clarification and/or an enhanced application. This chapter also addresses specific Structures Division practices on structural analysis. Chapters 17 and 18 provide provisions on structural analysis procedures for foundations and substructures.

12.1 DISTRIBUTION OF SUPERIMPOSED DEAD LOAD


Distribute superimposed dead loads (e.g., curbs, barriers, sidewalks, parapets, future wearing surfaces) placed after the deck slab has cured equally to all girders as specified by the LRFD Specifications. For staged construction, phased construction, bridge widenings and bridges carrying utilities, analyze all critical loading conditions and apply a more accurate distribution of superimposed dead loads.

12.2 DISTRIBUTION OF LIVE LOAD


12.2.1 Definition of Live Load Distribution

Live load distribution refers to determining the maximum number of loaded lanes that an individual girder of the superstructure is expected to carry. The live load distribution factor defines the maximum number of loaded lanes per girder for analysis application.

12.2.2 Approximate Methods for Determining the Distribution Factor


Distribution factors allow for a simple, approximate analysis of bridge superstructures. Live load distribution factors uncouple the transverse and longitudinal distribution of force effects in the superstructure. The approximate method distributes live load force effects transversely by proportioning the design lanes to individual girders through the application of distribution factors. Therefore, the method allows the use of a one dimensional structural element (line girder) for girder analysis.


12-2 Structural Analysis and Evaluation

Use distribution factors and line girder analysis where allowed by the LRFD Specifications. Distribution factors reduce the necessity of modeling the entire bridge using 2D or 3D structural elements.

12.2.2.1 Approximate Distribution Factors for Girder and Slab Bridges


LRFD Article 4.6.2.2.2 presents several common bridge superstructure types with empirically derived equations for live load distribution factors for each type. Each distribution factor provides a number of design lanes to be applied to a girder to evaluate the girder for moment or shear. The factors account for interaction among loads from multiple lanes.

The distribution factors represent the placement of design lanes to generate the maximum effect in a specific girder. Figure 12.1 depicts the design lane location and the wheel line location within the design lane used to develop the empirically derived equations for lane load distribution factors. The location of design lanes is unrelated to the location of striped lanes on the bridge. Summing all of the distribution factors for all girders produces a number of design lanes greater than the bridge can physically carry. The apparent overdesign occurs because each girder must be designed for the maximum load to which the girder could individually be subjected. Collectively, the individual load conditions producing the distribution factors cannot exist simultaneously on the bridge, yet each girder must be designed for the worst case.

Figure 12.1 — DESIGN LANE AND TRUCK PLACEMENT PRODUCING THE WORST CASE FOR AN INDIVIDUAL INTERIOR GIRDER, G4

The properties used in calculating the live load distribution factors vary along the span; for example, steel plate girder moments of inertia vary at the flange or web plate transitions. However, do not recalculate the distribution factor at each change in property. Use weighted average properties or maximum properties (e.g., in the span for positive moment and at the bent for negative moment) to calculate a distribution factor for the positive moment region and the negative moment region.



12.2.2.1.1 Limitations

The tables of distribution factor equations given in LRFD Article 4.6.2.2 include a column entitled Range of Applicability. The LRFD Specifications specify that bridges with parameters falling outside the indicated ranges be designed using the refined analysis requirements of LRFD Article 4.6.3. In fact, the ranges of applicability do not necessarily represent limits of usefulness of the distribution factor equations, but the ranges represent the range over which bridges were examined to develop the coefficients and exponents of the empirical equations. Research studies demonstrate that the factors can be used beyond the range of parameters that were specifically studied. For more details on the development of the distribution factors, see Distribution of Wheel Loads on Highway Bridges by T. Zokaie, T. A. Osterkamp and R.A. Imbsen, Final Report, NCHRP Project No. 12-26.

The Structures Design Manager must approve using the distribution factor equations beyond the ranges of applicability specified in the tables in LRFD Article 4.6.2.2 without the use of a refined analysis. See Section 12.5 for a discussion on refined analyses.

12.2.2.1.2 Skewed Bridges

The bending moment in the longitudinal direction in a skewed bridge is generally smaller than the bending moment in a rectilinear bridge of the same span. However, do not use the skew correction factors for moment in LRFD Table 4.6.2.2.2e-1 to reduce the calculated live load moments in skewed bridges. Ignoring the reduction in moment distribution factors for bridges on skews is conservative and, for the majority of bridges, the correction only results in a slight reduction in moment distribution factor.

Torsional moments exist about the longitudinal axis in skewed bridges due to gravity loads (both dead and live load). The moments increase the reactions and shear forces at the obtuse corners compared to the acute corners. The potential also exists for reactions to become small or negative at acute corners.

Use the skew correction factors for shear in LRFD Table 4.6.2.2.3c-1 to adjust the live load shears and reactions in skewed bridges. Apply the skew correction factor as defined in LRFD Article C4.6.2.2.3c or perform a supplementary investigation of uplift for acute corners.

Bridges with skews over 30° require either a refined finite element or grid analysis to evaluate reactions, girder shear demands, girder torsion demands, cross frame demands and integral abutment or bent demands. Refer to Section 12.5.4.

12.2.2.2 Precast, Prestressed Concrete Girder Example

The following presents a girder distribution example for a precast, prestressed concrete girder bridge.



Example: Given: Precast bulb tee girder bridge Span length, L = 96′-0″ Girder spacing, S = 9′-0″ Depth of concrete slab, ts = 8 in.

ksi4fD

C=′

ksi8fGC

=′

Note: In the LRFD Specifications, .EEandff BGBCGC

=′=′

Section properties (see Figure 12.2): Area = A = 726 in2

Moment of inertia = I = 183,993 in4 Distance from CG to top = yt = 21.70 in. Longitudinal stiffness parameter:

+= 2

gGAeInK LRFD Equation 4.6.2.2.1-1

D

G

E

En = LRFD Equation 4.6.2.2.1-2

=G

E modulus of elasticity of girder material LRFD Equation C5.4.2.4-1

GC

f1820 ′=

ksi5148=

DC

f1820 ′=

DC

f1820 ′=

ksi3640=

41.1n =

( )

.in70.26

0.40.170.21

)slabofdepth(sthickneshaunchaverageassumedy

deckandirdergtheofCGsbetweendistancee

21

t

g

=

++=

++=

=

materialdeckofelasticityofmodulusED

=



Figure 12.2 — UTAH BULB TEE GIRDER (UBT42)



( ) ( ) ( )

4

2

G

in187,989

70.26726993,18341.1K

=

+=

Moment of interior girders with two or more design lanes loaded:

1.0

3

s

G2.06.0

interiorLt0.12

K

LS

5.9S075.0g

+= LRFD Table 4.6.2.2.2b-1

95.05.9

S =

09.0LS =

68.1Lt0.12

K3s

G =

( ) ( ) ( )( ) ( ) ( )

girderperlanes71.0

05.162.097.0075.0

68.109.095.0075.0g 1.02.06.0interior

=

+=

+=

12.3 MODELING CONCRETE BRIDGE PARAPETS


The LRFD Specifications allow the use of the structural contribution of any structurally continuous parapet to resist transient loads at the service and fatigue and fracture limit states as a part of the cross section of the exterior girder. Do not allow any structural contribution for new designs, except as defined in LRFD Article 4.6.2.6.1, for checking the composite girder resistance and for structural modeling. Coordinate with the Structures Design Manager if consideration of the parapet offers significant advantages on a preservation or rehabilitation project. Use a 3D refined analysis to estimate the contribution of the barrier.

12.4 INFLUENCE LINE ANALYSIS

Influence lines are a tool to position live loads for maximum force effect and for evaluating the magnitude of the force effect.

Constructing an influence line by analysis consists of dividing the structure into intervals, calculating the force effects due to a unit load at each resulting node and connecting the ordinates. For a determinate structure, connect the ordinates with a straight line; for an indeterminate structure, use a smooth curve that is consistent with the boundary conditions.



Constructing influence lines graphically recognizes that the influence line is essentially a deformation diagram drawn for a unit relative deformation introduced into the structure at the point of interest and consistent with the boundary conditions. For flexure, the relative displacement represents a unit rotation. For shear or reaction, the relative displacement represents a unit linear deflection.

For the influence analysis of a single girder line, construct an influence line either by analysis or through graphical means as discussed above. The influence analysis of an entire bridge results in an influence surface instead of a simple influence line. The influence surface represents not only the influence of loads positioned along a girder line, but also loads positioned transversely on the bridge.

Determining the magnitude of the force effects from an influence line consists of multiplying the magnitude of the load applied at a point by the ordinate under the influence line at that point.

12.5 REFINED ANALYSIS

Reference: LRFD Articles 4.6.2.2 and 4.6.3

Refined analyses include both 2D and 3D structural elements (sometimes called grid and finite element models, respectively). 2D structural element models are composed of elements lying in a single plane with the third dimension represented only through the stiffness properties of the elements. Typically, in a grid analysis, longitudinal elements represent the girders including any composite deck, and the transverse elements represent the deck. 3D structural element models are composed of elements in all three dimensions or of elements with three dimensions (e.g., brick elements). LRFD Article 4.6.3.3 provides general requirements for grid and finite element analyses in terms of the number of elements and aspect ratios.

Use a 2D refined analysis on the following bridge types:

• Bridges with nonstandard framing • Bridges with straight girders and girder spacing, if required by the Structures Design

Manager • Bridges with span lengths or girder spacing falling outside the range of applicability of

live load distribution factor equations • Bridges with curved girders (3D refined analysis also permitted) • Bridges with skews exceeding 30° Use a 3D refined analysis on the following bridge types:

• Bridges with skews exceeding 45° • Bridges with curved girders (2D refined analysis also permitted) • Bridges lifted and moved with temporary supports more than 10% of the span away from

the permanent supports



Modeling errors are more likely when using a refined analysis. Modeling errors can result in unconservative or unbuildable structures. Refer to Section 12.7 for a discussion on modeling and analysis verification. Only use a refined analysis for bridges not meeting the above requirements when approved by the Structures Design Manager. Where refined analysis is used, show back calculated, live load distribution factors for each girder in the contract documents for future use in rating or rehabilitating the bridge.

12.5.1 2D Analysis (Straight, Zero Skew Bridges)

Use a 2D analysis for a straight, zero skew bridge with complicated geometry or complex girder framing such as for an urban interchange bridge or bridges with girder spacing that varies by more than ±20% from the average girder spacing. Line girder analysis with point loads applied at girder framing locations does not adequately capture the true distribution of loads.

12.5.2 2D Analysis (Straight Bridges with Long Spans or Wide Girder Spacing)

Use a 2D analysis for a bridge with straight girders and girder spacing or span lengths falling outside the range of applicability of live load distribution factor equations.

12.5.3 2D Analysis (Horizontally Curved Bridges)

The design of all superstructures must account for the effect of curvature where the components are constructed on horizontal curves.

The magnitude of the effect of horizontal curvature is primarily a function of the curve radius, girder spacing, span length, diaphragm spacing and, to a lesser extent, web depth and flange proportions. The effect of curvature develops in two ways. First, the general tendency is for each girder to overturn, which has the effect of transferring both dead and live load from one girder to another transversely. The net result of the load transfer is that some girders carry more load and others carry less. The load transfer is carried through the diaphragms and the deck.

The second effect of curvature is that flange bending caused by torsion in curved components is almost totally resisted by horizontal shear in the flanges. The horizontal shear results in moments in the flanges. The stresses caused by the moments either add to or reduce the stresses from vertical bending. The torsion also causes warping of the girder webs.

Use refined analysis methods, either grid or finite element, for the analysis of horizontally curved bridges. LRFD Article 4.6.2.2.4 states that approximate analysis methods can be used for the analysis of curved bridges, but then highlights the deficiencies of the analyses, specifically the V-load method for I-girders and the M/R method for boxes. The use of V-load method for I-girders and the M/R method for boxes is not permitted for final design. The V-load and M/R methods are appropriate for preliminary design purposes or as an order of magnitude checking tool.



12.5.4 2D Analysis (Skewed Bridges)

Reference: LRFD Article 4.6.2.2.3c

Use a 2D refined analysis for skewed bridges with an angle of skew greater than 30°. Areas of concern include:

• Uplift of girders at acute corners • Cross frame loads near supports • Torsion on girders from cross frame effects • Torsion on girders due to restraint at integral abutments • Deck stresses near supports 12.5.5 3D Analysis (Highly Skewed or Horizontally Curved Bridges or Bridges

Moved into Place)

A 3D analysis, and the associated increase in design costs, is often not warranted for the initial design of a bridge. For the analysis of complex structures or for the investigation of a problematic bridge (e.g., a bridge experiencing unexplained fatigue cracking), a 3D analysis could be warranted.

A 3D analysis is required for highly skewed bridges and bridges moved into place. A 2D grid analysis does not adequately model the deck and girder interaction near supports and does not properly capture warping torsion effects. Bridges on high skews require a 3D analysis to adequately define member forces near the bearings. Bridges moved into place with SPMTs require a 3D analysis to define the twist or displacement limitations. Lateral slides using rigid slide supports are exempt. A 3D analysis is required for lateral slides using hydraulic support systems. Run bridge move models with and without the parapet to evaluate the variation in bridge response.

12.6 WIND LOAD DISTRIBUTION

Reference: LRFD Articles 3.4.1, 3.8.1 and 4.6.2.7.1

LRFD Article 4.6.2.7.1 discusses load paths for transferring wind loads transversely applied to the fascia girder to the bridge bearings. The commentary to the Article provides guidelines on how girders resist the wind loads. The provisions are directly applicable to steel girder bridges. In typical concrete girder bridges, the distribution of wind load becomes insignificant due to the greater out of plane stiffness in comparison with steel girders.



12.7 MODELING AND ANALYSIS VERIFICATION

The Structures Division uses many programs for structural analysis and design. The programs create mathematical models of the structure and permit modeling of various loading conditions. The models allow structural engineers to quickly analyze several alternative designs (i.e., simulation capabilities). The models also reduce the probability of mathematical errors, and save time by avoiding laborious hand calculations. However, the user of any model must:

• Use engineering judgment and experience to evaluate the accuracy of the model output and to properly interpret the output

• Learn the advantages and limitations of each model • Recheck the input to ensure accuracy • Check all output to ensure that answers are reasonable and logical and that there are no

obvious errors. The check must include, but not necessarily be limited to, the following: ○ Check equilibrium:

+ Does the sum of all dead load reactions equal the intended applied load? + Is the distribution of dead load reasonable? + Do the reactions have associated moments? + Are the reaction moments reasonable?

○ Review the boundary conditions: + Do the boundary conditions in the model reflect the physical boundary

conditions? + How does a change in fixity at the support change the results?

○ Verify the coordinate system, units and member properties: + Is member output in the local or global coordinate system? + Do you understand how the model defines the coordinate system? + Are units in the model consistent? + Are the member properties consistent with the member orientation in the

model? + Are the member property units consistent with the model units?

○ Evaluate the model response: + Check simple free body diagrams by cutting the structure at a section

where a free body can easily be taken. + Review the model deflections; are they reasonable?

The improper use of models has resulted in inadequately sized elements causing structural failures. The EOR is responsible for any modeling errors. Model results that yield significant increases or decreases in capacity compared to typical results are often caused by errors in the model.

FEBRUARY 2015

SEISMIC



Seismic 13-i

TABLE OF CONTENTS

13.1 INTRODUCTION ........................................................................................................ 13-1

13.1.1 Objective ...................................................................................................... 13-1 13.1.2 Bridges ........................................................................................................ 13-1 13.1.3 Miscellaneous Structures ............................................................................ 13-1

13.2 EARTHQUAKE RESISTING SYSTEMS AND ELEMENTS ...................................... 13-3

13.2.1 Earthquake Resisting Systems .................................................................... 13-3 13.2.2 Earthquake Resisting Elements .................................................................. 13-3

13.3 SEISMIC GROUND SHAKING HAZARD .................................................................. 13-3

13.3.1 Design Seismic Levels for Bridges, Walls, Slopes and Soils

near Bridges ................................................................................................ 13-4 13.3.2 Vertical Accelerations .................................................................................. 13-4 13.3.3 Site Effects .................................................................................................. 13-4

13.3.3.1 Site Class ................................................................................... 13-4 13.3.3.2 Deep Soils ................................................................................. 13-5 13.3.3.3 Depth of Controlling Motion ....................................................... 13-5

13.3.4 Acceleration Time Histories ......................................................................... 13-5

13.4 SEISMIC DESIGN CATEGORY SELECTION ........................................................... 13-5

13.4.1 Permanent Bridges ...................................................................................... 13-5 13.4.2 Temporary Bridges ...................................................................................... 13-5

13.5 LOAD AND RESISTANCE FACTORS ...................................................................... 13-6 13.6 ANALYSIS ................................................................................................................. 13-6

13.6.1 Balanced Stiffness and Balanced Frames ................................................... 13-6 13.6.2 Damping ...................................................................................................... 13-6 13.6.3 Combination of Orthogonal Seismic Displacement Demands ..................... 13-7 13.6.4 Analytical Procedures .................................................................................. 13-7 13.6.5 Single Span Bridges .................................................................................... 13-7 13.6.6 Structure Displacement Demand ................................................................. 13-7 13.6.7 Bearing Modeling ......................................................................................... 13-9

13.7 SPECIFIC ELEMENTS AND MATERIALS ............................................................... 13-10

13.7.1 In Ground Hinging ....................................................................................... 13-10 13.7.2 Restrainers .................................................................................................. 13-10 13.7.3 Shear Keys and Backwalls .......................................................................... 13-11 13.7.4 Structural Steel ............................................................................................ 13-11


13-ii Seismic

13.7.4.1 Pipe Piles and H-Piles ............................................................... 13-11 13.7.4.2 Girders or Structural Systems .................................................... 13-11

13.7.5 Reinforcing .................................................................................................. 13-11

13.7.5.1 Steel Reinforcing ....................................................................... 13-11 13.7.5.2 Alternative Nonmetallic Reinforcing ........................................... 13-11 13.7.5.3 Reinforcing Details ..................................................................... 13-13

13.7.6 Expansion Joints ......................................................................................... 13-13

LIST OF FIGURES

Figure 13.1 — BRIDGE CLASSIFICATIONS ........................................................................ 13-2 Figure 13.2 — LOAD CASES (ORTHOGONAL SEISMIC DISPLACEMENT DEMANDS) .... 13-8 Figure 13.3 — STRESS PROPERTIES OF TYPICAL REINFORCING STEEL BARS ......... 13-12 Figure 13.4 — STRESS PROPERTIES OF OTHER REINFORCING STEEL BARS ............ 13-12


Seismic 13-1

Chapter 13 SEISMIC

UDOT has adopted the AASHTO Guide Specifications for LRFD Seismic Bridge Design, which supersedes Section 3.10 of the LRFD Specifications. This chapter discusses seismic provisions of the AASHTO Guide Specifications for LRFD Seismic Bridge Design that require amplification or clarification.

13.1 INTRODUCTION

13.1.1 Objective

The primary goal for seismic design is to provide ductile structures that meet the performance objective defined in the project documents or as defined by the Structures Design Manager. All structures require detailing for ductility, even structures expected to respond elastically to seismic loading. Use the SDSR to document the seismic design approach. See Section 3.4 for additional information on the SDSR.

13.1.2 Bridges

Use the AASHTO Guide Specifications for LRFD Seismic Bridge Design and Chapter 13 to determine seismic design loadings and resistances. Do not use Section 3.10 of the LRFD Specifications for bridge design.

All interstate bridges are classified as essential but can be escalated to a critical classification by the Structures Design Manager. All noninterstate bridges are classified as normal unless otherwise specified by the Structures Design Manager. Coordinate with the Structures Design Manager to determine requirements for nonconventional bridges. Refer to the AASHTO Guide Specifications for LRFD Seismic Bridge Design for a definition of conventional and typical nonconventional structures.

Figure 13.1 defines performance objectives and ductility limits for the bridge classifications. Coordinate with the Structures Design Manager to determine if the default classification and performance objective is appropriate for the project.

13.1.3 Miscellaneous Structures

Miscellaneous structures, such as small culverts, vaults or other in ground structures, do not require seismic design. Culverts meeting the requirements defined in Section 22.1 require seismic design. Coordinate with the Structures Design Manager to determine structure specific requirements for culverts requiring seismic design. This chapter defines seismic levels for


13-2 Seismic

checking wall stability and strength. Design wall structural elements to meet seismic load requirements elastically using a φ factor of 1.0.

Bridge Classification

Performance Objective

Expected Element

Behaviors Ductility Limits and Permitted Damage

Critical Operational Linear elastic, essentially elastic

Permissible elements designed to resist all seismic loads within displacement constraints; expansion joints must continue to function after the seismic event; minor spalling is permitted. An essentially elastic plastic hinge meets the following requirements: • µD < 2, single column bent • µD < 2, multiple column bent • µD < 2, bent wall in weak direction • µD < 1, bent wall in strong direction Cantilever wingwalls can fully plastic hinge when failure of the wing does not compromise the roadway above or below the structure.

Essential Repairable Linear elastic, essentially elastic, inelastic

Permissible elements designed to resist all seismic loads within displacement constraints; joints can fail and plastic hinging can occur; structure could be permanently displaced; a repairable plastic hinge meets the following requirements: • µD < 3, single column bent • µD < 4, multiple column bent • µD < 3, bent wall in weak direction • µD < 1, bent wall in strong direction Permanent offsets in a horizontal direction up to 8 in. are permitted. The permanent offset is defined as the maximum displacement at the deck level in a bridge where support elements have undergone plastic hinging during the seismic design event. Cantilever wingwalls can fail.

Normal Life safety Linear elastic, essentially elastic, inelastic

The life safety performance objective is intended to prevent bridge collapse in rare earthquakes. Structures could require partial or complete replacement. Refer to the AASHTO Guide Specifications for LRFD Seismic Bridge Design for a thorough description of potential damage.

Figure 13.1 — BRIDGE CLASSIFICATIONS


Seismic 13-3

13.2 EARTHQUAKE RESISTING SYSTEMS AND ELEMENTS

The AASHTO Guide Specifications for LRFD Seismic Bridge Design define earthquake resisting systems and elements. The following sections define permitted systems, systems not permitted and modifications to loading.

13.2.1 Earthquake Resisting Systems

Article 3.3 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design defines three types of ERS — Type 1 (ductile substructure with essentially elastic superstructure), Type 2 (essentially elastic substructure with ductile superstructure) and Type 3 (elastic superstructure and elastic substructure with a fusing element between the two). Use Type 1 or Type 3 Earthquake Resisting Systems. The Structures Design Manager must approve the use of Type 2 systems.

13.2.2 Earthquake Resisting Elements

All EREs defined in Figure 3.3-1B of the AASHTO Guide Specifications for LRFD Seismic Bridge Design are permitted with the following exception:

• 11 — Do not reduce the passive pressure; use the passive soil pressures and factors defined in the SD drawings

The following EREs requiring owner approval and defined in Figure 3.3-2 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design are permitted:

• 1 — Passive pressure; use the passive soil pressures and factors defined in the SD drawings

• 2 — Sliding footings

• 4 — Rocking footings; permitted when combined with integral abutments; rocking not permitted if footing is located under a travel lane of the roadway crossed

• 7 — Yielding; this chapter defines pile yield limits

• 8 — In ground hinging; this chapter defines in ground hinging limits and use limitations

13.3 SEISMIC GROUND SHAKING HAZARD

Use the procedures defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design to determine the design response spectra or use Geotechnical Design Division approved project specific criteria when required.


13-4 Seismic

13.3.1 Design Seismic Levels for Bridges, Walls, Slopes and Soils near Bridges

Use an earthquake hazard corresponding to 7% probability of exceedence in 75 years for all bridges.

At bridges classified as normal, essential or critical, use an earthquake hazard corresponding to 3% probability of exceedence in 75 years to evaluate slope stability, lateral spread, liquefaction, wall stability and wall strength in an area within 50 ft of the centerline of bearing of any bridge support.

At retaining walls beyond 50 ft of bridges, use an earthquake hazard corresponding to 7% probability of exceedence in 75 years to evaluate wall stability and wall strength.

13.3.2 Vertical Accelerations

Use vertical accelerations for straddle bents and cantilever bents in near fault environments. Follow the AASHTO Guide Specifications for LRFD Seismic Bridge Design in determining appropriate design vertical accelerations in consultation with the Geotechnical Design Division to determine the appropriate vertical accelerations for the site. Document the vertical accelerations in the SDSR.

Use vertical accelerations for bridges classified as critical unless directed otherwise by the Structures Design Manager. Use vertical accelerations to verify superstructure capacity for essential or critical bridges governed by Strength IV loading.

13.3.3 Site Effects

The following sections provide insight into site effects. The project geotechnical engineer classifies the site and, in consultation with the Geotechnical Design Division, determines if a site specific hazard analysis is required. Coordinate with the Geotechnical Design Division when performing a site specific hazard analysis.

13.3.3.1 Site Class

Do not use average N -values or us -values (AASHTO Guide Specifications for LRFD Seismic Bridge Design, Equations 3.4.2.2-2 through 3.4.2.2-4) directly to determine the site class. Use site specific sv measurements. For smaller projects where site specific response analyses are not feasible, infer sv estimates from nearby, pre-existing sv data for the corresponding geological unit or obtain from empirical correlations with SPT, N and us values. Use the resulting shear wave velocities in the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Equation 3.4.2.2-1 to obtain the average shear wave velocity and determine the site class. If empirical relations are used, consider the uncertainty in the derived sv values. Coordinate with the Geotechnical Design Division if site specific sv measurements are not feasible.


Seismic 13-5

13.3.3.2 Deep Soils

The definitions of site class based on the average parameters of the upper 100 ft of the site profile are not typically applicable in deep soil basin conditions where the thickness of the soil overburden is much greater than 100 ft. Soil amplification/deamplification effects can significantly change the spectral values for deep soil sites. The effects are not always adequately represented by using soil amplification factors based on site class and given in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.

In the AASHTO Guide Specifications for LRFD Seismic Bridge Design, special investigations including site specific hazard analyses often are warranted for deep Site Class D profiles and all Site Class E and F soil profiles. The Geotechnical Design Division has developed additional guidance for performing hazard analyses for the soils. See UDOT Research Report UT-03.19, Bartlett, Steven F., “Ground Response Analyses and Design Spectra for UDOT Bridges on Soft Soil Sites,” January 2004, for more information.

13.3.3.3 Depth of Controlling Motion

Use site specific hazard analyses for cases involving deep foundations where the controlling motion is more appropriately specified at depth rather than near the ground surface.

13.3.4 Acceleration Time Histories

For sites with potential near field effects (distance to active fault is less than 6.25 miles), select candidate time histories for time domain analyses that include near field effects (e.g., directivity pulses). Do not use the generation of synthetic time histories unless the algorithm used is capable of generating near field effects.

13.4 SEISMIC DESIGN CATEGORY SELECTION

Determine the SDC according to the process defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design, except as modified in the following sections.

13.4.1 Permanent Bridges

All bridges in SDC B must meet the detailing requirements of SDC C.

13.4.2 Temporary Bridges

A temporary structure for the application of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Article 3.6, is a temporary widening or temporary bridge that is only used during a construction project to maintain traffic flow and when the construction duration is less than five years.


13-6 Seismic

Use the SDC determined from the AASHTO Guide Specifications for LRFD Seismic Bridge Design, except base the SDC on the 1 second period design spectral acceleration divided by 2. Develop the design spectra using the same accelerations and site factors as a permanent bridge, but divide the response spectra by 2 for use in the design model.

Coordinate with the Structures Design Manager to determine the required seismic design loads for emergency replacement structures required to maintain traffic while a permanent replacement project is funded and developed.

13.5 LOAD AND RESISTANCE FACTORS

Use load factors of 1.0 for all permanent loads. Use the load factors, ɣ, defined in the SD drawings for seismic passive pressures. All φ factors are 1.0 for seismic checks unless defined otherwise in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.

Use the live load factor defined in Section 11.1.4.3 of the SDDM. When considering live load effects, consider the live load envelope (due to gravity of the live loading) to only add and increase component responses (i.e., live load cannot cancel and/or reduce the seismic design demands due to other loads). Generally, live load considerations seek the worst case scenarios where the presence of live load further increases the demands only. Consider the live load as a static load (i.e., do not include braking, acceleration and centrifugal forces) and do not include any amplification or reduction in force due to the vehicle’s suspension. Refer to Section 11.1.4.3 for further clarification of live load application.

Do not include live load in a pushover analysis to determine displacement capacity.

13.6 ANALYSIS

13.6.1 Balanced Stiffness and Balanced Frames

Meet the requirements of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Article 4.1.2, Balanced Stiffness SDC D, and Article 4.1.3, Balanced Frame Geometry SDC D, for all bridges regardless of the SDC category.

Use of pinned columns to meet the stiffness ratios is permitted.

Coordinate with the Structures Design Manager and obtain approval when impractical to meet the balanced stiffness and frame requirements.

13.6.2 Damping

Use of damping ratios up to 10% is permitted on all integral abutment bridges and single span semi-integral abutment bridges on skews less than 20°.


Seismic 13-7

13.6.3 Combination of Orthogonal Seismic Displacement Demands

According to Article 4.3.1 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, determine displacement demands by using two independent load cases where each case consists of a single directional ground motion and the directional ground motions are perpendicular to each other.

Combine the forces as defined in Article 4.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. See Figure 13.2 for additional information.

13.6.4 Analytical Procedures

Article 5.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design defines analytical procedures. Only use Procedure 1, Equivalent Static Analysis (ESA) on single span bridges with integral or semi-integral abutments. Procedure 2, Elastic Dynamic Analysis (EDA) is permitted on all other structures. Use Procedure 3, Nonlinear Time History Method, when required by the Structures Design Manager.

13.6.5 Single Span Bridges

Meet the requirements of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. In addition to the requirements of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, verify the following:

• Pile displacements are less than the maximum permitted displacement. Base the displacement on the horizontal load defined for single span bridges in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.

• Abutment and abutment diaphragms meet the design requirements in the SD drawings.

13.6.6 Structure Displacement Demand

Determining accurate foundation flexibility data is difficult, and results can vary significantly depending on the method used. Do not include the effects of foundation flexibility when determining the displacement demand unless a fixed bent foundation model is also run.

For example:

1. Option 1. The bridge model included foundation flexibility, but a separate model with a fixed foundation was not completed. The total displacement is 2 in.; 0.5 in. of the total displacement is from lateral pile displacement. Use 2 in. when checking Equation 4.8-1 in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.


13-8 Seismic

Figure 13.2 — LOAD CASES (ORTHOGONAL SEISMIC DISPLACEMENT DEMANDS)


Seismic 13-9

2. Option 2. The bridge model included foundation flexibility and a separate model with a fixed bent foundation was also completed. The total displacement with foundation flexibility is 2 in.; 0.5 in. of the total displacement is from lateral pile displacement. The total displacement with no foundation flexibility is 1.6 in. Use the maximum of the actual column displacement when checking Equation 4.8-1 in the AASHTO Guide Specifications for LRFD Seismic Bridge Design (i.e., the maximum actual column displacement is the maximum of 1.5 in. and 1.6 in.).

Check the displacement demand against the displacement capacity defined in Article 4.8 of AASHTO Guide Specifications for LRFD Seismic Bridge Design.

If χ according to Equation 4.8.1-3 in the AASHTO Guide Specifications for LRFD Seismic Bridge Design is less than or equal to 0.2 and the SDC is C, check μD according to the requirements of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Article 4.9, and provide details according to SDC D.

Essential and critical bridges must also meet the ductility limits defined in Figure 13.1.

13.6.7 Bearing Modeling

Assume that rigid type bearings do not move in the restrained directions. Transmit the seismic forces from the superstructure through diaphragms or cross frames and the connections to the bearings and then to the substructure without reduction due to local inelastic action along that load path.

Seismic isolation bearings can reduce column and foundation demands. Fully or partially isolated structures are permitted. Partially isolated structures use isolation bearings to minimize force transfer to specific elements. Partial isolation is also used to balance stiffness in bents. Model isolation bearings and sliding bearings according to the requirements of the AASHTO Guide Specifications for Seismic Isolation Design.

Use the full seismic design load to design shear keys or other seismic load transfer elements. Do not reduce the shear key load through transfer of transverse or longitudinal seismic loads through elastomeric bearings when the system is restrained by shear keys or the bearing anchorage is designed to transfer the seismic loads. Do not use the bearing response before engaging shear keys to reduce the response of the structure.

Model the pads according to AASHTO Guide Specifications for Seismic Isolation Design when using elastomeric expansion bearings without shear keys, guides or restrainers. Only expansion bearings with a movement capacity equal to 1.2 times the EQ displacements are considered deformable for seismic modeling. Refer to Chapter 19 for minimum lateral loads transferred to substructure units.


13-10 Seismic

13.7 SPECIFIC ELEMENTS AND MATERIALS

13.7.1 In Ground Hinging

In ground hinging is not permitted on single column bents supported on a single shaft.

Do not use in ground hinging except as follows:

• Column hinging above the footing but below the finished grade with the footing less than the maximum of 3′-6″ or Lp below finished grade. Obtain approval from the Structures Design Manager for footings deeper than 3′-6″ or Lp below finished grade.

• Essentially elastic behavior is allowed for drilled shafts at the junction between the drilled shaft and the foundation element when approved by the Structures Design Manager. µD

< 2.0 is permitted where µD is calculated based on design properties. Do not use expected properties or overstrength properties to estimate µD because the system is not capacity protected.

• Inelastic behavior of drilled shafts due to liquefaction and lateral spread is permitted on bridges classified as normal when approved by the Structures Design Manager. Limit µD < 4. Limit compressive strain in the shaft at the hinge location to the smaller of 0.008 or the limit determined from Mander’s confined concrete model.

• Inelastic behavior of steel H-piles or pipe piles is permitted. Do not splice the H-pile or pipe pile near the anticipated plastic hinge zone.

13.7.2 Restrainers

Use longitudinal restrainers or equivalent extended support lengths according to Article C4.13.1-1 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design at expansion joints at bents. Restrainers are permitted at other locations as needed. Design restrainers at abutments for longitudinal movement into the approach fill, and design transverse movements to transfer the design passive pressure and pile loads as defined in the SD drawings. Design restrainers at abutments to transfer two times the pile capacity for movements away from the approach fill. Use minimum support lengths as defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Article 4.12, on new structures. Do not reduce the minimum support length based on the fact that the restrainer can potentially limit the displacement to much less than the minimum support length calculation. Refer to the SS sheets for sample restrainer details.

Use restrainers as a primary means of preventing unseating in the seismic retrofitting of existing bridges. However, even for existing bridges, other methods of preventing unseating are preferable, including:

• Providing bolsters at girder supports • Eliminating intermediate expansion joints • Replacing expansion bearings with fixed or isolation bearings


Seismic 13-11

13.7.3 Shear Keys and Backwalls

Do not design shear keys or backwalls to fuse. If shear keys or backwalls are used, the element must remain essentially elastic during the design event. Localized spalling and impact damage is permitted.

13.7.4 Structural Steel

13.7.4.1 Pipe Piles and H-Piles

All steel pipe piles must meet the requirements for ductile members as defined in Article 7.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. Determine displacement limits based on Mrc as defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Article 7.6.1, but not less than 3 in. The R-factor, referenced in the definition of Mu, for pipe piles is 1.0.

Use Mp to determine displacement limits of H-piles meeting the requirements for ductile members as defined in Article 7.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design but not less than 3 in. Use My to determine displacement limits of H-piles not meeting the requirements for ductile members as defined in Article 7.4 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design. The R-factor for H-piles is 1.0.

13.7.4.2 Girders or Structural Systems

Do not use the Type 2 (essentially elastic substructure with ductile superstructure) performance criteria. Provide shear connectors on the top of nonintegral bridge end diaphragms or cross frames and on diaphragms or cross frames at expansion joints.

13.7.5 Reinforcing

13.7.5.1 Steel Reinforcing

Use ASTM A706 or ASTM A955 reinforcing for use in plastic hinge zones.

Use the properties listed in Figures 13.3 and 13.4 when determining the strength and displacement capacities of the elements examined.

13.7.5.2 Alternative Nonmetallic Reinforcing

Coordinate with the Structures Design Manager to determine appropriate design properties. Plastic hinge zones require ductile reinforcing.


13-12 Seismic

Property Notation Bar Size ASTM A706

ASTM A615 Grade 60

Specified minimum yield stress (ksi) fy #3 – #18 60 60

Expected yield stress (ksi) fye #3 – #18 68 68

Expected tensile strength (ksi) fue #3 – #18 95 95

Expected yield strain εye #3 – #18 0.0023 0.0023

Onset of strain hardening εsh

#3 – #8 0.0150 0.0150

#9 0.0125 0.0125

#10 & #11 0.0115 0.0115

#14 0.0075 0.0075

#18 0.0050 0.0050

Reduced ultimate tensile strain; use to determine ultimate capacity ε

#4 – #10 0.0900 0.0600

#11 – #18 0.0600 0.0400

Ultimate tensile strain εsu #4 – #10 0.1200 0.0900

#11 – #18 0.0900 0.0600

Figure 13.3 — STRESS PROPERTIES OF TYPICAL REINFORCING

Property Notation Bar Size ASTM A615

Grade 40

ASTM A955

Grade 60

ASTM A955

Grade 75

Specified minimum yield stress (ksi) fy #3 – #18 40 60 75

Expected yield stress (ksi) fye #3 – #18 48 75 94

Expected tensile strength (ksi) fue #3 – #18 81 112 125

Expected yield strain εye #3 – #18 0.0017 0.0035 0.0035

Onset of strain hardening εsh

#3 – #8

0.0193 0.0035 0.0035

#9

#10 & #11

#14

#18

Reduced ultimate tensile strain; use to determine ultimate capacity ε

#4 – #10 0.0900 0.0900 0.0900

#11 – #18 0.0600 0.0900 0.0900

Ultimate tensile strain εsu #4 – #10 0.1200 0.2000 0.2000

#11 – #18 0.0900 0.2000 0.2000

Figure 13.4 — STRESS PROPERTIES OF OTHER REINFORCING


Seismic 13-13

13.7.5.3 Reinforcing Details

Meet the detailing requirements defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design, except as noted in the following.

For drilled shafts, develop column reinforcing into oversized drilled shafts according to the WSDOT method repeated below, or according to the method defined in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.

Do not hook column reinforcing to reduce the development length. The minimum embedment length is:

lns = ls + s

Where:

ls = the larger of 1.7 × lac or 1.7 × ld (for Class C lap splice) lac = development length from Article 8.8.4 of the AASHTO Guide Specifications for

LRFD Seismic Bridge Design for the column longitudinal reinforcing ld = tension development length of the AASHTO LRFD Specifications, Article 5.11.2.1

for the column longitudinal reinforcing s = distance between the shaft and column longitudinal reinforcing Do not use the development length reduction factor based on the (As required / As provided).

13.7.6 Expansion Joints

Design the expansion joints and expansion joint gaps on bridges with the operational performance objective to remain functional after the design seismic event. Expansion joints on bridges with the repairable or life safety performance objective do not require specific seismic load or displacement checks. Section 19.1 discusses expansion joints in more detail.

Use longitudinal restrainers or equivalent extended support lengths according to Article C4.13.1-1 of the AASHTO Guide Specifications for LRFD Seismic Bridge Design at all expansion joints at bents.


13-14 Seismic

FEBRUARY 2015

CONCRETE STRUCTURES



Concrete Structures 14-i

TABLE OF CONTENTS

14.1 INTRODUCTION .......................................................................................................... 14-1

14.1.1 Reinforced Concrete Structures ................................................................... 14-1 14.1.2 Prestressed Concrete Structures ................................................................. 14-1

14.1.2.1 Pretensioning ............................................................................. 14-1 14.1.2.2 Post-Tensioning ......................................................................... 14-2

14.2 STRUCTURAL CONCRETE DESIGN ......................................................................... 14-2

14.2.1 Member Design Models ............................................................................... 14-2 14.2.2 Sectional Design Model ............................................................................... 14-2

14.2.2.1 Flexural Resistance .................................................................... 14-2 14.2.2.2 Minimum Limits for Flexural Steel Reinforcing ........................... 14-3 14.2.2.3 Crack Control Reinforcing .......................................................... 14-3 14.2.2.4 Shear Resistance ....................................................................... 14-4

14.2.3 Strut and Tie Model ...................................................................................... 14-5 14.2.4 Fatigue ......................................................................................................... 14-6 14.2.5 Torsion ......................................................................................................... 14-6

14.3 MATERIALS ................................................................................................................ 14-7

14.3.1 Structural Concrete ...................................................................................... 14-7 14.3.2 Reinforcing ................................................................................................... 14-7 14.3.3 Welded Wire Reinforcing ............................................................................. 14-8 14.3.4 Prestressing Strands and Tendons .............................................................. 14-9 14.3.5 Prestressing Bars ......................................................................................... 14-9

14.4 REINFORCING DETAILS ............................................................................................ 14-9

14.4.1 Reinforcing ................................................................................................... 14-9

14.4.1.1 Reinforcing Sizes ....................................................................... 14-9 14.4.1.2 Concrete Cover .......................................................................... 14-9 14.4.1.3 Spacing of Reinforcing ............................................................... 14-10 14.4.1.4 Fabrication Lengths .................................................................... 14-10 14.4.1.5 Lateral Confinement Reinforcing ................................................ 14-11 14.4.1.6 Corrosion Protection ................................................................... 14-12 14.4.1.7 Development of Reinforcing ....................................................... 14-12 14.4.1.8 Splices ........................................................................................ 14-12 14.4.1.9 Bundled Reinforcing ................................................................... 14-14

14.4.2 Welded Wire Reinforcing ............................................................................. 14-14 14.4.3 Prestressing Strand and Tendon Details ..................................................... 14-15

14.4.3.1 Pretensioned Members .............................................................. 14-15 14.4.3.2 Post-Tensioned Members .......................................................... 14-16


14-ii Concrete Structures

14.5 REINFORCED CIP SLAB SUPERSTRUCTURES ...................................................... 14-17 14.5.1 General ........................................................................................................ 14-17

14.5.1.1 Haunches ................................................................................... 14-17

14.5.2 Allowance for Dead Load Deflection and Settlement ................................... 14-17 14.5.3 Construction Joints ...................................................................................... 14-17 14.5.4 Longitudinal Edge Beam Design .................................................................. 14-18 14.5.5 Shrinkage and Temperature Reinforcing ..................................................... 14-18 14.5.6 Distribution of Concrete Parapet Dead Load ............................................... 14-18 14.5.7 Distribution of Live Load .............................................................................. 14-18 14.5.8 Shear Resistance ......................................................................................... 14-19 14.5.9 Minimum Thickness of Slab ......................................................................... 14-19 14.5.10 Development of Flexural Reinforcing ........................................................... 14-19 14.5.11 Skews on Reinforced CIP Slab Superstructures .......................................... 14-19 14.5.12 Abutment Type ............................................................................................. 14-20

14.6 PRESTRESSED CONCRETE SUPERSTRUCTURES ............................................... 14-20

14.6.1 Basic Girder Design Criteria ........................................................................ 14-20

14.6.1.1 Concrete Stress Limits ............................................................... 14-20 14.6.1.2 Concrete Strength at Release .................................................... 14-20 14.6.1.3 Maximum Stirrup Spacing .......................................................... 14-20 14.6.1.4 Haunch Thickness for Design .................................................... 14-20

14.6.2 Jacking ......................................................................................................... 14-21 14.6.3 Precast, Prestressed Concrete Girders ....................................................... 14-21

14.6.3.1 Precast I-Girder Sections ........................................................... 14-21 14.6.3.2 General Design Theory .............................................................. 14-28 14.6.3.3 Loading Conditions ..................................................................... 14-28 14.6.3.4 Debonded Strands ..................................................................... 14-29 14.6.3.5 Intermediate Diaphragms ........................................................... 14-29 14.6.3.6 Sole Plates ................................................................................. 14-30

14.6.4 Camber and Deflections .............................................................................. 14-30 14.6.5 Sweep .......................................................................................................... 14-31 14.6.6 Bursting Reinforcing ..................................................................................... 14-31

14.7 SEGMENTAL CONCRETE POST-TENSIONED BOX GIRDERS .............................. 14-32


Concrete Structures 14-iii

LIST OF FIGURES

Figure 14.1 — END HOOK FOR CLOSED TIES ................................................................ 14-7 Figure 14.2 — COMPRESSIVE STRENGTH OF CONCRETE .......................................... 14-8 Figure 14.3 — REINFORCING SIZES ................................................................................ 14-10 Figure 14.4 — MINIMUM SPACING OF REINFORCING ................................................... 14-11 Figure 14.5 — SPIRAL TERMINATION IN PLASTIC HINGE ZONE .................................. 14-12 Figure 14.6 — STRAND SIZE, WEIGHT AND SPACING ................................................... 14-15 Figure 14.7 — SHRINKAGE AND TEMPERATURE REINFORCING FOR

REINFORCED CIP SLAB SUPERSTRUCTURES ...................................... 14-18 Figure 14.8 — BULB TEE GIRDERS ( cf ′ = 6.5 ksi) ............................................................ 14-22

Figure 14.9 — BULB TEE GIRDERS ( cf ′ = 8.5 ksi) ............................................................ 14-23

Figure 14.10 — DECK BULB TEE GIRDERS ( cf ′ = 6.5 ksi) ................................................. 14-24

Figure 14.11 — DECK BULB TEE GIRDERS ( cf ′ = 8.5 ksi) ................................................. 14-25

Figure 14.12 — PT BULB TEE GIRDERS ( cf ′ = 6.5 ksi) ....................................................... 14-26

Figure 14.13 — PT BULB TEE GIRDERS ( cf ′ = 8.5 ksi) ....................................................... 14-27 Figure 14.14 — MULTIPLERS FOR ESTIMATING LONG TERM DEFLECTION OF

PRESTRESSED CONCRETE GIRDERS ................................................... 14-30 Figure 14.15 — DEFINITION OF SWEEP ............................................................................ 14-31


14-iv Concrete Structures


Concrete Structures 14-1

Chapter 14 CONCRETE STRUCTURES

Section 5 of the LRFD Specifications presents design requirements for reinforced and prestressed concrete in all structural elements. ACI similarly uses unified provisions in ACI 318. This chapter discusses structural concrete provisions in Section 5 of the LRFD Specifications that require amplification or clarification.

14.1 INTRODUCTION

Concrete structures can be reinforced, prestressed or a combination of reinforcing and prestressing. Unreinforced structures are not permitted. The design requirements are presented as unified design requirements because the equations carry terms for both regular reinforcing and prestressing.

14.1.1 Reinforced Concrete Structures

Reinforced concrete structures add reinforcing to the concrete to increase the system strength. The reinforcing is primarily a tension element but also adds compression capacity to the concrete. The tension capacity of the concrete is very low compared to the reinforcing and, therefore, the concrete cracks before any significant tensile capacity is reached. The design requirements have serviceability checks to limit cracking.

14.1.2 Prestressed Concrete Structures

The term prestressing relates to a method of construction in which a strand is tensioned and anchored to the concrete. Upon release of the tensioning force, the concrete is largely in residual compression and the strand is in residual tension. Regular reinforcing is also placed in the structure to control cracking. There are two methods of applying the prestressing force, as discussed in the following sections.

14.1.2.1 Pretensioning

In the pretensioning method, tensioning of the strands is accomplished before the concrete is placed. When the concrete surrounding the strands attains a specified minimum strength, the strands are released, thereby transmitting the prestressing force to the concrete by bond and wedge action at the girder ends. The initial prestress is immediately reduced due to the elastic shortening of the concrete. Further losses occur over time due to shrinkage and creep of concrete and relaxation of prestressing strand.

The generic term prestress or prestressed is often used to mean pretensioning.


14-2 Concrete Structures

14.1.2.2 Post-Tensioning

In the post-tensioning method, tendon tensioning occurs after the concrete has attained a specified minimum strength. The tendons, usually comprised of several strands, are loaded into ducts cast into the concrete. Jacks stress the tendons to the specified prestressing level. Once stressed, proprietary systems anchor the tendons, and the jacks are released.

Several post-tensioning systems and anchorages are used in the United States. Manufacturers provide information on available systems. Post-tensioned concrete is also subject to losses from shrinkage and creep, although at a reduced magnitude because a significant portion of shrinkage usually occurs before stressing, and the rate of creep decreases with the age at which the prestress is applied.

After anchoring the tendons, the ducts are pressure filled with grout, which protects the tendons against corrosion and provides composite action by bonding the strand and the concrete.

14.2 STRUCTURAL CONCRETE DESIGN

14.2.1 Member Design Models

Reference: LRFD Articles 5.6.3, 5.8.1, 5.8.3 and 5.13.2

The LRFD Specifications allow two approaches to the design of concrete members ⎯ the traditional sectional design model and the strut and tie model. The basic application is:

1. Sectional Design Model. Use the sectional design model for the design of typical bridge girders, slabs and other regions of components where the assumptions of traditional beam theory are valid. The model assumes that the response at a particular section depends only on the calculated values of the sectional force effects such as moment, shear, axial load and torsion. The model does not consider the specific details of how the force effects were introduced into the member. LRFD Article 5.8.3 and Section 14.2.2 of this chapter discuss the sectional design model. Subarticles 1 and 2 describe the applicable geometry required to use the technique to design for shear.

2. Strut and Tie Model. Use the strut and tie model in regions near discontinuities (e.g., abrupt changes in cross section, openings, coped (dapped) ends, deep beams, corbels). See LRFD Articles 5.6.3 and 5.13.2 and Section 14.2.3 of this chapter.

14.2.2 Sectional Design Model


14.2.2.1 Flexural Resistance




Determine the flexural resistance of a girder section using the rectangular stress distribution of LRFD Article 5.7.2.2. The rectangular stress block is the basis for the general equation for structural concrete flexural resistance of LRFD Article 5.7.3.2.1. The approximation of the rectangular stress block adequately models the resistance of practical cross sections.

Applying the rectangular stress block to unusual cross sections can result in variations of resistance beyond the range of variability assumed by the LRFD Specifications. Use a strain compatibility approach as outlined in LRFD Article 5.7.3.2.5 in lieu of using the rectangular stress block when evaluating unusual cross sections. The AASHTO Guide Specifications for LRFD Seismic Bridge Design present acceptable material models; however, any accepted material model is permitted. Use the nominal properties, not the expected properties, when determining resistance using a strain compatibility approach for strength and service load checks.

14.2.2.2 Minimum Limits for Flexural Steel Reinforcing

Use cr f24.0f ′= to determine Mcr in LRFD Article 5.7.3.3.2.

Refer to the SD drawings for additional minimum reinforcing requirements for abutments, wingwalls and finwalls.

14.2.2.3 Crack Control Reinforcing


Distribute reinforcing in all reinforced concrete members in tension to control cracking in accordance with LRFD Article 5.7.3.4. Use γe = 1.00 (Class 1 exposure condition) when designing for crack control. Do not use γe = 0.75 (Class 2 exposure condition).

Several smaller reinforcing bars at moderate spacing are more effective in controlling cracking than fewer larger reinforcing bars.

Use additional skin reinforcing, Ask, when the member depth exceeds 3 ft. Use the following equations to determine Ask :

( )30d012.0Ask −≥ (Ask is in in2/ft, dℓ in inches)

But:

( ) ( )2/)12/d(4

AAA pss

sk

+≤ (Ask is in in2/ft ; dℓ in inches (see note below))

Note that LRFD Equation 5.7.3.4-2 is often misinterpreted, resulting in significant over reinforcing. The above equations have been intentionally rewritten to clarify the LRFD equations.

Skin reinforcing runs parallel to the main reinforcing.



14.2.2.4 Shear Resistance


14.2.2.4.1 Sectional Design Model

Use a sectional design model to calculate shear capacity for flexural regions, regions away from reactions, applied loads and changes in cross section where conventional methods for the strength of materials are applicable and strains are linear. The LRFD Specifications present three alternative sectional shear design models for estimating the shear resistance of concrete members. Use Method 1 “General Procedure: Modified Compression Field Theory.” Method 2 “Simplified Procedure for Nonprestressed Sections” and Method 3 “Simplified Procedure for Prestressed and Nonprestressed Sections” are listed with explanations of why the methods are not recommended:

• Method 1, General Procedure: Modified Compression Field Theory. (Reference: LRFD Article 5.8.3.4.2 and Appendix B5). Use the MCFT procedure to determine the shear resistance of concrete members.

• Method 2, Simplified Procedure for Nonprestressed Sections. (Reference: LRFD Article 5.8.3.4.1). Do not use the procedure. The shear resistance determined by the procedure is essentially identical to the resistance traditionally used for evaluating shear resistance. The procedure can be unconservative for large members not containing transverse reinforcing.

• Method 3, Simplified Procedure for Prestressed and Nonprestressed Sections. (Reference: LRFD Article 5.8.3.4.3). Do not use the procedure. The simplified procedure is similar to the traditional approach in the AASHTO Standard Specifications. The procedure can be more conservative than the MCFT approach.

14.2.2.4.2 Additional Longitudinal Reinforcing For Shear


Shear induces tension in the longitudinal reinforcing. The free body diagram in LRFD Figure C5.8.3.5-1 illustrates the tension in the longitudinal reinforcing in reaction to the diagonal compression field. The tension becomes larger as the angle of inclination of diagonal compressive stresses, θ, becomes smaller and as Vc becomes larger.

Check the longitudinal reinforcing provisions of LRFD Article 5.8.3.5. Use both the developed prestressed and nonprestressed reinforcing present at the cross section to satisfy the provisions of LRFD Article 5.8.3.5.

The LRFD Specifications check the longitudinal reinforcing at the face of the bearing. Assume that the face of bearing is the face of the concrete diaphragm at integral or semi-integral abutments or at bents made continuous with solid concrete diaphragms. At this section, which usually lies within the transfer length of the strands, the effective prestressing force in the



strands is not fully developed. Calculate the term fps as a portion of the effective prestress force using a linear variation starting from zero at the end of the girder to full effective prestress at the transfer length. An increase in strand stress, fps, up to 60 ksi is permitted when the strands are well anchored at the end of the member, by embedment in a diaphragm or by use of a mechanical device.

For the ends of prestressed girders embedded into diaphragms (making them continuous for live load with deck reinforcing meeting the requirements of LRFD Articles 5.14.1.4.7 and 5.14.1.4.8), additional longitudinal reinforcing in the embedded girder to comply with LRFD Article 5.8.3.5 is not required.

14.2.3 Strut and Tie Model


Use the strut and tie model to determine internal force effects in disturbed regions, regions near reactions or applied loads, near changes in cross section, or where the sectional design model is not appropriate (e.g., for deep beams). Laboratory tests on loaded members indicate the presence of stress fields. The strut and tie method models the stress fields with a vector sum of tensile or compressive resultant forces. The load paths taken by the resultants form a truss pattern that is optimum for the given loading, and the resultants are in reasonable equilibrium, especially at ultimate loads.

The objective is to replicate the optimum pattern (truss) in developing the strut and tie model. The closer the estimated pattern is to the optimum pattern (truss), the more efficient the use of materials. Material use is less efficient in poorly conceived strut and tie models, yet the structure is safe. The compressive concrete paths are the struts, and the reinforcing groups are the ties. The model does not involve shear or moment because the modeled stresses are only axial loads.

The application of the strut and tie model encompasses several simple steps:

• Develop a truss model and define the truss geometry that carries the applied loads to the reactions.

• Proportion the struts according to the provisions of LRFD Article 5.6.3.3 and the ties according to LRFD Article 5.6.3.4.

• Proportion the nodal regions connecting the truss members according to the provisions of LRFD Article 5.6.3.5, wherein concrete compression stresses are limited.

• Provide crack control reinforcing according to LRFD Article 5.6.3.6 to control the significant cracking necessary to facilitate the strut and tie model.

The following lists strut and tie model reference materials:

• NCHRP 20-7, Task 217 Verification and Implementation of Strut and Tie Model in LRFD Bridge Design Specifications, Final Report, November 2007

• D. Mitchell, M. Collins, S. Bhidé and B. Rabbat, AASHTO “LRFD Strut and Tie Model Design Examples,” EB231, PCA



• Article 8.12 of the PCI Precast Prestressed Concrete Bridge Design Manual • J. Schlaich, et al, “Towards a Consistent Design of Structural Concrete,” PCI Journal,

Vol. 32, No. 3, 1987 Strut and tie models also provide a fast check to ensure the adequacy of a design using a sectional design model, especially for the appropriate anchorage of the reinforcing.

Cracking is associated with partial debonding and, thus, the bonding capacity of cracked concrete is not completely reliable. The LRFD Specifications generally require that reinforcing not be anchored in cracked zones of concrete. Improperly anchored reinforcing is commonly overlooked in strut and tie models. Consider the use of mechanical anchors in cracked regions.

14.2.4 Fatigue

Reference: LRFD Articles 3.4.1, 3.6.1.4 and 5.5.3

The fatigue limit state is not normally a critical issue for concrete structures.

In the determination of fmin for application in LRFD Equations 5.5.3.2-1 and 5.5.3.2-2, when the Fatigue I limit state produces only tensile stresses (e.g., simple spans), the minimum live load stress is zero.

14.2.5 Torsion


Where torsion effects are present, design the member according to LRFD Articles 5.8.2 and 5.8.3.6. Situations that can require a torsion design include:

• Cantilever brackets connected perpendicular to a concrete girder, especially if a diaphragm is not located opposite the bracket

• Abutment caps, if unsymmetrically loaded • Bent caps • Bent cap extensions supporting sign structures • Horizontally curved members • Pile supported footings Consider transverse torsion reinforcing fully continuous when consisting of a single reinforcing bar or consisting of piecewise continuous reinforcing anchored by 135° standard hooks around longitudinal reinforcing. See Figure 14.1 for an example of piecewise continuous reinforcing.



Figure 14.1 — END HOOK FOR CLOSED TIES

14.3 MATERIALS

14.3.1 Structural Concrete


Figure 14.2 presents design criteria for the minimum compressive strength of concrete in structural elements.

Use of lightweight concrete decks is permitted. Account for the reduced elastic modulus and reduced modulus of rupture. When using lightweight concrete, add 10 pcf for reinforcing to the nominal equilibrium concrete weight for dead load calculations. Do not use lightweight concrete in approach slabs.

Use of Type III cement (high early strength) is permitted with the approval of the Structures Design Manager. Plans or project specifications must indicate usage locations and requirements.

14.3.2 Reinforcing


Use AASHTO M31 (ASTM A615), Grade 60 or ASTM A955, Grade 60 unless specified otherwise. Where plastic hinging is possible, use reinforcing that conforms to the requirements of ASTM A706, Grade 60. The modulus of elasticity, Es, is equal to 29,000 ksi.

The ASTM A706 specification has strict material and property requirements. The properties include a maximum yield strength and a minimum ratio between the tensile and yield strengths. In addition, ASTM A706 reinforcing requires a controlled chemical composition making the reinforcing weldable with improved ductility. Weld the reinforcing according to AWS D1.4.



Structural Element Class Minimum 28 Day

Compressive Strength ( cf ′ )

Bridge decks/approach slabs AA(AE) 4.0 ksi

CIP concrete AA(AE) 4.0 ksi

Prestressed concrete 3A(AE) Varies 5.0 to 8.5 ksi;

up to 10.0 ksi permitted*

Precast concrete AA(AE) 4.0 ksi

Piles A(AE) 3.0 ksi

Drilled shafts A(AE) or AA(AE)

3.0 ksi or 4.0 ksi

Slope protection A(AE) 3.0 ksi

Noise walls AA(AE) 5.0 ksi

All other structural concrete components AA(AE) 4.0 ksi

* Do not use higher strengths without the approval of the Structures Design Manager and a review by the Materials Division. Avoid strengths over 8.5 ksi because the strengths often require an additional day in the casting bed and can increase girder cost by up to 50%.

Figure 14.2 — COMPRESSIVE STRENGTH OF CONCRETE

ASTM A955, Grade 75, is permitted for deck reinforcing. When all longitudinal reinforcing is ASTM A955, Grade 75, a design yield strength of 75 ksi is permitted. ASTM A706, Grade 80, is permitted for deck reinforcing. When all longitudinal reinforcing is ASTM A706, Grade 80, a design yield strength of 80 ksi is permitted.

Use the fy of the lowest strength bar if the project specifies different grades of longitudinal reinforcing.

Use other reinforcing with a yield strength greater than 60 ksi only with the approval of the Structures Design Manager. The design must satisfy all limit states, including serviceability (i.e., cracking). High strength reinforcing can have reduced ductility and toughness and requires the use of a reduced yield strength in design to provide an equivalent safety margin to fracture when compared to 60-ksi reinforcing. Coordinate with the Structures Design Manager to determine the reduced design yield strength of other high strength reinforcing.

14.3.3 Welded Wire Reinforcing

Welded wire reinforcing, also referred to as welded wire fabric, is an alternative to conventional concrete reinforcing for approved applications listed in Section 14.3.2. WWR is prefabricated in a series of parallel wires welded with cross wires to form square or rectangular grids. All wires in one direction are the same diameter, but the wires in the transverse direction are commonly different. Each wire intersection is resistance welded.



The WWR wires can be either smooth or deformed. WWR is generally used for MSE soil reinforcing and precast reinforced concrete box culverts and conforms to AASHTO M55 (ASTM A185) “Steel Welded Wire Reinforcement, Plain, for Concrete.”

14.3.4 Prestressing Strands and Tendons


Use low relaxation, 7-wire strand conforming to AASHTO M 203 “Steel Strand, Uncoated Seven-Wire for Prestressed Concrete” with a minimum tensile strength of fpu = 270 ksi; the yield strength is specified as 0.9fpu or 243 ksi. Note that prestressing steels do not exhibit a defined yield plateau. The minimum modulus of elasticity, Ep, is equal to 28,500 ksi.

14.3.5 Prestressing Bars


Use plain or deformed bars conforming to AASHTO M 275 “Uncoated High-Strength Steel Bars for Prestressed Concrete” with a minimum tensile strength of fpu = 150 ksi, with a yield strength of 127.5 ksi for plain bars and 120 ksi for deformed bars. The minimum modulus of elasticity, Ep, is equal to 30,000 ksi.

14.4 REINFORCING DETAILS

14.4.1 Reinforcing

14.4.1.1 Reinforcing Sizes

Reinforcing is referred to in structure plans and specifications by number. Reinforcing varies in size from #4 to #14. Figure 14.3 presents the sizes and properties of typical reinforcing.

14.4.1.2 Concrete Cover


Use the concrete cover requirements in the LRFD Specifications with the following exceptions:

• 2.5-in. cover on the top of CIP decks (2 in. for stainless reinforcing) • 2.75-in. cover on the top of precast decks (2.25 in. for stainless reinforcing) (cover

includes ¼ in. for profile grinding) • 1.00-in. cover on the bottom of precast or CIP decks



Reinforcing Size Designation

Nominal Dimensions

Weight (lb/ft)

Diameter (in.)

Area (in2)

#4 0.668 0.500 0.20

#5 1.043 0.625 0.31

#6 1.502 0.750 0.44

#7 2.044 0.875 0.60

#8 2.670 1.000 0.79

#9 3.400 1.128 1.00

#10 4.303 1.270 1.27

#11 5.313 1.410 1.56

#14 7.650 1.693 2.25

Figure 14.3 — REINFORCING SIZES

14.4.1.3 Spacing of Reinforcing


Figure 14.4 presents the minimum center to center spacing between reinforcing based on reinforcing size and spliced vs unspliced. The accompanying sketch illustrates how to measure the spacing for spliced reinforcing.

Check fit and clearance of reinforcing by calculations and large scale drawings. Skews tend to complicate problems with reinforcing fit. Consider tolerances normally allowed for cutting, bending and locating reinforcing. Refer to ACI 315 for allowed tolerances. Some of the common areas of interference are:

• Anchor bolts in abutment caps • Between slab reinforcing and reinforcing in monolithic abutments or bents • Vertical column reinforcing projecting through main reinforcing in bent caps and footings • Near expansion devices • Embedded plates for prestressed concrete girders • Anchor plates for steel girders • Between prestressing strands and reinforcing stirrups, ties, etc. • Drilled shaft reinforcing and main reinforcing in abutments and footings 14.4.1.4 Fabrication Lengths

On DBB projects, use a maximum length of 40 ft for #4 reinforcing and 60 ft for #5 and larger. On DB projects, coordinate with the fabricator; if the fabricator can supply longer reinforcing, then designing for longer reinforcing is an option.



Reinforcing Size

Minimum Spacing

Unspliced Reinforcing (in.)

Spliced Reinforcing (assumes a side by side lap)

(in.)

#4 3 3½

#5 3½ 4

#6 3½ 4

#7 4 5

#8 4 5

#9 4 5

#10 4 5½

#11 4 5½

#14 4½ 6

Figure 14.4 — MINIMUM SPACING OF REINFORCING

14.4.1.5 Lateral Confinement Reinforcing

14.4.1.5.1 Columns


Detail all lateral column reinforcing according to the AASHTO Guide Specifications for LRFD Seismic Bridge Design. Lateral reinforcing for compression members consists of either spiral reinforcing, welded hoops or a combination of lateral ties and cross ties. Only use ties when not practical to provide spiral or hoop reinforcing. Where longitudinal reinforcing is required outside the spiral or hoop reinforcing, provide lateral support with reinforcing spaced and hooked as required for cross ties. Extend the hooked reinforcing into the core of the spiral or hoop a full development length. For closed ties, always fold the hooked end at 135° into the core. See Figure 14.1. Extend tails into the core with the specified length (LRFD Article 5.10.2.2) or 6 in., whichever is greater.

See Figure 14.5 for the termination of a spiral in the plastic hinge zone.

14.4.1.5.2 Drilled Shafts

Determine the length of the plastic hinge confinement reinforcing by appropriate analysis but not less than the requirements of LRFD Article 5.13.4.6.3d.



Figure 14.5 — SPIRAL TERMINATION IN PLASTIC HINGE ZONE Maximize the size of longitudinal and transverse reinforcing to increase the openings between all reinforcing to allow concrete to pass through the cage during placement. Do not exceed the maximum spacing requirements of LRFD Article 5.13.4.6.3d.

Meet the requirements of the AASHTO Guide Specifications for LRFD Seismic Bridge Design, Sections 8.8.10 and 8.8.11.

14.4.1.6 Corrosion Protection

Use coated reinforcing in all locations except for reinforcing in piles.

Stainless steel reinforcing is considered a coated reinforcing bar with respect to corrosion protection.

14.4.1.7 Development of Reinforcing

Develop reinforcing on both sides of a point of maximum stress at any section of a reinforced concrete member, which is specified as the development length, ld.

Fully develop the reinforcing in ties and reinforced struts of members designed with the strut and tie model where the reinforcing departs from the nodal regions. See the example in LRFD Figure C5.6.3.2-1(A), Flow of Forces. The left support shows the length over which the tension tie must be developed.

Consider partially developed reinforcing capable of resisting stresses equal to the yield strength multiplied by the embedded length divided by the development length. On hooked reinforcing, the embedded length is measured from the point in question to the base of the hook.

14.4.1.8 Splices




14.4.1.8.1 Types/Usage

The following presents practices on the types of splices and usage:

1. Lap Splices. Use conventional lap splices when practical and when permitted in the LRFD Specifications.

Where feasible, stagger lap splices for main member reinforcing such that no more than 50% are lapped in any one location. Use a minimum stagger of Ld between adjacent centerlines of splices for individual and bundled reinforcing. When the above two conditions are met, Class A and Class B splice lengths are permitted as defined in the LRFD Specifications.

If transverse reinforcing in a bridge deck is lapped near a longitudinal construction joint, place the entire lap splice on the side of the construction joint that is poured last.

2. Mechanical Splices. (Reference: LRFD Articles 5.11.5.2.2, 5.11.5.3.2 and 5.11.5.5.2). The LRFD Specifications define a mechanical reinforcing connector as a device that can develop 125% of the specified yield strength of the reinforcing. AASHTO places specific limits on the use of mechanical splices in the plastic hinge zones of members that are contrary to current UDOT practice.

UDOT has selected a family of seismic connectors for the prefabricated connections that can develop forces that are larger than specified in the LRFD Specifications. The basis for use of mechanical splices is ACI 318 Building Code Requirements for Structural Concrete and Commentary. Chapter 21 of ACI 318 covers earthquake resistant structures.

ACI 318 includes two types of mechanical connectors. An ACI Type 1 connector has the same strength requirements as the LRFD Specifications and has similar restrictions for use in plastic hinge locations. An ACI Type 2 connector is required to develop 100% of the specified tensile strength of the reinforcing, which equates to 150% of the specified yield strength for AASHTO M31 reinforcing. ACI allows the unrestricted use of Type 2 connectors in members subjected to plastic hinging. In addition, research indicates that the connections can emulate a CIP concrete connection, even when subjected to the extreme ductility rotations that occur during earthquakes.

Use of grouted splice couplers or other splice systems meeting the ACI Type 2 requirements in plastic hinge zones is permitted when connecting precast elements.

3. Field Welded Splices. Do not use field welded splices.

4. Full Mechanical/Welded Splices. (Reference: LRFD Articles 5.11.5.2.3 and 5.11.5.3.2). Shop fabricated, butt welded hoops can be used as confinement reinforcing for columns. The AASHTO/AWS D1.5 Bridge Welding Code does not address the welding of reinforcing. Reference the AWS D1.4 Structural Welding Code ⎯ Reinforcing Steel. Use only ASTM A709 reinforcing. Coat welded bars after fabrication.



14.4.1.8.2 Deck Reinforcing Over Bents

Do not provide lap splices in the longitudinal deck reinforcing within 15 ft of the centerline of the bent.

14.4.1.8.3 Plastic Hinge Regions

1. CIP Construction. In columns and drilled shafts, do not splice longitudinal reinforcing or lap splice spiral reinforcing within the plastic hinge regions. See Figure 14.5 for the termination of spirals in the plastic hinge zone.

2. Precast Elements. Mechanical splices meeting ACI Type 2 requirements are permitted at the top and bottom of columns.

14.4.1.9 Bundled Reinforcing

Reference: LRFD Articles 5.11.2.3 and 5.11.5.2.1

Use either two bundled or three bundled reinforcing bars. Do not use four bundled reinforcing bars.

Determine the lap splices of bundled reinforcing upon development lengths as specified in the LRFD Specifications. Do not lap splice entire bundles at the same location. Individual reinforcing within a bundle can be lap spliced, but do not overlap the splices. Check the fit and clearance of reinforcing by calculations and large scale drawings.

14.4.2 Welded Wire Reinforcing

Concrete cover, development length and lap length for WWR must meet the requirements of the LRFD Specifications. See the Wire Reinforcement Institute Manual of Standard Practice, Structural Welded Wire Reinforcement for standard practices for detailing WWR. The Manual also provides commonly available wire sizes and spacing and available mat lengths.

WWR is a substitute for AASHTO M31 (ASTM A615) reinforcing for miscellaneous structural applications, including:

• Precast box culverts • Precast MSE wall panels • Precast soundwall panels • Drainage structures and appurtenances • Channel linings • Slope protection • Catch basins The Structures Design Manager must approve all other applications. Do not use WWR as a substitute for ASTM A706 reinforcing.



Use WWR as a direct replacement, with equivalent cross sectional area, for the specified reinforcing. Do not reduce the area based on WWR having a higher yield strength.

Replace coated reinforcing with coated WWR. Coat WWR according to ASTM A884, Class A AASHTO M111.

14.4.3 Prestressing Strand and Tendon Details

14.4.3.1 Pretensioned Members

14.4.3.1.1 Strand Size and Minimum Spacing

Common sizes of prestressing strand used in bridge construction are 0.375-in., 0.5-in. and 0.6-in. diameter. The preferred diameter of the prestressing strands in pretensioned girders is 0.6 in. The standard half depth deck panel uses 0.375-in. strands. Figure 14.6 lists unit weights and areas for typical diameters.

Diameter (in.)

Unit Weight (lb/ft)

Area (in2)

Minimum Spacing (in.)

0.375 0.29 0.085 1.75

0.500 0.52 0.153 1.75

0.600 0.74 0.217 2.00

Figure 14.6 — STRAND SIZE, WEIGHT AND SPACING

14.4.3.1.2 Strand Profile

Use a straight and/or harped strand profile. Harped strands (i.e., deviated, draped, deflected) offer greater shear capacity. Use debonded or harped strands to control stresses and camber. Debonded strands are only permitted in girders. For debonded strands, see Section 14.6.3.4.

14.4.3.1.3 Harped Strands

The maximum number of harped strands is 18 for all girder sizes. The maximum hold down force is 40 kips and/or a maximum of 12 strands per hold down point. Specify the hold down location on the plans, but allow for minor adjustments because fabricators use hold down points at a nominal spacing. Exactly matching plan hold down points could be impossible. Fabricators stagger the hold down points if using more than 12 harped strands or if the hold down force exceeds 40 kips. Do not use bundled harped strands. The maximum slope of harped strands is 6°.



14.4.3.1.4 Strand Patterns

Refer to the WS sheets for the strand template and required reinforcing. Fully detail the strand pattern showing the total number of strands, layout and spacing, which strands are harped and/or debonded, and the layout of all mild reinforcing. Frequently, precast, pretensioned girders of the same size and similar length in the same bridge or within bridges on the same project specify a slightly different number of strands. In this case, consider using the same number and pattern of strands to facilitate fabrication.

14.4.3.1.5 Strand Splicing

Do not splice prestressing strand.

14.4.3.2 Post-Tensioned Members

14.4.3.2.1 Strand Size

The preferred diameter of the prestressing strand used for post-tensioning is 0.6 in. See Figure 14.6 for typical strand sizes and weights.

14.4.3.2.2 Prestressing Bar Size

Prestressing bar is available in nominal diameters from 1 in. to 2.5 in. Refer to the manufacturer’s literature for bar sizes and weights.

14.4.3.2.3 Tendons

A post-tensioning tendon is made up of strands through a single duct. Tendons are proprietary systems that consist of an anchorage, duct, grout injection pipes and prestressing strand or prestressing reinforcing.

Tendon systems for post-tensioned decks use round or flat ducts containing up to four 0.6-in. strands. Tendon systems for larger post-tensioned elements use round ducts that contain up to 55 0.6-in. strands. Tendons using more than 31 0.6-in. strands are rare.

Post-tensioning tendons using prestressing bar consist of a single reinforcing bar in a duct.

The outside diameter of the ducts vary from approximately 2 in. to 6 in. depending upon the number of strands or bar size and system supplier. Use HDPE or galvanized ducts.

Consult specific post-tensioning system literature for the actual size of ducts, anchor systems and other system specific requirements.



14.4.3.2.4 Duct Spacing

Reference: LRFD Article 5.4.6.2 Apply the limits of LRFD Article 5.4.6.2 to all CIP post-tensioned structures. Use ducts up to 4 in. in diameter in UBTXX-PT girders.

14.5 REINFORCED CIP SLAB SUPERSTRUCTURES

14.5.1 General


This section presents information for the design of reinforced CIP slab superstructures that amplify or clarify the provisions in the LRFD Specifications.

14.5.1.1 Haunches

Haunches at interior supports of continuous bridges allow an increase in span by reducing the maximum positive moment and increasing the negative moment resistance. Parabolic haunches are preferable if aesthetics are important; otherwise, use straight haunches for easier construction. The length of haunch on either side of an interior support is approximately 15% of the interior span. The depth of haunch at an interior support is approximately 20% deeper than the structure depth at the location of maximum positive moment.

14.5.2 Allowance for Dead Load Deflection and Settlement


When designing or reviewing falsework for reinforced CIP slab superstructures, make an allowance for:

• Deflection of the falsework • Any settlement of the falsework • The dead load deflection of the span In addition, for the long term dead load deflection of the span, make an allowance such that, on removal of the falsework, the top of the structure conforms to the theoretical finished grade plus the allowance for long term deflection.

14.5.3 Construction Joints

Longitudinal construction joints in reinforced CIP slab superstructures are undesirable. However, bridge width, phased construction, the method of placing concrete, rate of delivery of



concrete, and the type of finishing machine used by the contractor dictate whether or not a reinforced CIP slab superstructure must be poured in more than one pour.

If the slab is constructed in phases, show the entire lap splice for all transverse reinforcing on the side of the construction joint that is poured last.

14.5.4 Longitudinal Edge Beam Design

Reference: LRFD Articles 5.14.4.1, 9.7.1.4 and 4.6.2.1.4

Provide edge beams along the edges of reinforced CIP slab superstructures. The edge beams consist of more heavily reinforced sections of the slab. Select the width of the edge beams as the width of the equivalent strip as specified in LRFD Article 4.6.2.1.4b. Structurally continuous barriers can only be considered effective for the service limit states, not the strength or extreme event limit states.

14.5.5 Shrinkage and Temperature Reinforcing

Reference: LRFD Articles 5.6.2 and 5.10.8

Evaluating the redistribution of force effects as a result of shrinkage, temperature change, creep and movements of supports is not necessary when designing reinforced CIP slab superstructures. Figure 14.7 provides the shrinkage and temperature reinforcing as a function of slab thickness.

Slab Thickness (in.)

Reinforcing (Top and Bottom) (in.)

< 18 #4 @ 12

18 to 28 #5 @ 12

> 28 Design according to LRFD Article 5.10.8

Figure 14.7 — SHRINKAGE AND TEMPERATURE REINFORCING FOR REINFORCED CIP SLAB SUPERSTRUCTURES

14.5.6 Distribution of Concrete Parapet Dead Load

Distribute the dead load of the parapet uniformly over the entire bridge width. Account for unbalanced loading effects in phased construction projects.

14.5.7 Distribution of Live Load


The following applies to the distribution of live load to reinforced CIP slab superstructures:



• For continuous slabs with variable span lengths, develop one equivalent strip width (E) using the shortest span length for the value of L1. Use the strip width for moments throughout the entire length of the bridge.

• Specify different strip widths for the reinforced CIP slab superstructure and the edge beams in LRFD Articles 4.6.2.3 and 4.6.2.1.4, respectively.

• Do not use LRFD Equation 4.6.2.3-3 for the reduction of moments in skewed slab type bridges. The equation does not significantly change the reinforcing requirements.

14.5.8 Shear Resistance

Single span and continuous span reinforced CIP slab superstructures, designed for moment in conformance with LRFD Article 4.6.2.3, are satisfactory for shear.

14.5.9 Minimum Thickness of Slab


When using the equations in LRFD Table 2.5.2.6.3-1, assume that:

• S is the length of the longest span • The calculated thickness includes the ½-in. sacrificial wearing surface • The thickness used can be greater than the value obtained from the LRFD table 14.5.10 Development of Flexural Reinforcing


LRFD Article 5.11.1.2 presents specifications for the portion of the longitudinal positive moment reinforcing that must be extended beyond the centerline of support. Similarly, LRFD Article 5.11.1.2.3 addresses the location of the anchorage (embedment length) for the longitudinal negative moment reinforcing.

14.5.11 Skews on Reinforced CIP Slab Superstructures


For skew angles up to 20°, place the transverse reinforcing parallel to the skew. For skews in excess of 20°, place the transverse reinforcing perpendicular to the centerline of the bridge and place additional top and bottom mat reinforcing parallel to the abutment over the end 5 ft of the bridge.



( )cif ′

14.5.12 Abutment Type

Use an integral or semi-integral abutment.

14.6 PRESTRESSED CONCRETE SUPERSTRUCTURES

14.6.1 Basic Girder Design Criteria

This discussion applies to both pretensioned and post-tensioned concrete members.

14.6.1.1 Concrete Stress Limits

Reference: LRFD Article 5.9.4 Tensile stress limits for fully prestressed concrete members must conform to the requirements for “Other Than Segmentally Constructed Bridges” in LRFD Article 5.9.4. Use the moderate corrosion conditions for checking tension stress in the bottom flange of prestressed girders unless indicated otherwise in the contract documents or directed otherwise by the Structure Design Manager.

Use gross section properties in conjunction with the Service III load combination or transformed section properties with the Service I load combination. The requirement applies within the transfer length of the prestressing strands in addition to beyond the transfer length.

14.6.1.2 Concrete Strength at Release


Calculate the minimum concrete compressive strength at release for each prestressed girder, and list the required release strength on the girder sheet. Concrete compressive strengths at release of between 5 ksi and 7.5 ksi are typical. For specified concrete release strengths less than 7 ksi, round up the value shown on the plans to the next increment of 0.25 ksi. For release strengths greater than 7 ksi, round up to the next increment of 0.1 ksi.

14.6.1.3 Maximum Stirrup Spacing

Do not exceed a stirrup spacing of 18 in.

14.6.1.4 Haunch Thickness for Design

For girders supporting a CIP concrete slab, use the maximum thickness for dead load calculations and use a 0-in. haunch for girder resistance calculations.



Refer to the SD drawings for a description of the required haunch calculation and Section 14.6.4 for the multipliers used to estimate the girder camber at the time of deck placement.

14.6.2 Jacking


Integral abutments and integral bents do not require jacking provisions.

Provide details allowing replacement or realignment of bearings for bridges on elastomeric pads at expansion bearings. For bearings similar to sample details in the WS sheets, assume that the bridge is lifted ¼ in. and girders are lifted in pairs. Provide girders or diaphragms capable of supporting the bridge during bearing replacement.

Provide a jacking plan for high load multirotational (HLMR), isolation or other specialty bearings. The jacking plan must include the necessary bearing stiffeners, jack locations and clearances, factored reactions and jacking height. Design all cross frames and diaphragms for the jacking loads. Provide only conceptual falsework requirements when required.

14.6.3 Precast, Prestressed Concrete Girders

14.6.3.1 Precast I-Girder Sections

Select the type of girders based upon geometric restraints, economy and appearance. See the SD drawings for standard precast concrete I-girder sections.

The following graphs (Figures 14.8 through 14.13) present typical girder spacings and span lengths for UDOT bulb tee girders.



Approximate Maximum Spans

Figure 14.8 — BULB TEE GIRDERS ( cf ′ = 6.5 ksi)




Figure 14.9 — BULB TEE GIRDERS ( cf ′ = 8.5 ksi)




Figure 14.10 — DECK BULB TEE GIRDERS ( cf ′ = 6.5 ksi)




Figure 14.11 — DECK BULB TEE GIRDERS ( cf ′ = 8.5 ksi)




Figure 14.12 — PT BULB TEE GIRDERS ( cf ′ = 6.5 ksi)




Figure 14.13 — PT BULB TEE GIRDERS ( cf ′ = 8.5 ksi)



14.6.3.2 General Design Theory


This section addresses the general design theory and procedure for precast, prestressed (pre-tensioned) concrete girders. For design examples, consult the PCI Bridge Design Manual, Chapter 9.

Design bridges consisting of simple span precast concrete girders and CIP concrete slabs to be continuous for live load and superimposed dead loads by using a CIP continuity diaphragm at bents, when possible. The design of the girders for continuous structures is similar to the design for simple spans except that, in the area of negative moments, the member is treated as an ordinary reinforced concrete section, and the bottom flanges of adjoining girders are connected at the interior supports by reinforcing projecting from girder ends into a common diaphragm. Assume that the members are fully continuous with a constant moment of inertia when determining both the positive and negative moments due to loads applied after continuity is established.

The resistance factor, ϕ, (LRFD Article 5.5.4) for flexure is 1.0. An exception is for the design of the negative moment reinforcing in the deck for structures made continuous for composite loads only and having a CIP continuity diaphragm between the ends of the girders over the bents. For this case, the resistance factor is 0.90 for reinforced concrete members in flexure.

14.6.3.3 Loading Conditions

Consider five loading conditions in the design of a precast, prestressed girder:

1. The first loading condition is when the strands are tensioned in the bed before placement of the concrete. Seating losses, relaxation of the strand and temperature changes affect the stress in the strand before placement of the concrete. The fabricator must consider the factors during the fabrication of the girder and make adjustments to the initial strand tension to ensure that the tension before release meets the design requirements for the project. The prestressing working drawings present a discussion on the fabricator’s proposed methods to compensate for seating losses, relaxation and temperature changes.

2. The second loading condition is when the strands are released and the force is transferred to the concrete. After release, the girder cambers up and is supported at the girder ends only. In this condition, the region near the end of the member is not subject to bending stresses and can develop tensile stresses in the top of the girder large enough to crack the concrete. The critical sections for computing the critical temporary stresses in the top of the girder is near the end and at all debonding points. Assume that the stress in the strands is zero at the end of the girder or debonding point and varies linearly to the full transfer of force to the concrete at the end of the strand transfer length.

Several methods are available to relieve excessive tensile stresses near the ends of the girder:



• Debonding, where the strands remain straight but wrapped in plastic over a predetermined distance to prevent the transfer of prestress to the concrete through bonding

• Harping some of the strands to reduce the strand eccentricity at the end of the girder

Use the level of effective prestress immediately after release of the strands, which includes the effects of elastic shortening and the initial strand relaxation loss, to compute the concrete stresses at the second loading condition stage.

3. The third loading condition occurs a few weeks to a few months after strand release when the girder is transported. Do not consider the lifting and shipping loads in design, but the fabricator must provide a shipping method that does not overstress the girder. The main concern for the loading condition is lateral loads. Fabricators have used additional bonded and unbonded strands in the top flange to minimize the likelihood of damage during shipping and to control sweep in long girders before deck placement.

4. The fourth loading condition occurs several weeks to several months after strand release when the girder is erected and the composite deck is cast. Camber growth and prestress losses are design factors at the stage. Field adjustments to the haunch thickness are required to provide the proper vertical grade on the top of deck and to keep the deck thickness uniform. Reliable estimates of deflection and camber are needed to avoid significant encroachment of the top of girder into the bottom of the concrete deck. Stresses at the stage are usually not critical.

See Section 14.6.4 for determining the girder camber at erection.

5. The fifth loading condition is after an extended period of time during which all prestress losses have occurred and loads are at the maximum, which is often referred to as the maximum service load, minimum prestress stage. The tensile stress in the bottom fibers of the girder at midspan generally controls the design. The effects of imposed deformations are also examined at the stage. Checks for imposed deformation due to creep and shrinkage are not required for fully integral bridges.

14.6.3.4 Debonded Strands

Debonding of strands at the ends of precast, pretensioned concrete girders is acceptable. Do not debond any strands in the bottom row. Round the theoretical number of debonded strands to the closest even number (pairs) of strands.

When analyzing stresses and/or determining the required length of debonding, limit stresses to the values in LRFD Article 5.9.4, except limit tension to 0.0948 cf ′ for all exposure conditions.

14.6.3.5 Intermediate Diaphragms




Refer to the SD drawings for intermediate diaphragm spacing requirements. Use WS sheets for steel intermediate diaphragms. Use a minimum thickness of 6 in. for CIP intermediate diaphragms, and extend the diaphragm from the top of the bottom flange to the bottom of the top flange.

14.6.3.6 Sole Plates

For a final slope at the bottom of the girder greater than or equal to 1%, use beveled sole plates to allow for level girder seats.

14.6.4 Camber and Deflections

Base the calculation of the dead load deflections on the gross section properties and LRFD Article 5.7.3.6. The deflection multipliers in Figure 14.14 are appropriate for the majority of bridges. Structural engineers with specific concerns relating to long term drainage or sag in girders or concerns specific to the project can use refined methods, such as the time step method, to estimate initial and long term girder deflections.

Load Typical

DisplacementDirection

Multipliers for Each Stage

AR AD B CD CF

Prestressing 1.0 1.80 N/A 1.80 2.20

Girder dead load 1.0 1.85 N/A 1.85 2.40

Noncomposite dead load N/A 1.0 1.0 1.0 2.3

Composite dead load N/A N/A 1.0 1.0 3.0

Future wearing surface N/A N/A N/A N/A 1.0

Figure 14.14 — MULTIPLIERS FOR ESTIMATING LONG TERM DEFLECTION OF PRESTRESSED CONCRETE GIRDERS

AR = Camber at release; use the multipliers in the column to estimate the camber at release AD = Girder camber at deck placement (assumes deck placed at 40 days); use the multipliers

in the column to estimate the camber at the time of deck placement B = Girder deflection due to superimposed dead loads; use the multipliers in the column to

estimate the deflections listed on the screed elevation sheet CD = Girder camber just after all dead loads applied to bridge; use the multipliers in the

column to estimate the camber after deck and composite loads placement CF = Girder camber at 20 years; CF is a theoretical estimate used to evaluate the potential for

long term sag in the girder; do not use the CF multipliers for determining screed elevations; see discussion below on long term camber

In general, current simplified estimates of girder cambers tend to overestimate both initial camber and potential for long term sag. Girder shape, strand density and material properties all



contribute to camber estimate errors. Evaluate the impacts of reduced camber on bridges where the maximum haunch is at midspan. Typical methods can overestimate initial camber by a factor of 2. Much of the error in camber estimates is attributed to an underestimation of the girder modulus of elasticity and concrete strength at release.

When using refined methods, evaluate adjusting the girder properties used to estimate camber. Evaluate the potential for ponding on bridges with the potential for long term sag and on flat grades or in sag curves. Additional analysis could be warranted in these situations. The multipliers in Figure 14.14 under CF are based on research published in 1977 and do not properly account for a large CIP deck. Use the CF multipliers to evaluate the potential for long term sag. If the CF multipliers indicate long term sag, a refined analysis can be run to verify the potential for sag. Also, note that the PCI Bridge Design Manual discourages increasing prestress to reduce the long term sag predicted by the CF multipliers.

14.6.5 Sweep

Sweep is a measure of the girder out of straightness measured from a chord between ends. See Figure 14.15. Girders over approximately 145 ft have the potential for excess sweep at erection. Sweep is caused by a number of factors, including strand release patterns and temperature differentials. Fabricators use unbonded and bonded top flange strands or bracing during girder storage to control erection sweep and improve girder stability during erection. Use of the methods is at the fabricator’s discretion.

Figure 14.15 — DEFINITION OF SWEEP 14.6.6 Bursting Reinforcing

The working standards set the end reinforcing for all girders meeting the conditions in the Prestressed Girder Design and Detailing Checklist. The working standards permit an end zone for splitting resistance that is slightly longer than permitted in LRFD Article 5.10.10 for highly prestressed UBT42, UBT50 and UBT58 girders.



14.7 SEGMENTAL CONCRETE POST-TENSIONED BOX GIRDERS

Segmental bridges are beyond the scope of the SDDM. Coordinate with the Structures Design Manager for specific design requirements for projects using segmental systems. At a minimum, all segmental bridges must meet AASHTO requirements and use a minimum 3-in. sacrificial concrete overlay (or additional 3 in. of cover) over the structural box.

Detail all new concrete box girder bridges with access openings to allow inspection of the girder interior. Do not locate access openings over travel lanes or railroad tracks and, preferably, not over shoulders. Locate the inspection accesses such that the general public cannot gain easy entrance. Provide one access opening at each end of the bridge when the total span length is 100 ft or more.

Provide an opening that is at least 3 ft × 3 ft, has a hinged metal door that swings into the box girder and has a removal bolt for locking. Where required, provide a method of ladder support for inspection access. Coordinate with the Structures Design Manager to determine if interior power and lighting are required.

See Section 2.11 for more discussion.

FEBRUARY 2015

STEEL STRUCTURES


UDOT Structures Design & Detailing Manual February 2015

Steel Structures 15-i

TABLE OF CONTENTS

15.1 ECONOMICAL STEEL SUPERSTRUCTURE DESIGN ............................................ 15-1

15.1.1 Number of Girders/Spacing ......................................................................... 15-1 15.1.2 Exterior Girders ........................................................................................... 15-1 15.1.3 Span Arrangements for Continuous Girders ............................................... 15-2 15.1.4 Girder Proportioning .................................................................................... 15-2

15.1.4.1 Welded Plate Girders ................................................................. 15-2 15.1.4.2 Rolled Beams ............................................................................ 15-6

15.1.5 Falsework .................................................................................................... 15-7

15.2 MATERIALS .............................................................................................................. 15-7

15.2.1 Structural Steel ............................................................................................ 15-7

15.2.1.1 Grade 36 .................................................................................... 15-7 15.2.1.2 Grades 50 and 50W ................................................................... 15-7 15.2.1.3 Unpainted Weathering Steel (Grades 50W and HPS70W) ........ 15-8 15.2.1.4 High Performance Steel ............................................................. 15-9

15.2.2 Bolts ............................................................................................................ 15-10

15.2.2.1 Type ........................................................................................... 15-10 15.2.2.2 Hole Size ................................................................................... 15-10

15.2.3 Splice Plates ................................................................................................ 15-10

15.3 HORIZONTALLY CURVED MEMBERS.................................................................... 15-10 15.4 FATIGUE CONSIDERATIONS .................................................................................. 15-11

15.4.1 Load Induced Fatigue .................................................................................. 15-11

15.4.1.1 Fatigue Stress Range ................................................................ 15-12 15.4.1.2 Fatigue Resistance .................................................................... 15-12

15.4.2 Distortion Induced Fatigue .......................................................................... 15-13 15.4.3 Other Fatigue Considerations ..................................................................... 15-13

15.5 DETAILING REQUIREMENTS .................................................................................. 15-13

15.5.1 Deck Haunches ........................................................................................... 15-14 15.5.2 Camber ........................................................................................................ 15-14 15.5.3 Diaphragms and Cross Frames .................................................................. 15-14 15.5.4 Lateral Bracing ............................................................................................ 15-17


15-ii Steel Structures

15.5.5 Inspection Access (Box Girders) ................................................................. 15-17 15.5.6 Jacking ........................................................................................................ 15-17

15.6 I-SECTIONS IN FLEXURE ........................................................................................ 15-18

15.6.1 Limit States .................................................................................................. 15-18

15.6.1.1 Positive Moment Region Maximum Moment Section ................ 15-18 15.6.1.2 Negative Moment Region Bent Section ..................................... 15-18 15.6.1.3 Negative Flexural Deck Reinforcement ..................................... 15-19 15.6.1.4 Rigidity in Negative Moment Regions ........................................ 15-19

15.6.2 Shear Connectors ....................................................................................... 15-19

15.6.2.1 Requirements ............................................................................ 15-19 15.6.2.2 Modified Requirements for Precast Decks ................................. 15-20

15.6.3 Stiffeners ..................................................................................................... 15-20

15.6.3.1 Intermediate Transverse Stiffeners ............................................ 15-20 15.6.3.2 Diaphragm Connection Stiffener ................................................ 15-20 15.6.3.3 Bearing Stiffeners ...................................................................... 15-20

15.7 CONNECTIONS AND SPLICES ............................................................................... 15-21

15.7.1 Bolted Connections ..................................................................................... 15-21 15.7.2 Welded Connections ................................................................................... 15-21

15.7.2.1 Welding Process ........................................................................ 15-21 15.7.2.2 Welding Types and Symbols ..................................................... 15-22 15.7.2.3 Field Welding ............................................................................. 15-22 15.7.2.4 Design of Welds ......................................................................... 15-22

15.7.3 Field Splices ................................................................................................ 15-24

LIST OF FIGURES

Figure 15.1 — MINIMUM DIMENSIONS ............................................................................. 15-2 Figure 15.2 — GROUPING FLANGES FOR EFFICIENT FABRICATION .......................... 15-4 Figure 15.3 — FLANGE WIDTH TRANSITION ................................................................... 15-4 Figure 15.4 — DRIP BAR DETAIL ...................................................................................... 15-9 Figure 15.5 — TYPICAL DIAPHRAGMS AND CROSS FRAMES ...................................... 15-16 Figure 15.6 — WELDING SYMBOLS .................................................................................. 15-23


Steel Structures 15-1

Chapter 15 STEEL STRUCTURES

Section 6 of the LRFD Specifications present design requirements for steel structures. This chapter discusses structural steel provisions in Section 6 of the LFRD Specifications that require amplification or clarification. This chapter also addresses specific practices for the design and detailing of steel superstructures. Chapter 10 provides criteria for the general site considerations for which steel structures are appropriate, including span lengths, girder spacing, geometrics, aesthetics and cost.

15.1 ECONOMICAL STEEL SUPERSTRUCTURE DESIGN

Factors that influence the initial cost of a steel bridge include, but are not limited to, detailing practices, the number of girders, the grade of steel, type and number of substructure units (i.e., span lengths and arrangements), steel weight, fabrication, transportation and erection. The cost associated with the factors changes periodically in addition to the cost relationship among the factors. Therefore, evaluate and modify the guidelines as necessary for each bridge to determine the most economical type of steel girder.

Based upon market factors, the availability of steel (especially rolled wide flange sections and HPS) can affect the construction schedule. The structural engineer must verify the availability and required lead times of the specified steel. Contact producers to ensure the availability of plates and rolled beams.

For more detailed information on all aspects of steel design and detailing, see the current AASHTO/NSBA Steel Bridge Collaboration’s Guidelines for Design for Constructability.

15.1.1 Number of Girders/Spacing

See Section 10.2.6 for a discussion on the number of girders and Section 10.3.3 for typical girder spacings for both I-girder and box girder steel bridges.

15.1.2 Exterior Girders

The following factors control the location of the exterior girder with respect to the overhang:

• Locate the exterior girder to limit the dead load and live load on girders such that the demands on interior and exterior girder sections are similar.

• Locate the exterior girder to allow for deck drains. • Consider aesthetics when determining the location of the exterior girder lines. See Section 16.2.15.1 for additional overhang limits.


15-2 Steel Structures

15.1.3 Span Arrangements for Continuous Girders

Provide span arrangements that balance the moments in the spans (i.e., equal maximum moments in end and interior spans). The end span lengths are typically between 70% and 80% of the length of interior spans. As a result, the optimum proportions of the girder in all spans are nearly the same, resulting in a more efficient and cost effective design. To prevent uplift at the abutments, avoid end spans less than 70% of the interior spans. Span arrangements not meeting the above ratios are permitted when the span arrangement reduces total project cost and the girder connections are designed for uplift when uplift is present.

15.1.4 Girder Proportioning

Make girders composite with the bridge deck and continuous over interior supports. To achieve economy in the fabrication shop, use identical girders in a straight girder bridge. If multiple girder designs are required due to varying girder spacing or other load effects, attempt to minimize the number of different plate sizes. Group curved girders into two to four girder groups with the plate sizes in a group consistent within the group.

15.1.4.1 Welded Plate Girders

Design welded steel plate girders to optimize total cost including material costs while also considering fabrication and erection costs. Top flanges of composite plate girders are typically thinner and/or narrower than bottom flanges. Vary the flange section along the length of the bridge generally following the moment envelope to save cost by offsetting the increased fabrication costs of welded flange transitions with larger savings in material costs. The webs of plate girders are typically deeper and thinner than the webs of rolled beams.

Due to buckling considerations, address the stability of the compression flange (i.e., the top flange in positive moment regions and the bottom flange in negative moment regions) by providing lateral brace locations based upon calculations.

15.1.4.1.1 Minimum Dimensions

See Figure 15.1 for the minimum dimensions for components of structural steel plate girders.

Components Minimum Thickness (in.) Width (in.) Webs ½ N/A Flanges 1 12 Bearing Stiffener Plates 1 5 Transverse Stiffeners ½ 4 Gusset Plates ½ N/A Angles/Channels ⅜ N/A

Figure 15.1 — MINIMUM DIMENSIONS



15.1.4.1.2 Haunched (Variable Depth) Girders

When practical, use constant depth girders (i.e., girders with constant web depths). Haunched girders are generally uneconomical for interior span lengths less than 240 ft. Consider using parabolic haunched girders where aesthetics or other special circumstances are encountered, but constant depth girders are generally more cost effective. An effective alternative to haunched girders is the use flanges with a higher yield strength in negative moment regions. See Section 15.2.1.4 for additional information on high performance steel.

15.1.4.1.3 Flange Plate Sizes

Provide bottom flanges with a constant width within a frame. Use as wide a flange girder plate as practical, consistent with stress and b/t (flange width/thickness ratio) requirements. The wide flange contributes to girder stability during handling and in service, and the additional width reduces the number of passes and weld volume at flange butt welds. As a guide, the minimum flange width is approximately 20% of the web depth, and the maximum is approximately 50% of the web depth. The maximum flange thickness is 3 in. to ensure uniform material properties through the thickness of the flange. Thicker plates can have a less desirable grain structure in the mid thickness of the plate, which increases the likelihood of cracking.

Proportion flanges so that the fabricator can economically cut the flanges from steel plate between 60-in. and 120-in. wide. The most economical mill widths are 72 in., 84 in., 96 in. and 120 in. Allow ¼ in. for internal torch cutting lines and ½ in. for exterior torch cutting lines; see Figure 15.2. Group flanges to provide an efficient use of the plates. Because structural steel plate is most economically purchased in the typical widths, repeat plate thicknesses as much as practical. If practical, group plates of like width by thickness to meet the minimum width purchasing requirement, but an economical purchasing strategy could be unavailable for thicker, less used plates.

The most efficient method to fabricate flanges is to groove weld together several wide plates of varying thicknesses received from the mill. After welding and nondestructive testing, the individual flanges are stripped from the full plate. The method of fabrication reduces the number of welds, individual runoff tabs for both start and stop welds, the amount of material waste and nondestructive testing. The objective, therefore, is for flange widths to remain constant within an individual shipping length by varying material thickness as required. Figure 15.2 illustrates one example of an efficient fabrication for girders.

Constant top flange width within a field section can be impractical in girder spans over 300 ft where a flange width transition could be required in the negative bending regions. Though not preferred, if a transition in width must be provided, shift the butt splice a minimum of 3 in. from the transition into the narrower flange plate. See Figure 15.3. The 3-in. shift makes it simpler to fit runoff tabs, weld and test the splice, and grind off the runoff tabs.



Figure 15.2 — GROUPING FLANGES FOR EFFICIENT FABRICATION (Reference: AASHTO/NSBA Steel Bridge Collaboration)

Figure 15.3 — FLANGE WIDTH TRANSITION



15.1.4.1.4 Field Splices

Use field splices to reduce shipping lengths, but minimize the number because field splices are expensive. The preferred maximum length of a field section is 120 ft. Longer lengths are possible, but do not use field sections greater than 120 ft without considering shipping, erection and site constraints. As a rule, use a shipping length to compression flange width less than approximately 85. Good design practice is to reduce the flange cross sectional area by no more than approximately 25% of the area of the heavier flange plate at field splices to reduce the buildup of stress at the transition. For continuous spans, use constant length field sections to simplify erection.

The fabricator has the option of proposing to eliminate or move the field splice. The fabricator must submit the request to eliminate or move the field splice for review by the EOR. The EOR evaluates the request and approves the request when appropriate. Section 6.4 provides additional information on the shop drawing review process.

15.1.4.1.5 Shop Splices

Include no more than two shop flange splices in the top or bottom flange within a single field section with a length up to 120 ft. Weigh the cost of groove welded splices against the cost of an extra plate when determining the points where changes in plate thickness occur within a field section.

The current edition of the AASHTO/NSBA Steel Bridge Collaboration Guidelines for Design for Constructability provides guidelines for weight savings for Grade 50 steel required to justify a flange shop splice.

Also consider the length of the plate when determining if a plate transition is cost effective. Available plate lengths vary depending on the plate thickness and the original plate width of a shop splice. If the design plate length is longer than the available plate, a shop splice is required; therefore, a plate thickness change can be made without considering the additional cost for a weld. Most plates less than or equal to 2-in. thick are available in lengths from 78 ft to 86 ft, depending on thickness. Plates thicker than 2 in. are available in lengths from 52 ft to 69 ft. Fifty ft is the maximum length of plates that are normalized, quenched and tempered (e.g., Grade HPS70W).

To facilitate testing of the weld, locate flange shop splices at least 2 ft from web splices, and locate flange and web shop splices at least 1 ft from transverse stiffeners.

15.1.4.1.6 Web Plates

Where no vertical clearance restrictions exist, optimize the web depth. NSBA provides design assistance for bridge owners to assist in optimizing web depths. Use other sources if the web depths are based upon material use and fabrication unit costs. Do not change web thickness at any splice by less than 1/16 in. Maintain symmetry by aligning the centerlines of the webs at splices.



Web design can have a significant impact on the overall cost of a plate girder. Thin webs reduce steel quantities, but installing transverse stiffeners is one of the most labor intensive of shop operations. The following guidelines apply to the use of transverse stiffeners:

• Unstiffened webs are generally more economical for web depths approximately 48 in. or less.

• For web depths greater than 48 in., consider options for a partially stiffened or an unstiffened web. A partially stiffened web is one where the web thickness is proportioned at least 1/16 in. less than that allowed by specification for an unstiffened web at a given depth and, therefore, stiffeners are required only in areas of higher shear. Evaluate the cost of stiffeners against the cost of added web thickness. Only add stiffeners where a cost reduction is shown. If the total cost of the stiffened web is essentially the same as the unstiffened web, select the unstiffened web.

15.1.4.1.7 Transverse Stiffeners

Flat bars (i.e., bar stock rolled to widths up to 8 in. at the mill) are typically more economical than plates for stiffeners. The stiffeners can be fabricated by shearing flat bars of the specified width to length. Proportion stiffeners in ¼-in. increments in width and in ⅛-in. increments in thickness. Consult a fabricator for available flat bar sizes.

15.1.4.1.8 Longitudinally Stiffened Webs

Do not use longitudinally stiffened webs.

15.1.4.2 Rolled Beams

Rolled beams are doubly symmetrical as rolled cross sections with equal dimensioned top and bottom flanges and relatively thick webs. Thus, rolled beams do not optimize the cross sections for weight savings (as a plate girder does) but are cost effective due to lower fabrication and erection costs. The relatively thick webs preclude the need for intermediate web stiffeners, but full height bearing stiffeners are required at all support locations. Rolled beam superstructures are cost effective for spans less than 50 ft.

Rolled beams are more readily available in depths up to 36 in., with deeper beams rolled less frequently at intervals of approximately 16 weeks. Before beginning final design, verify with one or more potential fabricators that the section size and length are available and that delivery can meet project schedule requirements.

If a rolled beam design is proposed for a new bridge, provide language in the contract documents that permits the substitution of a welded plate girder design.

Do not use cover plates on rolled beams.



15.1.5 Falsework

Do not use shored construction unless approved by the Structures Design Manager. Design steel superstructures to not require intermediate falsework during the placing of the concrete deck slabs.

15.2 MATERIALS

15.2.1 Structural Steel


The following presents typical practices for the material type selection for structural steel members. Apply Temperature Zone 2 when using LRFD Table 6.6.2-1.

15.2.1.1 Grade 36

Grade 36 steel is typically only specified for secondary structural members, such as:

• Transverse stiffeners • Sole plates • Bearing plates • Angle sections Grade 36 steel is becoming obsolete and the availability is limited for WT, I, C and MC sections. Specifying Grade 36 is acceptable, but contractors and fabricators often use Grade 50. Generally, little or no cost difference exists between Grade 50 and Grade 36 steel.

When specifying Grade 36 steel, provide sections that also meet design requirements assuming that Grade 50 steel is substituted for Grade 36 steel.

15.2.1.2 Grades 50 and 50W

Grades 50 and 50W steel are the most commonly used grades. The grades are typically used for primary and secondary members such as:

• Rolled beams • Plate girders • Splice plates • Bent plate diaphragms • Channels • Bearing plates • Steel H-piles



• Sole plates • Stiffeners Grade 50W can be painted or unpainted. See Section 15.2.1.3 for limitations on the application of unpainted Grade 50W.

15.2.1.3 Unpainted Weathering Steel (Grades 50W and HPS70W)

Unpainted weathering steel is more cost effective than painted steel. The initial cost advantage when compared to painted steel can range up to 15%. When future repainting costs are considered, the cost advantage is more substantial, especially for bridges over deep canyons where no access from the ground is available. The savings in repainting costs reflects, for example, environmental considerations in the removal of paint, which significantly increases the life cycle cost of painted steel. The application of weathering steel and the potential problems are discussed in depth in FHWA Technical Advisory T5140.22 “Uncoated Weathering Steel in Structures,” December 3, 1989. Also, the proceedings of the “Weathering Steel Forum,” July 1989, are available from the FHWA Office of Implementation, HRT-10.

Despite the cost advantage, the use of unpainted weathering steel is not appropriate in all environments and at all locations. The most prominent disadvantage of weathering steel is aesthetics. The natural weathering of the unpainted steel and the inevitable staining of concrete where susceptible to water leakage from above (e.g., below deck joints) creates the image of lack of proper maintenance to the traveling public. Do not use weathering steel where the following conditions exist:

• In industrial areas where concentrated chemical fumes could drift onto the structure, or where the nature of the environment is questionable

• Over bodies of water where the clearance over the ordinary high water is less than 10 ft • Bridges over roads For additional guidance on the appropriate application of unpainted weathering steel, see the AISI publication Performance of Weathering Steel in Highway Bridges: A Third Phase Report.

15.2.1.3.1 Design Details for Unpainted Weathering Steel

Where weathering steel girders are used, provide bearing plates using the same steel as the girders the plates support. The bolts, nuts, washers and DTIs are Type 3 as specified in ASTM A325/ASTM A563 and ASTM F959.

When using unpainted weathering steel, use the details provided in the SD drawings and the following drainage treatments:

• Eliminate details that serve as water and debris traps. Seal or paint overlapping surfaces exposed to water. The sealing or painting applies to nonslip critical bolted joints. Slip critical bolted joints or splices do not produce pack rust when the bolts are



spaced according to the LRFD Specifications and, therefore, do not require special protection.

• Place a drip plate or other material transverse across the top of the bottom flange in front of the substructure elements to prevent water from running off the flange onto the concrete. Ensure that the attachments meet all fatigue requirements. Figure 15.4 and the SD drawings show typical drip plate details.

Figure 15.4 — DRIP BAR DETAIL Refer to Section 16.5 for more information on deck drainage requirements.

15.2.1.4 High Performance Steel

15.2.1.4.1 Grade HPS70W

Grade HPS70W is cost competitive in multispan bridge applications. (Note: The “W” designates weathering grade steel; however, the steel can still be painted.) In addition to increased strength, the high performance steels exhibit enhanced weathering, toughness and weldability properties. A savings in weight offsets the premium on material costs.

Cost effective design solutions tend to be hybrid girders with Grade 50 webs and HPS70W tension and compression flanges in the negative moment region over the bent. On very long bridges, HPS70W tension flanges in the high positive moment region can be effective. HPS70W is rarely cost effective on single span bridges. For more information, see the



AASHTO Guide Specifications for Highway Bridge Fabrication with HPS70W Steel. The cost of steel fluctuates with the market; therefore, coordinate with suppliers when evaluating the cost of Grade 70 steel versus Grade 50 steel.

See Section 15.2.1.3 for limitations on the application of unpainted Grade HPS70W.

15.2.1.4.2 Grade HPS100W

The industry has introduced new high performance steel with minimum specified yield strength of 100 ksi. Do not use Grade HPS100W because the grade has yet to prove cost effective for bridge girder applications.

15.2.2 Bolts


15.2.2.1 Type

For normal construction, high strength bolts are:

• Painted Steel. Use ⅞-in. A325 (Type 1) • Weathering Steel. Use ⅞-in. A325 (Type 3) .

15.2.2.2 Hole Size

Typically, use a standard hole size. Do not use oversized or slotted holes, except in unusual circumstances where the additional tolerance could be advantageous. Examples include a bridge widening or phased construction with large girder deflections.

15.2.3 Splice Plates

Use the same material for steel in all splice and filler plates that is used in the corresponding web and flanges of plate girders.

15.3 HORIZONTALLY CURVED MEMBERS

Reference: LRFD Articles 6.10 and 6.11

The LRFD Specifications include horizontally curved girders in the provisions for proportioning I-shaped and box girders at both the strength and service limit states. In addition, the LRFD Specifications specify analysis methodologies that detail various required levels of analysis.



The use of horizontally curved steel members requires the consideration of many factors that differ from straight girders including but not limited to:

1. Cross Frames/Diaphragms. Use cross frames and diaphragms that are as close as practical to the full depth of the girders. See Section 15.5.3 for additional cross frame and diaphragm information. All curved steel simple span and continuous span bridges must have diaphragms directed radially except end diaphragms. Place end diaphragms parallel to the centerline of bearings. Charpy V-notch tests on cross frames, diaphragms and cross frame connection plates are not required.

2. Load Considerations. Design all cross frames and diaphragms, including the connections to the girders, to carry the total transferred load at each diaphragm location. Design cross frame and diaphragm connections according to the provisions of LRFD Article 6.13.1. LRFD Article 6.13.1 allows the design of connections for cross frames and diaphragms using only the calculated loads. The average of the load and resistance provision or the 75% of resistance provision can result in large diaphragm connections that are difficult to detail.

3. Expansion/Contraction. Consider providing restraint either radially and/or tangentially to guide the thermal movement of the structure. For ordinary geometric configurations where the bridge length is long relative to the bridge width and the degree of curvature is moderate (i.e., satisfying the requirements of LRFD Article 4.6.1.2.4b), no additional consideration is necessary for the unique expansion characteristics of horizontally curved structures. Wide, sharply curved or long span structures could require the use of HLMR bearings.

4. Flange Splices. Design the splices in flanges of curved girders to carry flange bending or lateral bending stresses and vertical bending stresses in the flanges.

15.4 FATIGUE CONSIDERATIONS


LRFD Article 6.6.1 categorizes fatigue as either load induced or distortion induced. Load induced fatigue is a direct cause of loading. Distortion induced fatigue is an indirect cause in which the force effect, normally transmitted by a secondary member, tends to change the shape of or distort the cross section of a primary member.

15.4.1 Load Induced Fatigue


Avoid the use of steel bridge details with fatigue resistances lower than Detail Category C′ (i.e., Detail Categories D, E and E′).



Design all bridges for the Fatigue I load combination providing infinite fatigue life unless otherwise directed by the Structures Design Manager.

LRFD Article 6.6.1.2 provides the framework to evaluate load induced fatigue, which is determined by:

• The stress range induced by the specified fatigue loading at the detail under consideration

• The nominal fatigue resistance for the detail category being investigated • For finite fatigue life design, the number of repetitions of fatigue loading a steel

component experiences during the 75 year design life

15.4.1.1 Fatigue Stress Range

The following applies:

1. Regions. Consider fatigue in the regions of a steel member that experience a net applied tensile stress. Also consider fatigue if the compression stress from the unfactored permanent loads is less than the Fatigue I load combination stress range when the Fatigue I load combinations results in tension stress. Therefore, when designing for finite life using the Fatigue II load combination, check fatigue even though the Fatigue II load combination does not produce a net tensile stress. Refer to AASHTO C6.6.1.2.1 for additional discussion.

2. Range. Define the fatigue stress range as the difference between the maximum and minimum stresses at a structural detail subject to a net tensile stress as described in Item 1, Regions. The stress range is caused by a single design truck that can be placed anywhere on the deck within the boundaries of a design lane. If a refined analysis method is used, position the design truck to maximize the stress in the detail under consideration. The design truck has a constant 30-ft spacing between the 32-kip axles. The dynamic load allowance is 0.15. The Fatigue I load factor is 1.5. The Fatigue II load factor is 0.75.

3. Analysis. Use the single design lane load distribution factor in LRFD Article 4.6.2.2 to determine fatigue stresses, unless a refined analysis method is used. The tabularized distribution factor equations incorporate a multiple presence factor of 1.2 that must be removed by dividing either the distribution factor or the resulting fatigue stresses by 1.2. The division does not apply to distribution factors determined using the lever rule.

15.4.1.2 Fatigue Resistance

LRFD Article 6.6.1.2.3 groups the fatigue resistance of various structural details into eight categories (A through E′). Experience indicates that Detail Categories A, B and B′ are seldom critical. Investigation of details with a fatigue resistance greater than Detail Category C could be appropriate in unusual design cases. For example, Category B applies to base metal adjacent to slip critical bolted connections and is only evaluated when thin splice plates or connection plates are used. For Detail Categories C, C′, D, E and E′, the LRFD Specifications require that



the fatigue stress range must be less than the specified fatigue resistance for each of the respective categories.

The fatigue resistance of a category is determined from the interaction of a Category Constant A and the total number of stress cycles, N, experienced during the 75 year design life of the structure. The resistance is defined as (A/N)1/3. A constant amplitude fatigue threshold ((ΔF)TH) is also established for each category. If the fatigue stress range using the Fatigue I load combination is less than the threshold value, the detail has infinite fatigue life.

For bridges designed for infinite fatigue life, the applied fatigue stress range using the Fatigue I load combination is less than the threshold value, (ΔF)TH. The practice provides an infinite theoretical design life. For bridges designed for finite life, calculate the fatigue resistance according to LRFD Article 6.6.1.2.3.

Fatigue resistance is independent of the steel strength. The application of higher grade steels causes the fatigue stress range to increase, but the fatigue resistance remains the same. The independence implies that fatigue can become more of a controlling factor where higher strength steels are used.

15.4.2 Distortion Induced Fatigue


LRFD Article 6.6.1.3 provides specific detailing practices for transverse and lateral connection plates intended to reduce significant secondary stresses that could induce fatigue crack growth. The provisions of the LRFD Specifications are prescriptive and require no mathematical computation of stress range.

15.4.3 Other Fatigue Considerations

Reference: Various LRFD Articles

In addition to the considerations in Sections 15.4.1 and 15.4.2, investigate the fatigue provisions in other articles of Section 6 of the LRFD Specifications, including:

• Fatigue due to out of plane flexing in webs of plate girders — LRFD Article 6.10.5.3 • Fatigue at shear connectors — LRFD Articles 6.10.10.1.2 and 6.10.10.2 • Bolts subject to axial tensile fatigue — LRFD Article 6.13.2.10.3

15.5 DETAILING REQUIREMENTS




15.5.1 Deck Haunches

A deck haunch is an additional thickness of concrete between the top of the girder and the bottom of the deck to provide adjustability between the top of the cambered girder and the roadway profile. For rolled beams, measure the depth of the haunch from the top of the girder section and, for a welded plate girder, from the top of the web. Dimension the haunch at the centerline of bearing. See the SD drawings for the haunch calculation procedure. Typically, neglect the haunch when determining the resistance of the section. See Section 16.2.6 for calculations and additional details.

15.5.2 Camber

Where dead load deflection and vertical curve offset are greater than ¼ in., provide girders with a compensating camber. Camber the entire girder length as required by the loading and profile grade. Calculate camber to the nearest 0.01 ft, with ordinates matching the screed elevation spacing (typically, tenth points or equal spaces less than 15′-0″) throughout the length of the spans. Show the required camber values from a chord line that extends from point of support to point of support.

Provide a camber diagram in all contract documents with structural steel girders. Include a camber diagram with ordinates as follows:

• Steel DL deflection • Noncomposite DL deflection • Composite DL deflection • Total DL deflection 15.5.3 Diaphragms and Cross Frames

Reference: LRFD Articles 6.7.4 and 6.6.1.3.1

Diaphragms and cross frames stabilize the girders in the positive moment regions during construction and in the negative moment regions during and after construction. Cross frames also serve to distribute gravitational, centrifugal and wind loads. Determine the spacing of diaphragms and cross frames based upon the provisions of LRFD Article 6.7.4.1. The design of the spacing of diaphragms and cross frames is iterative. A good starting point is the traditional diaphragm and cross frame spacing of 25 ft. Most economical steel girder designs use spacings greater than 25 ft in the positive moment regions with the first diaphragm or cross frame off of the bent in the negative moment regions spaced at less than 25 ft.

The following applies to diaphragms and cross frames:

1. Location. Place diaphragms or cross frames at each support and throughout the span at an appropriate spacing. Plan the location of the field sections to avoid conflict between the connection plates of the diaphragms or cross frames and any part of the splice material.



2. Skew. Place all intermediate diaphragms and cross frames perpendicular to the girders or parallel to the skew for a skew angle up to 20°. For a skew angle greater than 20°, locate intermediate diaphragms and cross frames perpendicular to the girders and stagger cross frames near the support (see the SD drawings). Evaluate the effects of staggered cross frames. When locating a cross frame between two girders, the relative stiffness of the two girders must be similar. Otherwise, the cross frame acts as a primary member supporting the more flexible girder. This could be unavoidable on bridges with exceptionally high skews where a rational analysis of the structural system is required to determine actual forces.

3. End Diaphragms. Place end diaphragms along the centerline of bearing on all bridges. Set the top of the diaphragm below the top of the girder to accommodate the joint detail and the thickened slab at the end of the superstructure deck, where applicable. Design the end diaphragms to support the edge of the slab including live load plus impact. On integral or semi-integral abutment bridges where the steel diaphragm is encased in concrete or supplemented by a concrete diaphragm, using an end steel diaphragm matching the intermediate diaphragm style is permitted.

4. Interior Support Diaphragms and Cross Frames. Generally, place interior support diaphragms and cross frames along the centerline of bearing, which provides lateral stability for the bottom flange and bearings.

5. Curved Girder Structures. Design diaphragms or cross frames connecting horizontally curved girders as primary members oriented radially. Refer to Section 15.3 for additional information on curved girders.

6. Detailing. Typically, detail diaphragms and cross frames to follow the cross slope of the deck; i.e., the diaphragm or cross frame is parallel to the bottom of the deck. The practice allows the fabricator to use a constant drop on each connection plate (i.e., the distance from the bottom of the flange to the first bolt hole on the connection plate is constant). Allow the contractor to substitute diaphragms or cross frames fabricated as a rectangle (as opposed to a skewed parallelogram). If used, the drops vary across the bridge.

The following identifies typical practices on the selection of diaphragms and cross frames:

1. X-Frames. For relatively narrow girder spacings relative to the girder depth, an X-frame could be more appropriate than a K-frame.

2. Inverted K-Frames. Preferred for the majority of plate girder bridges.

3. Channel/Bent Plate Diaphragms. Preferred for rolled beams or webs less than 48 in. Use full depth end diaphragms for rolled beam bridges at seat abutments to provide sufficient lateral restraint.

See Figure 15.5 and the SD drawings for typical diaphragms, cross frames and additional information.



Figure 15.5 — TYPICAL DIAPHRAGMS AND CROSS FRAMES



15.5.4 Lateral Bracing


The LRFD Specifications require the investigation for lateral bracing for all construction stages. If the bracing is included in the structural model used to determine force effects, design the lateral bracing for all applicable limit states.

In general, lateral bracing is only required on very deep girders where the bottom flange cannot accommodate the cross bending from wind. The vast majority of steel I-girder bridges (short through medium spans) do not require lateral bracing; however, the structural engineer must verify that lateral bracing is not required. Typical diaphragms and cross frames transfer lateral loads adequately to eliminate the need for lateral bracing.

For box girders, internal top lateral bracing is typical.

LRFD Article 4.6.2.7 provides various alternatives relative to lateral wind distribution in multigirder bridges.

15.5.5 Inspection Access (Box Girders)

Detail all new steel box girder bridges with access openings to allow inspection of the girder interior. Provide lighting and power when required by the Structures Design Manager or as noted in the project documents. Do not locate access openings over travel lanes or railroad tracks and, preferably, not over shoulders. Locate the inspection accesses such that the general public cannot gain easy entrance. Provide one secured access opening at each end of the bridge when the total span length is 100 ft or more.

See Section 2.11 for more information.

15.5.6 Jacking


Integral abutments and integral bents do not require jacking provisions.

Provide details allowing replacement or realignment of bearings for bridges on elastomeric pads at expansion bearings. For bearings similar to sample details in the SS sheets, assume that the bridge is lifted ¼ in. and that girders are lifted in pairs. Provide jacking stiffeners or diaphragm connections capable of supporting the bridge during bearing replacement.

Provide a jacking plan sheet for HLMR, isolation or other specialty bearings. The jacking plan sheet and other plan sheets must include the necessary bearing stiffeners, jack locations and clearances, factored reactions and jacking height. Design all cross frames and diaphragms for the jacking loads. Provide only conceptual falsework requirements when required.



Include live load when preparing the jacking plan for bridges with no readily available detour. Include the live load reactions on the jacking plan sheet. See Chapter 19 for additional bearing information.

15.6 I-SECTIONS IN FLEXURE


15.6.1 Limit States


15.6.1.1 Positive Moment Region Maximum Moment Section

For a composite girder, consider the positive moment region maximum moment section to be compact in the final condition (see LRFD Article 6.10.7.1). The cured concrete deck in the positive moment region provides a large compression flange, and the deck laterally braces the top flange. Very little, if any, of the web is in compression.

15.6.1.1.1 Top Flange (Compression Flange)

In the final condition after the deck has cured, the top flange adds little to the resistance of the cross section. During curing of the concrete deck, however, the top flange is very important. The strength limit state during construction when the concrete is not fully cured could govern the design of the top flange in the positive moment region, as specified in LRFD Article 6.10.3.4.

15.6.1.1.2 Bottom Flange (Tension Flange)

The bottom flange, if properly proportioned, is not governed by the construction phase. The bottom flange is typically governed by the final condition. The Service II load combination permanent deformation provisions of LRFD Article 6.10.4.2 could govern and must be checked.

15.6.1.2 Negative Moment Region Bent Section

The negative moment region bent section is typically a noncompact section during all conditions. The concrete deck over the bent is in tension in the negative moment region and, thus, considered cracked and ineffective for nominal resistance calculations (i.e., strength load combinations). Thus, a good portion of the steel cross section is in compression. To qualify as compact, the web is usually too thick to be cost effective. Thus, the cost effective section is normally a noncompact section.



Both top and bottom flanges in the negative moment region are typically governed by the strength limit state in the final condition. Furthermore, the bottom flange in compression is typically governed by the location of the first intermediate diaphragm off the bent because it provides the discrete bracing for the flange.

15.6.1.3 Negative Flexural Deck Reinforcement


Provide longitudinal steel not less than 1% of the total cross sectional area of the deck slab (excluding the wearing surface) in negative moment regions with longitudinal tensile stress in the slab, due to factored construction loads or the Service II load combination. Also ensure that sufficient negative moment steel is provided for the applied loads.

15.6.1.4 Rigidity in Negative Moment Regions

Reference: LRFD Articles 6.10.1.5 and 6.10.1.7

LRFD Article 6.10.1.5 permits the assumption of uncracked concrete in the negative moment regions for member stiffness. The stiffness is used to obtain continuity moments due to live load, future wearing surface and parapet weights placed on the composite section.

For the service limit state control of permanent deflections under LRFD Article 6.10.4.2 and the fatigue limit state under LRFD Article 6.6.1.2, the concrete slab can be considered fully effective for both positive and negative moments for members with shear connectors throughout the full girder length and satisfying LRFD Article 6.10.1.7.

15.6.2 Shear Connectors


15.6.2.1 Requirements

Use shear connectors over the full length of the girder. The preferred size for shear studs for use on the flanges of girders is ⅞-in. diameter. The minimum number of studs in a group is three in a single transverse row. Increase the stud length in 1-in. increments when necessary to maintain a 2-in. minimum penetration of the stud into the deck slab. Provide a minimum 3-in. cover over the top of the shear stud. On relatively thin elements, less than 1 in., use ¾-in. diameter studs. Do not place shear studs on splice plates. Additional requirements are in the AASHTO Guide Specifications for LRFD Seismic Bridge Design.



15.6.2.2 Modified Requirements for Precast Decks

Space groups of shear connectors at less than 4 ft. Provide the number of shear connectors required for strength and fatigue. Use n equal to the number of studs according to group and the pitch, p, equal to the center to center spacing between groups. The minimum transverse and longitudinal spacing between studs is 3.0 stud diameters. The maximum center to center requirement of 24 in between groups of studs is waived.

On deck replacement projects, use a finite fatigue life of 50 years to design the shear studs.

15.6.3 Stiffeners


Refer to the WS sheets for standard stiffener details and the SD drawings for diaphragm connection stiffener layout.

15.6.3.1 Intermediate Transverse Stiffeners


Weld intermediate transverse stiffeners near side and far side to the compression flange. Do not weld intermediate transverse stiffeners on straight girders to tension flanges. For the distance between the end of the web to stiffener weld and the near toe of the web to flange fillet weld, provide between 4tw and 6tw or 4-in. maximum.

The width of the projecting stiffener element, moment of inertia of the transverse stiffener and stiffener area must satisfy the requirements of LRFD Article 6.10.11.1.

Orient intermediate transverse stiffeners normal to the web.

15.6.3.2 Diaphragm Connection Stiffener

Diaphragm connection stiffeners are transverse stiffeners used to connect diaphragms or cross frames. Where the angle of crossing is between 70° and 90°, skew the stiffeners so that the diaphragms of cross frames can be connected directly to the stiffeners; otherwise, place the stiffeners normal to the web.

15.6.3.3 Bearing Stiffeners


Provide bearing stiffeners for all plate girders to prevent the possibility of web buckling. Provide bearing stiffeners on both web faces and at the bearing points of rolled beams and plate girders.



Design the weld connecting the bearing stiffener to the web to transmit the full bearing force from the stiffener to the web due to the factored loads.

Detail bearing stiffeners with the stiffener ends bearing on the loaded flange being fit to bear, or weld with a full penetration butt weld. The opposite end must also be fillet welded to the girder flange.

Elimination of the bearing stiffener is permitted on the exterior side of exterior girders at temporary supports used for ABC bridges. Design the remaining bearing stiffeners and webs for the temporary loading condition according to AASHTO requirements.

15.7 CONNECTIONS AND SPLICES


15.7.1 Bolted Connections


Design all bolted connections as slip critical at the Service II limit state, except for secondary bracing members.

LRFD Table 6.13.2.8-3 provides values for the surface condition. Use Class B surface condition for the design of slip critical connections. Class B is applicable to unpainted, blast cleaned surfaces and to blast cleaned surfaces with a Class B coating.

15.7.2 Welded Connections


15.7.2.1 Welding Process

The governing specification for welding new steel girders is the AASHTO/AWS D1.5, Bridge Welding Code. However, the specification does not provide control over all of the welding issues that could arise on a project. Consult the following additional reference specifications as needed:

• AWS D1.1 “Structural Welding Code – Steel” for welding of tubular members and strengthening or repair of existing structures

• AWS D1.4 “Structural Welding Code – Reinforcing Steel” if the welding of reinforcing steel must be covered by a specification

Welding processes include:



• Shielded metal arc • Submerged arc • Gas metal arc • Flux cored arc 15.7.2.2 Welding Types and Symbols

The primary types of welds used in bridge fabrication are fillet welds and groove welds. Welding symbols must comply with AWS A2.4:2007 “Standard Symbols for Welding, Brazing, and Non-Destructive Examination.” Welding symbols provide an instruction on the type, size and other characteristics of the desired weld. When the symbols are properly used, the meaning is clear and unambiguous. If not used exactly as prescribed, the meaning could be ambiguous, leading to problems for all involved. The AISC Steel Construction Manual and most steel design textbooks have examples of welding symbols that, although technically correct, are more complicated than the typical structural engineer needs. With minor modifications, the examples in Figure 15.6 suffice for the majority of bridge fabrication circumstances.

15.7.2.3 Field Welding

Field welding is not permitted except at bearing sole plates.

15.7.2.4 Design of Welds

The weld strength calculations of LRFD Section 6 assume that the strength of a welded connection is dependent only on the weld metal strength and the area of the weld. The area of the weld that resists load is a product of the theoretical throat multiplied by the length. The theoretical weld throat is the minimum distance from the root of the weld to the theoretical face. See Figure 15.6. Fillet welds resist load through shear on the throat; groove welds typically resist load through tension, compression or shear depending upon the application.

Often, the best approach is to only show the type and sizes of the weld required and leave the details for the specific weld geometry to the fabricator.

When considering design options, note that the most significant factor in the cost of a weld is the volume of the weld material that is deposited. Oversizing a welded joint is unnecessary and uneconomical. Welds sized in a single pass are preferred because the welds are most economical and least susceptible to resultant flaws. The maximum weld size for a single pass fillet weld applicable to all weld types is 5/16 in. The AWS D1.1 Structural Welding Code, Table 3.7, provides more specific maximum single pass fillet weld sizes for various welding processes and positions of welding. Design the weld economically, but the minimum weld size is ¼ in. and, in no case, less than the requirements of LRFD Article 6.13.3.4 and/or AWS D1.5, Table 2.1, for the thicker of the two parts joined. Show the weld terminations.



Figure 15.6 — WELDING SYMBOLS



The following types of welds are prohibited:

• Field welded girder splices • Intersecting welds • Intermittent fillet welds • Partial penetration groove welds (except for the connection of tubular members in hand

rails) Review the accessibility of welded joints to assure constructability. Provide sufficient clearance to allow placement of the welding rod at the joint. Often, a large scale sketch or an isometric drawing of the joint reveals difficulties in welding or where critical weld stresses must be investigated.

15.7.3 Field Splices


Do not use welded field splices.

In general, locate field splices in main girders at low stress areas and near the points of dead load contraflexure for continuous spans. Long spans can require field splices located in higher moment areas.

Calculate design loads for bolts by an elastic method of analysis. Provide at least two lines of bolts on each side of the web splice and four lines in flange splices. Do not place shear studs on splice plates.

Locate field splices such that the maximum shipping width for a horizontally curved girder is 10 ft within a single field section.

FEBRUARY 2015

BRIDGE DECKS



Bridge Decks 16-i

TABLE OF CONTENTS

16.1 DECK PROTECTIVE MEASURES ............................................................................ 16-1

16.1.1 Reinforcing Corrosion Protection ................................................................. 16-1

Epoxy Coated ............................................................................ 16-1 16.1.1.1 Galvanized ................................................................................. 16-1 16.1.1.2 Stainless Steel ........................................................................... 16-1 16.1.1.3 Fiber Reinforced Polymer .......................................................... 16-2 16.1.1.4 Cathodic Protection ................................................................... 16-2 16.1.1.5

16.1.2 Prestressing Strand ..................................................................................... 16-2 16.1.3 Healer/Sealers or HMWMs .......................................................................... 16-2 16.1.4 Deck Overlay Systems ................................................................................ 16-2

Thin Bonded Polymer Overlay ................................................... 16-3 16.1.4.1 Polyester Polymer Concrete Overlay ......................................... 16-3 16.1.4.2 Concrete Overlays ..................................................................... 16-3 16.1.4.3 Waterproof Membrane/Asphalt Overlay ..................................... 16-4 16.1.4.4

16.2 DESIGN DETAILS ..................................................................................................... 16-4

16.2.1 Empirical Deck Design ................................................................................ 16-4 16.2.2 Traditional Design Using the Strip Method .................................................. 16-5 16.2.3 Cast-In-Place Decks .................................................................................... 16-5 16.2.4 Full Depth Precast Deck Panels .................................................................. 16-6

Post-Tensioning ......................................................................... 16-6 16.2.4.1 Lap Splices and Closure Pours ................................................. 16-7 16.2.4.2 Alternative Details ...................................................................... 16-7 16.2.4.3

16.2.5 Screed Deflections ...................................................................................... 16-7 16.2.6 Deck Haunches ........................................................................................... 16-7

Haunch Dimensions for Steel Girders........................................ 16-8 16.2.6.1 Haunch Dimensions for Precast Concrete Girders .................... 16-8 16.2.6.2 Reinforcing for Deep Haunches ................................................. 16-8 16.2.6.3

16.2.7 Stay in Place Forms .................................................................................... 16-8 16.2.8 Skewed Decks ............................................................................................. 16-10 16.2.9 Deck Pouring Sequence for Composite Bridge Decks ................................ 16-10 16.2.10 Full Depth Precast Deck Panel Placing Sequence ...................................... 16-12 16.2.11 Transverse Construction Joints ................................................................... 16-12 16.2.12 Longitudinal Construction Joints .................................................................. 16-12 16.2.13 Longitudinal Deck Joints .............................................................................. 16-14 16.2.14 Transverse Edge Beam ............................................................................... 16-14 16.2.15 Deck Overhang/Bridge Parapet ................................................................... 16-14

Overhang Width and Thickness ................................................. 16-14 16.2.15.1 Construction ............................................................................... 16-14 16.2.15.2


16-ii Bridge Decks

Structural/Performance Design of Bridge Parapet ..................... 16-16 16.2.15.3 Parapet Joints ............................................................................ 16-16 16.2.15.4

16.3 PEDESTRIAN BRIDGE DECKS ............................................................................... 16-17 16.4 APPROACH SLABS ................................................................................................. 16-17 16.5 DECK DRAINAGE ..................................................................................................... 16-17

16.5.1 Drainage System Design and Coordination ................................................ 16-17

Structural Engineer/Hydraulics Engineer ................................... 16-17 16.5.1.1 Structural Engineer/Roadway Designer ..................................... 16-18 16.5.1.2 Structural Engineer/Environmental Services Division ................ 16-18 16.5.1.3

16.5.2 Drainage Systems ....................................................................................... 16-18 16.5.3 Deck Drainage Design Elements ................................................................. 16-19

Deck Slope ................................................................................ 16-19 16.5.3.1 Sag Vertical Curves ................................................................... 16-19 16.5.3.2 Superelevation Transitions ........................................................ 16-19 16.5.3.3 Inlets/Downspouts/Pipes ........................................................... 16-19 16.5.3.4 Structural Considerations .......................................................... 16-20 16.5.3.5 Maintenance Considerations ..................................................... 16-21 16.5.3.6

16.6 BRIDGE DECK APPURTENANCES ......................................................................... 16-21

16.6.1 Bridge Parapets ........................................................................................... 16-21

Test Levels ................................................................................ 16-21 16.6.1.1 Bridge Parapet Types/Usage ..................................................... 16-21 16.6.1.2 Guardrail to Bridge Parapet Transitions..................................... 16-22 16.6.1.3 Bridge Parapet/Sidewalk ........................................................... 16-22 16.6.1.4

16.6.2 Protective Fencing ....................................................................................... 16-22 16.6.3 Utility Attachments ....................................................................................... 16-22 16.6.4 Sign Attachments/Luminaire/Traffic Signal/Underdeck Lighting Attachments16-22

LIST OF FIGURES

Figure 16.1 — HAUNCH DIMENSION FOR STEEL PLATE GIRDERS ............................. 16-9 Figure 16.2 — HAUNCH DIMENSION FOR CONCRETE I-GIRDERS ............................... 16-9 Figure 16.3 — HAUNCH REINFORCING ........................................................................... 16-10 Figure 16.4 — DECK POURING SEQUENCE (Continuous Steel Girder with

Potential Uplift at Abutment #1) ................................................................... 16-11 Figure 16.5 — SUPPORT FOR FINISHING MACHINE ...................................................... 16-13 Figure 16.6 — TRANSVERSE EDGE BEAM ...................................................................... 16-15 Figure 16.7 — TYPICAL OVERHANG FORMING SYSTEM (Concrete and

Steel Girders) ............................................................................................... 16-16


Bridge Decks 16-1

Chapter 16 BRIDGE DECKS

Sections 3, 4 and 9 of the LRFD Specifications present design requirements for bridge decks. Section 3 specifies loads, Section 4 specifies the modeling and analysis, and Section 9 specifies bridge deck design. This chapter discusses bridge deck provisions in Sections 3, 4 and 9 of the LFRD Specifications that require amplification or clarification. This chapter also addresses specific practices for the design and detailing of bridge decks. This chapter documents criteria on the design of bridge decks that are constructed compositely in conjunction with concrete or steel girders.

16.1 DECK PROTECTIVE MEASURES

Coat all miscellaneous steel placed in the deck except for hangers, brackets and other accessories used for forming the deck and placed in the bottom half of the deck.

16.1.1 Reinforcing Corrosion Protection

Reference: LRFD Articles 2.5.2.1 and 5.12

Use coated or corrosion resistant reinforcing in the bridge deck, approach slabs and all reinforcing extending into the deck from precast or CIP construction.

Epoxy Coated 16.1.1.1

Epoxy coated reinforcing is effective in increasing the corrosion resistance of reinforcing. The epoxy coating increases development and lap lengths. Damage in the coating can reduce the effectiveness. Field repair or touch up of damaged areas according to project specifications is required.

Galvanized 16.1.1.2

Galvanized reinforcing is effective in increasing the corrosion resistance of reinforcing. Damage in the coating can reduce the effectiveness. Properly applied galvanized coatings are not easily damaged during handling and placement. Field repair or touch up of damaged areas according to project specifications is required.

Stainless Steel 16.1.1.3

Stainless steel reinforcing is corrosion resistant and can improve ductility. The effectiveness is not reduced through chipping or scratching before concrete placement.


16-2 Bridge Decks

Fiber Reinforced Polymer 16.1.1.4

FRP reinforcing is corrosion resistant. Chipping or scratching of FRP reinforcing before concrete placement does not reduce the effectiveness. Field bending is normally not possible, and bends in FRP reinforcing normally reduce the strength. Use a special provision for use of FRP reinforcing, and obtain approval from the Structures Design Manager. ACI 440.R-06 “Guide for the Design and Construction of Structural Concrete Reinforced with FRP Bars” and the AASHTO LRFD Bridge Design Guide Specifications for GFRP-Reinforced Concrete Bridge Decks and Traffic Railings, First Edition, provide information on the use of FRP reinforcing.

Cathodic Protection 16.1.1.5

Cathodic protection can halt the progress of corrosion without the removal of chloride contaminated concrete. Corrosion requires an anode, which is a point on the reinforcing where ions are released. Cathodic protection is either the application of direct current to artificial anodes such that the steel becomes cathodic or the installation of passive sacrificial anodes.

Cathodic protection is seldom used because of several disadvantages, including the need for:

• Expertise in design and construction • Periodic adjustment and maintenance • Power requirement For more information, see the AASHTO Guide Specifications for Cathodic Protection of Concrete Bridge Decks, 1994, AASHTO Task Force 29.

16.1.2 Prestressing Strand

Uncoated prestressing strand in partial depth deck panels is permitted. Uncoated prestressing strand in full depth panels is permitted when the prestressing strand is only secondary reinforcement to limit panel cracking during shipping and handling. Uncoated strand in the cast-in-place portion of decks is not permitted.

16.1.3 Healer/Sealers or HMWMs

One method of slowing the entry of chloride ions into concrete is by sealing the concrete surface. Healer/sealers or HMWMs have a service life of 3 to 5 years but are a low cost preventive maintenance alternative for sound decks. The entire surface is treated and applied as recommended by the manufacturer.

16.1.4 Deck Overlay Systems

Deck overlay systems provide additional deck protection and corrosion protection. Use initial overlays on all bridges except for bridges using stainless steel reinforcing or FRP reinforcing in the deck. Thin bonded polymer overlays are standard for typical bridges. Research indicates


Bridge Decks 16-3

that the life and performance of the overlay is more dependent on the surface preparation and contractor skill than with the actual type of overlay. Coordinate with the Structures Design Manager to determine the appropriate overlay system.

All overlay systems have limited lifespans and require replacement throughout the life of the structure.

Account for the dead load of the system in design. The standard FWS load defined in Section 11.2.2 typically controls the design. Verify that the system chosen does not exceed the design FWS load. If the design FWS is exceeded, recheck the system with the increased weight.

Thin Bonded Polymer Overlay 16.1.4.1

A thin bonded polymer overlay is a two part polymer resin system applied as a wearing surface and saturated with a broadcast aggregate before it cures. The minimum thickness is ⅜ in. Use a thin bonded polymer Type I overlay for interstate bridges and a Type II overlay for noninterstate bridges. Extend the overlay to include approach slabs.

Polyester Polymer Concrete Overlay 16.1.4.2

PPC is a combination of a polymer resin (polyester/styrene) and well graded durable aggregates. Unlike concrete overlays, polymer overlays provide a waterproof barrier. The minimum thickness is ¾ in. but can vary from ¾ in. to 12 in. A high molecular weight methacrylate (HMWM) primer is needed to keep the polyester/styrene resin from contacting the alkaline concrete deck. The primer also seals any cracks in the deck.

Traffic can be placed on the overlay usually on the same day of construction. Provide a special provision when specifying polyester polymer concrete overlays.

Concrete Overlays 16.1.4.3

Concrete overlays are typically used on bridges where the deck cannot be replaced. Typical structures using concrete overlays include precast segmental boxes, CIP segmental boxes and CIP boxes. Numerous types of concrete overlays are available — low slump high density concrete (LSDC), latex modified concrete (LMC), microsilica modified concrete (MMC) and fiber reinforced concrete (FRC). All properly applied concrete overlays provide a durable, smooth and economical riding surface that is resistant to chloride penetration and delamination. Provide a special provision when specifying concrete overlays. Concrete overlays require approval from the Structures Design Manager.

16.1.4.3.1 Low Slump High Density Concrete

Typically, the permeability is greater than MMC and less than normal concrete mixes. The strength is typically similar to MMC and greater than normal concrete.


16-4 Bridge Decks

16.1.4.3.2 Latex Modified Concrete

Rapid set latex modified concretes are available to reduce cure time. Typically, the permeability is greater than MMC and less than normal concrete mixes. The strength is typically less than MMC and equal to normal concrete.

16.1.4.3.3 Microsilica Modified Concrete

Microsilica is a pozzolanic material that is much finer than cement particles, which allows the material to produce a denser matrix. One of the biggest advantages of a MMC overlay is the reduced permeability to chloride penetration. MMC also enhances compressive strength. Although MMC is highly resistant to chloride penetration, the permeability of MMC also depends on the quality of construction and proper curing of the deck. Shrinkage cracking is the most common problem. Durability is sensitive to evaporation rates after placement.

Due to curing and quality concerns, do not use MMC unless approved by the Structures Design Manager.

16.1.4.3.4 Fiber Reinforced Concrete

FRC overlays provide the highest tensile strength of all concrete overlay systems. Compressive strength and permeability are similar to normal concrete.

Waterproof Membrane/Asphalt Overlay 16.1.4.4

Waterproof membranes with asphalt overlays are not typically used on new bridges. Visual inspection of a bridge deck covered with asphalt is impossible. The overlay adds dead load to the bridge, which can reduce live load capacity, and the overlay traps moisture in the concrete further aggravating corrosion of the slab reinforcing. However, on certain bridges such as side by side box girders, a waterproof membrane with asphalt overlay has demonstrated better performance than concrete or polymer overlays. The concrete and polymer overlays have developed cracking at the joints between the box girders due to the differential movement of the boxes. Refer to Section 2.7.3 for additional information on asphalt overlays.

16.2 DESIGN DETAILS

16.2.1 Empirical Deck Design


Use the modified empirical deck design as defined in the SD drawings for all new full depth, CIP decks. The modified empirical design requires a thicker deck for wider girder spacing and increases the required reinforcing.


Bridge Decks 16-5

Evaluate stresses in CIP decks on bridges moved into place, and increase deck reinforcing as required according to the analysis results.

16.2.2 Traditional Design Using the Strip Method

Reference: LRFD Articles 9.7.3, 4.6.2.1.1, 4.6.2.1.3 and Appendix A4

Use the traditional deck design using the strip method based on LRFD Articles 9.7.3 and 4.6.2.1 for deck design using precast elements.

Apply the strip method to concrete decks using the design table for deck slabs in the Appendix to Section 4 of the LRFD Specifications (LRFD Table A4-1). An introduction to the LRFD table discusses the application and the inherent assumptions.

Apply LRFD Table A4-1 to design the concrete deck reinforcing. LRFD Table A4-1 tabulates the resultant live load moments based on the unit width for reinforcing design as a function of the girder or web spacings, S. The table distinguishes between positive moments and negative moments and tabulates negative moments for various design sections as a function of the distance from the girder or web centerline to the design section. LRFD Article 4.6.2.1.6 specifies the design sections.

16.2.3 Cast-In-Place Decks

The following criteria apply to composite bridge decks:

1. Thickness. The minimum thickness is 8 in. Refer to the SD drawings for minimum thicknesses based on the girder spacing.

2. Cover. Refer to the SD drawings for cover requirements.

3. Steel Reinforcing Strength. Use fy equal to the yield strength of the reinforcing used, but not greater than 60 ksi for deck design checks. Use fy equal to the yield strength of the reinforcing used, but not greater than 90 ksi for composite girder strength design checks where the longitudinal deck reinforcing is part of the structural system and when the following conditions are met:

• All deck reinforcing is the same grade. • Service load checks using fy equal to the yield strength of the reinforcing used

but not greater than 60 ksi do not control the girder design. • Minimum reinforcing requirements defined in the LRFD Specifications are met. • Minimum reinforcing requirements defined in Chapter 15 are met. • The Structures Design Manager has approved the use of higher reinforcing

strengths for design or the deck reinforcing is ASTM A955 Grade 75 or ASTM A706 Grade 80.

4. Exposure Condition. Use a Class 2 exposure factor in LRFD Equation 5.7.3.4-1 for all bridge decks.


16-6 Bridge Decks

5. Placement of Top and Bottom Transverse Reinforcing. Offset the top and bottom transverse reinforcing, preferably at half the spacing. Do not place the top mat directly above the bottom mat.

6. Reinforcing Size. The minimum longitudinal and transverse reinforcing is #4 reinforcing. The maximum transverse reinforcing is #6 reinforcing. The maximum longitudinal reinforcing in negative moment regions requiring continuity reinforcing is #8 reinforcing; elsewhere, use #6 reinforcing.

7. Sacrificial Wearing Surface. The top reinforcing concrete cover includes a ½-in. sacrificial wearing surface. For both the deck and superstructure, include the sacrificial wearing surface weight as a dead load, but do not include the structural contribution in the structural design.

8. Placement of Transverse Reinforcing on Skewed Bridges. The following applies:

• Skews ≤ 20°: Place the transverse reinforcing parallel to the skew. • Skews > 20°: Place the transverse reinforcing perpendicular to the longitudinal

reinforcing.

See Section 16.2.8 for a definition of skew angle and for structural considerations related to skewed reinforcing placement.

9. Shear Connectors. Use stirrups or shear studs extending from concrete girders and shear studs extending from steel girders over the full length of the girders. Extend shear connectors at least 2 in. into the deck not including the haunch. See Section 15.6.2 for more discussion on shear connectors.

10. Precast Concrete Deck Panel – Half Depth. Use of stay in place, precast concrete partial depth panel forms is permitted. Use the panels defined on the WS sheets for panel lengths up to 11′-6″. Precast partial depth panel lengths larger than 11′-6″ are not permitted.

16.2.4 Full Depth Precast Deck Panels

The minimum thickness is 8¾ in. Refer to the SD drawings for design details. Provide a connection between panels either by post-tensioning or with lap splices with a closure pour or alternative details providing reinforcing across the joint. Make all panels composite with the girders.

Post-Tensioning 16.2.4.1

The effects of creep from post-tensioned decks on girders is difficult to quantify. According to PCI recommendations, ignore the losses in post-tensioning associated with panel creep restrained by the girders. The deck/girder interaction tends to restrain the creep while also transferring post-tensioning force into the girder. Research and numerical analysis demonstrate losses in deck compression due to creep. Research also suggests that the 0.25-ksi


Bridge Decks 16-7

compression requirement of LRFD Article 9.7.5.3 could be conservative. Creep in the new deck system can transmit forces into the girder system. The increase in stress in the girder is typically small. Structural engineers concerned with the increase in girder stress can estimate the effects of creep using a procedure similar to the procedure defined in LRFD Article C4.6.6, which discusses the effects of temperature differential across a structural system. Replace the temperature differential terms with the creep differential.

Design the post-tensioning system to provide a minimum 0.25 ksi across the joint after all losses except losses due to restraint of creep. Post-tension the system before grouting the haunch and filling the shear stud blockouts.

Lap Splices and Closure Pours 16.2.4.2

Design lap splices according to the LRFD Specifications. When sizing the closure pour width, consider the panel size tolerance and layout tolerance. Use a closure pour at least 3 in. larger than the required splice length.

Alternative Details 16.2.4.3

A variety of methods to connect full depth precast deck panels are available. Do not use details relying on a shear key alone. Methods using dropped in lapped bars are permitted.

16.2.5 Screed Deflections

Ignore the future wearing surface when calculating screed deflections, unless the future wearing surface is placed on the bridge during initial construction.

Do not use the long term multipliers when listing screed deflections on prestressed girder bridges. Evaluate the impacts of phased construction on the screed deflections. See Section 14.6.4 for more discussion on deflections.

Calculate screed deflections based on the defined pour sequence. Evaluate the impacts of pouring the entire deck in a single pour during design. Use this information when reviewing contractor requests for alternative pour sequences.

16.2.6 Deck Haunches

Haunches consist of concrete between the top of a steel flange or concrete girder and the bottom of the bridge deck. Haunches account for construction variations, tolerances and beam camber. The haunch varies across the width of the flange based on the cross slope. The haunch also varies along the length of the girder due to flange thickness variation, camber variation and roadway profile.

Refer to the SD drawings for a detailed description on how to calculate the required haunch. The haunch thickness calculation is based on providing at least a ¾-in. haunch at the minimum


16-8 Bridge Decks

haunch location for CIP decks and a 1¾-in. haunch at the minimum haunch location for partial or fully precast decks.

Include the girder haunch in the load calculations as dead load by applying the maximum haunch dimension throughout the span; however, ignore the haunch in the calculation of the section resistance.

Define the control dimension, A (see Figures 16.1 and 16.2), at the centerline of bearing. The dimension varies along the span to compensate for variations in camber and superelevation. Detail the haunch flush with the vertical edge of the top flange between girders and at the overhang. See Figures 16.1 and 16.2.

Haunch Dimensions for Steel Girders 16.2.6.1

Figure 16.1 illustrates the controlling factors used to determine the haunch dimension for steel plate girders. Calculate the required haunch using the procedure defined on the SD drawings. When using rolled beams, set the haunch to provide adequate tolerance for geometric effects and beam rolling tolerances.

Haunch Dimensions for Precast Concrete Girders 16.2.6.2

Figure 16.2 illustrates the controlling factors used to determine the haunch dimension for precast concrete girders. Calculate the haunch using the procedure defined on the SD drawings.

Reinforcing for Deep Haunches 16.2.6.3

Provide additional reinforcing in haunches when H is greater than 4.0 in. on concrete girders and when (H – TFT) is greater than 4.0 in. on steel girders, where TFT is the top flange thickness in inches. For the additional reinforcing, provide a minimum of #4 reinforcing spaced at a maximum of 12 in. Provide a minimum horizontal length of 12 in. on each end of the bar in the deck. See Figure 16.3.

16.2.7 Stay in Place Forms

Do not use stay in place metal forms. Use of stay in place precast concrete deck forms is permitted. Refer to the WS sheets for standard panels.


Bridge Decks 16-9

Figure 16.1 — HAUNCH DIMENSION FOR STEEL PLATE GIRDERS

Figure 16.2 — HAUNCH DIMENSION FOR CONCRETE I-GIRDERS


16-10 Bridge Decks

Figure 16.3 — HAUNCH REINFORCING 16.2.8 Skewed Decks


Skew is defined as the angle between the alignment crossed and a line normal to the alignment carried by the structure. See Section 10.4.6. A crossing angle less than 90° equates to a left skew. A crossing angle greater than 90° equates to a right skew.

The LRFD Specifications suggest that the effects of skew angles not exceeding 25° can be neglected for concrete decks, but the LRFD Specifications assume the typical case of bridges with relatively large span length to bridge width ratios. Further, the commentary indicates that the 25° limit is “somewhat arbitrary.” Therefore, use a 20° threshold for the consideration of skew in reinforcing detailing. See Section 16.2.3.

16.2.9 Deck Pouring Sequence for Composite Bridge Decks


Include a deck pouring sequence for all CIP concrete decks. Determine the pouring sequence to avoid or minimize the dead load tensile stresses in the slab caused by the pouring sequence. The pour sequence must also account for rotation of the girders at supports. Arrange the sequence to cause the least disturbance to the portions poured previously. Typically, the positive moment regions are placed before the negative moment regions and the integral diaphragms are placed last to permit girder rotation. The default pouring direction is uphill. The negative moment regions for steel girders extend between the points of dead load contraflexure. For precast concrete girders, use a minimum of 15 ft on each side of the center of support or 20% of the span length, whichever is greater.


Bridge Decks 16-11

Allow the contractor to combine pours for integral abutments and integral bent diaphragms with the deck pours when the diaphragm pours remain plastic during the deck pour or when the diaphragm is placed immediately following the deck pour.

In continuous steel girder bridges, the pouring sequence changes the stresses when compared to stresses associated with the instantaneous placement typically assumed in design. The pouring sequence can also change the required girder camber and screed deflections. Consider the pouring sequence in the design of the girders. Typically, the plans permit combining all pours into a single pour. Verify that the girder design, camber and screed deflections are compatible with a single continuous pour. If not, place a note on the plan sheet indicating that the pouring sequence cannot be altered without also modifying the girder camber, the screed deflections and verifying the design.

Figure 16.4 illustrates a sample pouring sequence diagram for a continuous bridge with potential uplift at abutment 1. In this example, minimal rotation exists at abutment 1 and the girder, diaphragm and abutment were designed to account for the restraint loads and, by placing the end diaphragm first, the potential for uplift is eliminated.

Figure 16.4 — DECK POURING SEQUENCE

(Continuous Steel Girder with Potential Uplift at Abutment #1)


16-12 Bridge Decks

16.2.10 Full Depth Precast Deck Panel Placing Sequence

Provide a placing sequence for full depth precast deck panel. Also, provide a construction sequence for all activities associated with placing and connecting the panels to each other and the girder.

16.2.11 Transverse Construction Joints

Place transverse construction joints parallel to the skew. Do not place the joints over girder field splices.

16.2.12 Longitudinal Construction Joints

Avoid longitudinal construction joints in bridge decks. Only use longitudinal construction joints when unavoidable (e.g., widenings, phased construction, very wide structures). The following applies to longitudinal construction joints.

For deck widths greater than 120 ft (i.e., where the finishing machine span width must exceed 120 ft), make provisions to permit placing the deck in practical widths If a longitudinal construction joint is necessary, avoid locating the joint underneath a wheel line. Closure pours are not required but can be useful for phased construction projects. A closure pour serves two useful purposes:

• Defers final connection of the phases until after the deflection from deck slab weight has occurred

• Provides the width needed to provide a smooth transition between differences in final grades that result from differential deflection between the phases

When a closure pour is used, the following applies:

• Use a minimum closure pour width of 3 ft. • Locate lap splices in the transverse reinforcing within the longitudinal closure pour.

Allow transverse shrinkage of the deck concrete to occur by leaving the joint open as long as the construction schedule permits.

• Do not tie contact lap splices or couple reinforcing between different phases until placing adjacent phases of the deck.

• Consider the deflections of the bridge on either side of the closure pour to ensure proper transverse fit up.

• Do not rigidly connect diaphragms/cross frames in the closure pour bay of structural steel girders or prestressed concrete girders until after placing adjacent phases of the deck. If concrete diaphragms are used for prestressed girders, construct the concrete diaphragms in the closure pour bay of prestressed concrete girders after adjacent portions of the bridge are complete. Pour the diaphragms as part of the closure pour.


Bridge Decks 16-13

• Support the finishing machine on an overhang jack connected to the girder loaded by the deck pour. Do not place one edge of the finishing machine on a previously poured deck. Indicate in the plan sheets or the project specifications that this method of constructing the closure pour is not allowed. See Figure 16.5.

Figure 16.5 — SUPPORT FOR FINISHING MACHINE All structures deflect and vibrate when subjected to live loading, and many bridges with staged construction or bridge widenings are constructed with traffic on the previously constructed or existing structure. Fresh concrete in the deck is subjected to deflections and vibrations caused by traffic. Studies such as NCHRP 86 Effects of Traffic-Induced Vibrations on Bridge-Deck Repairs have shown that:

• Good quality reinforced concrete is not adversely affected by jarring and vibrations of low frequency and amplitude during the period of setting and early strength development.

• Traffic induced vibrations do not cause relative movement between fresh concrete and embedded reinforcing.

• Investigations of the condition of widened bridges have shown that the performance of attached widenings, with and without the use of a closure pour placed under traffic, is satisfactory.


16-14 Bridge Decks

16.2.13 Longitudinal Deck Joints


Do not use open longitudinal joints. Obtain approval from the Structures Design Manager for a specific case where a longitudinal joint provides a benefit.

16.2.14 Transverse Edge Beam


Provide a transverse edge beam to support wheel loads near the transverse edge of deck when the deck is not supported by an integral concrete diaphragm. See Figure 16.6 for a steel girder example. Prestressed girders also require an edge beam when the deck is not supported by an integral concrete diaphragm.

16.2.15 Deck Overhang/Bridge Parapet


Overhang Width and Thickness

The deck overhang is the distance between the centerline of the exterior girder to the outside edge of deck. The overhang width for a balanced design in a girder bridge is approximately 30% of the girder spacing. Typical overhang widths are less than 40% of the girder spacing for I-girders and less than 50% for box girders. The maximum overhang width is 5.5 ft. The thickness of the overhang is constant and matches the deck thickness between girders.

Refer to Section 15.1.2 for additional information.

Construction

During construction, overhang jacks are connected to the girder at the top flange and braced against the web or bottom flange. The overhang and construction loads can result in lateral distortion of the bottom flange and web of the girder. Strut B in Figure 16.7 is required at a minimum 8-ft spacing unless the contractor provides calculations demonstrating that displacements in the deck forming is accounted for and that the stresses do not exceed limits defined in the LRFD Specifications.

Refer to the SD drawings for girder design loads associated with overhang jacks.


Bridge Decks 16-15

Figure 16.6 — TRANSVERSE EDGE BEAM


16-16 Bridge Decks

Figure 16.7 — TYPICAL OVERHANG FORMING SYSTEM (Concrete and Steel Girders)

Structural/Performance Design of Bridge Parapet 16.2.15.3

Reference: LRFD Articles 13.6.1, 13.6.2 and 13.7.2

Use the barriers defined in the WS sheets. The WS sheets for bridge parapets meet the structural design requirements to sustain TL-2 and TL-4 collision forces in LRFD Article A13.2. The SD drawings list the minimum deck thickness and deck moment capacity required at the face of the barrier in the deck. Check the deck overhang at the girder according to AASHTO requirements.

Parapet Joints 16.2.15.4

Provide joints in parapets and curbs at expansion joint locations. Extend the expansion joint seal or hardware up into the barrier at least 12 in. or to the top of curbs. Provide joints in the barrier over bents. Use the Type D detail defined in the WS sheets. Consider additional Type D joints on spans over 200 ft.


Bridge Decks 16-17

16.3 PEDESTRIAN BRIDGE DECKS

Pedestrian bridges and bridge decks are discussed in Chapter 22. Refer to Section 22.6.2.6 for specific deck requirements.

16.4 APPROACH SLABS

Approach slabs are an extension of the deck used to transition from the bridge to the roadway. The minimum approach slab length is 25 ft. Provide approach slabs and sleeper slabs on all bridges. Use the approach slab design defined in the WS sheets for standard approach slabs. Longer approach slabs require a project specific design. The WS sheets also represent the minimum required reinforcing for approach slabs of any length.

16.5 DECK DRAINAGE


The bridge deck drainage system includes the bridge deck, sidewalks, parapets, gutters and inlets. The primary objective of the drainage system is to remove runoff from the bridge deck before it collects in the gutter to a point that exceeds the allowable design spread (typically, the design year runoff water must be restricted to the shoulder portion of the deck) and to eliminate or minimize water flowing over expansion joints. Proper bridge deck drainage provides many other benefits, including:

• Efficiently removing water from the bridge deck to enhance public safety by decreasing the risk of hydroplaning

• Enhancing long term maintenance of the bridge • Preserving the structural integrity of the bridge • Enhancing aesthetics (e.g., the avoidance of staining substructure and superstructure

members) • Reducing erosion on bridge end slopes 16.5.1 Drainage System Design and Coordination

Structural Engineer/Hydraulics Engineer 16.5.1.1

The hydraulics engineer:

• Calculates the flow of water on the deck based on the design frequency • Determines if a free falling or piped drainage system is required


16-18 Bridge Decks

• Determines the hydraulic inlet spacing and size of inlets on the bridge deck to intercept the calculated flow to meet the allowable water spread criteria and deck drain size limitations provided by the structural engineer

• Eliminates deck drains when possible The structural engineer evaluates the impacts of the proposed bridge deck drainage design on the structural design of the bridge. The potential impacts include:

• Location of downspouts with respect to structural elements • Compatibility of deck reinforcing with inlet location, spacing and size • Providing a piped drainage design underneath the bridge After the structural engineer and hydraulics engineer have identified the final design details, the structural engineer incorporates the drainage design information into the structural design of the bridge and designs the deck drains, pipes, cleanouts, support system and outlets according to Section 16.5.3.

Structural Engineer/Roadway Designer 16.5.1.2

The roadway designer is responsible for the roadway profiles and drainage design for any runoff approaching or leaving the bridge deck. Refer to Section 16.5.3 for drainage related criteria for the roadway profile. Refer to the WS sheets for standard approach slab drains and grates.

At a minimum, provide approach slab drains at all locations where runoff flows from the approach slab to the roadway section, and verify that roadway drains are provided at all locations where runoff flows from the roadway section to the approach slab.

Structural Engineer/Environmental Services Division 16.5.1.3

The structural engineer coordinates with the Environmental Services Division to ensure that the proposed disposal of bridge deck water meets all project environmental requirements. For example, requirements include applicable best management practices for erosion control and the impact of water disposal on water quality requirements.

16.5.2 Drainage Systems

Use a free falling drainage system when all of the following are satisfied:

• The free falling discharge is not over travel lanes, shoulders, bicycle facilities or sidewalks beneath a bridge and does not cause any erosion below.

• The free falling discharge does not fall or blow onto substructure elements. • The free falling discharge does not free fall over the traveled way portion of an

underpassing highway, sidewalk or erodible embankment.


Bridge Decks 16-19

Use a piped system when a free falling system is not permitted. A piped system delivers deck drainage to an underdeck drainage system that is sized for the flow and meets environmental requirements. Typically, the drainage is routed to the roadway storm drain system. Do not run the drain pipe inside structural elements.

16.5.3 Deck Drainage Design Elements

Deck Slope 16.5.3.1

Proper deck drainage requires a minimum profile grade of 0.5%. For crest vertical curves, an average profile grade from the high point to the ends of the bridge of 0.5% typically provides adequate drainage. When the average is less than 0.5%, coordinate with the roadway designer to determine if the vertical curve can be adjusted. In locations where the vertical curve cannot be adjusted, provide drains at a 50-ft spacing. Evaluate the potential for ponding due to flat profiles and residual camber or long term deflections. Adjust the profile or provide deck drains when potential ponding is identified.

Sag Vertical Curves 16.5.3.2

Coordinate with the roadway designer and relocate low points in sag vertical curves off the bridge. When a relative low point cannot be relocated off the bridge, provide deck drains at the low point to collect and remove the drainage.

Superelevation Transitions 16.5.3.3

Coordinate with the roadway designer and move superelevation transitions off the bridge where possible. If a superelevation transition is located on the bridge, check for low points due to the superelevation transition causing the edge of deck to rise faster than a vertical curve or vertical slope. When the low point is located on the bridge, provide a deck drain to collect and remove the drainage.

Inlets/Downspouts/Pipes 16.5.3.4

Use a rigid steel pipe for downspouts, pipes and cleanouts, either galvanized or painted, with a diameter not less than 6 in. (preferably 8 in.) and a minimum wall thickness of ⅛ in. Provide cleanouts at each turn in the pipe and every 100 ft, where practical.

Consider the following when locating inlets and downspouts:

1. Location With Respect To Structural Elements. Extend freefall downspouts a minimum of 6 in. below structural elements. Do not locate freefall downspouts within 5 ft of the end of any substructure unit or where water could easily blow over and run down a substructure element. Downspouts must not encroach upon the required vertical or horizontal clearances.


16-20 Bridge Decks

2. Location With Respect To Ground. A free fall exceeding 25 ft sufficiently disperses the falling water so that minimal erosion damage occurs beneath the bridge. Where less than 25 ft of free fall is available, coordinate with the roadway designer to provide erosion protection on natural ground beneath the outlet. Free falls of less than 25 ft are acceptable where the water free falls onto slope paving, riprap or flowing water.

Use the following guidelines for underdeck piping:

1. Aesthetics. Avoid piping exposed to view, which detracts from the appearance of the structure.

2. Hydraulic Design. For multiple inlets, flat horizontal slopes or runs of 50 ft or more, 8-in. piping is preferred. Design the runs with as steep a grade as conditions allow with a maximum of 4 inlets per run. Locate inlets upgrade from the bent or abutment outlets when possible. Design all bends to be smooth and on an 18-in. minimum radius for 6-in. diameter pipe and a 24-in. minimum radius for 8-in. diameter pipe. Do not use mitered bends. Minimize the length of horizontal (i.e., 2% minimum) runs.

3. Expansion Joints. Show expansion couplings on the plans where drain pipes cross expansion joints at hinges and abutments.

4. Cleanout Openings. When the piping system consists of a single run from inlet to outlet, maintenance personnel usually clean from the outlet end with a power driven plumber’s auger. For this situation, do not use a cleanout opening because the opening could result in a blind alley for the auger and make cleaning from the outlet impossible. For a more complex piping system, properly placed cleanout openings can facilitate cleaning by providing additional access points in the line.

Structural Considerations 16.5.3.5

Inlet sizing and placement must be compatible with the structural reinforcing and other components of a bridge deck. Evaluate the inlet size and provide additional reinforcing or slab thickness if required.

Design the drainage system to deter runoff from contacting vulnerable structural members and to minimize the potential for eroding embankments.

The structural considerations for a piped system include:

1. Expansion, Deflection and Rotation. Provide special attention to where drainage pipes cross points of expansion or where the superstructure is more flexible than the substructure. Where horizontal pipes cross a point of expansion, the pipe must be capable of expanding, contracting and deflecting with thermal movements of the bridge. Provide pipe expansion joints when required. When the superstructure is flexible compared to the substructure, a vertical pipe must have some flexibility to account for structure rotation.


Bridge Decks 16-21

2. Pipe Supports. Support pipes from the deck or cross frames. Use pipe hangers with rollers and vertical adjustment capability to facilitate erection of the pipe and to set the proper pipe grade. The maximum spacing of hangers is 25 ft but no longer than that required by design. Assume that the pipe is full of water when designing hanger spacings.

Maintenance Considerations 16.5.3.6

Provide easy access, adequate space and safe working conditions for maintenance to maintain the drainage features of the bridge.

Daylight outlets above the ground to provide access for back flushing, rodding or air pressure cleaning equipment.

16.6 BRIDGE DECK APPURTENANCES

16.6.1 Bridge Parapets


Test Levels 16.6.1.1

LRFD Article 13.7.2 identifies six test levels for bridge parapets, adopted from NCHRP 350 Recommended Procedures for the Safety Performance Evaluation of Highway Features and the AASHTO Manual for Assessing Safety Hardware (MASH). TL-1 and TL-2 are typically used in work zones in Utah. UDOT parapets meet the performance criteria for TL-4. Coordinate with the Structures Design Manager if a TL-5 or TL-6 barrier is required.

Bridge Parapet Types/Usage 16.6.1.2

The following identifies typical parapet usage:

1. 42-in. Concrete Single Slope Parapet. Use on new and replaced bridge parapet installations on state highways. The single slope parapet meets the TL-4 performance criteria. Refer to the WS sheets for parapet details. The minimum deck reinforcing at the face of the 42-in. single slope parapet must provide a minimum nominal moment capacity, Mr, greater or equal to:

• 14.5 kip-ft/ft at parapet interior sections (parapet reinforcing into the deck of #4 at 12 in.) or end sections (parapet reinforcing into the deck of #4 at 4 in.) supported by an integral end diaphragm

• 43.0 kip-ft/ft at end sections (parapet reinforcing into the deck of #4 at 4 in.) not supported by an integral end diaphragm


16-22 Bridge Decks

Mr limits assume 4.0-ksi parapet concrete. Revise limit if higher strength concrete is used. The 42-in. single slope standard parapet has the following properties when cf ′ is 4.0 ksi. Lc = 13.04 ft for an interior section and Lc = 4.33 ft for an end section. Refer to LRFD A13.3.1-2 for information on parapet design capacity.

2. Aesthetic Rail. This is a decorative bridge parapet that meets the TL-4 performance criteria. Use the aesthetic rail when required by the bridge owner. Do not use the aesthetic rail on bridges owned by the state. Refer to the WS sheets for parapet details.

Guardrail to Bridge Parapet Transitions 16.6.1.3

The roadway designer is responsible for any transitions to the bridge parapet. Verify that the transition is addressed in the roadway plans.

Bridge Parapet/Sidewalk 16.6.1.4

Reference: LRFD Articles 13.4 and 13.7.1.1

The roadway designer determines the roadway typical section and the need for a sidewalk on a bridge. Refer to the DD series in the UDOT Standard Drawings for more information on required sidewalk and parapet geometry. Refer to the WS sheets for typical parapet and sidewalk details.

16.6.2 Protective Fencing

Use protective fencing across bridges when protection to facilities adjacent to or beneath the structure is warranted. Fencing is typically required for:

• All overpasses with sidewalks • All overpasses over railroads Protective fencing can be considered at other locations on a case by case basis. Use the fencing details on the WS sheets.

16.6.3 Utility Attachments

See Section 2.8.

16.6.4 Sign Attachments/Luminaire/Traffic Signal/Underdeck Lighting

Attachments

If the traffic and safety engineer proposes to attach a sign to a bridge, the traffic and safety engineer must coordinate with the structural engineer, who assesses the structural impact on the bridge. If the sign attachment is approved, the structural engineer designs the attachment


Bridge Decks 16-23

details. See Section 2.2.3 for additional information. Attachment of guide signs to bridges is typically not permitted.

The traffic and safety engineer determines the need for traffic signals and highway lighting on or under a bridge. The traffic and safety engineer performs the design work to determine the type, size and location of the luminaires or signals and the provision of electricity. The structural engineer designs the structural support details for the luminaire and/or traffic signal that is attached to the bridge.


16-24 Bridge Decks

FEBRUARY 2015

FOUNDATIONS



Foundations 17-i

TABLE OF CONTENTS

17.1 DESIGN ..................................................................................................................... 17-1

17.1.1 Design Methodology .................................................................................... 17-1 17.1.2 Bridge Design/Geotechnical Design Interaction .......................................... 17-1

17.1.2.1 Preliminary Geotechnical Design Recommendations ................ 17-2 17.1.2.2 Geotechnical Report .................................................................. 17-2

17.1.3 Bridge Design/Hydraulic Design Interaction ................................................ 17-4 17.1.4 Total and Differential Settlement ................................................................. 17-4

17.1.4.1 Estimating Settlement ................................................................ 17-4 17.1.4.2 Effects of Foundation Settlement ............................................... 17-6 17.1.4.3 Mitigation of Foundation Settlement .......................................... 17-9

17.2 DRIVEN PILES .......................................................................................................... 17-9

17.2.1 Pile Types/Selection .................................................................................... 17-9

17.2.1.1 Steel Pipe Piles .......................................................................... 17-9 17.2.1.2 Steel H-Piles .............................................................................. 17-10 17.2.1.3 Prestressed Concrete Piles ....................................................... 17-10 17.2.1.4 Pile Selection ............................................................................. 17-10 17.2.1.5 Pile Capacity Verification ........................................................... 17-11

17.2.2 Design Details ............................................................................................. 17-11

17.2.2.1 Pile Length ................................................................................. 17-11 17.2.2.2 Reinforced Pile Tips ................................................................... 17-11 17.2.2.3 Battered Piles ............................................................................ 17-11

17.2.3 Force Effects ............................................................................................... 17-12

17.2.3.1 Downdrag Loads ........................................................................ 17-12 17.2.3.2 Uplift Forces ............................................................................... 17-12

17.2.4 Piles Placed within Mechanically Stabilized Earth Walls ............................. 17-12

17.3 DRILLED SHAFTS .................................................................................................... 17-13

17.3.1 Usage .......................................................................................................... 17-13 17.3.2 Drilled Shaft Axial Compressive Resistance at the Strength Limit State ..... 17-13 17.3.3 Structural Design ......................................................................................... 17-13 17.3.4 Design Details ............................................................................................. 17-14

17.4 SPREAD FOOTINGS, PILE FOOTINGS AND PILE CAPS ...................................... 17-16


17-ii Foundations

17.4.1 Thickness .................................................................................................... 17-16 17.4.2 Depth ........................................................................................................... 17-16 17.4.3 Joints ........................................................................................................... 17-17 17.4.4 Stepped Footings ........................................................................................ 17-17 17.4.5 Rocking Spread Footings ............................................................................ 17-17 17.4.6 Bearing Resistance and Eccentricity ........................................................... 17-18 17.4.7 Sliding Resistance ....................................................................................... 17-18 17.4.8 Reinforcing .................................................................................................. 17-18

17.5 LATERAL LOADING OF DEEP FOUNDATION ELEMENTS ................................... 17-21

17.5.1 Pile/Drilled Shaft Supported Footings .......................................................... 17-21 17.5.2 Pile/Drilled Shaft Extension Bents ............................................................... 17-21

17.5.2.1 Closed Form Linear Models ....................................................... 17-21 17.5.2.2 Nonlinear Models ....................................................................... 17-23

17.5.3 Minimum Penetration ................................................................................... 17-23

17.6 LIQUEFACTION ........................................................................................................ 17-24

LIST OF FIGURES

Figure 17.1 — ADJACENT SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT ................................................................... 17-6

Figure 17.2 — ADJACENT SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT LIMITS FOR STRUCTURAL CHECKS ..... 17-6

Figure 17.3 — SINGLE SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT LIMITS FOR STRUCTURAL CHECKS ..... 17-7

Figure 17.4 — SINGLE SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT ................................................................... 17-8

Figure 17.5 — DRIVEN PILE SELECTION GUIDE ............................................................. 17-10 Figure 17.6 — DRILLED SHAFT (Socketed in Rock) .......................................................... 17-15 Figure 17.7 — STEPPED FOOTING DETAILS ................................................................... 17-17 Figure 17.8 — EXAMPLE ANALYSIS OF SPREAD FOOTING ON COMPETENT SOIL ... 17-19 Figure 17.9 — EXAMPLE ANALYSIS OF A PILE CAP ....................................................... 17-20 Figure 17.10 — METHOD OF MODELING DEEP FOUNDATION STIFFNESS

(Closed Form Linear Model) ......................................................................... 17-22 Figure 17.11 — METHOD OF MODELING DEEP FOUNDATION STIFFNESS

(Nonlinear Model) ......................................................................................... 17-23 Figure 17.12 — LIQUEFACTION MITIGATION PROCEDURE ............................................. 17-25


Foundations 17-1

Chapter 17 FOUNDATIONS

Section 10 of the LRFD Specifications presents structural design requirements for foundations. This chapter discusses foundation provisions in Section 10 of the LFRD Specifications that require amplification or clarification. This chapter also addresses specific practices for the design and detailing of foundations.

17.1 DESIGN

This chapter provides foundation design information directed to structural engineers. The UDOT Geotechnical Manual of Instruction, which is the responsibility of the Geotechnical Design Division, discusses the geotechnical considerations for bridge foundation type selection and design.

17.1.1 Design Methodology

The LRFD Specifications distinguish between the strength of the in situ materials (soils and rock strata) and the strength of the structural components. The LRFD Specifications address in situ materials in Section 10 and structural components in Sections 5 and 6.

Target safety levels for the geotechnical aspects of each type of foundation are comparable to foundations designed with the AASHTO Standard Specifications for Highway Bridges. The target safety levels for the geotechnical aspects of each type of foundation are not calibrated to the geotechnical aspects used for structural components. Structural components use a common safety level. Due to the unknown nature of in situ materials, the target safety levels are typically higher and rely on past performance instead of significant physical testing used to set structural component safety levels.

17.1.2 Bridge Design/Geotechnical Design Interaction

The primary functions of the foundation are to transfer structure loads to stable ground with adequate bearing resistance and to limit settlement. Structure loads are transferred to the ground through shallow or deep foundations. Shallow foundations use spread footings near the ground surface. Deep foundations use piles or drilled shafts that extend through weak or unstable ground layers to transfer structure loads to a stronger stable subsurface layer through end bearing or to multiple subsurface layers through friction or combined friction and end bearing. Knowledge of the subsurface soil conditions, ground water conditions and scour is necessary to evaluate the strength and stability of the bearing layers.


17-2 Foundations

The geotechnical engineer is responsible for developing a subsurface exploration plan, preparing preliminary geotechnical design recommendations and preparing the Geotechnical Report. Use the information contained in the Geotechnical Report to design bridge foundations and other structures. The successful integration of the geotechnical design recommendations into the bridge design requires close coordination between the geotechnical engineer and the structural engineer.

17.1.2.1 Preliminary Geotechnical Design Recommendations

The preliminary Geotechnical Report provides recommendations based on existing soil information and the preliminary subsurface investigation conducted for the project. The geotechnical engineer and structural engineer use the information to select the bridge foundation and initiate the preliminary structure design. Use the geotechnical recommendations in conjunction with the input of the hydraulics engineer (as applicable) to establish support locations.

Before preliminary bridge design, review the preliminary Geotechnical Report and Structures Foundation Type Memo to gain knowledge of the anticipated soil conditions at the bridge site and the recommended general foundation types. The Structures Foundation Type Memo recommends either shallow or deep foundations. A shallow foundation recommendation provides a preliminary footing elevation, expected allowable bearing pressures and settlement information. A deep foundation recommendation includes pile or drilled shaft sizes, depths, expected capacity and settlement information. Use the Structures Foundation Type Memo to estimate the size of foundation members and to prepare the preliminary bridge design. Collaborate with the geotechnical engineer to refine and revise the recommendations as the design progresses.

17.1.2.2 Geotechnical Report

17.1.2.2.1 Subsurface Exploration

The geotechnical engineer performs a detailed subsurface exploration based on the anticipated bridge abutment/bent locations and anticipated foundation type. The geotechnical engineer determines the proposed boring locations.

Typically, the structural modeling and analysis of the bridge proceed based on the preliminary Structures Foundation Type Memo while the geotechnical engineer finalizes the subsurface exploration and Structures Foundation Type Memo. In the interim, the structural engineer collaborates with the geotechnical engineer to determine preliminary foundation modeling parameters. The structural engineer determines, verifies and provides foundation loads (vertical and horizontal) or calculated bearing pressures to the geotechnical engineer. The structural engineer also provides the elevation at which the foundation loads or bearing pressures are applied.

When the geotechnical subsurface exploration has been completed, the geotechnical engineer performs laboratory testing and geotechnical design. The geotechnical engineer issues a Structures Foundation Type Memo and a Geotechnical Report based on the field exploration,


Foundations 17-3

laboratory testing, geotechnical design, preliminary bridge design and the loads provided by the structural engineer.

17.1.2.2.2 Foundation Design

The structural engineer uses the Geotechnical Report to design foundations for bridges and other structures.

For deep foundations, the Geotechnical Report provides tip elevations, pile capacity, anticipated settlement and p-y soil models of the subsurface soils. The geotechnical engineer and/or the structural engineer perform lateral soil structure interaction analysis using the p-y soil models with computer programs such as StrainWedge, LPile Plus or similar pile analysis programs. Use the information to compute lateral displacements and analyze the structural adequacy of the columns and foundations. Use the lateral soil structure interaction analysis to select the appropriate method (calculated point of fixity, stiffness matrix, linear stiffness springs or p-y nonlinear springs) to model the bridge foundation in the structural design software.

For shallow foundations, the Geotechnical Report provides the estimated footing elevation, strength and service loads, bearing resistance, estimates on settlements and lateral resistance. Use the information to finalize the design of the footing and verify that members are not overstressed.

The Geotechnical Report can also include notes and tables for inclusion in the plan set or specifications. Refer to the SS and WS sheets for typical geotechnical information presented in the plan set.

17.1.2.2.3 Seismic Design

Refer to Chapter 13 for specific design requirements.

Collaborate with the geotechnical engineer to develop drilled shaft or pile response models for the anticipated displacements. Include the lateral soil structure interaction analyses in the model used to determine Extreme Event I loadings. The geotechnical engineer also provides any lateral soil forces that act on the foundation as a result of seismically induced stability movements of earth retaining structures (e.g., embankments, retaining walls) or lateral soil movements attributable to lateral spread. Evaluate the loads due to lateral spread separately from the inertial response of the bridge.

If structural members are overstressed or if deflections exceed acceptable limits from any loading combination, redesign the foundation. Redesign can include the adjustment of support member spacing or modification of member sizes. When a redesign of the foundation is required, the structural engineer submits the redesign information (new foundation layout, sizes, foundation load combinations, etc.) to the geotechnical engineer. The geotechnical engineer analyzes the new foundation and submits the necessary information to the structural engineer.


17-4 Foundations

17.1.3 Bridge Design/Hydraulic Design Interaction

Bridges and other structures exposed to stream flow can be subject to local and/or contraction scour. The structural engineer works closely with the hydraulics engineer to determine the extent of scour, which often requires an interactive design process. When a redesign of the foundation is required, the structural engineer must resubmit the redesign information (e.g., new foundation layout, sizes, foundation load combinations) to both the hydraulics engineer and the geotechnical engineer. The geotechnical engineer analyzes the new foundation and resubmits the necessary information to the structural engineer. The hydraulics engineer analyzes the new foundation and provides local and contraction scour information and flowline elevations.

The structural engineer is responsible for providing a stable foundation based on the anticipated scour. Scour can undermine footings, damage piles, reduce the capacity of piles and change the lateral load response of the foundation systems. Refer to Section 17.4.2 for additional guidance when placing spread footings in or near waterways.

17.1.4 Total and Differential Settlement

Reference: LRFD Articles 3.12.6, 10.6.2.2 and 10.7.2.3

Settlement occurs due to a number of reasons. Collaborate with the geotechnical engineer to estimate total and differential settlement. Construction sequencing impacts differential settlement. Inform the geotechnical engineer of the planned construction sequence. Define the construction sequence in the plan set when a specific sequence is required to control total and differential settlement.

Uniform settlement impacts vertical clearances and roadway geometry but has no impact on the structure itself.

Differential settlement introduces loads into the structure and redistributes loads within the structure. The load redistributes due to the rigidity of the structural system. Account for the redistribution of load in design. The redistribution reduces settlement and increases loads in elements that do not settle.

There is no specified limit in the UDOT Geotechnical Manual of Instruction on total settlement and differential settlement. Normally, the total settlement is restricted to 1 in., which by default restricts differential settlement to 1 in. DB project documents often set project specific limits.

17.1.4.1 Estimating Settlement

Collaborate with the geotechnical engineer to determine total settlement and differential settlement. The following sections discuss the simplified estimate and the construction point estimate.


Foundations 17-5

17.1.4.1.1 Simplified Estimate

Apply all loads in a phase at the same time. Set a total settlement estimate and estimate the potential differential settlement. The practice is the typical procedure and is appropriate for most projects.

Compare the settlement limit to estimated settlement using the simplified estimate.

17.1.4.1.2 Construction Point Estimate

The construction point estimate results in the same total settlement as the simplified method but permits a more detailed evaluation of the settlement impacts. The simplified estimate applies to all loads at the same time. In reality, loads increase as construction proceeds. Consequently, settlements also increase as construction progresses. The construction point estimate evaluates settlement at several critical construction points.

Identify the construction points to evaluate. Typical construction points are:

1. Embankment or Foundation Construction. Settlement due to placing embankments, driving piles, installing drilled shafts, etc., do not impact the structure because formwork elevations for substructure elements are set after the foundation is in place.

2. Substructure Construction. Settlement during foundation construction can impact reinforcing lengths in subsequent construction tasks and bearing seat elevations. Mitigate settlements during the substructure construction stage by providing plan sheets that require placement of pedestals for bearing seats after the initial settlement has occurred and provide details that permit variation in element heights.

3. Superstructure Construction. Settlements during superstructure construction can impact load distribution throughout the structure, final ride and aesthetics. Settlements due to superstructure construction can be further segregated to specific loads if needed (i.e., girder placement, deck placement, placement of final wearing surface or topping).

4. Between Construction Phases at any of the Previously Listed Construction Points. Settlement between phases is the most common source of structural distress due to differential settlement.

The consideration of relevant settlements in conjunction with the construction sequence, type of superstructure and bearings can lead to a more rational consideration of spread footings on soils for highway bridges rather than an uninformed decision to select a more costly deep foundation system. See “Selection of Spread Footings on Soils to Support Highway Bridge Structures,” Samtani, Nowatzki and Mertz, FHWA, 2010.

Consider using a construction point estimate when the majority or all of the settlement occurs before superstructure construction or when phased construction is planned.


17-6 Foundations

17.1.4.2 Effects of Foundation Settlement

In the LRFD Specifications, the differential settlement of two foundations is a superstructure load. The following sections define the types of differential settlements and required actions during design.

17.1.4.2.1 Differential Settlement Between Adjacent Supports

Angular distortion is the differential settlement between adjacent supports divided by the distance between the supports. See Figure 17.1. An adjacent support in this context is the support at the other end of the span. The limits in Figure 17.2 are only for checks for load induced due to settlement and normally do not govern design. Rideability and aesthetics typically govern the allowable amount of settlement. In addition, project specific criteria can also limit the angular distortion to values much less than the values in Figure 17.2.

Figure 17.1 — ADJACENT SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT

Case Angular Distortion

(γ), Radians Required Action

Simple span γ > 0.008 Redesign foundation to reduce angular distortion

Continuous span γ > 0.004 Redesign foundation to reduce angular distortion

Simple span 0.004 ≤ γ ≤ 0.008 Include load effects in design

Continuous span 0.002 ≤ γ ≤ 0.004 Include load effects in design

Simple span γ < 0.004 Ignore load effects in design

Continuous span γ < 0.002 Ignore load effects in design

Figure 17.2 — ADJACENT SUPPORT ANGULAR DISTORTION/

DIFFERENTIAL SETTLEMENT LIMITS FOR STRUCTURAL CHECKS

SETTLEMENTAFTERDIFFERENCEELEVATIONFINALHDIFFERENCEELEVATIONINITIALH

HHdS/d

r

i

ri

==

−==γ


Foundations 17-7

Project requirements associated with rideability or aesthetics typically govern the allowable amount of settlement. For example, a 100-ft long single span structure could structurally accommodate over 9 in. of settlement, but rideability, aesthetics or other project requirements often limit the settlement to 1 in.

17.1.4.2.2 Differential Settlement Within a Single Support

A single support may not settle in a uniform manner from one end of the support to the other. The limits in Figure 17.3 are only for checks for load induced settlement and can be superseded by requirements associated with rideability or aesthetics.

17.1.4.2.3 Differential Settlement Between Adjacent Elements

Allowances must be made to permit adjacent elements to settle at different rates without causing structural distress or damaging utilities running across joints between the elements. The limits in Figure 17.3 are only for checks for loads induced due to settlement. Rideability and aesthetic limits could govern the allowable amount of settlement. In addition, project specific criteria can also limit the angular distortion to values less than the values in Figure 17.3.

Case Angular Distortion (γ)

or Differential Displacement (d)

Required Action

Continuous footing d > 0.5 in.

Include load effects in design, or redesign foundation to reduce differential settlement

d ≤ 0.5 in. Ignore load effects in design

Phased continuous footing

γ > 0.001 radians Include load effects in design, or redesign foundation to reduce differential settlement between phases

γ ≤ 0.001 radians Ignore load effects in design

Discontinuous footings supporting columns

γ > 0.001 radians Include load effects in design, or redesign foundation to reduce differential settlement between phases

γ ≤ 0.001 radians Ignore load effects in design

Note: See Figure 17.4 for illustrations.

Figure 17.3 — SINGLE SUPPORT ANGULAR DISTORTION/ DIFFERENTIAL SETTLEMENT LIMITS FOR STRUCTURAL CHECKS


17-8 Foundations

S

d=γ

S

d=γ

Figure 17.4 — SINGLE SUPPORT ANGULAR DISTORTION/DIFFERENTIAL SETTLEMENT


Foundations 17-9

17.1.4.2.4 Additional Effects of Settlement

When evaluating settlements, also consider the following effects:

1. Joint Movements. Excessive differential settlement can damage deck joints or make deck joints more prone to damage from tire impacts or snow plow impacts.

2. Profile Distortion. Excessive differential settlement can cause undesirable distortion of the roadway profile for vehicles traveling at high speed.

3. Aesthetics. Excessive differential settlement can create a perception of lack of safety.

17.1.4.3 Mitigation of Foundation Settlement

Settlement can be mitigated using a variety of methods from load reduction to ground modification. Collaborate with the geotechnical engineer to determine the best mitigation method when predicted settlements are unacceptable. Available ground modification methods include:

• Chemical grouting • Overexcavation and replacement • Surcharging • Installation of stone columns • Compaction grouting • Deep dynamic compaction

17.2 DRIVEN PILES

Piles transfer loads to deeper suitable strata. Piles function through skin friction, end bearing or a combination of both skin friction and end bearing.

17.2.1 Pile Types/Selection

Avoid the use of differing pile types and sizes within the same bridge.

17.2.1.1 Steel Pipe Piles

Reference: LRFD Articles 6.9.5 and 6.12.2.3

Steel pipe piles are viable for the majority of bridge locations. Steel pipe piles are especially advantageous in waterways where the predicted scour is deep, at sites prone to settlement and at sites prone to liquefaction.


17-10 Foundations

The following applies:

1. Diameter. Use pipe pile diameters of 12 in. to 48 in. The wall thickness typically is not less than 1:48 of the pipe diameter.

2. Interior Filler. Fill steel pipe piles with concrete to strengthen and stiffen the pipe and use reinforcing to connect the pile to the cap/footing. Reinforcing can also increase the moment capacity when extended past the maximum moment location.

17.2.1.2 Steel H-Piles

Use steel H-piles where cost effective. The geotechnical engineer in coordination with the structural engineer determines the steel H-pile shape based on the loads and soil capacity. Do not use steel H-piles when artesian groundwater conditions are present.

Orientation of steel H-piles (strong vs weak axis) is a design decision. Typically, orient all piles in the same direction. Typically, at bridge abutments, orient the piles with the strong axis perpendicular to the centerline of bearing. Pile deflection at pile yield is typically larger for bending about the strong axis.

17.2.1.3 Prestressed Concrete Piles

Use prestressed concrete piles where cost effective. Where prestressed concrete piles are used, typical sizes are 12 in. to 18 in. square or octagonal sections. Use of round reinforcing cages in piles that are not round is permitted. UDOT standard prestressed concrete pile details are not available.

17.2.1.4 Pile Selection

The geotechnical engineer generally selects the pile type. Figure 17.5 provides guidance in selecting pile types. Collaborate with the geotechnical engineer to determine any reduction in effective thickness due to corrosion.

Pile Type Soil Conditions and Structural Requirements

Steel pipe pile (closed end)

Loose to medium dense soils or clays where skin friction is the primary resistance and lateral stiffness in both directions is desirable, especially in rivers where deep scour or liquefaction is anticipated and high lateral stiffness is needed

Steel H-pile Rock or dense soil where end bearing is desirable and lateral flexibility in one direction is not critical

Prestressed concrete pile Loose to medium dense soils or clays where skin friction is the primary resistance

Figure 17.5 — DRIVEN PILE SELECTION GUIDE


Foundations 17-11

17.2.1.5 Pile Capacity Verification

Dynamic pile monitoring is required according to the standard pile specification. During the installation of production piles, dynamic pile monitoring ensures that driving occurs according to the established criteria. The monitoring provides information on soil resistance at the time of monitoring and on driving performance. Dynamic pile monitoring also reveals driving stresses, which helps prevent pile damage. Geotechnical engineers use data obtained during pile driving monitoring to verify pile resistance.

UDOT permits static load tests to determine pile capacity. The geotechnical engineer determines the number and location of the static load tests. Present the test locations and sizes in the contract documents. Collaborate with the geotechnical engineer to develop a special provision when specifying static load tests.

17.2.2 Design Details


Use the WS sheets when preparing plan sheets. Show applicable pile loads on the plans. Geotechnical engineers use the information to evaluate pile driving results during driving and to permit flexibility in accepting piles during construction.

17.2.2.1 Pile Length

Reference: LRFD Articles 10.7.1.10, 10.7.1.11 and 10.7.1.12

Determine pile length based on the Geotechnical Report. Specify the same length for all piles for a specific bent or abutment, where practical. Show pile lengths in whole foot increments.

Show the estimated pile tip elevations and minimum penetration on the driven pile plan sheets. The minimum penetration reflects the penetration required, considering scour, liquefaction and settlement, to support both axial and lateral loads.

17.2.2.2 Reinforced Pile Tips

Use reinforced pile tips to minimize pile damage where hard layers are anticipated and as recommended in the Geotechnical Report. Show the type of pile tip reinforcing on the driven pile plan sheet.

17.2.2.3 Battered Piles

Do not use battered piles because battered piles:

• Increase restraint forces in integral abutment bridges • Attract significant load due to temperature effects when used with integral abutments


17-12 Foundations

• Attract significant load during seismic events • Increase bending loads due to settlement • Are challenging to control during difficult driving conditions Obtain approval from the Structures Design Manager when the project could significantly benefit from the use of battered piles.

17.2.3 Force Effects

Section 17.5 discusses pile analysis for lateral loading and resistance.

17.2.3.1 Downdrag Loads

Evaluate the force effects of downdrag or negative loading on the foundations. Downdrag acts as an additional axial load on the pile and could cause additional settlement. Do not include transient loads, including live load, when evaluating the structural capacity of the pile for downdrag loads.

Collaborate with the geotechnical engineer to determine the dead load capacity of the pile when considering downdrag loads. The structural capacity of the pile normally controls the dead load limit in conjunction with downdrag. Normally, the downdrag load is subtracted from the braced pile capacity to determine the maximum factored dead load, QDL. QDL is the maximum factored dead load according to the downdrag load case and is listed in the pile data table on the driven pile plan sheet. Refer to the WS sheets for typical driven pile plan sheets.

Where the pile is a true end bearing pile, the maximum factored dead load, QDL, could be a function of the geotechnical pile capacity. The geotechnical engineer makes the determination and supplies the appropriate QDL limit.

Do not use friction reducing rings to attempt to reduce downdrag.

17.2.3.2 Uplift Forces

Design piles for no uplift for strength and service load cases. Avoid uplift where practical when checking extreme event load cases. Design piles to resist uplift forces. Design the connection of the pile to the cap or footing to resist the extreme event uplift forces when present.

17.2.4 Piles Placed within Mechanically Stabilized Earth Walls

Piles placed within the MSE backfill require special consideration. Specify on the project plan sheets that the piles are placed before the construction of the wall. Do not use pile sleeves to reduce downdrag loads on the pile. Modify the soil reinforcement when piles are located within the MSE wall. See Section 18.1.4 and Section 22.4.6.


Foundations 17-13

17.3 DRILLED SHAFTS

17.3.1 Usage

Section 10.10 presents practices for selecting drilled shafts as the foundation type.

Drilled shafts derive load resistance either as end bearing drilled shafts transferring load by end bearing or as friction drilled shafts transferring load by side resistance or a combination of both. Use drilled shafts where driven piles are not economically viable due to high loads or obstructions to driving. Limitations on vibration or construction noise can also dictate the selection of drilled shafts.

17.3.2 Drilled Shaft Axial Compressive Resistance at the Strength Limit State


The LRFD Specifications provide procedures to estimate the axial resistance of drilled shafts in cohesive soils and cohesionless soils in LRFD Articles 10.8.3.5.1 and 10.8.3.5.2. In both cases, the resistance is the sum of the drilled shaft and tip resistances. LRFD Article 10.8.3.5.4 discusses the determination of axial resistance of drilled shafts in rock.

17.3.3 Structural Design

Because even soft soils provide sufficient support to prevent lateral buckling of the drilled shaft, design drilled shafts surrounded by soil according to the criteria for short columns in LRFD Article 5.7.4.4 when soil liquefaction is not anticipated. If the drilled shaft is extended above ground to form a bent, design the drilled shaft as a column. Similarly, consider the effects of scour around the drilled shafts in the analysis.

Drilled shaft casings can be temporary, removed after the construction of the drilled shaft or left in place. Use casings to maintain the excavation, especially when placing a drilled shaft within the water table. Indicate on the drilled shaft plan sheet when casing is required by design. The casing is normally neglected in the determination of the structural resistance of the drilled shaft. When the casing is used in the structural capacity, a special provision is required and the minimum casing thickness is ⅝ in. The special provision must define the casing material and any special procedures or submittals required. Collaborate with the geotechnical engineer to determine any reduction in effective casing thickness due to corrosion. In seismic analysis and design, use a strain compatibility method to determine the stiffness and strength of the cased drilled shaft.

Section 17.5 discusses drilled shaft analysis for lateral loading and resistance.


17-14 Foundations

17.3.4 Design Details

Collaborate with the geotechnical engineer to determine the most efficient diameter. When the drilled shaft supports a single column, a drilled shaft size that is 18 in. larger than the maximum column dimension provides flexibility for drilled shaft location areas and allows for easier placement of concrete where the column reinforcing and the drilled shaft reinforcing overlap. Use a drilled shaft at least 6 in. larger than the minimum column dimension.

Typically, terminate drilled shafts 6 in. to 12 in. below the finished grade or at 12 in. above the water elevation anticipated during construction when the drilled shaft supports a single column. Set the top of drilled shaft at the bottom of footing elevation when using a footing cap.

Chapter 14 discusses practices for reinforcing structural concrete, which apply to the design of drilled shafts. Additional reinforcing criteria include:

• Use a minimum reinforcing of 0.8% of the gross concrete area. Extend the drilled shaft reinforcing a minimum of 10 ft beyond the point of fixity for all load cases including seismic induced liquefaction load cases.

• For confinement reinforcing, use spirals (up to #7) or butt welded hoops. • In the design and detailing of drilled shafts, provide 3 in. of cover. Maintain the annular

space around the cage with noncorrosive spacers. • Detail drilled shafts and columns to accommodate concrete placement considering the

multiple layers of reinforcing including lap splices. Maximize lateral reinforcing spacing to permit better consolidation of concrete during drilled shaft construction.

• Provide 5-in. or larger spacing for vertical reinforcing and a 5-in. pitch or spacing for spirals or hoops reinforcing, where practical.

• Refer to Section 13.7.5.3 for detailing requirements at the drilled shaft to column interface.

See the SS and WS sheets and SD drawings for additional information. Figure 17.6 illustrates a drilled shaft supporting a single column and socketed into rock. Drilled shafts used in conjunction with pile caps or pile footings use similar details except at the top of the drilled shaft. When pile caps or pile footings are used, extend drilled shaft reinforcing into the pile cap or pile footing.

Detail drilled shafts and columns to accommodate concrete placement through the layers of reinforcing. Stagger lap splices in the drilled shaft locations and provide adequate openings. Use of cased drilled shafts with relatively open reinforcing cages minimizes concrete consolidation problems.

Where casing through overburdened soils is required, design the rock socket as one size and, if necessary, increase the cased drilled shaft diameter to easily permit the rock drill to extend though the casing.

Collaborate with the geotechnical engineer to determine the most cost effective solution from a project wide perspective. Multiple small drilled shafts used in conjunction with a pile cap or footing are usually more cost effective than a single large drilled shaft. Single drilled shafts can accelerate construction and minimize the work zone size.


Foundations 17-15

Figure 17.6 — DRILLED SHAFT (Socketed in Rock)


17-16 Foundations

Collaborate with the geotechnical engineer to determine required integrity testing. Crosshole sonic logging is a type of integrity testing. Where integrity testing is required, provide a special provision defining the required integrity testing and methods of repair when shaft integrity testing indicates voids or caving.

17.4 SPREAD FOOTINGS, PILE FOOTINGS AND PILE CAPS

Use spread footings, pile footings and pile caps to transfer wall or column loads to the ground or to piles or drilled shafts:

• Spread footings are concrete slabs transferring load directly to the soil. • Pile caps are concrete beams transferring load to a single row of piles or drilled shafts. • Pile footings are concrete slabs transferring load to multiple rows of piles or drilled

shafts. 17.4.1 Thickness


The development length of the column/wall reinforcing or the shear requirements can govern the footing thickness. Generally, avoid shear reinforcing for the Strength I design loads in footings. If Strength I shear governs the thickness, a thicker footing without shear reinforcing, instead of a thinner footing with shear reinforcing, is usually more economical.

Use a minimum footing thickness greater than the following:

• 2 ft • Thickness of the wall in the plastic hinge direction • Column diameter • Maximum dimension of the column in the plastic hinge direction 17.4.2 Depth

Reference: LRFD Articles 5.8.3, 5.13.3.6 and 5.13.3.8

Embed spread footings a sufficient depth to provide:

• Adequate bearing, scour and frost heave protection • 3-ft minimum to the bottom of footing • 1-ft minimum cover over the footing (2 ft preferred) • Maximum cover over footing of 3′-6″ or Lp (plastic hinge length) when plastic hinging is

anticipated


Foundations 17-17

In waterways:

• Typical practice is to not use spread footings. Where used, locate the top of a spread footing on soil at least 1 ft below the design scour depth.

• Locate the bottom of a spread footing on rock 1 ft below the surface of the scour resistant rock. Collaborate with the hydraulics engineer to determine scour depth. Some rock formations are highly erodible.

• Where practical, locate the top of a footing on piles or drilled shafts below the scour depth. In areas with excessive scour, design the piles to accommodate the anticipated scour.

• Avoid pile caps or footings that pose an obstacle to water traffic or are exposed to view during low flow.

17.4.3 Joints

Footings do not generally require construction joints. Where used, offset footing construction joints at least 2 ft from expansion joints or construction joints in walls. Use 3-in. deep keyways at cold joints.

17.4.4 Stepped Footings

Stepped footings are permitted but must meet the requirements shown in Figure 17.7.

Figure 17.7 — STEPPED FOOTING DETAILS 17.4.5 Rocking Spread Footings

Use of rocking spread footings designed to the requirements in the AASHTO Guide Specifications for LRFD Seismic Bridge Design is permitted when the footing does not extend below a roadway section.


17-18 Foundations

17.4.6 Bearing Resistance and Eccentricity


Provide bearing resistance information on the foundation plan sheets. Refer to the Foundation Design and Detailing Checklist for required foundation plan information.

Figure 17.8 presents a schematic example of the analysis of a spread footing on soil.

Figure 17.9 presents a schematic example of the analysis of a pile cap to support a bent.

17.4.7 Sliding Resistance


Do not consider passive pressure from soil around the footing when evaluating sliding resistance. The use of passive pressure from keys beneath footings to develop passive pressure against sliding is permitted; however, keys are not commonly used for bridges. When it becomes necessary to use a key, consult with the geotechnical engineer and Structures Design Manager.

Use seismic passive pressure from fill around column footings when evaluating sliding from seismic loads in locations not subject to scour.

17.4.8 Reinforcing

Reference: LRFD Articles 5.10.8 and 5.13.3

Design spread footings, pile caps and pile footings to meet all applicable requirements in Chapter 14. Unless other design considerations govern, reinforce footings as follows:

• Extend vertical reinforcing from columns or walls to the bottom mat of reinforcing and hook the reinforcing on the bottom end regardless of the footing thickness.

• The minimum spacing of reinforcing in either direction is 6 in. on center. • LRFD Article 5.13.3 specifically addresses concrete footings. For items not included,

use the other relevant provisions of LRFD Section 5. For narrow footings with loads transmitted by walls or wall like bents, the critical moment section is at the face of the wall or bent stem; the critical shear section is a distance equal to the larger of dv (dv is the effective shear depth of the footing) or 0.5dv cot θ (θ is the angle of inclination of diagonal compressive stresses as defined in LRFD Article 5.8.3.4) from the face of the wall or bent stem where the load introduces compression in the top of the footing section. For other cases, either use LRFD Article 5.13.3 or a 2D analysis for greater economy of the footing.


Foundations 17-19

FootingCR PPP +=

R

fCCL

P

DVMe

+=

CR VV =

Le2LL −′ =

In two dimensions, bearing pressure:

( ) ( )BL

Pp R

R ′′′ =

Where:

L′ = L – 2eL

B′ = B – 2eB

Note: See LRFD Articles 10.6.1.3 and 10.6.3.3.

Figure 17.8 — EXAMPLE ANALYSIS OF SPREAD FOOTING ON COMPETENT SOIL


17-20 Foundations

PR = Pc + Pfooting + Pseal – Buoyancy

Assumptions: Pile footing is rigid (footing is considered rigid if Le/Df ≤ 2.2). Pile connections are pinned for nonseismic loads, or shear force in pile is small. VR = Vc – Vpassive soil pressure on footing and seal Note: Ignore passive soil pressure for

nonseismic loads. MR = Mc + Vc (Df + Ds) Pile Loads:

2i

2RRmax

d

dM

pilesof#

PP

Σ+=

2i

2RRmin

d

dM

pilesof#

PP

Σ−=

Figure 17.9 — EXAMPLE ANALYSIS OF A PILE CAP


Foundations 17-21

17.5 LATERAL LOADING OF DEEP FOUNDATION ELEMENTS

17.5.1 Pile/Drilled Shaft Supported Footings

Pile and drilled shaft supported footings typically behave as fixed supports, and the lateral stiffness of deep foundation elements does not typically need to be considered in the nonseismic design of the elements. Lateral stiffness of the deep foundation elements could need to be included in the seismic analysis of the bridge when the structural engineer anticipates soft soils, liquefaction or other factors that affect the lateral stiffness of the footing. Use the modeling techniques addressed in Section 17.5.2 to determine the lateral stiffness of deep foundation elements.

17.5.2 Pile/Drilled Shaft Extension Bents

Include the lateral stiffness of deep foundations in both the nonseismic (small lateral deflection) and seismic (large lateral deflection) where a column rests directly on a single drilled shaft or if piles are extended up to the bent cap. Include the effects of scour, liquefaction and frozen soil, when applicable, in the lateral stiffness analysis.

Several methods of analysis are available for calculating the lateral stiffness of deep foundation elements. Not all of the methods discussed below are applicable to all situations. Review the methods and be aware of each method’s limitations.

17.5.2.1 Closed Form Linear Models

For small lateral deflections, closed form solutions have been developed based upon a beam on an elastic foundation model. The methods provide a depth to effective fixity for moment (lm) and deflection (ls) wherein the actual soil pile system is replaced by an equivalent fixed base cantilever. LRFD Article C10.7.3.13.4 provides the equations describing the systems for both cohesive and cohesionless soils. The equations are often referred to as the 4th root or 5th root equation, depending upon the soil type. The equations typically provide sufficiently accurate results for most situations where the deflections are small and the response is elastic.

Closed form solutions also exist for large deflection stiffness determination but, like most hand methods, are not readily capable of addressing soil layering and other real world variability. Nonetheless, the methods provide a good means of checking the more sophisticated computer generated results. Figure 17.10 shows a closed form linear model.


17-22 Foundations

LS LM

Cohesive soil constant, kh

4

k

EI4.1h

4

k

EI44.0h

Cohesionless soil constant, nh

5

n

EI8.1h

5

n

EI78.0h

Coefficient nh (kips per cubic ft) kh = Coefficient of horizontal subgrade reaction for fine grained soil

= ( )2ft/k-inb

cm160

In which: m = 0.32 for c < 1 ksf = 0.36 for 1 < c < 4 ksf = 0.40 for c > 4 ksf b = width of pile (ft) c = soil cohesion

Relative Density Loose Medium Dense

Above ground water 14 42 112

Below ground water 8 28 68

Figure 17.10 — METHOD OF MODELING DEEP FOUNDATION STIFFNESS (Closed Form Linear Model)


Foundations 17-23

17.5.2.2 Nonlinear Models

As the lateral demands increase, the soil and pile/drilled shaft can behave in a nonlinear manner. Numerical modeling of the soil pile/soil drilled shaft interaction is often required. The numerical approaches are capable of incorporating the nonlinear soil and structure response, but rely upon computer software. The most commonly used software is FB-Pier and L-Pile. Use the results of nonlinear models to provide a depth to effective fixity. Nonlinear models are also used to develop an equivalent soil spring model, such as that shown in Figures 17.10 and 17.11. The data listed in the figures is adequate for preliminary design. Coordinate with the geotechnical engineer to obtain final design data.

Figure 17.11 — METHOD OF MODELING DEEP FOUNDATION STIFFNESS (Nonlinear Model)

17.5.3 Minimum Penetration

Collaborate with the geotechnical engineer when using short piles with large lateral loads. Typically, the geotechnical engineer specifies the minimum penetration into the soil so that the deflected shape of the pile subjected to lateral loads crosses a zero deflection point at two places.


17-24 Foundations

17.6 LIQUEFACTION

Liquefaction effects caused by seismic induced ground motion reduce the vertical and lateral resistance of the deep foundation member. The Geotechnical Report includes the soil liquefaction potential, liquefied soil properties, deformations due to lateral soil flow and settlement and subsequent downdrag loads.

Consider liquefaction as specified in the AASHTO Guide Specifications for LRFD Seismic Bridge Design. See Figure 17.12.

Run models with and without soil liquefaction when liquefaction is anticipated. Include foundation downdrag loads due to liquefaction in the vertical loads due to seismic response when developing the Extreme Event I load combination.

Inelastic pile response to lateral spread or lateral flow is permitted for normal bridges using steel pipe piles or steel H-piles. Collaborate with the Structures Design Manager to determine the foundation design criteria for critical or essential bridges in areas with lateral spread or lateral flow. Use SDC D for all locations where liquefaction is possible (Article 3.5 in the AASHTO Guide Specifications for LRFD Seismic Bridge Design).

Do not use shallow foundations in liquefiable soils where lateral spread is possible.


Foundations 17-25

LARGE EMBANKMENTDEFORMATION

POTENTIAL?

SIGNIFICANT POTENTIAL

FOR DAMAGE TO BRIDGE?

ISSTRUCTURE

LOCATED ON A DESIGNATED LIFE-

LINE ROUTE?

OTHER CRITERIA (FOR CONSIDERATION):

• ADT ON OR UNDER BRIDGE ―IS ADT ON OR UNDER BRIDGECONSIDERED HIGH

• ECONOMIC RECOVERY ROUTE ―IS BRIDGE ON OR OVER A CRITICAL ROUTE(EMERGENCY OR ECONOMIC)

• DOES THE RATIO OF MITIGATION COSTTO STRUCTURE REPLACEMENT COSTJUSTIFY MITIGATION

DOESSTRUCTURE

QUALIFY FOR MITIGATION? (DECISION BY

STRUCTURES DESIGN MANAGER/PROJECT

MANAGER)

DO NOT MITIGATELATERAL SPREAD

DO NOT MITIGATELATERAL SPREAD

DOCUMENT LIQUEFACTIONAND LATERAL SPREADDAMAGE POTENTIAL

BUT DO NOT MITIGATE LATERAL SPREAD

NO

YES

NO

NO

NO

YES

YES

YES

GEOTECHNICAL ENGINEEREVALUATES LIQUEFACTION

AND APPROACH FILL DEFORMATION POTENTIAL (LATERAL DISPLACEMENTS

AND SETTLEMENT)

PROCEED WITH MITIGATION DESIGN

GEOTECHNICAL AND STRUCTURAL ENGINEERS

DETERMINE DAMAGE POTENTIAL TO STRUCTURE

Figure 17.12 — LIQUEFACTION MITIGATION PROCEDURE


17-26 Foundations

FEBRUARY 2015

SUBSTRUCTURES



Substructures 18-i

TABLE OF CONTENTS

18.1 ABUTMENTS ............................................................................................................. 18-1

18.1.1 Abutment Design and Detailing Criteria ...................................................... 18-1 18.1.1.1 All Abutments ........................................................................... 18-1 18.1.1.2 Integral and Semi-Integral Abutments ...................................... 18-2 18.1.1.3 Seat Abutments........................................................................ 18-3

18.1.2 Seismic Analysis and Design ...................................................................... 18-4 18.1.3 Abutments Types ........................................................................................ 18-4

18.1.3.1 Integral Abutments ................................................................... 18-4 18.1.3.2 Semi-Integral Abutments .......................................................... 18-5 18.1.3.3 Seat Abutments........................................................................ 18-6

18.1.4 Walls at Abutments ..................................................................................... 18-6

18.1.4.1 Mechanically Stabilized Earth Walls ........................................ 18-6 18.1.4.2 Geosynthetic Reinforced Soil Walls ......................................... 18-7 18.1.4.3 Soil Nail Walls .......................................................................... 18-7

18.1.5 Spread Footings at Abutments .................................................................... 18-7 18.1.6 Piles at Abutments ...................................................................................... 18-8 18.1.7 Drilled Shafts at Abutments ......................................................................... 18-8 18.1.8 Abutment Construction Joints ..................................................................... 18-9 18.1.9 Wingwalls .................................................................................................... 18-9 18.1.10 Drainage ...................................................................................................... 18-10 18.1.11 Geofoam Backfill ......................................................................................... 18-10

18.2 BENTS ....................................................................................................................... 18-10

18.2.1 Seismic Considerations ............................................................................... 18-11 18.2.2 Bent Caps .................................................................................................... 18-11

18.2.2.1 Drop Caps ................................................................................ 18-11 18.2.2.2 Integral Caps ............................................................................ 18-11 18.2.2.3 Straddle Caps .......................................................................... 18-12

18.2.3 Columns and Walls ..................................................................................... 18-12

18.2.3.1 Column Reinforcing .................................................................. 18-13 18.2.3.2 Transverse Reinforcing ............................................................ 18-13 18.2.3.3 Longitudinal Reinforcing ........................................................... 18-13 18.2.3.4 Column Construction Joints ..................................................... 18-14

18.2.4 Extended Pile Bents .................................................................................... 18-14 18.2.5 Bent Foundations ........................................................................................ 18-14 18.2.6 Dynamic Load Allowance ............................................................................ 18-14


18-ii Substructures

18.2.7 Moment Magnification ................................................................................. 18-15 18.2.8 Distribution of Live Load .............................................................................. 18-15

LIST OF FIGURES


Substructures 18-1

Chapter 18 SUBSTRUCTURES

Section 11 of the LRFD Specifications presents design requirements for substructure elements (e.g., abutments, bents, walls). This chapter discusses substructure provisions in Section 11 of the LFRD Specifications that require amplification or clarification. This chapter also addresses specific practices for the design and detailing of substructures.

18.1 ABUTMENTS

Abutments are substructure elements at the ends of bridges. The abutment serves two primary purposes:

• Provides a transition from the bridge to approach roadway support • Provides vertical support for the superstructure An abutment can include a footing or pile cap, stem wall, backwall and wingwalls. End diaphragms of integral and semi-integral abutments are part of the superstructure. In addition to providing a transition and vertical support, abutments can provide resistance to seismic movements and damping during a seismic event.

An abutment can be one of the following basic types:

• Integral • Semi-integral • Seat The following sections discuss the abutment types and design requirements. 18.1.1 Abutment Design and Detailing Criteria

18.1.1.1 All Abutments

The following applies to the design and detailing of abutments:

1. Thickness. Limit the minimum thickness of any abutment element to 12 in.

2. Pile Cap Width. Limit the minimum pile cap width to the maximum of 3 ft, 2.5 times the pile diameter, or the drilled shaft diameter plus 12 in. The drilled shaft diameter plus 12-in. requirement does not apply when using a pinned connection between the cap and drilled shaft. Reinforcing extending into the cap for a pinned connection must be at least 9 in. from the face of the pile cap. Refer to the SD drawings for a typical pinned detail.


18-2 Substructures

The SD drawings show a column to bent connection, but the concept for drilled shaft to pile cap is similar.

3. Pile Cap Height. Limit the minimum pile cap height to the maximum of 2′-6″, the stem thickness or the drilled shaft diameter when the shaft uses a fixed connection. The maximum pile cap height for an integral abutment bridge without a defined construction sequence and procedure is 8 ft. Greater heights are permitted when a specific construction sequence and procedure is defined.

4. Abutment Fill Slopes. Limit the steepest abutment slope in front of the abutment to 1½H:1V when located in fill slopes and 2H:1V in cut slopes, unless superseded by the Geotechnical Report. Typical side slopes are 2H:1V.

5. Slope Protection. Use slope protection on all slopes steeper than 2H:1V when the slope is located under the bridge. When transitioning from 1½H:1V to 2H:1V in the slope, terminate the protection when the slope reaches 1¾H:1V and the 1¾H:1V slope is not under the bridge. Do not use slope protection, and use slopes 2H:1V or flatter, when the area under the bridge is primarily a wildlife crossing.

6. Vertical Expansion Joints. Use vertical expansion joints when the wall or abutment length exceeds 125 ft. Use a water stop or other means of control to prevent leakage at the joint.

7. Abutment Bearing Area. Use level abutment bearing areas. On seat type abutments, set the bearing area a minimum of 1 in. above the top of abutment seat. Slope the abutment seat between the bearing areas a minimum of 2% perpendicular to the backwall.

8. Approach Slab Seat. Provide a minimum 12-in. approach slab seat. Connect all approach slabs to the abutment. Use a minimum of 0.79 in2/ft of reinforcing across the joint between the approach slab and the deck.

9. Dead Load. Include one half of the dead load of the approach slab as an abutment dead load.

10. Live Load. Include one half of the live load of the approach slab as an abutment live load. Do not apply a horizontal earth load due to live load surcharge to abutments with approach slabs. Do not apply a horizontal earth load due to live load surcharge to wingwalls less than one-half of the approach slab length and located beneath the approach slab.

11. Pile Extensions. Refer to WS sheets for standard pile extension lengths and details.

12. Design Loads. Refer to the SD drawings for minimum design loads.

18.1.1.2 Integral and Semi-Integral Abutments

The following are specific requirements for integral or semi-integral abutments:


Substructures 18-3

1. End Diaphragm. Detail the end diaphragm to match the width of the abutment. Cast the end diaphragm and end portion of the deck after or concurrently with the deck.

2. Cover to Girder. Provide a minimum of 6 in. from the end of the girder to the back face of the end diaphragm. Provide a minimum of 4 in. from the end of the girder to the approach slab seat blockout. Increase the abutment width, or clip the top flange of steel girders or prestressed girders on skewed supports to meet the requirement. Do not clip the girder web or bottom flange.

3. Steel Girder Anchorage. Provide holes at a 12-in. maximum spacing through the webs of steel girders and place #6 or larger reinforcing through the hole. Position the holes so that, when the reinforcing is inserted, the reinforcing is within the integral diaphragm reinforcing cage. For bridges on large skews, ensure that reinforcing does not conflict with bearing stiffeners.

4. Prestressed Girder Anchorage. Place #6 or larger reinforcing through the holes provided in the girder. Refer to the WS sheets for the standard hole spacing. Position the holes so that, when the reinforcing is inserted, the reinforcing is within the integral diaphragm reinforcing cage.

5. Deck Slab Reinforcing. Use L- or U-shaped reinforcing extending from the end diaphragm into the top of the slab at a 12-in. spacing or less.

6. Design Details. Refer to the SD drawings for typical integral abutment and semi-integral abutment details.

7. Expansion Joints. Provide expansion joints at the roadway end of the approach slab when using integral and semi-integral abutments. Refer to Chapter 19 for a discussion on expansion joints and SD drawings for joint information.


Do not use seat type abutments without the approval of the Structures Design Manager. The following are specific requirements for seat abutments:

1. Seat Width. Limit the minimum seat width to the maximum of 24 in. or as specified in other design requirements. The seat width is the dimension from the backwall to the front face of the abutment measured perpendicular to the backwall.

2. Bearing Seat. Detail to minimize the effects of leaking joints.

3. Girder to Backwall. Provide sufficient distance to accommodate temperature movements. Provide restrainers or alternative methods to prevent the girder from impacting the backwall during a seismic event.

4. Backwall. Do not detail the backwall to fuse in a seismic event. Backwall yielding is permitted for bridges classified as normal under seismic loading.


18-4 Substructures

18.1.2 Seismic Analysis and Design

Refer to Chapter 13 for a detailed discussion on seismic design. Design abutments for all seismic forces. Refer to the SD drawings for minimum design requirements.

18.1.3 Abutments Types

18.1.3.1 Integral Abutments

Use integral abutments for bridges meeting the following conditions:

• The displacement due to temperature loads is less than or equal to 3 in. • The abutment is on a single row of steel pipe piles or H-piles. • If on drilled shafts or precast piles, the temperature displacements must be

accommodated elastically. Refer to the SD drawings for definitions of expansion lengths. No expansion length limits are provided for integral abutments used in conjunction with an intermediate expansion joint. Evaluate the anticipated abutment movement and provide appropriate details.

Finwalls can be added to engage passive earth pressure during transverse displacements in a seismic event. Place interior finwalls perpendicular to the abutment. Align finwalls on the exposed edge of a bridge with the edge of the approach slab above the finwall. Wingwalls can be added to finwalls to retain fill.

Wingwalls and/or finwalls are typically cantilevered from the abutment and move with the structure. Orient wingwalls and finwalls parallel to the bridge to minimize passive earth pressures due to thermal movement. Support flared wingwalls or wingwalls parallel to the abutment on independent foundations.

Integral abutments are the most redundant and robust abutment type and provide good seismic performance. Integral abutments on high skews can transmit significant torsional forces into the girders and deck near the abutments. Use of integral abutments on skewed and/or curved structures results in unbalanced soil pressures because the lines of action of the soil pressures on the two abutments do not coincide. Use of integral abutments on structures with high skews and sharp curvature is permitted, but evaluate the effects of the unbalanced loads on the superstructure and intermediate supports. Several mechanisms resist the unbalanced loads:

• Rotation in the abutment that shifts the center of gravity of the soil pressure • Translation of the abutment engaging the piles, soil friction and passive pressure on

wingwalls • Interaction with twisting of the bents and the abutments Refer to the SD drawings for a schematic of the unbalanced loading.


Substructures 18-5

18.1.3.2 Semi-Integral Abutments

Use semi-integral abutments for bridges meeting the following conditions:

• An integral abutment is not permitted • The temperature movements at the abutment do not exceed 0.03H, where H is the

height of the semi-integral abutment diaphragm and the temperature movement is:

α × L/2 × T Where:

α = the coefficient of thermal expansion L = the distance from abutment to abutment T = the temperature change, which is set at 80° for this check

Consider the use of semi-integral abutments when the following conditions are met:

• Bridges with spliced post-tensioned concrete I-girders • ABC bridges to accelerate construction by eliminating the end diaphragm closure pour Finwalls can be added to engage passive earth pressure during transverse displacements in a seismic event. Place interior finwalls perpendicular to the abutment. Shear keys can also be added to transfer transverse forces to the substructure.

Wingwalls are typically cantilevered from the abutment and do not move with the superstructure.

Semi-integral abutments allow the bridge to move over the abutment. The superstructure rests on expansion bearings that minimize loads and movements transferred to the substructure. Use shear keys to provide lateral resistance. Use bolsters or longitudinal shear keys to limit longitudinal movement when required. Because the superstructure rests on bearings, the superstructure can be raised and bearings replaced or shimmed to accommodate differential settlement.

Semi-integral abutments are not as redundant or robust as integral abutments. A higher risk of abutment failure during a seismic event exists. Semi-integral abutments on high skews can transmit significant torsional forces into the girders and deck near the abutments. Use of semi-integral abutments on skewed and/or curved structures results in unbalanced soil pressures because the lines of action of the soil pressures on the two abutments do not coincide. Use of semi-integral abutments on structures with high skews and sharp curvature is permitted, but evaluate the effects of the unbalanced loads on the superstructure and intermediate supports. Several mechanisms resist the unbalanced loads:

• Rotation in the abutment that shifts the center of gravity of the soil pressure • Translation of the abutment engaging soil friction and passive pressure on wingwalls • Interaction with twisting of the bents and the abutments


18-6 Substructures

Lateral translation of the bridge due to unbalanced soil loads is more likely on semi-integral abutments without shear keys due to the lack of engagement of the substructure and piles. Shear keys can be added, but evaluate the possibility of the shear keys binding.

Refer to the SD drawings for a schematic of the unbalanced loading.


Seat abutments are only permitted when an expansion joint is required at the abutment. The Structures Design Manager must approve the use of seat abutments.

Seat abutments consist of a footing, stem wall, seat and backwall. Bearings support the superstructure on the abutment seat. The backwall retains the backfill above the abutment seat so that the backfill is not in contact with the superstructure. The approach slab extends over the top of the backwall. Use an expansion joint between the approach slab and the superstructure deck.

Seat abutments are the least redundant and least robust abutment type. Seat abutments have the highest risk of abutment failure during a seismic event. Seat abutments on high skews do not transfer as much torsional force into the girders and deck near the abutments as do integral and semi-integral abutments. Seat abutments do not move with the bridge and do not develop unbalanced soil pressures.

18.1.4 Walls at Abutments

18.1.4.1 Mechanically Stabilized Earth Walls

MSE walls are retaining walls using precast panels or blocks attached to soil reinforcement extending into the fill. The vertical spacing of reinforcing exceeds 1 ft. Section 22.4.6 presents design practices for MSE walls and discusses the respective responsibilities of the wall manufacturer and the designer in design and construction.

The use of a MSE wall as a support for a spread footing is a special application of the structural system and requires coordination with the geotechnical engineer and approval from the Structures Design Manager.

Spread footings on MSE walls can offer advantages when compared to conventional pile supported abutments. Advantages include:

• Eliminates or reduces the typical bump at the end of the bridge, because the footing settles with the MSE wall in contrast to a deep foundation that does not settle at the same rate as the surrounding MSE walls

• Eliminates piles Piles placed within the MSE backfill are permitted. Ensure that the piles are placed before the construction of the wall. Meet the geometric requirements defined in the DD series in the UDOT Standard Drawings.


Substructures 18-7

Construction of MSE walls around piles can cause settlement and downdrag on the piles. Depending on site materials, downdrag forces can be substantial and must be accounted for in design.

Modify the soil reinforcing when piles are located within the wall. Do not bend the soil reinforcing around the piles; the soil reinforcing must remain linear to develop the strength. Also, do not attach the soil reinforcing to the piles. Allow a reinforcing skew of up to 15° from a line perpendicular to the wall face when accounted for in the wall design.

18.1.4.2 Geosynthetic Reinforced Soil Walls

A GRS wall is a type of gravity retaining wall using precast panels or blocks in front of a compacted granular fill with closely spaced (less than 12 in.) geosynthetic reinforcing extending into the fill.

The use of a GRS wall as a support for a spread footing is a special application of the structural system and requires coordination with the geotechnical engineer and approval from the Structures Design Manager.

Spread footings on GRS walls can offer advantages when compared to conventional pile supported abutments. Advantages include:

• Eliminates or reduces the typical bump at the end of the bridge, because the footing settles with the GRS wall in contrast to a deep foundation that does not settle at the same rate as the surrounding GRS walls

• Eliminates piles Do not place piles within the GRS backfill.

18.1.4.3 Soil Nail Walls

Soil nail walls are retaining walls using precast panels, blocks or a shotcrete face attached to soil nails extending into the fill. The main advantage of a soil nail wall is the top down construction method. Section 22.4.9 presents design practices for soil nail walls.

Piles placed within the nail zone in a soil nail wall are permitted. Ensure that the piles or casing elements are placed before the construction of the wall. Meet the geometric requirements defined in the DD series in the UDOT Standard Drawings.

18.1.5 Spread Footings at Abutments

Only bearing pressure or settlement limitations control the size of spread footings at abutments. There are no minimum size requirements, and the footing can be the same width as the cap when soil conditions permit. Refer to Section 17.4 for additional information.


18-8 Substructures

18.1.6 Piles at Abutments


The following discussion specifically addresses the use of driven piles with abutments. See Section 17.2 for additional information on piles. The following criteria apply to piles for abutments:

1. Number. Use the most cost effective pile type and size, but do not use fewer than three piles to support an abutment.

2. Rows. Use a single row of piles for integral abutments. Use at least two rows for seat abutments.

3. Pile Spacing. Refer to the Geotechnical Report for minimum pile spacing. Placing a pile beneath each girder is not required. Space the piles across the length of the abutment to distribute abutment loads to each pile. Consider phasing requirements when determining the pile spacing.

4. Cap Overhang. Limit the minimum cap overhang to 12 in. plus half the pile diameter measured from the centerline of the pile. Ensure that the cap overhang reinforcing is adequately developed. Hooked or headed bars could be required to develop the cap reinforcing.

18.1.7 Drilled Shafts at Abutments


The following discussion specifically addresses the use of drilled shafts with abutments. See Section 17.3 for additional information on drilled shafts. The following criteria apply to drilled shafts for abutments:

1. Number. Use the most cost effective drilled shaft size. Use a minimum of two drilled shafts for typical applications or when the skew is greater than or equal to 20°. Use a similar detail at the abutment if the bridge is a multispan bridge with single column bents, the bridge has a skew less than 20°, and the columns extend into a single drilled shaft.

2. Rows. Use a single row of drilled shafts for integral abutments.

3. Drilled Shaft Spacing. Refer to the Geotechnical Report for minimum drilled shaft spacing.

4. Cap Overhang. Limit the minimum cap overhang to 12 in. plus half the drilled shaft diameter measured from the centerline of the drilled shaft when using fixed shafts. Ensure that the cap overhang reinforcing is adequately developed. Hooked or headed bars could be required to develop the cap reinforcing.


Substructures 18-9

18.1.8 Abutment Construction Joints

Contractors use construction joints to accommodate normal construction practices. Detail reinforcing to accommodate normal construction joints.

Vertical construction joints are common in phased construction. Make provisions for splicing or mechanical reinforcing couplers on horizontal reinforcing. Place vertical reinforcing approximately 3 in. from the construction joint. Show keyways or roughened surfaces consistent with the structural design of the joint. When the joint is exposed to public view in the finished structure, provide a chamfered groove or similar technique to hide the joint. Allow a vertical construction joint at the wingwall to abutment interface.

18.1.9 Wingwalls


Provide wingwalls of sufficient length to retain the roadway embankment and to furnish protection against erosion. The following applies:

1. Orientation. Standard practice aligns wingwalls parallel with the shoulders on the bridge. ABC bridges or bridges with specific aesthetic requirements use wingwalls aligned parallel to the roadway or feature crossed. Flared wingwalls are the least common and can be considered on ABC bridges or for bridges with specific aesthetic requirements.

2. Length. For wingwalls parallel to the centerline of the bridge, the length is determined by extending the wingwall 2 ft beyond the catch point between the embankment slope and the approach slab. Do not cantilever wingwalls more than 20 ft behind the rear face of the abutment without special design and detailing. Consider unattached or other wingwall types for lengths greater than 20 ft.

3. Thickness. Size the thickness of the wingwall to minimize cost but no less than 12 in.

4. Independent Wingwalls. Independent wingwalls are not attached to the abutment. Design independent wingwalls as retaining walls. See Section 22.4 for retaining walls. Provide an expansion joint between the independent wingwall and abutment.

5. Wingwall/Abutment Connection. The junction of the abutment and wingwall is a critical design element. Typical practice is to use a 6-in. fillet at the junction of the back of the abutment and wingwall. The minimum fillet is 3 in. Larger fillets are permitted. Use of fillet reinforcing properly anchored into the wingwall and abutment can significantly improve the capacity.

6. Design Forces. The design forces for wingwalls are due to earth pressure only. Extend the approach slab over the wingwall, which eliminates the live load surcharge in the design of the wingwall. Also, consider seismic forces from the soil behind the wingwall.


18-10 Substructures

18.1.10 Drainage

Provide positive drainage in the embankment behind the abutment and wingwalls by using select backfill, porous backfill, weep holes, perforated drain pipe, a manufactured backwall drainage system or a combination of the options.

Always consider ground water levels when evaluating an appropriate drainage system. Do not install drainage systems that allow pressurized backwater to saturate the abutment backfill during high water events.

Generally, for integral and semi-integral abutments, select backfill and porous backfill over a permeable layer is sufficient to promote good drainage. Always provide drainage for abutments on spread footings.

18.1.11 Geofoam Backfill

Geofoam backfill is used to reduce or eliminate fill settlement behind the abutment. Even if the geofoam is detailed with a gap between the foam and abutment, assume that the geofoam transmits lateral force to the abutment. Design the abutment for a minimum horizontal load equal to 10% of the overlying dead load. If the slope of the geofoam surface behind the abutment exceeds 1½H:1V, evaluate the effects of soil loads transferred through the geofoam. Geofoam backfill design is beyond the scope of the SDDM. Coordinate with the geotechnical engineer and/or a geofoam specialist when designing and planning geofoam backfills.

18.2 BENTS


A bent is an intermediate support for the superstructure on multispan bridges. UDOT does not use the term pier. Bents typically consist of a bent cap supported on single or multiple columns or a bent wall resting on a spread footing or pile cap or drilled shafts. Both continuous and individual footings for each column are permitted. Continuous footings require more design effort to account for the complex interaction between column plastic hinges, piles and the pile cap.

Structural engineers occasionally eliminate the bent cap by placing a column under every girder, eliminating the need for a bent cap. Eliminating the bent cap is often not cost effective, and the superstructure must be designed to transfer the transverse loads to the columns.

Aesthetics also have an important role in determining the size and shape of the columns and bent cap.


Substructures 18-11

18.2.1 Seismic Considerations

Refer to Chapter 13 for information on seismic design. The key element of seismic design is proper confinement and detailing.

18.2.2 Bent Caps

Bent caps are usually reinforced concrete members that transfer girder loads into columns or bent walls. Caps can be integral, drop or straddle caps. Drop caps are the most common.

Consider aesthetics when proportioning the bent cap. Refer to the SD drawings for bent proportioning guidelines. Normally, the cap width is 6 in. wider than the columns. Smaller caps are typically not possible due to seismic detailing requirements. Larger caps are permitted to accommodate ABC construction and/or as required to satisfy the beam seat width requirements. The bottom of the cap can be level, sloped or parallel to the slope of the deck.

The cap depth versus the cap span length affects the design of the bent caps. Where the distance between the centerline of the girder bearing and the column is less than approximately twice the depth of the cap, consider using the strut and tie model in LRFD Article 5.6.3 for the design of the cap; otherwise, use the sectional (beam) model for moment and shear.

18.2.2.1 Drop Caps

In a drop cap, the bent cap is located beneath the girders. Drop caps are the most common cap and are the preferred solution for most locations.

On prestressed girders made continuous, the preferred detail between the drop cap and integral diaphragm permits rotation. Typically, the bent cap uses a key running down the center of the cap with a single row of reinforcing connecting the diaphragm to the cap. Place a layer of rigid plastic foam under the diaphragm outside of the key. Refer to the SS sheets for typical details. Fixed connections are permissible, but the superstructure must be capacity protected for the overstrength plastic hinge forces. The required bent cap and deck reinforcing to achieve capacity protection can be significant.

Ignore the contribution of the diaphragm to the strength of the system when designing drop cap reinforcing.

18.2.2.2 Integral Caps

In an integral cap, all or most of the bent cap is located beneath the deck and between the girders. The girders frame directly into the cap. Integral caps are preferred for CIP box superstructures. Integral bent caps can also minimize grade raises when the cap overhang extends over a traveled way. Only use integral caps on steel girder or prestressed girder bridges when no other viable option exists.


18-12 Substructures

Integral caps are often post-tensioned to reduce the cap depth, reduce weight and improve long term performance. The construction sequence must be carefully monitored on integral caps. Design of the cap must permit future complete removal and replacement of the deck.

Do not use integral caps made of steel framing.

18.2.2.3 Straddle Caps

Use straddle caps when a column must be located outside of the footprint of the bridge due to roadways under the cap or other structures or utilities. A straddle cap can be a drop cap or integral cap. Consider pinned connections or isolation bearings to connect straddle caps to columns. Pinned connections reduce the torsional shear forces in the straddle cap. Most straddle caps use post-tensioning to minimize the depth, control cracking and enhance torsional resistance. Consider precast straddle caps to eliminate shoring and construction over roadways.

18.2.3 Columns and Walls

Column design requires coordination with adjacent structures and project specific aesthetic requirements. Consider a single column bent for narrow bridges over waterways. Water impacting a bent at an angle greatly increases scour, which does not adversely affect a single round column. However, in this case, single columns are usually at least 6 ft in diameter. Refer to the SD drawings for additional information on bent proportioning.

On columns that require protection by a railroad crash wall, separate the crash wall from the column by a gap sized to accommodate the anticipated seismic event displacement. Form the gap with rigid plastic foam or removable forms. Separating crash walls from the column can improve the seismic response.

A bent wall is a continuous wall extending to almost the outside edge of bridge. Bent walls are typically 2′-6″ wide with tied reinforcing. Bent walls are rarely used due to aesthetics, cost and seismic response. The structural engineer can use bent walls for bridges over railroads to satisfy AREMA crash wall requirements.

The following summarizes typical practices for the bent cross section:

1. Round Columns. Limit the minimum column diameter to 3 ft. Typically, columns are specified at even foot increments to reduce construction costs.

2. Architectural Shape/Square. Design the column with a round cage for ease of construction unless the round cage is not cost effective. When designed with a round core, the corners must be lightly reinforced with reinforcing extending into the core, which minimizes falling debris in a seismic event. Calculate the plastic hinge forces using all of the reinforcing in the section. Spalling of the corner sections is permitted during plastic hinging.


Substructures 18-13

3. Column Spacing. Space columns to minimize the project costs. Column spacing exceeding approximately 25 ft center to center of columns or less than 15 ft center to center of columns is normally not cost effective.

4. Solid Walls. Limit the minimum thickness to 2 ft for the entire height of the wall.

18.2.3.1 Column Reinforcing

Chapter 14 discusses design practices for the reinforcing of structural concrete, which applies to columns, including:

• Concrete cover • Bar spacing • Lateral confinement reinforcing • Corrosion protection • Development of reinforcing • Splices 18.2.3.2 Transverse Reinforcing

The AASHTO Guide Specifications for LRFD Seismic Bridge Design supersede LRFD Article 5.10.11.

Typically, use spirals as transverse reinforcing steel in columns. Butt welded spliced hoops can be used as an alternative. Stirrups and tie bars are appropriate for walls and columns when the column proportions are not compatible with round reinforcing cages.

18.2.3.2.1 Spiral Splices

Almost all spiral reinforcing requires a splice. The AASHTO Guide Specifications for LRFD Seismic Bridge Design provide requirements for splices in spiral reinforcing. The plan sheets must identify plastic hinge regions where a spiral lap splice is not allowed. Refer to Chapter 14 for a discussion on the use of welded and mechanical splices.

At locations where the spiral reinforcing extends into a footing or cap, the spiral reinforcing can be discontinuous. The practice allows easier placement of the top mat of footing or bottom mat of cap reinforcing. Provide a detail or note in the plan sheets that shows an allowed discontinuity in the spiral with a splice. Detail the spiral with 1¼ full flat turns with the tail extending through the center of the column and anchored to the opposite side of the reinforcing cage. See Section 14.4.1.8, Figure 14.5 for details.

18.2.3.3 Longitudinal Reinforcing

Use #7 or larger longitudinal column reinforcing. Detail the longitudinal reinforcing continuous with a maximum spacing of 8 in. center to center. Fully develop the longitudinal column


18-14 Substructures

reinforcing where the reinforcing enters into the bent cap and the spread footing, pile cap or drilled shaft. Longitudinal column reinforcing extends into the bent cap to within 6 in. of the top of the cap.

The preferred detail for longitudinal reinforcing is continuous, unspliced reinforcing. Provide a note on the bridge plans delineating the no lap splice zones.

If longitudinal column reinforcing requires splices, do not locate splices within the plastic hinge regions of the column. Refer to Section 14.4.1.8. Use a minimum stagger of 2 ft between adjacent splices. Also, stagger splices in bundled bars at a minimum of 2 ft.

The contractor is not permitted to change the location or type of splice from the types in the contract documents unless approved by the EOR.

18.2.3.4 Column Construction Joints

Use construction joints at the top and bottom of the column. Where columns exceed 25 ft in height, permit intermediate construction joints. Where applicable, locate all construction joints at least 12 in. above the water elevation expected during construction.

18.2.4 Extended Pile Bents

Do not use extended pile bents without approval from the Structures Design Manager. Under certain conditions, extending a deep foundation above ground level to the superstructure forming an extended pile bent can improve the economy of substructures.

Do not use pile bents where large lateral forces could develop due to collision, scour or stream flow intensified by accumulated debris.

18.2.5 Bent Foundations

Refer to Chapter 17 for foundation information.

18.2.6 Dynamic Load Allowance


The LRFD Specifications allow the dynamic load allowance (IM), traditionally called impact, to only be omitted on “foundation components that are entirely below ground level.” Consider the dynamic load allowance in the structural design of bent caps and columns.


Substructures 18-15

18.2.7 Moment Magnification


Bents, bent columns and piles are referred to as compressive members, although the design is normally controlled by flexure. In most cases, use the moment magnification approach in LRFD Article 5.7.4.3. For exceptionally tall or slender columns/drilled shafts where the slenderness ratio (Kl/r) is greater than 100, use a refined analysis, as outlined in LRFD Article 5.7.4.1. Where P-delta design procedures are used, consider the initial out of straightness of columns and the sustained dead load.

18.2.8 Distribution of Live Load

On bridges with integral diaphragms at the bents, distribute live load uniformly along the bent cap over a 12-ft lane width. On bridges without integral diaphragms, distribute the live load as girder reactions. Determine the girder reactions by any of the following methods:

• Use a refined analysis. • Apply maximum and minimum girder reactions to the bent to maximize bent cap and

column demands. • Assume that the live load reaction per lane is uniformly distributed to a 12-ft lane and the

uniformly distributed live load is distributed to girders assuming a simple span between the girders.


18-16 Substructures

FEBRUARY 2015

EXPANSION JOINTS AND BEARINGS



Expansion Joints and Bearings 19-i

TABLE OF CONTENTS

19.1 EXPANSION JOINTS .................................................................................................. 19-1

19.1.1 Design and Detailing ..................................................................................... 19-1 19.1.2 Selection ........................................................................................................ 19-3

19.1.2.1 Backer Rod with Sealant ............................................................... 19-3 19.1.2.2 Compression Seal ......................................................................... 19-3 19.1.2.3 Strip Seal ....................................................................................... 19-4 19.1.2.4 Modular Expansion ........................................................................ 19-4

19.1.3 Example Problem — Steel Girder Bridge with Concrete Deck ...................... 19-4

19.2 BEARINGS .................................................................................................................. 19-7

19.2.1 Design Guidance ........................................................................................... 19-7

19.2.1.1 Integral Abutment Bearing Design Criteria .................................... 19-7 19.2.1.2 Movements .................................................................................... 19-8 19.2.1.3 Effect of Camber and Construction Procedures ............................ 19-8 19.2.1.4 Serviceability, Maintenance and Protection Requirements ........... 19-8 19.2.1.5 Seismic Requirements .................................................................. 19-8 19.2.1.6 Anchor Bolts .................................................................................. 19-9 19.2.1.7 Sole Plates .................................................................................... 19-10

19.2.2 Bearing Types and Selection ........................................................................ 19-10

19.2.2.1 Plain Elastomeric Bearing Pads .................................................... 19-11 19.2.2.2 Steel Reinforced Elastomeric Bearing Pads ................................. 19-12 19.2.2.3 High Load, Multirotational Bearings .............................................. 19-12 19.2.2.4 Isolation Bearings .......................................................................... 19-13

19.2.3 Design of Elastomeric Bearing Pads ............................................................. 19-14

19.2.3.1 Elastomer ...................................................................................... 19-14 19.2.3.2 Plain Elastomeric Bearing Pads .................................................... 19-14 19.2.3.3 Steel Reinforced Elastomeric Bearing Pads ................................. 19-15

LIST OF FIGURES

Figure 19.1 — EXPANSION JOINT SELECTION ................................................................. 19-3 Figure 19.2 — SUMMARY OF BEARING CAPABILITIES .................................................... 19-11 Figure 19.3 — STRAINS IN A STEEL REINFORCED ELASTOMERIC BEARING PAD ...... 19-15


19-ii Expansion Joints and Bearings


Expansion Joints and Bearings 19-1

Chapter 19 EXPANSION JOINTS AND BEARINGS

Section 14 of the LRFD Specifications presents design requirements for expansion joints and bearings. This chapter discusses expansion joint and bearing provisions in Section 14 of the LFRD Specifications that require amplification or clarification. This chapter also addresses specific practices for the design and detailing of expansion joints and bearings.

19.1 EXPANSION JOINTS

Reference: LRFD Articles 14.4 and 14.5

19.1.1 Design and Detailing

Expansion joints in bridges accommodate the expansion and contraction of bridges due to temperature variations. Integral and semi-integral abutment bridges require expansion joints at the ends of the approach slabs. Nonintegral abutment bridges require expansion joints at abutments and/or bents. The following general criteria apply to all expansion joints in bridges:

1. Minimize Number. Use integral abutments unless substructure, geometry or other design requirements dictate otherwise. Refer to Section 18.1 for limitations on abutment types. Minimize the number of expansion joints to minimize operational and maintenance problems, but evaluate the cost differential between modular joints and strip seals. When cost effective, use multiple strip seals instead of a single modular joint. Girder ends, bearing seats and decks adjacent to joints tend to deteriorate due to leaky joints. Bearing seats also collect debris and provide locations for animal and human habitation. When evaluating multiple strip seals versus a modular joint, consider the bearing type, girder type, drainage requirements and consequences of leaking joints.

2. Tributary Expansion Length. Refer to the SD drawings for sketches of tributary length. For all bridges except single span integral abutment bridges, the tributary expansion length equals the distance from the expansion joint to the point of assumed zero movement, which is the point along the bridge that is assumed to remain stationary when expansion or contraction of the bridge occurs. The location of the point of zero movement is a function of the longitudinal stiffness of the substructure elements and bearing fixity at the locations.

3. Service Requirements. Consider the long term performance and maintenance requirements of the expansion joints and the impacts of leaking joints on adjacent elements. Failed joints contribute to many of the maintenance problems on bridges.

4. Consistency of Joint Details. Use the same type of joint and joint construction details throughout the bridge when conditions permit. Approaches to sleeper slab joints are exempt when there is an expansion joint at the abutment.


19-2 Expansion Joints and Bearings

5. Temperature Range. Use Procedure B of LRFD Article 3.12.2 for girder bridges with concrete decks. Use Procedure A for all other bridges (e.g., trusses, segmental concrete). Use the cold climate temperature ranges when using Procedure A. Construction at extreme temperatures (i.e., at or near the minimum or maximum temperatures of the assumed range) results in thermal movements in a single direction.

6. Recess Detail. Recess embedded steel elements, such as approach slab protection angles and strip seal expansion joint restrainers, ¼ in. from finished grade. The recess provides protection from snow plow blades and accommodates milling of the concrete adjacent to the joints.

7. Effects of Skew. Include skew effects when sizing joints. Movement along the centerline of the bridge results in a transverse movement in the joint. Thermal movements of skewed bridges often include an asymmetrical movement (racking), which can increase the movement demands in the joint. The acute corners of a bridge with parallel skewed supports tend to expand and contract more than the obtuse corners, causing the joint to rack.

8. Other Geometric Considerations. Consider geometric effects when evaluating movements. Horizontally curved bridges and bridges with other special geometric elements, such as splayed girders, do not necessarily expand and contract in the longitudinal direction of the girders. A refined analysis of the entire bridge could be necessary to characterize the thermal movement of complex bridges. The effect of thermal movements on the joints of complex bridges is more pronounced compared to bridges with simple geometrics. Use a refined analysis for horizontally curved, steel girder bridges to estimate thermal effects, because even slight curvature can develop significant movements in the radial direction.

9. Blockouts. Provide details on the plans for blockouts in decks and approach slabs at strip seal or modular expansion joints to allow for placement of the joint. During construction, contractors install the expansion joint assembly and place the blockout concrete after profile grinding is complete.

10. Cover Plates Over Expansion Joints. Use cover plates over expansion joints at sidewalks.

11. Creep and Shrinkage. Include the effects of creep and shrinkage in the total movement for nonintegral prestressed concrete bridges. Assume that the joint is set 56 days after casting and that creep/shrinkage continues for 20 years.

For steel girder structures and integral abutment prestressed girder bridges, creep and shrinkage effects are minimal and can be neglected in expansion joint design.

12. Setting Temperature. Determine gap widths at setting temperatures of 60°. Determine the minimum and maximum installation temperature and complete the table provided in the WS sheets. See the design example in Section 19.1.3 for an illustration of typical calculations.



13. Miscellaneous Details. Use deck drains to intercept drainage in advance of all expansion joints and place the drain as close as possible to the joint.

19.1.2 Selection

Figure 19.1 presents the types of expansion joints and the maximum joint movement. Refer to the SD drawings for expansion joint design and detailing information. Refer to the WS sheets for the required expansion joint data table.

Select the type of expansion joint and the required movement rating based on the expansion and racking demands, skew, gap widths and whether the joint is new or a retrofit. Gap width is the perpendicular distance between the faces of the joint at the road surface. Use a minimum gap of not less than 1 in. for steel or concrete bridges with expansion joints at bents or abutments, as suggested in LRFD Article 14.5.3. Use a maximum gap width of 4 in. for strip seals and 3 in. for individual components of modular joints.

Refer to the manufacturer’s literature for information on joint materials and movement capacity.

Joint Type Total Joint Movement

(in.)

Backer rod with sealant ≤ 2

Compression seal ≤ 3

Strip seal 2 to 4

Modular expansion > 4

Figure 19.1 — EXPANSION JOINT SELECTION

19.1.2.1 Backer Rod with Sealant


Use a backer rod with sealant where expansion lengths are less than 100 ft. Use of the system is viable on bridges with expansion lengths up to 200 ft. The joint width at the time of installation dictates the movement capacity of the joint. The movement capacity is a function of the installation width plus or minus some percent of original gap size. The joint sealant is easily maintained because local joint failures can be easily repaired. The system can be bonded to concrete or steel.

19.1.2.2 Compression Seal

Compression seals consist of preformed shapes compressed into the joint. Large compression seals can be difficult to install at the hottest times of the year.



19.1.2.3 Strip Seal


A strip seal consists of a gland rigidly attached to a steel restrainer on both sides of the joint. The material is premolded into a V-shape that opens as the joint width increases and closes as the joint width decreases.

Strip seal joints are watertight when properly installed. However, the seals can be difficult to replace. Avoid splices in the gland. Snowplows can damage the joint, especially if the skew is 20° or greater.

19.1.2.4 Modular Expansion


Due to the expense and maintenance requirements, use modular joints only where necessary to accommodate movements greater than 4 in. In selecting modular joint systems, use only types that have been designed to facilitate the repair and replacement of components and that have been verified by long term in service performance. Include a detailed description of the requirements for the modular joint system in the specifications or plan sheets.

The following applies to the design of modular expansion joints:

1. Joint Support. The blockouts and supports needed for modular joint systems are large and require special attention when detailing. For modular joints supported from the top of the girder, provide a detail of the supporting device in the contract documents.

2. Splices. Where practical, use full length modular joints with no field splices across the roadway width. If a field splice is required for phased construction of a CIP bridge deck, space the support girders at a maximum of 2 ft from the splice location and outside of the wheel path.

3. Synthetic Rubber Seal. For the synthetic rubber seal, which is a strip seal gland in a modular joint, use one piece across the roadway width, regardless of phased construction considerations.

19.1.3 Example Problem — Steel Girder Bridge with Concrete Deck

Structures react to temperature changes by expanding and contracting in all directions. The expansion and contraction of unrestrained structures is easy to calculate using the following equation:

( )MinDesignMaxDesignT TTL −α=Δ (LRFD Equation 3.12.2.3-1)



Where:

L = Design expansion length α = 6.5 ×10-6 in./in./ F = coefficient of thermal expansion α = 6.0 ×10-6 for concrete girder bridges α = 6.5 ×10-6 for steel girder bridges The exact proportions and directions of expansion and contraction of bridges is difficult to predict for the following reasons:

• Temperature differentials in the structure • Temperature differential between superstructure and substructure • Restraint from bearings • Restraint from soils and piles at integral or semi-integral abutments • Restraint from bents at fixed bearings • Location of center of expansion or contraction For simplicity in calculating expansion and contraction effects, assume the following:

• Temperature change is uniform across the structure when sizing bearings and expansion joints.

• No temperature differential exists between approach slabs and sleeper slabs. • The bridge side of the expansion joint moves in the longitudinal direction and the

abutment or sleeper slab does not move longitudinally. • Both sides of joints move equally in the direction parallel to the centerline of the joint.

When an expansion joint is located at the abutment, the assumption is not conservative. • Effects of restraint can be ignored. • The default maximum setting temperature is 90° F (can be superseded by specific joint

requirements). • The default minimum setting temperature is 40° F (can be superseded by specific joint

requirements). Detailed analysis of thermal movements accounting for restraint effects is permitted. When using a detailed analysis, the model must include the following:

• Use volumetric expansion/contraction. • Model all restraint forces. • Use a temperature range of 80° F maximum and a 20° F minimum for substructures

against earth (e.g., pile caps, abutments, approach slabs, sleeper slabs). • Model rotational effects. • Model the entire structure. A detailed analysis is typically not warranted. On longer structures, consideration of restraint effects is appropriate when the design movement slightly exceeds the capacity of a strip seal. In this case, consideration of restraint effects can reduce the demand to allow the use of a strip seal.



Given: Steel plate girders supporting a reinforced concrete bridge deck in Salt Lake County Expansion length, approach slab to sleeper slab joint at abutment #1 = 250 ft Expansion length, approach slab to sleeper slab joint at abutment #4 = 250 ft L = design expansion length = 250 ft W = bridge width = 46′-10″ θ = skew angle = 30°

Problem: Determine expansion joint movement requirements

Solution: Estimated unfactored thermal movement:

( )MinDesignMaxDesignT TTL −=Δ α (LRFD Equation 3.12.2.3-1)

For a steel superstructure:

F/.in/.in105.6 6 °×= −α

TMaxDesign = 120°F based upon the bridge location TMinDesign = -20°F based upon the bridge location

ΔT = (6.5 × 10-6 in./in./°F) (250 ft) (12 in./ft) (120° – (-20°)) ΔT = 2.73 in.

Use the factored movements in the joint data table defined in the WS sheets. The supplier uses the data to size the gland. Factored movement, ΔTF = 1.2 × 2.73 = 3.28 in Factored movement perpendicular to joint, ΔTF(perp) = 1.2 × 2.73 × (cos 30°) = 2.84 in. Factored movement parallel to joint, ΔTF(trans) = 1.2 × 2.73 × (sin 30°) = 1.64 in.

A strip seal joint is acceptable because the estimated design thermal movement perpendicular to the joint and parallel to the joint are within the range for strip seals.

Movement per 1°F temperature change:

2.73 in./(120°F – (-20°F)) = 0.02 in./°F

Set the minimum joint opening as 1.0-in. minimum perpendicular to the joint according to the LRFD Specifications. Use 1.0-in. perpendicular to the joint at 120°F. Estimate the opening at the setting temperature and at the minimum temperature:

@ -20°F = 1.0 in. (assumed minimum gap) + 3.28 in. (estimated design thermal movement) × (cos 30°) = 3.84 in.

@ 60°F = 1.0 in. + 1.2 × (0.02 in./°F)(120°F – 60°F)(cos 30°) = 2.22 in.

Complete the joint table and include on the joint detail sheet.



JOINT DATA TABLE

LOCATION

TOTAL FACTORED DESIGN MOVEMENT DESIGN OPENINGS

PERPENDICULAR TO THE OPENING INSTALLATION LIMITS

DIMENSION A ADJUSTMENT

PER 10°F

(INCH)

IN DIRECTION OF

MOVEMENT (INCH)

PERPENDICULAR TO THE

CENTERLINE OF THE JOINT

(INCH)

PARALLEL TO THE

CENTERLINE OF THE

JOINT (INCH)

MAXIMUMOPENING,

AMAX (INCH)

MINIMUMOPENING,

AMIN (INCH)

OPENING AT SETTING

TEMPERATURE, T = 60°F,

ASET

(INCH)

MINIMUMINSTALLATION TEMPERATURE,

(°F)

MAXIMUM INSTALLATION TEMPERATURE,

(°F)

ABUT #1 3.28 2.84 1.64 3.84 1.00 2.22 40° 90° 0.2

ABUT #4 3.28 2.84 1.64 3.84 1.00 2.22 40° 90° 0.2

Conclusion: The gap width of the seal varies from 1.0 in. to 3.84 in. A strip seal with a

longitudinal movement rating of 4 in. and transverse movement rating of +1.29 in. and -0.94 in. satisfies the movement requirements. The required transverse movement rating is directly controlled by the minimum and maximum setting temperatures.

19.2 BEARINGS

19.2.1 Design Guidance

Reference: LRFD Articles 14.4, 14.6, 14.7 and 14.8

Design all integral abutment bearings based on the requirements of Section 19.2.1.1. Design all other bearings based on the LRFD Specifications.

19.2.1.1 Integral Abutment Bearing Design Criteria

Integral abutment bearings are bearings used to support the girder during construction. During construction, the girder end at the abutment is encased in a concrete end diaphragm, which is made integral with the abutment cap. Once the end diaphragm is placed, all future loads are transferred to the abutment cap through the end diaphragm. Long term performance of the bearing is not required because the end diaphragm is capable of transferring all loads to the substructure after construction is complete. Design the bearings to the following criteria:

• Use Method A. • Design for only the DL applied before the bridge is made integral. • Design the bearing for ±50° of temperature change. • Provide a beveled sole plate when the expected bottom of girder slope at completion of

the deck placement exceeds 1.0%. Note that rotation checks are implicit in the geometric and stress requirements; therefore, no specific rotation check is required. Refer to the WS sheets for standard plain elastomeric bearing pads for use with UBT girders.



19.2.1.2 Movements

Bridge bearings accommodate the movements of the superstructure and transmit the loads to the substructure. The consideration of movement is important for bearing design, which includes both translations and rotations. The sources of movement include initial camber or curvature, construction loads, misalignment, construction tolerances, settlement of supports, thermal effects, creep, shrinkage, seismic and traffic loading.

19.2.1.3 Effect of Camber and Construction Procedures

The initial camber of bridge girders induces bearing rotation. Initial camber can cause a larger initial rotation on the bearing, but the rotation could decrease as the construction of the bridge progresses. Rotation due to camber and the initial construction tolerances are sometimes the largest component of the total bearing rotation.

Evaluate both the initial rotation and the short duration of the initial rotation. At intermediate stages of construction, add deflections and rotations due to the progressive weight of the bridge elements and construction equipment to the effects of live load and temperature. Also, consider the direction of loads, movements and rotations. Do not simply add the absolute maximum magnitudes of the design requirements. Do not consider combinations of absolute maximums that cannot occur.

19.2.1.4 Serviceability, Maintenance and Protection Requirements


Bearings under deck joints can be exposed to dirt, debris and moisture that promote corrosion and deterioration. Design bearings to minimize environmental damage and to allow easy access for inspection.

The service demands on bridge bearings are severe and result in a service life that is typically shorter than that of other bridge elements. Therefore, include allowances for bearing replacement in the design. Bearings at integral abutments with a concrete diaphragm surrounding the girder and resting on the abutment do not require a replacement strategy.

19.2.1.5 Seismic Requirements

Reference: LRFD Articles 14.6.5 and 14.8.3.2

Bearing selection and design must be consistent with the intended seismic response of the entire bridge system.

Bearings (other than seismic isolation bearings or structural fuse bearings) can be classified as rigid or deformable. Rigid bearings transmit seismic loads without any movement or deformations. Deformable bearings transmit seismic loads limited by plastic deformations or a restricted slippage of bearing components. Only elastomeric expansion bearings where 1.2



times the seismic movement is less than the bearing movement capacity are considered deformable for seismic loads. All other expansion bearings are rigid and all fixed bearings are rigid. Refer to Section 13.6.7 for a discussion on bearing modeling.

Where rigid bearings are used, assume that the seismic forces from the superstructure are transmitted through diaphragms or cross frames and connections to the bearings, and then to the substructure without reduction due to local inelastic action along the load path.

Do not use plain elastomeric pads as structural fuse bearings.

Use steel reinforced elastomeric pads with PTFE sliding surfaces as structural fuse bearings. Design the substructure for a minimum of 20% of the DL, and do not include the substructure element under the bearing as a resisting element in the seismic response of the bridge.

Do not use steel reinforced elastomeric pads without PTFE sliding surfaces as structural fuse bearings, unless the seismic movements are less than the permitted temperature displacements for the bearing. Design the substructure for a minimum of 20% of the DL, and do not include the substructure element under the bearing as a resisting element in the seismic response of the bridge.

Elastomeric bearing pads provide adequate seismic performance for most bridges. Do not rely on the bearing to transmit seismic forces to the substructure if the bearing is not a structural fuse bearing. Design anchor bolts or restrainer systems to transfer the seismic load to the substructure.

Typically, use shear keys or dowels to transfer superstructure seismic forces to the substructure. In unusual situations, use restrainers, shock transmission units or dampers to control structure displacements and load transfer to substructure elements.

19.2.1.6 Anchor Bolts

Although the LRFD Specifications require anchor bolts in various circumstances, design needs dictate anchor bolt use. Do not rely on a uniform distribution of loads to anchor bolts.

Use anchor bolts to transfer horizontal forces through bearing assemblies when external devices such as shear keys are not present. In addition, use anchor bolts as hold downs for bearings. Use shear keys in lieu of bolts when geometry permits.

Holes for anchor bolts in steel elements of bearing assemblies must be ¼ in. larger in diameter than the diameter of the anchor bolt. The centerlines of anchor bolts are a minimum of 2 in. from the edge of the girder. A larger offset could be necessary to facilitate installation. Consider the space necessary for nuts, washers, base plate welds and construction tolerances and establish anchor bolt locations accordingly. Maintain ½-in. clearance from the edge of the elastomeric bearing to the edge of the anchor bolt.

Provide sufficient reinforcement around the anchor bolts to develop the horizontal forces and anchor the bolts into the mass of the substructure unit. Identify potential concrete crack surfaces next to the bearing anchorage and evaluate the shear friction capacity. Conflicts



between anchor bolt assemblies and substructure reinforcement or superstructure cross frames is common, especially for skewed bridges. Therefore, ensure that all reinforcing steel can fit around the bearing assemblies and that the anchor bolts are accessible and do not interfere with cross frames.

19.2.1.7 Sole Plates

The sole plate must be at least 1 in. wider than the elastomeric bearing. Use a minimum sole plate thickness of 1½ in. When the instantaneous slope of the grade plus the final in place camber exceeds 1%, bevel the sole plate to match the grade plus final camber. For beveled sole plates, maintain a minimum of 1½-in. thickness at the edge of the sole plate. Refer to the SS sheets for sample bearing details. In typical applications, the sole plate is shop welded and the top plate is field welded to the sole plate, which permits adjustments to fit field conditions.

At expansion bearings with anchor bolts, provide slotted top plates. Determine the minimum slot size according to the amount of movement and end rotation calculated. The slot length, L, is:

L = (diameter of anchor bolt) + 1.2 (total movement) + 1.0 in.

The multiplier of 1.2 represents the load factor from LRFD Table 3.4.1-1 for TU, CR and SH. Include the effect of girder end rotation at the level of the top plate when estimating the total movement. Round the slot length up to the nearest ¼ in. To account for the possibility of different setting temperatures during construction, provide offset dimensions on the plan sheets.

19.2.2 Bearing Types and Selection

Where possible, use steel reinforced elastomeric bearing pads for all girder bridges that are not integral. Bridges with large bearing loads and/or multidirectional movement could require other bearing devices such as pot, spherical or disc bearings.

Do not use roller bearings or rocker bearings. Do not use pot or disc bearings for seismic applications where significant vertical acceleration is present. Where the use of pot or disc bearings is unavoidable, provide an independent seismically resistant anchorage system.

Consider the impact on the lateral load path due to unequal participation of bearings considering connection tolerances, unintended misalignments, the capacity of individual bearings and skew effects.

Provide adequate support length for fixed bearings that are not fully integral. Provide restrainers, shear keys or other methods of restraint when the bearing movement capacity is less than 1.2 times the seismic displacement. In the restrained directions, detail bearings to engage at essentially the same movement.

Bearing selection is influenced by many factors including loads, geometry, maintenance, available clearance, displacement, rotation, deflection, availability, construction tolerances and cost. In general, restrain vertical displacements, allow rotations to occur as freely as possible,



and either accommodate or restrain horizontal displacements. Distribute the loads among the bearings according to the superstructure analysis.

Figure 19.2 summarizes bearing capabilities. The values shown in the table are for preliminary guidance only. The final step in the selection process consists of completing a design of the bearing according to the LRFD Specifications. If the load falls outside of the optimal ranges, contact the bearing manufacturer.

Type Load (kips)

Translation (in.) Rotation

limit (rad)

Cost

Optimal Design Range1

Min Max Initial Maintenance

Plain elastomeric bearing pad

0 to 220 0 ¾ 0.0175 low low

Steel reinforced elastomeric bearing pad

50 to 650 0 3 0.04 low low

Steel reinforced elastomeric bearing pad with PTFE sliding surface

50 to 650 0 > 3 0.04 low low

HLMR bearings

Pot bearing

270 to 2250 02 02 0.04 – 0.05

high high

Disc bearing

270 to 2250 02 02 0.03 high high

Spherical bearing

270 to 2250 02 02 > 0.05 high high

Isolation bearing 0 to 2250 0 03 0.04 high high

1 Higher and lower values could be applicable if necessary. 2 HLMR bearings have no inherent translational capability. Expansion bearings are achieved by using

HLMR bearings in conjunction with flat PTFE sliding surfaces. 3 Design isolation bearings to accommodate significant displacements during a seismic event.

Figure 19.2 — SUMMARY OF BEARING CAPABILITIES 19.2.2.1 Plain Elastomeric Bearing Pads

Plain elastomeric bearing pads are usually the preferred low cost option for integral abutments. See Section 19.2.3 for a discussion on the design of plain elastomeric bearing pads.



19.2.2.2 Steel Reinforced Elastomeric Bearing Pads

Steel reinforced elastomeric bearing pads are usually the preferred low cost option for nonintegral abutments and require minimal maintenance. Limit the height of steel reinforced elastomeric bearing pads to 6 in. Provide horizontal restraint greater than the maximum demands for fixed bearings. Refer to the SS sheets for sample details.

See Section 19.2.3 for a discussion on the design of steel reinforced elastomeric bearing pads.

Use a combination bearing where horizontal movements exceed 3 in. Combination bearings use a steel reinforced elastomeric bearing pad to accommodate rotation and a stainless steel plate/PTFE sliding surface to provide translational capability.

Size the steel reinforced elastomeric bearing pad and the required length of the sliding plate. The bearing supplier sizes the top plate, PTFE surface and stainless steel plate based on loads listed on the plan sheets.

19.2.2.3 High Load, Multirotational Bearings

HLMR bearings are generally avoided due to cost and maintenance concerns. HLMR bearings are appropriate for bridges with large vertical loads; i.e., in excess of 650 kips. The choice among HLMR bearings is based upon the rotational capabilities presented in Figure 19.2.

Do not include specific details for HLMR bearings in the plan set. Only show schematic bearing details, combined with specified loads, movements and rotations. Provide a jacking plan sheet. Refer to Chapters 14 and 15 for additional jacking information. The manufacturer designs the bearing. Provide a special provision when specifying HLMR bearings.

19.2.2.3.1 Pot Bearings

Reference: LRFD 14.7.4

Pot bearings consist of a pot/piston assembly within which an elastomeric disc is encapsulated and fitted with an anti extrusion sealing device. Under load, the encapsulated elastomeric disc acts similar to an uncompressible confined fluid, enabling the pot and piston to rotate relative to each other. Pot bearings enable rotation in any direction. The pot and piston feature fittings for securing the bearing to the bridge structure.

Fixed pot bearings are constrained horizontally. Free sliding pot bearings are fitted with a PTFE sliding surface in contact with a steel plate, enabling the bearing to slide in all directions. Guided sliding pot bearings are identical in construction to free sliding bearings but are also fitted with one or more guides to limit the bearing movement to only one direction.

Pot bearings are able to support large compressive loads, but the elastomer can leak and the sealing rings can suffer wear or damage.



19.2.2.3.2 Spherical Bearings


Spherical bearings, termed bearings with curved sliding surfaces, include bearings with both spherical and cylindrical sliding surfaces. Spherical bearings are able to sustain large rotations but require proper clearances and very smooth and accurate machining.

A spherical bearing relies upon the low friction characteristics of a curved PTFE stainless steel interface to provide a high level of rotational flexibility in multiple directions. An additional flat PTFE stainless steel surface can be incorporated into the bearing to provide either guided or nonguided translational movement capability. Woven PTFE is generally used on the curved surfaces of spherical bearings. Woven PTFE exhibits enhanced creep (cold flow) resistance and durability characteristics relative to unwoven PTFE. When spherical bearings are detailed to accommodate translational movement, woven PTFE is generally also specified on the flat sliding surface.

Most spherical bearings are fabricated with the concave surface oriented downward to minimize dirt infiltration between PTFE and the stainless steel surface. Refined modeling of the overall structure must consider that the center of rotation of the bearing is not coincident with the neutral axis of the girder above.

19.2.2.3.3 Disc Bearings

Reference: LRFD Article 14.7.8 A disc bearing is composed of an annular shaped urethane disc designed to provide moderate levels of rotational flexibility. A steel shear resisting pin in the center provides resistance against lateral force. A flat PTFE stainless steel surface can be incorporated into the bearing to also provide translational movement capability, either guided or nonguided.

Disc bearings are susceptible to uplift during rotation. Do not use a PTFE sliding surface when uplift is possible.

19.2.2.4 Isolation Bearings

Isolation bearings are used in high seismic zones to minimize force effects in the substructures and superstructures due to ground movements.

Various types of isolation bearings are available, most of which are proprietary. See the AASHTO Guide Specifications for Seismic Isolation Design and the FHWA Seismic Retrofitting Manual for Highway Structures: Part 1 – Bridges for detailed information. Isolation bearings increase the fundamental period of vibration of the bridge resulting in lower seismic forces. Although the period shift lowers the seismic forces, the shift increases the seismic displacements. Isolation bearings also provide improved damping characteristics to limit the seismic displacement demands. Use the WS sheets to detail the isolation bearing requirements



in the plans. Provide a jacking plan sheet. Refer to Sections 14.6.2 and 15.5.6 for additional jacking information. Provide a special provision when specifying isolation bearings.

19.2.3 Design of Elastomeric Bearing Pads

Plain elastomeric bearing pads and steel reinforced elastomeric bearing pads have fundamentally different behaviors and, therefore, the discussions are separate. Typically, orient plain elastomeric bearing pads and steel reinforced elastomeric bearing pads so that the long side is parallel to the pad’s principal axis of rotation. The orientation better accommodates rotation.

Design the pad according to the AASHTO Guide Specifications for Seismic Isolation Design when using elastomeric expansion bearings without shear keys, guides or restrainers.

19.2.3.1 Elastomer


Only use neoprene for plain elastomeric bearing pads and steel reinforced elastomeric bearing pads.

All elastomers are visco elastic, nonlinear materials and, therefore, the properties vary with strain level, rate of loading and temperature. Bearing manufacturers evaluate the materials on the basis of Shore A durometer hardness, but the parameter is not a good indicator of the shear modulus, G. Use a Shore A durometer hardness of 50 to 60, which produces shear modulus values in the range of 0.095 ksi to 0.200 ksi at 73°F (use the least favorable value for design). The shear stiffness of the bearing is the most important property because the shear stiffness affects the forces transmitted between the superstructure and substructure.

Elastomers are flexible under shear and uniaxial deformation, but are very stiff against volume changes. The feature makes possible the design of a bearing that is flexible in shear but stiff in compression.

Elastomers stiffen at low temperatures. The low temperature stiffening effect is very sensitive to the elastomer compound. The increase in shear resistance is controlled by selection of elastomer grade according to guidance in the LRFD Specifications.

19.2.3.2 Plain Elastomeric Bearing Pads

Plain elastomeric bearing pads can support modest gravity loads, but can only accommodate limited translation. Plain elastomeric bearing pads are best suited for bridges with small expansion lengths or integral abutment applications.

Plain elastomeric bearing pads rely on friction at the top and bottom surfaces to restrain bulging due to the Poisson effect. Friction is unreliable. Local slip during vertical loading results in a larger elastomer shear strain from compression than that which occurs in steel reinforced



elastomeric bearing pads. The increased elastomer strain limits load capacity and the pad must be relatively thin to carry the maximum allowable compressive load. Use a maximum friction coefficient of 0.20 for the design of plain elastomeric bearing pads that are in contact with clean concrete or steel surfaces. If the shear force is greater than 0.20 of the simultaneously occurring compressive force, then secure the plain elastomeric bearing pad against horizontal movement.

19.2.3.3 Steel Reinforced Elastomeric Bearing Pads


Steel reinforced elastomeric bearing pads have uniformly spaced layers of steel and elastomer. The bearing accommodates translation and rotation by deformation of the elastomer. The elastomer is flexible under shear stress but stiff against volumetric changes. Under uniaxial compression without steel reinforcement, the flexible elastomer shortens in height significantly and sustains large increases in plan dimension but, with the stiff steel layers, lateral expansion is restrained. The restraint induces a bulging pattern as shown in Figure 19.3 and provides a large increase in stiffness under compressive load. The result permits a steel reinforced elastomeric bearing pad to support relatively large compressive loads while accommodating large translations and rotations. If the shear force is greater than 0.20 of the simultaneously occurring compressive force, then secure the bearing against horizontal movement.

Figure 19.3 — STRAINS IN A STEEL REINFORCED ELASTOMERIC BEARING PAD



Large rotations and translations require thicker bearings. Translations and rotations can occur about the longitudinal or transverse axis of a steel reinforced elastomeric bearing pad.

Use Method A or B to design steel reinforced elastomeric bearing pads. The Method B design procedure allows significantly higher average compressive stresses than Method A. The higher allowable stress levels are justified by an additional acceptance test, specifically a long duration compression test. List the design method used on the plan sheet.

Assume that slippage will not occur unless a combination bearing is specified.

Use a setting temperature of 60°F for the installation of the bearings unless the time of construction is known, for which the setting temperature can be modified accordingly. Use 80% of the total movement range for checking movement in a single direction. The value assumes that the bearing is installed within 30% of the average of the maximum and minimum design temperatures.

The following also applies:

1. Load. Verify availability of steel reinforced elastomeric pads when the design load exceeds 650 kips. Steel reinforced elastomeric bearing pads can become excessively large if the pads are designed for loads greater than approximately 650 kips.

2. Orientation. Orient elastomeric steel reinforced elastomeric bearing pads so that the long side is parallel to the principal axis of rotation where practical.

3. Holes in Elastomer. Do not use holes in steel reinforced elastomeric bearing pads.

4. Edge Distance. Use 3 in. as the minimum edge distance from the edge of the pad to the edge of the concrete seat for steel reinforced elastomeric bearing pads resting directly on a concrete bridge seat.

5. Length. The minimum steel reinforced elastomeric bearing pad length or width is 6 in.

6. Shims/Elastomer Cover. Provide a minimum of ¼ in. of cover from the edges of the steel shims to the outside edge of the elastomer.

FEBRUARY 2015

ACCELERATED BRIDGE CONSTRUCTION



Accelerated Bridge Construction 20-i

TABLE OF CONTENTS

20.1 INTRODUCTION .......................................................................................................... 20-1

20.1.1 Policy ............................................................................................................. 20-1 20.1.2 Benefits ......................................................................................................... 20-1 20.1.3 Definitions ...................................................................................................... 20-2

20.2 DECISION MAKING PROCESS .................................................................................. 20-4

20.2.1 Accelerated Bridge Construction Rating Procedure ...................................... 20-4

20.2.1.1 Accelerated Bridge Construction Measures ................................. 20-4

20.2.2 Accelerated Bridge Construction Decision Flowchart ................................... 20-6

20.3 ACCELERATED BRIDGE CONSTRUCTION METHOD SELECTION ....................... 20-7

20.3.1 Guidelines to Determine Appropriate ABC Method ....................................... 20-7 20.3.2 Offline Construction ....................................................................................... 20-7

20.3.2.1 Self Propelled Modular Transporter Projects ............................... 20-8 20.3.2.2 Lateral Slides ............................................................................... 20-9 20.3.2.3 Longitudinal Launches ................................................................. 20-10 20.3.2.4 Crane Based Projects .................................................................. 20-11

20.3.3 Online Construction ....................................................................................... 20-12

20.3.3.1 Prefabricated Elements................................................................ 20-12

20.3.4 Required Information on Plans ...................................................................... 20-13

20.3.4.1 Prefabricated Element Sheet Requirements ................................ 20-14

20.4 TECHNICAL ................................................................................................................ 20-14

20.4.1 Materials ........................................................................................................ 20-14 20.4.2 Load and Resistance Factors ........................................................................ 20-14 20.4.3 Load Rating Existing Structures .................................................................... 20-14 20.4.4 Utilities ........................................................................................................... 20-15 20.4.5 Prefabricated Elements ................................................................................. 20-15

20.4.5.1 Element Size and Weight Guidelines ........................................... 20-16 20.4.5.2 Prefabricated Element Design ..................................................... 20-16 20.4.5.3 Lifting Hardware ........................................................................... 20-17 20.4.5.4 Tolerances ................................................................................... 20-17


20-ii Accelerated Bridge Construction

20.4.6 Connections .................................................................................................. 20-18 20.4.6.1 Emulative ..................................................................................... 20-18 20.4.6.2 Pin/Friction ................................................................................... 20-18 20.4.6.3 Commercial Grouted Splice Couplers.......................................... 20-18 20.4.6.4 Corrugated Pipe Voids ................................................................. 20-20 20.4.6.5 Post-Tensioning ........................................................................... 20-20 20.4.6.6 Shear Key .................................................................................... 20-21

20.4.7 Substructure Design ...................................................................................... 20-21

20.4.7.1 CIP Construction Under Existing Bridges .................................... 20-21 20.4.7.2 Spread Footings and Spread Footings on Stabilized Earth ......... 20-22 20.4.7.3 Piles ............................................................................................. 20-22 20.4.7.4 Micropiles ..................................................................................... 20-22 20.4.7.5 Drilled Shafts ............................................................................... 20-22 20.4.7.6 Re-Use of Existing Substructures ................................................ 20-23

20.5 BRIDGE MOVES USING SELF PROPELLED MODULAR TRANSPORTER

UNITS OR SIMILAR SYSTEMS .................................................................................. 20-23 20.5.1 Self Propelled Modular Transporter Units ..................................................... 20-23 20.5.2 Hydraulic Support Units ................................................................................. 20-24 20.5.3 Planning ........................................................................................................ 20-24 20.5.4 Plan Requirements ........................................................................................ 20-24 20.5.5 Bridge Removal ............................................................................................. 20-24 20.5.6 Design Approach ........................................................................................... 20-25

20.5.6.1 Load Conditions, Loads Cases and Load Factors ....................... 20-25 20.5.6.2 Connection to Bridge During the Move ........................................ 20-25 20.5.6.3 Stroke Demand ............................................................................ 20-26 20.5.6.4 Bearing on Self Propelled Modular Transporter Supports ........... 20-26 20.5.6.5 System Response During a Bridge Lift ........................................ 20-26 20.5.6.6 Tolerances ................................................................................... 20-29 20.5.6.7 Connection to Substructure ......................................................... 20-30 20.5.6.8 Bearings ....................................................................................... 20-31 20.5.6.9 Monitoring .................................................................................... 20-31 20.5.6.10 Deck/Parapet Reinforcing Requirement ...................................... 20-31 20.5.6.11 Prestressed Girder Stress Limits During the Move ...................... 20-31

20.6 LATERAL SLIDE BRIDGE MOVES ............................................................................ 20-32

20.6.1 Types of Slides .............................................................................................. 20-32

20.6.1.1 Rolling .......................................................................................... 20-32 20.6.1.2 Sliding .......................................................................................... 20-32

20.6.2 Types of Jacks .............................................................................................. 20-32


Accelerated Bridge Construction 20-iii

20.6.2.1 Pull Jacks ..................................................................................... 20-32 20.6.2.2 Push Jacks .................................................................................. 20-33 20.6.2.3 Push/Pull Jacks ........................................................................... 20-33

20.6.3 Key Design Considerations ........................................................................... 20-33

20.6.3.1 Vertical Loads .............................................................................. 20-33 20.6.3.2 Horizontal Loads .......................................................................... 20-34 20.6.3.3 Plan Requirements ...................................................................... 20-34 20.6.3.4 Approach Slab ............................................................................. 20-35 20.6.3.5 Vertical Clearance ....................................................................... 20-35

20.7 MISCELLANEOUS BRIDGE MOVE METHODS......................................................... 20-35

20.7.1 Crane ............................................................................................................. 20-35 20.7.2 Gantry Crane ................................................................................................. 20-36 20.7.3 Strand Jacks .................................................................................................. 20-36 20.7.4 Launches ....................................................................................................... 20-36

20.8 TEMPORARY SUPPORT STRUCTURES .................................................................. 20-36

20.8.1 Staging Area Supports .................................................................................. 20-36 20.8.2 During Move or on SPMT Supports .............................................................. 20-36

LIST OF FIGURES

Figure 20.1 — APPROXIMATE GROUTED SPLICE COUPLER DIMENSIONS .................. 20-19 Figure 20.2 — MINIMUM CORRUGATION SIZES FOR CORRUGATED STEEL PIPES ................................................................................................ 20-20 Figure 20.3 — METHOD B LIFT STRESSES ....................................................................... 20-28 Figure 20.4 — SHEAR KEY FOR SEMI-INTEGRAL ABUTMENT ........................................ 20-30


20-iv Accelerated Bridge Construction


Accelerated Bridge Construction 20-1

Chapter 20 ACCELERATED BRIDGE CONSTRUCTION

The LRFD Specifications do not specifically address accelerated bridge construction. Selected applications of the LRFD Specifications do apply to ABC as noted in this chapter, which addresses practices and criteria for design considerations for ABC.

20.1 INTRODUCTION

20.1.1 Policy

ABC is a tool for accelerating project delivery. The advantages include reducing construction schedules to lessen impacts to the traveling public and minimizing total project costs. Total project costs include both direct construction costs and indirect costs such as maintenance and user costs associated with delays. Evaluate ABC on all projects through a thorough understanding and analysis of the impacts to the public considering maintenance of traffic, construction schedule and project specific critical features (e.g., environmental or railroad constraints).

Use ABC in all projects where a reduction in total project cost (price plus time) is available. See Section 20.2 for the ABC decision making process.

20.1.2 Benefits

ABC techniques provide many benefits, including:

• Improves quality • Accelerates project delivery

o Removes the bridge as a critical element of the construction schedule o Reduces construction time for environmental requirements and weather

limitations • Encourages innovation

o Uses alternative bridge design and construction methods to meet the project goals

• Minimizes duration of maintenance of traffic o Adds value to the project by reducing impacts on the public o Improves worker safety and safety to the traveling public o Increases public support o Increases political capital

• Reduces project cost o Reduces user costs o Reduces oversight and inspection costs through reduction in project duration o Uses typical details and standards to lower project costs


20-2 Accelerated Bridge Construction

20.1.3 Definitions

Chapter 1 provides a list of definitions. The following apply specifically to ABC projects:

1. ABC Communication Plan. A plan to maintain contact between all parties involved during a bridge move.

2. Bridge Move Plan. A plan indicating a timeline for all bridge movement activities, itemizing potential threats to the movement schedule and identifying actions needed if an event disrupts the schedule of the bridge move.

3. Bridge Staging Area. Area in which a new bridge is constructed.

4. Bridge Temporary Works. Any structure used to provide temporary support to a bridge or bridge component.

5. Contingency Plans. Alternative plans and solutions to possible unexpected events during all aspects related to the construction and placement of the structure including move schedule.

6. Design Build. A contracting method in which UDOT hires a contractor to develop and execute all project plans.

7. Design Builder. The firm contracted to develop and construct all project plans.

8. Design Bid Build. The traditional contracting method in which UDOT develops a complete plan set before soliciting bids.

9. Engineer for Contractor. The engineer hired by the contractor to prepare and submit stamped drawings as required.

10. Fatal Flaws. Any obstacles to project completion that cannot be mitigated.

11. Final Bridge Location. The location where the new bridge is installed and placed into service.

12. Ground Bearing Capacity. The capacity of the ground to resist applied loads.

13. Heavy Lifter. The firm employed by the contractor to provide heavy lifting equipment, operation and engineering.

14. Lessons Learned Meeting. A meeting held to retain the knowledge gained from a project.

15. Monitoring. The act of measuring the changes in the geometry of the new bridge as a result of temporary support conditions, movement operations and setting the bridge in its final location.

16. Other Lift System. Any additional equipment, other than the SPMTs and SPMT blocking, that is required to move the new bridge.



17. Permanent Substructure. The foundation upon which the new bridge will permanently rest.

18. Prebid Meeting. A meeting held to show contractors the proposed project details and solicit input before bidding.

19. Preconstruction Meeting. A meeting held with the selected contractor to coordinate contract items necessary for the successful completion of the project. Typical discussions include schedule, roles and responsibilities, lines of communication, contact information and project specific topics.

20. Reference Points. Fixed points identified on the new bridge that are observed during the move to monitor deflections.

21. Safety Plan. A plan to protect all personnel, spectators and property during construction and movement of the new bridge.

22. Self Propelled Modular Transporter. Self propelled multi-axle platform vehicle with self leveling capabilities, able to move in any direction and place loads within millimeters.

23. Self Propelled Modular Transporter Axle Line. A row of paired wheels (4 wheels or 2 axles) positioned along a line across the narrowest dimension of an individual SPMT unit.

24. Self Propelled Modular Transporter Axle Load. The amount of force exerted by each axle (2 wheels) of the SPMTs.

25. Self Propelled Modular Transporter Blocking. The apparatus between the top platform of the SPMTs and the bottom of the new bridge.

26. Self Propelled Modular Transporter Carrier Beam. Part of the SPMT blocking; the carrier beam is positioned perpendicular to the girders if the SPMTs are positioned parallel to the girders.

27. Self Propelled Modular Transporter Support Point. Point where the SPMT blocking supports the new bridge.

28. Stroke. The distance that jacks or SPMTs can raise or lower the platform in a single operation.

29. Temporary Substructure. The temporary supports upon which the new bridge is constructed.

30. Travel Path. The route along which the SPMT or other equipment carries the new bridge from the BSA to the final bridge location.



20.2 DECISION MAKING PROCESS

This section presents the ABC decision making process and the use of the process during project development. ABC is a tool to support project delivery goals. The ABC decision making process consists of two steps — completing the ABC rating procedure and then using the rating in the ABC decision flowchart to determine if an ABC approach is required. The range of scores used in the ABC decision flowchart is set to ensure that accelerated construction is typical when the measured benefit is more significant than the measured cost with respect to accomplishing the project goals.

20.2.1 Accelerated Bridge Construction Rating Procedure

An ABC rating procedure spreadsheet is available to assist engineers in the implementation of the rating process. The evaluation spreadsheet is available on the website. Use the ABC rating procedure spreadsheet and the flowchart to determine if an ABC approach is required. Do not change the weighting factors for individual projects. The spreadsheet combines the weighting factors and assigned values to obtain an ABC rating.

The ABC rating procedure requires that structural engineers assign a value to each of the ABC measures. See Section 20.2.1.1 for descriptions of the ABC measures. The values are a function of the bridge location. The spreadsheet includes guidelines for assigning values. Use the standard weighting factors for each of the ABC measures. The weighting factors are subject to change to coincide with future changes in policies.

The spreadsheet multiplies the values assigned to each project decision by the corresponding weighting factor. The ABC rating score is the ratio of the weighted score to the maximum score shown as a percentage.

Scores higher than 20 require an ABC approach. The ABC threshold of 20 is intended to capture any project receiving a score of 5 in any one of the four most heavily weighted categories.

The higher ABC threshold score of 50 is intended to capture any project receiving an average score of 3.5 in the four most heavily weighted categories.

Use the ABC rating score to enter the flowchart and work toward a conclusion.

20.2.1.1 Accelerated Bridge Construction Measures

Nine measures of project constraints are applicable to the ABC decision making process:

• Average daily traffic • Delay/detour time • Bridge classification • User costs • Economy of scale



• Use of typical details • Safety • Environmental issues • Railroad impacts 20.2.1.1.1 Average Daily Traffic

ADT accounts for the volume of traffic traversing the bridge site. Use a value equal to the total number of vehicles on the bridge and on the roadway under the bridge (if applicable). The measure incorporates the value of maintaining the interstate highway network by assigning the maximum score when the bridge is on an interstate highway or over an interstate highway.

20.2.1.1.2 Delay/Detour Time

Delay/detour time accounts for the time impact that a project has on vehicles passing through the construction site and, therefore, the construction time delays due to detours and congestion. Obtain the estimated delay times from the TOC.

20.2.1.1.3 Bridge Classification

Bridge classification accounts for bridges that are on or over a designated evacuation route or part of a critical lifeline route used in an emergency such as a major earthquake.

20.2.1.1.4 User Costs

User costs account for the financial impact of a construction project on the traveling public. The major contributing factors in calculating user costs are delay time and ADT. The duration of the impact to users is also a key component in measuring the impact of construction. Use the standard methods for calculating user costs. Calculate the user costs in coordination with the Structures Project Engineer and the TOC to determine the total project cost for each construction option evaluated (e.g., SPMT bridge move, prefabricated elements, conventional construction).

20.2.1.1.5 Economy of Scale

Economy of scale accounts for the repetition of the elements and processes. Repetition of elements or processes can lower the overall cost of a project, and can lower costs on future projects. The total number of spans accounts for repetition of substructure and superstructure elements.



20.2.1.1.6 Use Consistent Details

Use consistent details for ABC projects. All bridges can be built using ABC; however, the complexity of the bridge geometry often renders the use of typical details impractical or expensive. Evaluate the bridge site conditions and determine the level of complexity as complexity relates to various ABC techniques. The use of consistent details leads to more repetition of elements, faster construction times, higher quality and reduced prices. Refer to the SD drawings and the WS sheets for typical details.

20.2.1.1.7 Safety

Safety accounts for the increase in safety provided to the traveling public and the work force at the construction site when using ABC. ABC reduces the exposure time of travelers and workers in work zones. Project sites requiring complex MOT schemes for extended periods are undesirable.

20.2.1.1.8 Environmental Challenges

Environmental issues account for the project impact to the surrounding environment. The presence of endangered species or annual spawning seasons often leads to short construction windows. Projects can also have limitations due to wetlands, air quality, extreme weather or noise. ABC can reduce impacts to the surrounding environment to an acceptable level.

20.2.1.1.9 Railroad Impacts

Railroad impacts account for the impact of railroad traffic on the project. Use the number of trains and type of train traffic to measure the impact.

20.2.2 Accelerated Bridge Construction Decision Flowchart

The ABC decision flowchart uses the ABC rating score and then addresses yes/no factors to consider before making a final decision on the construction approach. The factors include:

• Project schedule • Environmental issues • Total project cost • Site conditions • High level indirect costs (e.g., political capital, safety, possible impacts to stakeholders)



20.3 ACCELERATED BRIDGE CONSTRUCTION METHOD SELECTION

20.3.1 Guidelines to Determine Appropriate ABC Method

Many types of ABC methods are available. Determining the appropriate method of ABC for a specific project is highly dependent on the MOT requirements at the site, the site geometrics and project funding.

ABC methods are in two main categories:

1. Offline Construction. Constructs the bridge outside of the final location using normal construction and/or prefabricated elements. Once construction is essentially complete, the bridge is moved into place. Offline construction is divided into four subcategories — SPMT moves, lateral slides, longitudinal launches and crane based. The heavy lift ABC checklist provides a comprehensive summary of expectations for engineers and stakeholders.

2. Online Construction. Constructs the bridge in its final location using prefabricated elements to accelerate construction. Prefabricated elements range from localized use of prefabricated elements to structures entirely composed of prefabricated elements.

20.3.2 Offline Construction

Use offline construction when MOT requirements are too stringent for the use of prefabricated elements or when it is more cost effective to use offline construction. Offline construction uses prefabricated bridge systems. Prefabricated bridge systems are bridge superstructure systems fully constructed offline with the exception of closure pours, when required. The systems can use any type of girder (i.e., steel, concrete, composite). Prefabricated bridge systems are a large category of structures, including prefabricated segmental bridges.

Constructing the entire bridge offsite yields additional benefits, including:

• Permits longer cure times for all concrete components • Provides efficient use of construction equipment • Provides better control over the environment at the construction site • Lowers lifecycle costs • Promotes public support Budget issues associated with offline construction are difficult to quantify because cost is significantly affected by project specific issues. Typically, the following is true:

• SPMT systems have high mobilization costs and are normally more expensive than a lateral slide for a single move. SPMT per move costs are reduced when using the SPMT systems for multiple bridge moves in a single project.

• Lateral slides minimize bridge move costs. Costs are not significantly reduced with multiple moves.



• Longitudinal launches require the most design effort, and range between the cost of a lateral slide and the cost of a SPMT move.

• Crane based system placement costs are normally higher than lateral slides but less than SPMT moves.

20.3.2.1 Self Propelled Modular Transporter Projects

SPMT projects are effective when the ADT crossing over and under the bridge is high. SPMT projects construct the bridge offsite where construction does not impact traffic. The contractor moves the bridge into place after the superstructure and substructure construction is complete.

Section 20.5 presents specific SPMT design requirements and SPMT information.

20.3.2.1.1 Selection Criteria

SPMTs aid bridge replacement in two ways:

• Provides faster removal of the existing bridge compared to in place demolition • Transports a bridge from the staging area to the final bridge location SPMTs are especially advantageous for bridge replacements that require minimal roadway closure time. A project requires minimal closure time if:

• The bridge or cross street has high traffic volumes • The bridge or cross street is on an emergency evacuation route • The bridge is over a railroad or navigable waterway • Schools or hospitals are accessed via the bridge or underneath the roadway • The bridge is a primary emergency response route • Overhead or adjacent work space constraints such as power lines prevent the use of

conventional in place construction with cranes • Air or noise quality constraints limit the type or timing of construction activities • Endangered species on the site limit the timeline for construction activities • Weather constraints such as cold weather limit the length of time for construction

activities 20.3.2.1.2 Site Conditions

To construct a new bridge and move the bridge using SPMTs, the project site must include a staging area with adequate space to build the bridge upon a temporary substructure. Soil conditions must be sufficient to support all loads during construction at the bridge staging area and during transport of the new bridge. The travel path from the bridge staging area to the final bridge location must provide adequate clearance, grade and ground bearing capacity to allow the SPMT to transport the new bridge. The final bridge location must be accessible by the SPMT.



Contractors prefer a minimum 50-ft zone around the perimeter of the bridge footprint. The 50-ft zone is required for staging and crane pads.

The grading and geometry along the travel path is also critical. SPMT systems can accommodate significant grade changes with a well planned system. Use of SPMTs is difficult and requires significant planning and engineering if:

• Grades along the travel path exceed 4% • Superelevation transition is along the travel path • Travel path is along a road with a split profile • Travel path traverses a large area of noncompacted ground • Travel path crosses structures or sensitive utilities • Travel path goes under existing structures 20.3.2.1.3 Budget Challenges

The initial cost of a SPMT project is dictated by the base rate for reserving the equipment. Associated with the base rate is the mobilization time, which is usually ten days before operation and three days after operation. The amount of effort the heavy lifter must contribute to engineering also increases the cost of a project. Additional engineering requirements, such as site preparation at the bridge staging area and travel path, also add to the cost of a project.

20.3.2.2 Lateral Slides

Lateral slides are effective when the ADT under the bridge is low and the ADT over the bridge is high. Lateral slides construct the bridge adjacent to the existing bridge and over the feature crossed. The contractor slides or rolls the bridge into place after the superstructure and substructure construction is complete.

Section 20.6 presents specific lateral slide design requirements and slide equipment information.


Lateral slides are effective for projects if:

• The road crossed has low traffic volumes or low off peak hour demands • The bridge is on an emergency evacuation route • The bridge is over a waterway • Schools or hospitals are accessed via the bridge • The bridge is a primary emergency response route • Overhead or adjacent work space constraints such as power lines prevent the use of

conventional in place construction with cranes



20.3.2.2.2 Site Conditions

To construct a new bridge and move the bridge using a lateral slide, the project site must include an area adjacent to the bridge with adequate space to build the bridge. High skews and large superelevations complicate the design and the slide. Vertical clearance under the bridge in the temporary construction location is also required. Vertical clearance can be maintained during construction by building the bridge high and lowering the bridge before the move.

Contractors prefer a 50-ft zone around three sides of the bridge footprint and at least 10 ft between the new bridge in the staging area and the existing bridge. The 50-ft zone is required for staging and crane pads.

20.3.2.2.3 Budget Challenges

The initial cost of a lateral slide project is primarily a function of the temporary supports. Lateral slides are very cost effective. Lateral slide costs are approximately one half to one fifth of SPMT move costs for a simple single bridge. Complicated lateral slide systems that require lowering the bridge before the move can significantly increase costs.

20.3.2.3 Longitudinal Launches

Longitudinal launches are effective when the ADT under the bridge is high and no demand for traffic on the bridge is present. Longitudinal launches require a staging area behind one or both abutments where a partial or complete bridge is constructed. When the bridge is ready to launch, the bridge is pushed out over the gap.

Section 20.7 presents specific longitudinal launch design requirements and launching equipment information.


Longitudinal launches are effective for projects if:

• The bridge has no traffic demands • The bridge is over a major road • Overhead or adjacent work space constraints such as power lines prevent the use of

conventional in place construction with cranes • Environmental requirements limit access • The local bridge geography limits access 20.3.2.3.2 Site Conditions

To construct a new bridge and move the bridge using a longitudinal launch, the project site must include an area behind the bridge with adequate space and grade to build the bridge. High skews and large superelevations can complicate the design and the launch.



The area required is a function of the launch type. Staged launches require less area than single launches, which require an area longer than the bridge with construction and staging areas around the bridge.


The initial cost of a longitudinal launch is primarily a function of the temporary supports required for the launch and additional material to accommodate launch loads. Design effort for longitudinal launches is also more than other types of moves. The equipment cost can also be higher than that for a lateral slide. Longitudinal launch costs are approximately 50% to 100% of SPMT move costs for a single move.

20.3.2.4 Crane Based Projects

Crane based systems are effective when the site permits easy access for cranes and the section weights are reasonable. Crane based projects construct the bridge offsite and ship the prefabricated section to the bridge site before the final section placement. Crane based systems often require multiple sections with closure pours between the sections.


Crane based projects are effective for projects if:

• The project area is very confined and does not permit the use of a lateral slide or have adequate access to use SPMTs

• Locally available cranes have the capacity to move and place the bridge or bridge sections

• The bridge is small and easily handled or moved with a crane 20.3.2.4.2 Site Conditions

To place a new bridge with a crane requires a project site with an area adjacent to the bridge to set up a crane or cranes. Access for the prefabricated bridge sections to a location where the crane can pick up the element is also critical.


The initial cost of a crane based project is primarily a function of the weight of the bridge sections. Heavy sections and/or poor crane locations requiring a large reach require very large cranes. The use of large cranes that are not locally available can significantly increase the project cost.



20.3.3 Online Construction

Use online construction when offline construction is impractical due to geometric constraints or when online construction meets the project goals. Also, where appropriate, use online construction of substructure elements using prefabricated elements in conjunction with offline superstructure construction.

20.3.3.1 Prefabricated Elements

Prefabricated elements are especially effective when phased construction is possible. Section 20.4.5 presents specific prefabricated element design and construction requirements.

Prefabricated elements allow the construction of bridge elements in controlled environments, thus improving quality.

Constructing the bridge with prefabricated elements yields additional benefits, including:

• Permits longer cure times for concrete components • Controls cure conditions • Provides better control over materials and construction tolerances • Lowers life cycle costs • Promotes public support 20.3.3.1.1 Selection Criteria

The use of prefabricated elements is effective for phased construction; all elements are fabricated before assembly. Once the site is ready, the elements are shipped to the site and rapidly assembled. Prefabricated elements are often appropriate if:

• Phased construction is possible • The bridge is on a new alignment • The bridge is over a railroad or waterway • Air or noise quality constraints limit the type or timing of construction activities • Endangered species on the site limit the timeline for construction activities • Weather constraints such as cold weather limit the length of time for construction

activities 20.3.3.1.2 Site Conditions

To construct a new bridge using prefabricated elements, the project site must include a staging area with adequate space to set up a crane to lift the prefabricated elements into place.




The major costs associated with prefabricated elements is lifting and moving costs. The actual fabrication costs of the elements can be less than CIP construction. Lifting and moving costs are controlled by limiting element size and weight.

20.3.4 Required Information on Plans

All ABC projects require a construction phasing plan and construction notes sheet. The sheet defines the design move or construction sequence used in design and defines any special design requirements. Depending on the project, the sheet can be combined with other typical sheets.

Contractors must submit erection plans for placing bridge girders. Prefabricated elements also require preconstruction planning. Project specifications require that the contractor submit an assembly plan for the construction of the entire bridge including the prefabricated elements.

The design plans must include the following:

• Size and weights of all elements • Construction sequence when a special sequence is required • Temporary shoring and bracing if required • Required cure time for grouts and closure pours Consider the following, although the information is not required on the plans:

• Pick points of elements • Grouting procedures • Potential crane locations • Construction sequence Contractors can modify all details after submitting appropriate documentation according to the project specifications and after receiving approval of the modifications.

DBB plan sets provide the minimum structural requirements for the bridge in the final location and include all required specifications. The specifications define project requirements and submittals.

Document all assumptions on load location and construction sequences in the project calculations. Design major elements to work with the construction sequence shown. For example, if the bridge is designed as a lateral slide, design the abutments and bents to accommodate the moving load with the location of supports used in design identified on the plans. The plan set does not need to provide shoring or temporary support details.

Use the heavy lift ABC checklist and precast element checklists when preparing plan sheets or specifications and when reviewing contractor submittals.



20.3.4.1 Prefabricated Element Sheet Requirements

Prefabricated element sheets normally contain the items in the following list. Additional items are often required for complex projects:

• Plan view of each substructure unit • Elevation view of each substructure unit • Typical transverse sections as needed • Individual piece plans, elevations and sections showing:

o Dimensions o Internal reinforcing details including connection details o Approximate shipping weight of the piece o Connection details o Tolerance details for all applicable pieces o Reinforcing details

The SS and WS sheets represent typical details for prefabricated concrete elements. Design and detail the specific prefabricated element using the SS and WS sheets for guidance on general concepts and consistent detailing practices. The SD drawings address design requirements.

20.4 TECHNICAL

20.4.1 Materials

The use of lightweight concrete is permissible in decks with overlays, CIP elements and nonprestressed prefabricated elements. Use of lightweight concrete in prestressed elements requires approval from the Structures Design Manager.

The use of high strength steel (over 70 ksi) and composite materials is permissible with approval from the Structures Design Manager.

Approval requires appropriate technical information relating to the design, fabrication and anticipated performance of any of the elements. Refer to Sections 14.3 and 15.2 for more information on concrete and steel material requirements.

20.4.2 Load and Resistance Factors

Refer to Chapter 11 for load and resistance factors for ABC projects.

20.4.3 Load Rating Existing Structures

ABC projects often require transportation of heavy loads, which often far exceed typical highway loads. Avoid moving the loads over existing bridges. If avoiding an existing structure is not



possible, load rate the structure for the proposed loads. Define all requirements for moving the load across an existing bridge. Typical requirements include the exact location of the load on the structure; whether or not other traffic is allowed on the bridge during the move; and a defined shoring plan or strengthening when the existing bridge does not rate for the proposed load.

Use the AASHTO Manual for Bridge Evaluation and the BMM for additional load rating information.

Submit the load rating package and a description of any special requirements to the Structures Design Manager for approval. Note that approval is not guaranteed even if the structure has a safe operating load rating.

20.4.4 Utilities

Utility owners are concerned with superimposed loads damaging utility facilities. Coordinate with utility owners when moving heavy loads across utility facilities. The owner often requires special procedures or load mitigation during the move.

UDOT and utility owners are especially concerned with high capacity water lines or high pressure gas lines. Failure of the utility lines can result in catastrophic damage.

When required, typical procedures include having the owner (or owners) representative on site, shutting down the utility line during the move, or having a procedure in place to shut down the facility in case of damage. Typical mitigation involves bridging the utility or reducing the axle loads.

Coordinate with the utility owner when mitigating loads by bridging. The bridging method must meet owner approval. Bridging methods range from placing steel plates on the ground to removing fill over the utility and placing plates or other materials over the gap.

20.4.5 Prefabricated Elements

Prefabricated elements are elements cast and cured before arriving at the job site. Prefabricated girders and half depth deck panels are not ABC elements. Refer to the WS sheets, SD drawings, Chapter 14 and Chapter 16 for more information.

Prefabricated elements as defined for ABC include prefabricated:

• Full depth deck panels • Foundations • Columns • Bent caps • Abutments • Wingwalls • Parapets



• Approach slabs • Deck and girder systems 20.4.5.1 Element Size and Weight Guidelines

Use the following general guidelines for sizing prefabricated concrete substructure elements. Keep the maximum height of any element, including projecting reinforcing, to less than 10 ft to allow transportation under existing bridges. Keep the width of the element, including projecting reinforcing, to under 14 ft.

Carefully consider segment weights and potential crane locations when sizing elements. Excessive reach requirements severely limit the crane capacity. Consider the weight of the heaviest girder section on the project when determining prefabricated section weights. Balancing the weight demands from girder placement with prefabricated element placement allows efficiency in construction. Element weights over 100,000 lb require approval from the Structures Design Manager. Target element weights of 50,000 lb are reasonable. Follow the guidelines for DBB projects. On DB projects and CMGC projects, work with both the fabricator and contractor to size the elements based on the available equipment and the proposed shipping routes.

Cranes require a large, relatively level area to set up. Cranes typically need a 30-ft × 50-ft area to set up. In soft soil areas, additional crane pads can be required under the outriggers to distribute the load to the ground. Evaluate crane locations on fill slopes or on walls for global stability, and design the wall for the temporary crane loads.

20.4.5.2 Prefabricated Element Design

Design prefabricated elements considering constructability:

• Provide repetitive details, allowing the use of a single set of forms, small crews and efficiency in casting.

• Use simple details. Complex shapes that reduce quantities typically do not overcome the extra cost and risk associated with complex shapes and details.

• Minimize the number of connections. Fewer larger connections are more cost effective than a larger number of smaller connections and provide fewer chances for geometric errors. Eliminate connections where the connections are not needed.

• Provide as much tolerance in the system as possible to accommodate minor geometric inconsistencies. Adequate tolerance is especially important for elements spanning from support to support where temperature effects become measurable.

• Balance the number of elements required with the size of the element and access to the site. Larger elements in areas easy to access can provide the fastest construction but, in areas with difficult access, smaller sections can be faster to place.



20.4.5.3 Lifting Hardware

Lifting hardware and locations are the contractor’s responsibility. Review the PCI Design Handbook for Precast and Prestressed Concrete to understand lifting and handling stresses.

20.4.5.4 Tolerances

Allow for tolerances in fabricating and placing members, and account for several tolerance challenges:

• Fabrication tolerance • Dimensional growth • Hardware tolerance • Girder camber • Temperature effects Fabrication tolerance allows for slight geometric errors in fabrication. Prefabricated elements are typically constructed under well controlled conditions. Refer to the SD drawings for fabrication tolerance requirements.

Dimensional growth is caused by minor imperfections in the prefabricated element and minor placement errors combining and causing the physical length of the elements in place to exceed the sum of the length of the individual pieces. Avoid dimensional growth by designing a small gap between prefabricated elements that is sealed when connecting the elements. Also, counter the effects of dimensional growth by allowing variation in the length of the system. Provide a minimum gap between adjacent elements of 3/16 in. per 10 ft based on the maximum dimension of the connected element for horizontal runs of prefabricated elements. The gap can be capped at ⅜ in. at the discretion of the structural engineer. Larger gaps between elements are allowed.

Hardware tolerance is related to the connecting elements, reinforcing extending across the joint, reinforcing extending into splice sleeves, alignment of post-tensioning ducts, alignment of shear keys or other mechanical connections. The required tolerance for the various hardware elements varies significantly. Specify the tolerance for the system. Specify larger post-tensioning ducts or splice sleeves where additional tolerance is required. Review maximum duct size limits for post-tensioning systems.

Prefabricated deck systems must allow for the camber in the girder. Refer to Chapter 16 and the SD drawings for a discussion on setting the haunch.

Temperature effects typically only affect complete bridge systems placed on preconstructed supports. Consider the possibility of changes in length due to temperature variations when specifying tolerance limits for the structure.



20.4.6 Connections

Connections are the most critical elements on an ABC project. Many types of connections are available. Connections are in two groups — emulative connections and pin/friction connections.

20.4.6.1 Emulative

Emulative connections are based on a design process called emulative detailing. A Joint Committee of ACI and ASCE developed the process. ACI 550.1 “Emulating Cast-in-Place Detailing in Prefabricated Concrete Structures” documents the process. The process emulates CIP connections with prefabricated elements. Conventional CIP construction is not monolithic. Construction joints are common, and often use dowels and lap splices. Emulative design replaces the traditional lap splice with a mechanical coupler.

Mechanical couplers in areas away from plastic hinge zones must develop 125% of the specified yield strength of the connected reinforcing. Mechanical couplers in areas adjacent to or in plastic hinge zones must develop 150% of the specified yield strength of the connected reinforcing. One of the benefits of emulative detailing is that the design of the substructure element can be similar to a CIP concrete structure.

20.4.6.2 Pin/Friction

Pin/friction connections allow elements to rotate or move independently. Use caution when designing the connections; stability must be maintained. Semi-integral abutments are a common type of pin/friction connection.

20.4.6.3 Commercial Grouted Splice Couplers

Several manufacturers produce grouted splice couplers. The systems consist of reinforcing connected to a sleeve. The sleeve is placed over the reinforcing, and the area between the reinforcing and the sleeve is grouted. The basic principle is that confined high strength grout can develop and transfer the load in the reinforcing to the exterior sleeve and back to the reinforcing in a short distance.

Grouted splice couplers are an effective tool to connect prefabricated elements.

The challenges associated with grouted splice couplers are cost and tolerance. Mitigate cost by minimizing the number of grouted splice couplers required. Tolerance is an issue because the splice sleeves are cast into the prefabricated elements. Geometric inconsistencies can lead to the sleeves not lining up as needed. Mitigate tolerance challenges through the use of reinforcing templates in the casting bed, match casting and oversized splice sleeves.

The use of grouted splice couplers is permissible in plastic hinging zones. The standard requirements for column confinement apply around the couplers. Adjust the cover to the reinforcing and spiral or ties to accommodate the larger grouted splice coupler section.



Refer to the SD drawings for examples of how grouted splice couplers are used. The preferred configuration for constructability is to locate the grouted splice coupler above the joint, which reduces the chance of contamination with debris. Grouted splice couplers located below the joint must be sealed during fabrication and shipping. Also, placing the grouted splice coupler above the joint allows the reinforcing extensions at the top of the element, making shipping and handling easier. Placement of grouted couplers in the footing or in the cap improves the connection ductility capacity. Locate the coupler in the footing or in the cap when the ductility demand exceeds 4.

Design the reinforcing size and grouted splice couplers to allow for crossing reinforcing patterns. Detail the spacing at approximately the maximum reinforcing spacing requirements in the LRFD Specifications. Base the spacing on the connected reinforcing. Do not use the diameter of the grouted splice couplers in the calculations. Check the clear spacing between the grouted splice couplers using the following approach.

Use a grouted splice coupler sleeve size one reinforcing size larger than the reinforcing size used. Detail the minimum gap between the grouted splice couplers to be the greatest of the following:

• 1 in. • 1.33 × (maximum aggregate size of the coarse aggregate) • Nominal diameter of the connected reinforcing Provide cover for the element based on the diameter of the grouted splice coupler. The practice requires increased cover to the reinforcing to obtain the cover over the grouted splice couplers. Use the dimensional guidelines in Figure 20.1 for detailing the element with grouted splice couplers.

Reinforcing Size Outside Diameter

(in.) Length of Sleeve

(in.)

#4 2.625 14.125

#5 3.000 14.125

#6 3.000 14.125

#7 3.000 18.750

#8 3.500 18.750

#9 3.500 18.750

#10 3.500 23.500

#11 4.000 23.500

#14 4.000 28.375

#18 4.500 39.625

Figure 20.1 — APPROXIMATE GROUTED SPLICE COUPLER DIMENSIONS



20.4.6.4 Corrugated Pipe Voids

Corrugated steel pipe is an effective way of providing a void for making connections in prefabricated elements. Several details incorporate pipes as void forms. The key feature is the corrugations in the pipe, which provides additional capacity in load transfer between the concrete cast within the pipe and the surrounding prefabricated concrete.

Use continuous pipe with uniform corrugations along the entire length of the pipe. Do not use pipes with low friction walls designed to convey water more efficiently.

Inside Diameter Range Corrugation Pattern

4″ to 18″ 1.5″ × 0.25″

12″ to 84″ 2.66″ × 0.5″

36″ to 144″ 3″ × 1″ and 5″ × 1″

Figure 20.2 — MINIMUM CORRUGATION SIZES FOR CORRUGATED STEEL PIPES

Do not use corrugated aluminum pipes. Aluminum is reactive with the surrounding concrete, leading to degradation of the pipe over time and damage to the concrete.

Corrugated plastic pipe is allowed for nonstructural voids. Use of nonstructural voids can reduce shipping and handling weight.

Fully develop reinforcing extending into the voids. Do not reduce the development length based on confinement provided by the corrugated pipe.

20.4.6.5 Post-Tensioning

Post-tensioning is a traditional method of connecting prefabricated elements. Consult the PCI manuals for information on designing post-tensioning systems and elements.

Do not use post-tensioning systems that:

• Require shoring to completely remove the deck • Require shoring to place a new deck in a single stage pour Post-tensioning is a cost effective alternative to highly reinforced prefabricated elements. Prestressing concrete elements normally improves structural durability.

Refer to Section 16.2.4 for a discussion on post-tensioned, full depth precast deck panels.



20.4.6.6 Shear Key

Shear keys are an effective tool for transferring lateral or longitudinal loads to substructure units. One of the benefits is that shear keys can be constructed after bridge moves or after prefabricated elements are in place. The primary disadvantage is the lack of moment transfer.

Use exterior shear keys for easier inspection and repair after a seismic event.

The ultimate capacity of shear keys is difficult to determine, and traditional design methods can significantly underestimate the ultimate capacity of the shear key. Do not design shear keys to fuse in a seismic event.

Consider the effects of differential temperature effects and the direction of temperature movements and provide an adequate thickness of compressible material. The compressible material allows differential movement between the elements and minimizes the potential for cracking in the shear key due to service loads.

20.4.7 Substructure Design

Substructures can be especially challenging to construct rapidly. This section discusses a number of approaches for accelerated substructure construction.

20.4.7.1 CIP Construction Under Existing Bridges

Although technically not accelerated construction, CIP construction under existing bridges can offer many of the same benefits as accelerated construction. Frequently, new substructures under existing bridges can be constructed without impacting traffic.

The primary difficulty associated with construction under existing bridges is the lack of access and space to work. Existing bridges often have short end spans over fill slopes. New substructure units can be constructed between the bent and abutment. The critical aspects to consider are:

• Stability of the slope under the abutment as the slope is removed to place the new foundation

• Interference with existing battered piles • Utilities • Limited overhead access • Work zone exposure to traffic Contractors use partial or full height soil nail walls or other methods to stabilize the slope and provide room for construction.



20.4.7.2 Spread Footings and Spread Footings on Stabilized Earth

Use spread footings when geotechnical conditions allow. Spread footings are less expensive and easier to construct under existing bridges. Spread footings can also be prefabricated.

Spread footings in fill slopes are permissible when no retaining wall exists and when the fill slope is 2H:1V or flatter.

Spread footings on GRS walls require approval from the Structures Design Manager.

20.4.7.3 Piles

Piles are unavoidable in the majority of bridges constructed in Utah. Driving piles is difficult in confined locations and locations with strict traffic requirements. Pile driving is especially difficult in bridge replacement projects. Several methods allow the use of piles at existing bridges.

One method cores through the existing deck and drives the piles through the holes in the deck. The method allows for typical pile arrangements and minimizes quantities. The primary concerns are traffic control and the potential to damage existing girders.

Another option is to drive piles outside the footprint of the existing bridge and design the abutment to span between the pile groups. The primary concerns include unequal pile loading, lateral loads on the abutment walls, and additional material costs to accommodate the loads. Evaluate the effect of the moment transferred to the pile group and the abutment deflection between the pile groups in both the vertical direction and lateral direction. When using post-tensioning, also consider losses into the piles due to elastic shortening and creep in the concrete. New pile locations must be at least 5 ft from the existing bridge to allow pile driving.

20.4.7.4 Micropiles

Micropiles are small diameter drilled and grouted nondisplacement piles that are typically reinforced. Numerous styles and sizes are available for micropiles. Micropiles have several advantages when compared to driven piles, including installation without noise or vibration, installation close to existing bridges or under existing bridges and installations with confined access. Micropiles have been installed with as little as 10 ft of headroom.

20.4.7.5 Drilled Shafts

Drilled shafts can be installed with little noise and vibration. Drilled shafts can be more efficient in straddle abutments or bents due to the moment capacity of the shaft. Coordinate with the geotechnical engineer to determine if drilled shafts are cost effective for the project location.



20.4.7.6 Re-Use of Existing Substructures

Do not re-use existing substructures for a variety of reasons. Typically, existing bents, columns and footings do not meet current seismic design requirements and require significant rehabilitation and upgrades to accommodate seismic loads.

20.5 BRIDGE MOVES USING SELF PROPELLED MODULAR TRANSPORTER UNITS OR SIMILAR SYSTEMS

Bridges can be constructed offline and moved into place with SPMT units or with hydraulic lifts and trailers with similar functionality to SPMT units.

20.5.1 Self Propelled Modular Transporter Units

SPMT units use electronic steering that allows the vehicles to drive forward and backward, transversely, diagonally, at any angle and in a carousel motion. Heavy lifters link SPMT units longitudinally or laterally to achieve the number and configuration of axle lines required by the load. Linked units act as a single unit and are run off a single controller. The controller has four basic commands — steer, lift, drive and brake. Typical SPMT units have approximately 24 in. of total stroke and an approximate capacity of 30 tons per axle line.

The dimensions of SPMT units vary depending on the manufacturer and number of axles and wheels. The most common SPMT units have 4 to 8 axle lines. Each axle line consists of two bogeys (or two axles); each bogey (or axle) has two wheels. An axle line has two axles (four wheels). A typical SPMT unit is 8-ft wide with an axle line spacing of 4′-7½″. The axle line spacing remains constant between separate SPMT units. The typical bed height ranges from 36-in. minimum to 60-in. maximum.

SPMT units are hydraulic support units that have the ability to equalize the load to all wheels in a hydraulic group when the wheels are not at the maximum or minimum stroke. When a wheel reaches its maximum stroke, the load on that wheel is transferred to adjacent wheels that have not reached the stroke limit. When a wheel is at the minimum stroke, the load carried by that wheel can increase significantly. The systems typically have safeguards and are monitored during the move to eliminate the possibility of overloading the system.

To maintain stability in the system during the move, the SPMT units are divided into a minimum of three hydraulic groups. The feature provides a stable support, which is essentially a tripod support. The reactions in each hydraulic group can vary, which causes displacements or twist in the bridge during the move. The variability in reactions also provides the stability during the move.



20.5.2 Hydraulic Support Units

Numerous systems similar to SPMT units are used to move heavy loads. The systems typically do not have the flexibility in use, movement and placement that SPMT units possess. Typically, the other systems require external drive sources and do not have fine adjustment capabilities.

20.5.3 Planning

Use the following assumptions when planning a bridge move:

• Use the typical SPMT unit dimensions listed in this chapter. • Estimate the required number of SPMT units assuming a maximum bridge load to the

SPMTs of 11 kips per wheel, 22 kips per bogey and 44 kips per axle line, which allows for the additional weight of the support system and the self weight of the SPMT.

• Assume a maximum useable stroke of 12 in. when evaluating the path. CMGC and DB projects can coordinate with the SPMT supplier to determine the useable stroke.

• Assume that the bridge is connected to the SPMT supports through a pinned connection.

• Set lift locations at less than or equal to 20% of the span but no less than 12 ft from the centerline of bearing for bridges with MSE walls in front of the abutment.

• Provide a minimum of 2 ft from the edge of the SPMT unit to any obstruction or support.

20.5.4 Plan Requirements

List the following information on the plan sheets:

• Show the location of the center of gravity of the bridge. • List the maximum allowable twist. • List the maximum allowable differential deflection. Define the location and size of the bearing area between the SPMT units and the bridge used in design.

The contractor must be able to use a support matching the designated size and placed at the designated location without modifying any of the primary structural elements.

20.5.5 Bridge Removal

SPMT units are an effective tool in removing existing bridges. When removing an existing bridge using SPMT units, analyze the bridge and design the support apparatus to meet all requirements in the current edition of the AASHTO Guide Specifications for Bridge Temporary Works.

When planning to remove an existing bridge with SPMTs:



• Evaluate the existing bridge condition • Determine a demolition location • Consider lowering the bridge to ground level for demolition • Evaluate the stability of the bridge and shoring system during demolition 20.5.6 Design Approach

The bridge must meet all AASHTO requirements during all stages of the move and in the final location. Design bridges that are placed using SPMT units in the same manner as conventionally constructed bridges.

The following sections provide instruction to the structural engineer and the engineer for the contractor that is designing or redesigning the bridge or designing the support system. The structural engineer must make assumptions on how the bridge is lifted and supported during the move to prepare the initial design. The assumptions must be clearly stated on the plans. The following terms — detail, provide, check, evaluate and verify — are used in the following sections. The terms are directed at both the structural engineer and the engineer for the contractor and can be flipped at various stages during the project. The expectation is that the structural engineer evaluates the items noted during the design process based on the documented assumptions and verifies that the reviewed submittals address the items noted based on the actual move data supplied by the engineer for the contractor.

20.5.6.1 Load Conditions, Loads Cases and Load Factors

Refer to Chapter 11 for load factors, dynamic load allowance and design load combinations. Specific SPMT loads include lateral loads from starting, stopping, turning, climbing grades and displacements in the system due to unequal support reactions.

Check the system in the following load conditions:

• On temporary supports • On the SPMT supports during the move • On the SPMT supports during the move with the system displaced to the maximum

permitted twist or differential deflection • On the final supports 20.5.6.2 Connection to Bridge During the Move

Evaluate the effects of the support conditions from the bridge to the SPMT supports or verify that the effects of support conditions were considered during the design of the SPMT support system. Auxiliary connections to the bridge, such as chains or struts, can significantly change the response of the bridge during a move. If auxiliary supports are used, verify the capacity of the system and the response of the system to the revised support condition. Additionally, the length of the bearing area, the number of bearings or the type of connection affects the stability of the system, the stroke demand and the reactions at each support.



20.5.6.3 Stroke Demand

The stroke demand along the SPMT path is difficult to determine. Structural engineers do not set the SPMT height before the lift, and do not define the travel path geometry or grading. Structural engineers evaluate the stroke demand at the final location by assuming that the grade under the bridge matches the existing conditions or matches the final conditions. When the approach to the final bridge location requires over 12 in. of stroke to clear the bearing pads, evaluate alternative bearing/sole plate combinations that reduce the stroke demand and/or allow the contractor flexibility in modifying the bearing pads.

SPMT suppliers can supply secondary jack systems to assist in raising and lowering the bridge. The secondary jacks can assist in raising the bridge to clear the bearings or pedestals and can increase the range the bridge can be lowered. Supplemental jacks can reduce the possibility of project delays.

In addition to clearing bearings or pedestals, SPMT stroke is used in the following situations to:

• Compensate for superelevations • Compensate for superelevation transitions • Compensate for vertical curves • Compensate for curbs or dips in the path • Lift the bridge off the supports • Compensate for the change in deflection when lifting a bridge off the support (demand

can be significant for flexible, single span bridges) 20.5.6.4 Bearing on Self Propelled Modular Transporter Supports

The structural engineer verifies the bearing, bending and shear capacity at the documented SPMT support location and using the documented bearing length. Use suitable diaphragm or cross frame details to provide the necessary compression flange stability under temporary SPMT cantilevered support conditions. The engineer for the contractor can use the documented bearing location and support size, or adjust the locations of the SPMT support points according to the process defined in the project specifications. The process requires submittal of detailed calculations that demonstrate that the new support points do not adversely affect the bridge.

Consider sizing the girder such that the girder meets all AASHTO requirements without additional stiffeners or bracing. The practice allows minor variations in the support location during the move and allows the elimination of exterior stiffeners on exterior girders for aesthetics.

20.5.6.5 System Response During a Bridge Lift

SPMT move procedures expose the bridge superstructure to forces that are often opposite to the forces for the bridge under its final support conditions. Several different options exist for



supporting the bridge before and during the move. The two typical methods are discussed below.

20.5.6.5.1 Method A

Method A involves supporting the bridge during deck casting at the proposed pick points for the SPMT move. The primary advantages are that no additional stress is added to the deck during the move and the deck has a permanent compressive load after placement. The primary disadvantages include the difficulty in estimating the deflections to provide a smooth riding surface, providing adequate camber to accommodate any future redecking, and additional complexity in the temporary supports to permit the SPMTs to drive under the temporary supports before lifting the bridge.

Evaluate the effects of the change in loading conditions on the response of the bridge. The girder is a noncomposite system during the deck pour. All future loading and change in support locations are on a composite section, which alters the final stresses in the bridge. In the majority of applications, the change increases the load capacity of the bridge. Do not account for the increase in capacity when sizing elements because the bridge must permit redecking using conventional methods.

20.5.6.5.2 Method B

Method B involves supporting the bridge at the final support locations during deck casting, and transferring the bridge to intermediate supports for the move. The primary advantages are the simple transfer from the temporary support to the SPMT support and better control of elevations and grade. The major disadvantage is that the change in moment on the system due to the change in support location causes tension in the deck and parapet.

Evaluate the effects of the change in loading conditions on the response of the bridge. The girder is a noncomposite system during the deck pour. All future loading and change in support locations are on a composite section.

The stress in the deck and the parapet is caused by the change in moment from the final support condition to the SPMT support condition. Evaluate the stress in the deck and the parapets based on the composite section properties and the change in moment on the system. Note that the change in moment is greater than the absolute value of the moment on the system in the lifted condition.

Similarly, determine the deflections in the system based on the change in moment, not the absolute moment in the system. See Figure 20.3 for a graphic representation of the stresses from the change in support condition.



Figure 20.3 — METHOD B LIFT STRESSES



20.5.6.5.3 Modeling

Refer to LRFD Article 4.5 for a comprehensive discussion on bridge modeling.

All elements must remain elastic during a bridge move. Analyze the bridge based on elastic behavior.

Analyze the bridge with and without the stiffness of the barrier to determine the worst case scenario for the bridge. Support all formwork for the deck from the longitudinal girders similar to conventional construction methods. Do not use composite dead load designs. Shored construction is allowed, but do not design to take advantage of shored construction to reduce girder size.

Modeling and analyzing single or multispan bridges with flexible support elements requires a thorough understanding of the modeling software and structural systems. Multispan bridges also require significant coordination with the heavy lifter to determine the response during the lift. The hydraulic grouping in the SPMT supports can have a significant effect on the response of the bridge.

To properly calculate the internal forces in the superstructure supported with flexible framing, model the entire superstructure and support framing using 3D analysis methods. Do not use a grid analysis to evaluate deck stresses from twist. Calculate the stresses and check the design of the entire system (superstructure and support framing). Also, examine the effects of pinned connections or fixed connections that can physically behave as partially pinned.

Complex analysis methods are not required for preliminary design for lifts with systems that provide uniform support for all girders. In this case, use simplified analysis methods including 2D line girder analysis. The analysis of the support system is also simplified because the reactions at each girder are defined.

20.5.6.6 Tolerances

SPMT moves have two types of tolerances — installation tolerances and placement tolerances. Installation tolerances refer to the clearances required to move the bridge into place; placement tolerances refer to the fit up of the bridge with its connections and/or the final location of the placed bridge compared to the design location.

Installation tolerances are affected by the capabilities of the SPMT movement system, the geometry of the travel path, the new substructure geometry, obstacles along the path, etc. Consider how movement and placement of the bridge affects each element for grade effects, rotations, geometry of bearing seats and joints.

Structural engineers must provide designs that do not require tight placement tolerances. The controlling placement tolerances are typically controlled by nonstructural requirements such as barrier offsets. Structural engineers must verify that the placement tolerances provided in the project specifications are reasonable for the bridge being moved.



20.5.6.7 Connection to Substructure

Use closure pours to complete integral abutment connections. Semi-integral bridge abutments do not require completion of closure pours to open the bridge to traffic. Place shear keys or end blocks used to limit movement of semi-integral abutment bridges after the bridge is open. The key features to consider are location and tolerance of connecting elements. Account for placement tolerances in the bearing design and the design of connecting elements.

The contractor provides a detailed survey of the bridge substructure elements, including both horizontal and vertical geometry. The contractor surveys the as built superstructure and substructure elements at critical geometry points for horizontal and vertical fit. The contractor compares the as built survey data to theoretical design data to ensure fit. Make adjustments as required by providing shim plates, adjusting vertical and horizontal locations of moveable supports, etc.

Consider the path of the bridge during the move and provide mechanical splices where reinforcing extending from the abutment interferes with the move.

Provide tolerance in reinforcing cover in shear keys to allow for deviations from the anticipated placement of the bridge. Provide for temperature movements in the design of shear keys. Use externior shear keys or end blocks on the abutments when practical. Externior shear keys are easier to repair after a seismic event. See Figure 20.4.

Figure 20.4 — SHEAR KEY FOR SEMI-INTEGRAL ABUTMENT



20.5.6.8 Bearings

Detail the bearing with vertical adjustment devices. Several methods are available to provide vertical adjustment in bearings, including leveling plates supported by anchor bolts with leveling nuts, shim plates or other methods. All methods must account for differential reactions on the bearing and girder system during adjustment.

20.5.6.9 Monitoring

Project specifications define the monitoring requirements. The monitoring plan is used to identify:

• Measuring equipment • Measuring procedures • Reference points for geometric control on the bridge and ground • Minimum detectable movements • Limits to differential movements • Actions to take when differential movement limits are approached. The plan can also specify detailed crack mapping of the bridge deck. Map the deck before lifting and after the span is set on the final abutments.

20.5.6.10 Deck/Parapet Reinforcing Requirement

Refer to LRFD Article 5.7.3.4 and provide reinforcing in the deck and parapets meeting the requirements of LRFD Table 5.7.3.4-1 using the Class 1 exposure condition for all locations where the deck is in tension. Assume cracked section properties.

LRFD Article 5.7.3.4 requirements are waived for parapets reinforced as end sections with full depth joints at a spacing not exceeding 16 ft. LRFD Article 5.7.3.4 requirements are also waived when permanent or temporary post-tensioning eliminates additional tension in the deck and parapet during the move.

In addition to the tension loads in the deck due to the move, shrinkage of the concrete during curing produces tension in the deck.

20.5.6.11 Prestressed Girder Stress Limits During the Move

Refer to the current edition of the LRFD Specifications. Use the compression limits associated with shipping and handling.

Use the moderate corrosion condition when checking tension stresses during the move.



20.6 LATERAL SLIDE BRIDGE MOVES

20.6.1 Types of Slides

20.6.1.1 Rolling

Rolling supports are typically high capacity steel rolling bearings. Normally, the bearings are attached to the bridge. The bearings can be guided or unguided. The majority of applications use a steel channel as a guide. In general, rolling bearings have less friction allowing movement with less force but are more sensitive to the alignment of the bearing. The primary aspects to consider when using rolling bearings include:

• Size of the bearing • Alignment of the bearing • Cleanliness/smoothness of the track • Point loads through the bearing 20.6.1.2 Sliding

Sliding bearings consist of elastomeric bearing pads with a teflon sliding surface. The bearings do not move with the bridge. Normally, a temporary or permanent slide shoe is attached to the bridge, and the slide shoe slides over the bearings as the bridge is moved. In general, sliding bearings have more friction, requiring larger jacks for movement, but are less sensitive to alignment. The primary aspects to consider when using sliding bearings include:

• Anchorage of elastomeric pad • Smoothness of the sliding shoe • Friction on the sliding surface 20.6.2 Types of Jacks

Three main types of jacks are available — pull, push and push/pull; see the following sections. In general, the pull jacks are the least expensive but have the least control over the move, and the push/pull jack has the highest cost but offers considerably more control and versatility.

20.6.2.1 Pull Jacks

Pull jacks normally use a hydraulic strand or bar jack. The jack is stationary and pulls the cable or post-tensioning rod through the jack. Pull jacks are the simplest method of moving a bridge. Pull jacks using post-tensioning strand can be especially difficult to control due to elastic deformation of the strand storing spring energy combined with changes in friction in the system.



Pull systems using cranes or winches are also difficult to control due to elastic deformation of the cable storing spring energy combined with changes in friction in the system. Use of cranes or winches is not recommended.

20.6.2.2 Push Jacks

Push jacks are hydraulic rams used to push the bridge. Typically, the ram moves with the bridge. The jack sits on a skid track, which is similar to a ladder. The jack anchors to a rung on the skid track and pushes the bridge the length of the jack stroke. Once the stroke is complete, the jack is unhooked from the rung and moved up to the next rung to repeat the process.

20.6.2.3 Push/Pull Jacks

Push/pull jacks operate the same way as a push jack but have the capacity to pull the bridge back. Most push/pull jacks have significantly more push capacity than pull capacity. Push/pull systems typically offer the most control during the move.

20.6.3 Key Design Considerations

Consider two types of loads during the lateral move — vertical loads through the sliding bearings and lateral loads associated with friction or resistance in the bearings.

The following sections provide instruction to structural engineers and engineers for the contractor who is designing or redesigning bridges or designing the support system. The structural engineer must make assumptions on how the bridge is lifted and supported during the move to prepare the initial design. The assumptions must be clearly stated on the plans. The following terms — detail, provide, check, evaluate and verify — are used in the following sections. The terms are directed at both the structural engineer and the engineer for the contractor and can be flipped at various stages during the project. The expectation is that the structural engineer evaluates the items noted during the design process based on the documented assumptions and verifies that the reviewed submittals address the items noted based on the actual move data supplied by the engineer for the contractor.

20.6.3.1 Vertical Loads

In lateral slides, the vertical dead load is a moving load as the bridge moves across the support to the final location. Use the load factors and load cases defined in Chapter 11.

Consider the effect of deflections and variation in support elevations on the distribution of load on all projects. Support deflections in systems with two sliding supports normally do not significantly change the reaction through the support. Using three or more supports creates the potential for significant redistribution of load through the supports. For example, if a single high point is encountered along the path, the bridge could rock about a single support at the high point, allowing the entire load to be transferred through the single support.



Systems using slide shoes must accommodate a ⅛-in. variation in support elevations at the center of the shoe. The structural engineer must account for load redistribution when using more than two slide support points. For example, a system using three slide supports must be designed to accommodate a center support ¼ in. higher or lower than the end supports. The ¼ in. results when one support is ⅛ in. low and the other support is ⅛ in. high. Depending on the spacing of the shoes and the stiffness of the bridge, the entire load could be transferred to the center shoe. In this case, the superstructure design must accommodate the increased bending moments and shear from the cantilevered section, and the substructure must accommodate the increased reaction.

Systems relying on continuous slide supports or an even distribution of slide supports must accommodate a ⅛-in. variation in slide supports per 10 ft up to a maximum variation of ¼ in.

The structural engineer verifies the bearing, bending and shear capacity at the documented slide support locations and using the minimum documented slide bearing length. The structural engineer also verifies the capacity of the permanent substructure for the load through the sliding supports as the support moves across the substructure. Consider the effects of varying supports heights as noted above when verifying the capacity of the system. The engineer for the contractor can use the documented bearing location and minimum support size or adjust the locations of the slide support points according to the process defined in the project specifications. The process requires submittal of detailed calculations that demonstrate that the new support points do not adversely affect the superstructure or substructure.

20.6.3.2 Horizontal Loads

Account for lateral loads transferred to permanent and temporary substructures. The critical elements are the connection from the jack to the bridge and the connection from the temporary substructure to the permanent bridge.

The engineer for the contractor must define a clear load path for all lateral loads. The lateral load path can change as the bridge moves from the temporary to permanent location. Evaluate the lateral loads through all phases of the move.

The structural engineer can evaluate potential load paths and detail substructure elements such that they are compatible with various slide schemes. Use 20% of the factored dead load when evaluating potential lateral loads resisting elements. The engineer for the contractor must evaluate the lateral load system and revise the plans as permitted in the project specifications to meet the requirements of the slide system provided.

20.6.3.3 Plan Requirements

The plan set must define the location and size of the sliding supports assumed in design. The contractor must be able to use the locations without modifying any of the primary structural elements.



20.6.3.4 Approach Slab

When possible, move the approach slab with the bridge.

If the approach slab is moved with the bridge, design the approach slab to span from support to support with no intermediate fill support for the life of the bridge. If a standard approach slab is not used, check fatigue in the reinforcing assuming no support between the abutment and sleeper slab. Fatigue typically controls the design of approach slabs.

When moving the approach slab with the bridge, evaluate the type and method of placing backfill underneath the approach slab after the bridge move. In this case, the default backfill is flowable fill. Flowable fill has a significant amount of shrinkage during curing. Require two stages of flowable fill applications on the plan sheets in the project specifications. Place the second application 30 days after the placement of the first application to fill the gap formed by the shrinkage.

20.6.3.5 Vertical Clearance

For lateral slides over existing roads, maintain adequate vertical clearance under the bridge in the temporary location. Coordinate with the Structures Design Manager to determine the required minimum vertical clearance during construction.

20.7 MISCELLANEOUS BRIDGE MOVE METHODS

Numerous other methods are available to move bridges; this section discusses several options. All methods are subject to the same stress limitations noted in Section 20.6. Refer to Chapter 11 for dynamic load allowance and load factors associated with the various move methods.

20.7.1 Crane

Use cranes to lift partial or complete bridges into place. Partial bridge sections combined with closure pours reduce the required crane size. When planning to use cranes to place a bridge, consider the following:

• Required crane size • Potential crane locations • Weight of sections placed • Required reach to place sections • Location of overhead and underground utilities • Method of delivery of the bridge sections Crane lifts are effective for small bridges in accessible locations.



20.7.2 Gantry Crane

Gantry crane moves can be effective, especially for long viaducts where the number of sections is large. For viaduct construction, consider the weight of the bridge and trucks on the previously constructed bridge segment to allow delivery of the new sections using the previously constructed section.

20.7.3 Strand Jacks

Strand jacks attached to bents or cantilevered sections of bridges lift segments of the bridge into place. Strand jacks are effective when the bridge can be delivered to the site under the cantilevered sections.

20.7.4 Launches

Bridge launches are similar to bridge slides. Typical launches are much more design intensive than other move types due to the constant change in support conditions.

Single span launches can be completed by using temporary intermediate supports.

20.8 TEMPORARY SUPPORT STRUCTURES

Temporary support structures include any element used to support a bridge before or during a bridge move. At a minimum, all temporary works must meet the requirements of the current edition of the AASHTO Guide Specifications for Temporary Works.

20.8.1 Staging Area Supports

In addition to the requirements in the AASHTO Guide Specifications for Temporary Works, all temporary supports must:

• Meet the requirements in Section 17.1.4 for differential deflection between supports • Limit differential deflection in bearings along a support line to 1/16 in. or less or provide

bearings with vertical adjustment • Provide redundant load paths 20.8.2 During Move or on SPMT Supports

The heavy lift engineer designs SPMT support works. Requirements are defined in the project specifications.

FEBRUARY 2015

BRIDGE PRESERVATION ANDREHABILITATION OR WIDENING



Bridge Preservation and Rehabilitation or Widening 21-i

TABLE OF CONTENTS

21.1 INTRODUCTION .......................................................................................................... 21-1

21.1.1 Purpose ......................................................................................................... 21-1 21.1.2 Strategy ......................................................................................................... 21-1 21.1.3 Literature ....................................................................................................... 21-2

21.2 BRIDGE CONDITION ASSESSMENT ........................................................................ 21-2

21.2.1 Deck .............................................................................................................. 21-3

21.2.1.1 Visual Assessment ...................................................................... 21-3 21.2.1.2 Nondestructive Assessment ........................................................ 21-4

21.2.2 Superstructure ............................................................................................... 21-4


21.2.3 Substructure .................................................................................................. 21-6


21.3 CULVERT CONDITION ASSESSMENT ..................................................................... 21-8

21.3.1 Visual Assessment ........................................................................................ 21-8 21.3.2 Nondestructive Assessment .......................................................................... 21-9

21.4 DECK PRESERVATION .............................................................................................. 21-9

21.4.1 Evaluation ...................................................................................................... 21-9 21.4.2 Treatments .................................................................................................... 21-11

21.4.2.1 Healer/Sealer or HMWM .............................................................. 21-11 21.4.2.2 Structural Pothole Patching ......................................................... 21-11 21.4.2.3 Overlay ........................................................................................ 21-11 21.4.2.4 Joint Closure ................................................................................ 21-11 21.4.2.5 Joint Rehabilitation or Replacement ............................................ 21-11 21.4.2.6 Partial Deck Replacement ........................................................... 21-12 21.4.2.7 Deck Replacement ...................................................................... 21-12 21.4.2.8 Parapet Retrofit or Replacement ................................................. 21-13 21.4.2.9 Drainage System Retrofit ............................................................. 21-13

21.5 SUPERSTRUCTURE PRESERVATION ..................................................................... 21-14



21-ii Bridge Preservation and Rehabilitation or Widening

21.5.2.1 Concrete Repair or Rehabilitation ................................................ 21-14 21.5.2.2 Strengthening .............................................................................. 21-14 21.5.2.3 Bearing Rehabilitation .................................................................. 21-17 21.5.2.4 Continuous for Live Load Retrofit ................................................ 21-17 21.5.2.5 Link Slab Retrofit.......................................................................... 21-17 21.5.2.6 Fatigue Crack Retrofit .................................................................. 21-17 21.5.2.7 Cleaning and Repainting or Overcoating Structural Steel ........... 21-19 21.5.2.8 Heat Straightening ....................................................................... 21-20 21.5.2.9 Pin/Hanger/Hinge Rehabilitation or Replacement ....................... 21-20

21.6 SUBSTRUCTURE PRESERVATION .......................................................................... 21-21


21.6.2.1 Concrete Repair or Rehabilitation ................................................ 21-21 21.6.2.2 Abutment or Wall Stabilization ..................................................... 21-21 21.6.2.3 Integral Abutment Retrofit ............................................................ 21-22 21.6.2.4 Semi-Integral Abutment Retrofit................................................... 21-22 21.6.2.5 Strengthening .............................................................................. 21-22 21.6.2.6 Scour Mitigation ........................................................................... 21-24

21.7 CULVERT PRESERVATION ....................................................................................... 21-25


21.7.2.1 Concrete Repair or Rehabilitation ................................................ 21-25 21.7.2.2 Strengthening .............................................................................. 21-26 21.7.2.3 Scour Mitigation ........................................................................... 21-26

21.8 SEISMIC RETROFIT ................................................................................................... 21-26

21.8.1 Evaluation ...................................................................................................... 21-26 21.8.2 Seismic Retrofits ............................................................................................ 21-27

21.8.2.1 Column Jacketing ........................................................................ 21-27 21.8.2.2 Seat Width Extension .................................................................. 21-27 21.8.2.3 Structural Continuity .................................................................... 21-28 21.8.2.4 Restrainers and Ties .................................................................... 21-28 21.8.2.5 Bearing Replacement .................................................................. 21-28 21.8.2.6 Seismic Isolation Bearings ........................................................... 21-29 21.8.2.7 Modifying Seismic Response ....................................................... 21-29

21.9 BRIDGE WIDENING .................................................................................................... 21-29

21.9.1 Evaluation ...................................................................................................... 21-29 21.9.2 Design ........................................................................................................... 21-30 21.9.3 Details of Existing Structures ......................................................................... 21-30


Bridge Preservation and Rehabilitation or Widening 21-iii

21.9.3.1 Load Carrying Capacity ............................................................... 21-30 21.9.3.2 Materials ...................................................................................... 21-31 21.9.3.3 Substructures/Foundations .......................................................... 21-31

21.9.4 Details of Widened Structures ....................................................................... 21-31

21.9.4.1 Girder Type Selection .................................................................. 21-31 21.9.4.2 Deck Closure Pour ....................................................................... 21-32

LIST OF FIGURES

Figure 21.1 — CONDITION ASSESSMENT METHODS FOR SPECIFIC DECK DISTRESSES ........................................................................................ 21-5 Figure 21.2 — DECK CONDITION THRESHOLDS AND CORRESPONDING TREATMENTS ................................................................................................. 21-10 Figure 21.3 — HYDRAULIC SCOUR COUNTERMEASURES ................................................ 21-24


21-iv Bridge Preservation and Rehabilitation or Widening


Bridge Preservation and Rehabilitation or Widening 21-1

Chapter 21 BRIDGE PRESERVATION AND

REHABILITATION OR WIDENING

A successful bridge program seeks a balanced approach to preservation, rehabilitation and replacement. Focusing only on replacing deficient bridges and ignoring preservation needs is inefficient and cost prohibitive in the long term. Adopting a worst first approach to managing bridge assets can also yield ineffective results that allow bridges in good condition to deteriorate into the deficient category, which generally is associated with higher costs and other challenges.

The LRFD Specifications do not specifically discuss design requirements for bridge preservation and rehabilitation or widening. This chapter draws upon the structural literature to present practices and strategies for bridge preservation and rehabilitation or widening.

21.1 INTRODUCTION

21.1.1 Purpose

The objective of a good bridge preservation program is to employ cost effective strategies and actions to maximize the useful life of bridges. Applying the appropriate bridge preservation treatments at the appropriate time can extend bridge useful life at lower lifetime cost.

Preservation and rehabilitation activities often cost much less than reconstruction or replacement activities. Delaying or foregoing warranted preservation treatments accelerates deterioration and can escalate treatment activities from preservation to replacement. The latter results in extensive work and higher cost. A viable alternative is timely and selective bridge preservation activities to ensure continuing structural integrity and extend the useful life before replacement is required.

21.1.2 Strategy

A successful bridge program is based on a strategic, systematic and balanced approach to managing bridge preservation and replacement needs. Bridge planning and programming is presented in Chapter 2 of the BMM; however, the following repeats selected definitions, which helps establish clear and consistent terminology for the bridge preservation practitioners:

1. Bridge Preservation. Actions or strategies that prevent, delay or reduce deterioration of bridges or bridge elements, restore the function of existing bridges, keep bridges in good condition and extend bridge life. Preservation actions can be preventive or condition driven.

2. Bridge Rehabilitation. Work required to restore the structural integrity or correct safety deficiencies.


21-2 Bridge Preservation and Rehabilitation or Widening

3. Bridge Replacement. Total replacement of a bridge with a new facility constructed in the same general traffic corridor. The replacement structure must meet the current geometric, material and structural standards required for the types and volume of projected traffic on the facility over the design life.

Common bridge preservation strategies include:

• Protect decks with overlays • Paint steel surfaces • Repair spalled concrete • Replace or retrofit parapets • Close, rehabilitate or replace joints • Make abutments integral • Make bents integral • Replace or rehabilitate bearings • Correct drainage problems

Common bridge rehabilitation activities include:

• Bent cap strengthening • Column shear or confinement strengthening • Foundation strengthening • Girder strengthening • Deck replacement

21.1.3 Literature

The design of new bridges is based primarily on the LRFD Specifications. No single national publication exists that presents accepted practices and criteria for the rehabilitation of existing bridges. However, the highway research community has devoted significant resources to identify practical, cost effective methods to preserve and rehabilitate existing bridges.

Publications are readily available that have special interest when preserving and rehabilitating an existing bridge from ACI, FHWA, the National Park Service (NPS), NCHRP, SHRP and SHRP2 and other states. Publications cover a very broad range of topics, including fatigue in steel bridges, concrete repair, hydrodemolition, repair of damaged bridges, seismic retrofit, strengthening bridges and many other important treatments.

21.2 BRIDGE CONDITION ASSESSMENT

The proper assessment of the condition of bridge elements is the cornerstone of sound bridge management. Successful bridge management requires accurate condition assessment and application of the right treatment to the right bridge at the right time. Condition assessment can be performed using numerous tools and techniques, but some are more effective than others, depending on the condition of the bridge. Similarly, although many treatments are available, the



effectiveness in extending bridge service life depends on the condition of the bridge at the time of application.

Structural engineers rely heavily on visual inspection to conduct an accurate condition assessment of bridges but, although visual inspection can provide valuable information for many bridges, the presence of stay in place forms and/or deck surface treatments such as asphalt overlays can greatly limit the ability to accurately determine condition. Furthermore, visual inspection alone cannot be used to track changes in concrete bridge properties until damage is manifest, at which time the concrete could no longer be a good candidate for the application of cost effective preventive maintenance treatments.

The visual assessment of bridge condition is performed according to the AASHTO Manual for Bridge Element Inspection and Chapter 3 of the BMM. Nondestructive evaluation is performed when visual assessment cannot adequately describe the condition of the bridge.

21.2.1 Deck

Several research reports have been published on the topic of bridge deck condition assessment in Utah. Refer to the following research reports:

• Report No. UT-05.01 “Concrete Bridge Deck Condition Assessment Guidelines” • Report No. UT-05.05 “Performance of Concrete Bridge Deck Surface Treatments” • Report No. UT-06.01 “Condition Analysis of Concrete Bridge Decks in Utah” • Report No. UT-06.05 “Development of an Index for Concrete Bridge Deck Management

in Utah”

21.2.1.1 Visual Assessment

Visual inspection of the bridge deck is performed every two years as part of the bridge inspection program. Inspections performed according to the AASHTO Manual for Bridge Element Inspection quantify the square footage of deck in each condition state. Four condition states exist, with increasing severity of defect from one to four. The general terms corresponding with the four condition states are good, fair, poor and severe. The biennial inspection report records inspection findings and notes, which are documented in the bridge record.

Visual assessment of the bridge deck begins with a thorough review of the biennial inspection reports and also includes the following:

• Review all available information in the bridge record, including plans, calculations, load rating reports, photos, correspondence and planning reports.

• Determine if the deck has experienced previous patching or rehabilitation. • Determine the approximate percentage of previously patched deck area. • Determine the approximate area of deck that is potholing or delaminated. • Determine the expected percentage of deck that requires patching. • Determine the depth to the existing reinforcing.



• Assess the condition of the current overlay, if present. • Assess the condition of deck joints, railings and approach slabs. • Assess the smoothness of the riding surface, including the amount of approach slab

settlement. • Assess the safety of the railing system, including the transitions off the bridge. • Assess the functionality of the deck drainage system. 21.2.1.2 Nondestructive Assessment

When the severity and extent of bridge deck deterioration cannot be reasonably determined, a nondestructive assessment could be necessary to supplement the visual assessment. Formulate a preliminary plan of action by identifying the expected types of bridge distress to be investigated, and then select the nondestructive condition assessment methods that are appropriate for measuring the severity and mapping the extent of deck deterioration. The structural engineer must understand the nondestructive condition assessment methods proposed for the bridge deck. At a minimum, the preliminary plan of action proposes testing that:

• Determines the extent of deterioration with respect to plan dimensions and depth • Determines severity of deterioration by using reasonable thresholds • Describes limitations of the testing • Provides adequate redundancy of tests to explain the potential variance in results

Figure 21.1 presents common condition assessment methods for specific deck distress.

21.2.2 Superstructure


The superstructure consists of the bearings and all components and elements resting upon the bearings. Superstructure elements commonly assessed for preservation and rehabilitation include girders, stringers, floor beams, trusses, arches, bearings, gusset plates, pin and hanger assemblies and structural steel protective coatings. The bridge deck is part of the superstructure, but is discussed separately in Section 21.2.1.

Visual inspection of the bridge superstructure is performed every two years as part of the bridge inspection program. Inspections performed according to the AASHTO Manual for Bridge Element Inspection typically quantify the lineal feet of girders in each condition state; bearings, gusset plates and pin and hanger assemblies are quantified by each. Structural steel protective coatings are quantified by the area of steel covered. Four condition states exist with increasing severity of defect from one to four. The general terms corresponding to the four condition states are good, fair, poor and severe. Inspection findings and notes are recorded in the biennial inspection report and documented with the bridge record.



Distress Type Condition Assessment Method

Air pockets and honeycombing Chain dragging, coring, ground penetrating radar, hammer sounding, impact echo, ultrasonics, visual inspection

Alkali-silica reaction Coring, petrographic analysis, visual inspection

Carbonation Coring, penetration dyes, petrographic analysis

Chloride induced corrosion Chloride concentration testing, coring, half cell potential, rapid chloride permeability, resistivity

Cracking Impact echo, penetration dyes, ultrasonics, visual inspection

Delamination Chain dragging, coring, ground penetrating radar, hammer sounding, impact echo, infrared thermography, ultrasonics

Polishing Skid resistance testing

Popouts Visual inspection

Potholing Visual inspection

Scaling Visual inspection

Spalling Visual inspection

Sulfate attack Coring, petrographic analysis

Figure 21.1 — CONDITION ASSESSMENT METHODS FOR SPECIFIC DECK DISTRESSES

Visual assessment of the bridge superstructure begins with a thorough review of the biennial inspection reports and also includes the following:

• Review all available information in the bridge record, including plans, calculations, load rating reports, photos, correspondence and planning reports.

• Determine if the superstructure has experienced previous strengthening or rehabilitation. • Identify fracture critical members. • Assess steel elements for fatigue details and expected service life. • Determine if cracks are present in steel elements. • Determine if any rivets or bolts are missing. • Assess the severity of drainage or leakage onto the superstructure. • Assess the condition of girder ends, especially under expansion joints. • Assess collision damage by vehicles, vessels or debris. • Assess visible reinforcing or prestressing strand for loss of load carrying capacity. • Assess the condition of the protective coating. • Assess the condition of gusset plates and pin and hanger assemblies. • Measure any deformed shapes and assess the potential for moment magnification. • Assess the condition and functionality of bearings, including:

○ Bearing alignment ○ Evidence of movement of the bearing pad ○ Evidence of slip between the bearing and girder



○ Condition and alignment of guides ○ Percent of bearing contact area ○ Anchor bolt alignment and condition ○ General condition of all bearing components ○ Distress in pedestals and bearing seats due to improperly functioning bearings

21.2.2.2 Nondestructive Assessment

The following are the most common test methods performed to locate cracks in steel components and measure the extent and size of cracks:

• Dye penetrant is a common, low cost method of detecting surface cracks. • Magnetic particle is a commonly used method that can detect subsurface cracks or

cracks under a weld. • Ultrasonic testing (UT) is the standard practice for inspecting pins on bridges. • Eddy current (EC) can detect near surface defects through paint. • Radiographic testing (RT) uses X-rays or gamma rays to produce an image of the

object’s internal structure. RT works well for detecting cracks or section loss in multilayered plates such as a gusset plate connection.

The following are the most common test methods performed to assess the condition of concrete members:

• Hammer sounding is a common, low cost method of detecting surface cracks or delaminations.

• Impact echo (IE), or ultrasonic pulse echo, uses impact generated stress waves to assess subsurface flaws and material thickness.

• Magnetic flux leakage can detect ruptures in prestressing strands. • Ground penetrating radar (GPR) is used to assess subsurface flaws and to image

embedded reinforcing or tendons. • Infrared thermography evaluates heat flow to assess deterioration, flaws and moisture

intrusion.

21.2.3 Substructure


The substructure consists of all components and elements below the bearings. Substructure elements commonly assessed for preservation and rehabilitation include bent caps, columns and walls, abutments, wingwalls and sometimes footings. Bridge foundations, including piles and drilled shafts, are rarely preserved or rehabilitated.

Visual inspection of the bridge substructure is performed every two years as part of the bridge inspection program. Inspections performed according to the AASHTO Manual for Bridge Element Inspection typically quantify the lineal feet of abutments, walls and bent caps in each condition state; columns are quantified by each. Protective coatings are quantified by the area



covered. Four condition states exist with increasing severity of defect from one to four. The general terms corresponding to the four condition states are good, fair, poor and severe. The biennial inspection report records inspection findings and notes, which are documented in the bridge record.

Visual assessment of the bridge substructure begins with a thorough review of the biennial inspection reports and also includes the following:

• Review all available information in the bridge record, including plans, calculations, load rating reports, photos, correspondence, scour plan of action and planning reports.

• Determine if the substructure has experienced previous strengthening, scour mitigation or rehabilitation.

• Assess geometry changes such as settlement, rotation or tilt of retaining walls. • Assess the severity of drainage or leakage onto the substructure. • Measure any deformed shapes and assess the potential for moment magnification. • Assess collision damage by vehicles, vessels or debris. • Assess seismic vulnerabilities. • Assess vulnerability to scour, including the embankment and channel.

21.2.3.2 Nondestructive Assessment

The following are the most common test methods performed on substructure elements to determine length of unknown foundation depth or to evaluate the integrity of foundation elements:

• The sonic echo (SE) method is normally conducted together with the impulse response (IR) method as the SE/IR method, which can be used on both new and existing foundations. SE/IR is used for low strain integrity testing of piles and deep foundations for length and integrity determination. The two analysis methods complement each other to allow the most accurate foundation length and defect analysis possible.

• The parallel seismic (PS) method is used for length determination of unknown foundation depths.

• Ultraseismic (US) investigations are performed to evaluate the integrity and to determine the length of shallow and deep foundations.

• The GPR method as applied to foundation testing is primarily used to map reinforcing in foundation tops and to measure the depths of abutments, mats, spread footings and other relatively shallow concrete foundations. The method also locates and maps shallow buried foundations without excavation. The method determines both the depth and location of reflectors within the foundation.

• Another application of the GPR method to foundation testing is borehole GPR, where a borehole type antenna is used to look outward from the borehole to examine the surrounding material, including any nearby foundations. GPR measures foundation depth and offset distance from a borehole.

• The induction field (IF) method measures the depth of foundations that are steel (e.g., H-piles) or contain continuous reinforcing steel.

• The pulse velocity of longitudinal stress waves in a concrete mass is used to indicate the presence of voids and cracks and to evaluate the effectiveness of crack repairs. The



method is also applicable to indicate changes in the properties of concrete and in the survey of structures to estimate the severity of deterioration or cracking.

• Time domain reflectometry (TDR) measures reflections along a conductor to characterize and locate faults in strands or tendons.

• Crosshole sonic logging (CSL) is a method to verify the structural integrity of drilled shafts and other concrete piles. CSL normally requires steel or PVC access tubes installed in the drilled shaft and tied to the rebar cage.

• High-resolution scanning sonar can improve the quality of underwater inspections by directing the divers to areas of interest on the bents and can identify the presence of underwater bent elements, either not located or incorrectly located on existing plans and drawings.

21.3 CULVERT CONDITION ASSESSMENT

A structure that is designed to convey water and provide a path under an obstruction. Most culverts have a structural floor and are covered with embankment material. However, buried three sided structures, arches, pipes, boxes, etc., are also culverts if the structures are designed to convey water. If the structure is designed to convey water and has a structural floor, but is not covered with embankment material, the structure is still a culvert. The Structures Division assigns a structure number to all culverts requiring design plans; which typically applies to any box culvert with a span or rise greater than 12 ft.

21.3.1 Visual Assessment

Visual inspection of the culvert is performed every two years as part of the bridge inspection program, if the culvert span is 20 ft or longer. See Section 3.1.3.4 of the BMM. Inspections are performed based on Chapter 3 of the BMM and according to the AASHTO Manual for Bridge Element Inspection. Four condition states exist with increasing severity of defect from one to four. The general terms corresponding to the four condition states are good, fair, poor and severe. The biennial inspection report records inspection findings and notes, which are documented in the bridge record.

Visual assessment of the culvert begins with a thorough review of the biennial inspection reports and also includes the following:

• Review all available information including plans, calculations, load rating reports, photos, correspondence, scour plan of action and planning reports.

• Determine if the culvert has experienced previous strengthening, scour mitigation or rehabilitation.

• Assess geometry changes such as settlement or alignment. • Assess the severity of piping or leakage. • Assess the severity of deterioration. • Measure any deformed shapes and assess the potential for moment magnification. • Assess collision damage by debris, etc.



• Assess seismic vulnerabilities. • Assess vulnerability to scour or erosion, including the embankment and channel.

21.3.2 Nondestructive Assessment

Refer to Section 21.2.3.2 for typical nondestructive assessment tools.

21.4 DECK PRESERVATION

Chapter 16 provides an in-depth discussion on the design of bridge decks that are constructed compositely in conjunction with concrete and steel girders for new bridges. Many of the Chapter 16 design and detailing practices also apply to deck rehabilitation.

21.4.1 Evaluation

Both technical and economic factors influence the decision to preserve, rehabilitate or replace a bridge deck. Accurate condition assessment is vital to good decision making, but determining the proper treatment requires consideration of additional information. The goal is to identify a treatment recommendation that incorporates all relevant information. At a minimum, determination of deck treatments considers the following information:

• The bridge deck condition assessment, including the results of any NDE • Current design criteria • An economics analysis that compares life cycle costs of each feasible treatment • The expected service life of each treatment • The long range plan for the roadway corridor • The general condition of other bridges within the same roadway corridor • The age of the deck, the age of the overlay and the number of times the deck has been

rehabilitated • The load carrying capacity of the bridge (i.e., the load rating) • The AADT on the bridge and the corresponding limitations of operations that are

expected for the project, including both the duration and the timing required to perform the treatment

• Expected impacts to the feature crossed • The operational and material characteristics of the adjoining roadway • The performance and/or compatibility of the treatment on other bridges of similar type • Constructability items such as phasing, access and staging areas

Figure 21.2 presents deck condition thresholds and corresponding treatment guidelines. The figure does not present rigid limits or preferred solutions. Evaluate the proposed treatment based on complete project criteria. Incorporation of the complete project criteria can change the treatments suggested in the figure.



2 options:• Total deck replacement• Create bridge replacement/rehabilitation

strategy

Yes

Start

Is more than 50% of deck damaged?



Is there anydeck surface

damage?

Is the deckprotected with an

overlay?

Yes

Yes

Yes

3 options:• Do nothing and re-evaluate after next inspection• Partial deck replacement• Total deck replacement

4 options:• Do nothing and re-evaluate after next inspection• Place an asphalt overlay and waterproofing

membrane• Place a polyester polymer concrete overlay• Partial deck replacement

Does the deckhave an asphalt

overlay?

Yes 2 options:• Do nothing and re-evaluate after next inspection• Replace the asphalt overlay and waterproofing

membrane

3 options:• Do nothing and re-evaluate after next inspection• Apply a healer/sealer or HMWM• Place a polyester polymer concrete overlay

Is thehealer sealer appli-

cation older than 5 years, isthe thin bonded polymer overlay older

than 15 years, or is the rigidoverlay older than

25 years?

Yes

Does the deckhave an asphalt

overlay?

Is the asphaltoverlay older than

10 years?

1 option:• Do nothing and re-evaluate after next inspection

No

No

No

No

No

No

No

No

No

Yes

Yes

3 options:• Do nothing and re-evaluate after next inspection• Replace the asphalt overlay and waterproofing

membrane• Place a polyester polymer concrete overlay

4 options:• Do nothing and re-evaluate after next inspection• Apply a healer/sealer or HMWM• Place a thin bonded polymer overlay• Place a polyester polymer concrete overlay

Yes

Note: Deck pothole patching is included with overlays.

Figure 21.2 — DECK CONDITION THRESHOLDS AND CORRESPONDING TREATMENTS



21.4.2 Treatments

21.4.2.1 Healer/Sealer or HMWM

Widespread minor cracking in a bare deck can be repaired by flooding the deck with a low viscosity, low modulus, two component, epoxy based system commonly known as a concrete healer/sealer. The concrete healer/sealer fills the cracks by gravity and capillary action. Dry silica sand is broadcast over the epoxy to re-establish traction over the concrete deck. HMWM is also a type of healer/sealer. Refer to Section 16.1.3 for additional information.

21.4.2.2 Structural Pothole Patching

When unsound concrete comprises less than 30% of the entire deck area, structural pothole patching can effectively restore the deck to a serviceable condition. Consider the chloride content in the concrete. Unprotected reinforcing is actively corroding when chloride concentrations reach 2 pounds per cubic yard and epoxy coated reinforcing is actively corroding at 8 pounds per cubic yard. Avoid pothole patching when chloride levels are beyond the thresholds at the level of the reinforcing (typically between 1½ in. and 2 in. from the concrete surface), because the concrete surrounding the patches continues to spall. Do not use asphalt or any other product not specifically designed for bridge decks for structural pothole repair. Refer to the WS sheets for details.

21.4.2.3 Overlay

Use a deck overlay to slow chloride intrusion into the deck. Refer to Section 16.1.4 for overlay systems. Placing new overlays on existing overlays is typically not recommended. However, if an existing thin bonded polymer overlay is well bonded to the concrete, another application of a thin bonded polymer overlay can be placed over it. Refer to Section 2.7 for asphalt application guidelines.

21.4.2.4 Joint Closure

Make the deck continuous, eliminate all expansion joints and make the bridge integral when foundation conditions permit. However, the presence of battered piles at abutments generally precludes making bridges integral. Refer to the WS sheets for details for closing expansion joints.

Do not close expansion joints at abutments or in the deck on bridges with pin and hangers or in span hinges without also replacing the pin and hanger and or hinge with full splices.

21.4.2.5 Joint Rehabilitation or Replacement

When the structure geometry and details do not permit elimination of the joint, rehabilitating or replacing the system could be required. Joint rehabilitation refers to the repair of a portion of an existing joint and not complete replacement. Joint rehabilitation includes repairing or replacing



loose or broken restrainers on strip seal expansion joints, failed header materials adjacent to joints or torn seals.

Where joint rehabilitation is not feasible, replace an existing damaged or malfunctioning joint. Chapter 19 provides guidance on joint selection and design.

Refer to the WS sheets for joint rehabilitation and replacement details.

21.4.2.6 Partial Deck Replacement

Typical partial deck replacements include overhang replacements, replacement of deck adjacent to joints and replacement of the top several inches of the deck (typically to 1 in. below the top mat of reinforcing).

The removal of all concrete with chloride content sufficient to sustain corrosion is necessary to ensure a permanent repair. For partial depth repairs, remove concrete to a depth of ¼ in. plus the maximum size of the aggregate below the bottom of the top mat of reinforcing. Unless the contaminated concrete is removed, differences in the surface conditions on the reinforcing can cause the formation of anodic and cathodic areas and a resumption of the corrosion process.

21.4.2.7 Deck Replacement

To conduct a total deck replacement, use CIP concrete, precast concrete deck panels, a combination of half depth precast panels and CIP concrete overlay, or alternative systems. When replacing the deck on structures with substandard load ratings, evaluate the deck thickness and/or lightweight concrete to determine if significant rating improvements can be achieved. Structures with Inventory Ratings less than 1.0 based on the original design methodology (LFD or LRFD) are candidates for strengthening. Structures with Operating Ratings less than 1.0 are strong candidates for strengthening. Also, consider strengthening any structure with posted load restrictions. Coordinate with the Structures Design Manager to determine if strengthening is a goal of the deck replacement project.

Use CIP decks when phasing the construction is possible and traffic impacts are minimal. Refer to the SD drawings for requirements. Partial depth precast panels with CIP topping is a type of CIP deck. Precast partial depth panels can decrease construction time and reduce user impacts. Refer to the WS sheets for details.

Use precast concrete deck panels when excessive user impacts require a rapid deck replacement. Refer to the SS sheets for typical panel details.

Alternative deck systems consist of orthotropic systems, open steel grid systems, partially filled grid systems or other similar systems. Examine the use of alternative systems where extremely light weight decks are required. Coordinate and obtain approval from the Structures Design Manager when selecting an alternative deck system.



21.4.2.8 Parapet Retrofit or Replacement

Section 16.6.1 presents UDOT practices for new bridge parapets. Replace existing bridge parapets with parapets meeting the criteria in Section 16.6.1, unless directed otherwise by the Structures Design Manager. Occasionally, the existing parapet is left in place for a variety of reasons (e.g., dead load considerations, incompatibility with an existing bridge deck).

Examine the following when evaluating an existing bridge parapet:

• Review the crash history and the maintenance and repair history of the bridge parapet • Inspect the existing bridge parapet to verify the integrity of critical design details, such

as: ○ Base plate connections ○ Anchor bolts ○ Welding details ○ Concrete cracking ○ Reinforcing development

• Even in the absence of an adverse crash history, an inspection of the existing bridge parapet can reveal inherent safety deficiencies in the parapet design, such as: ○ Potential for snagging ○ Inadequate height ○ Inadequate guardrail to bridge parapet transition

Only minor repairs (e.g., surface repairs) are permitted on parapets that do not meet current standards. Minor changes/additions in barrier height such as replacing the pipe railing with an equivalent height concrete section dowelled into the existing barrier is also considered a minor repair. Where significant repair is required, replace the parapet with the standard single slope parapet. Bridges classified as historic require coordination the Utah State Historic Preservation Officer to determine if the parapet must be replaced with the same or a similar parapet.

21.4.2.9 Drainage System Retrofit

The most common drainage system problems are:

• Deterioration of or around drainage facilities • An inadequate number of facilities • Clogging of facilities • Water draining onto other structural components or the roadway below

Replace or repair drainage structures as required to provide adequate drainage and correct existing drainage problems.

Permanently seal abandoned deck drains such that no ponding occurs. Remove abandoned piping.



21.5 SUPERSTRUCTURE PRESERVATION

21.5.1 Evaluation

Chapter 14 provides a detailed discussion on the design of concrete superstructures. Chapter 15 provides a detailed discussion on the design of steel superstructures for new bridges. Many of the Chapters 14 and 15 design and detailing practices also apply to the preservation or rehabilitation of an existing superstructure.

21.5.2 Treatments

21.5.2.1 Concrete Repair or Rehabilitation

A clean, sound surface is required for any repair operation; therefore, remove all physically unsound concrete, including all delaminations.

Attempt to identify and remediate the mechanism causing the concrete to crack. Epoxy injection is used to fill cracks in beams or girders from 1/64 in. to ¼ in. Because the resin is injected under pressure, the resin can usually fill the entire crack. Do not use epoxy injection for a moving crack.

Repair cracks larger than ¼ in. and any localized damage according to the delamination repair procedure defined in the UDOT Standard Specifications.

21.5.2.2 Strengthening

Strengthening superstructures is required when the structure demonstrates evidence of overloading or damage caused by inadequate strength or when required by the Structures Design Manager. Structures with Inventory Ratings less than 1.0 based on the original design methodology (LFD or LRFD) are candidates for strengthening, and structures with Operating Ratings less than 1.0 are strong candidates for strengthening. Consider strengthening on any structure with posted load restrictions. Also, consider strengthening structures compromised by other events such as collision impacts, damage from illegal loading, flooding, seismic or other extreme events.

21.5.2.2.1 Stay in Place Forms or Wraps

Use external reinforcing in the form of steel jackets, fiber wraps or prefabricated fiber reinforced polymer (FRP) shapes to increase capacity. Numerous methods are available to place or form the systems. The typical construction sequence for steel jackets or prefabricated FRP shapes removes deteriorated concrete, places the stay in place form or jacket and grouts the gap. Alternatively, wet layup systems remove loose and deteriorated concrete, reconstruct the surface, then place and cure the FRP system. Refer to NCHRP Project 12-75 “Development of FRP Systems for Strengthening Concrete Girders in Shear” and ACI 440.2R-08 “Guide for



Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures” in developing a design method for the process.

The system can improve both the shear and bending capacity, but is usually used to increase the shear capacity and provide confinement in plastic hinge zones.

21.5.2.2.2 Post-Tensioning

Beam Strengthening

External post-tensioning can be applied to both steel and concrete beams to reduce tensile stresses, to strengthen beams, or to make simply supported beams continuous. Add post-tensioned tendons to restore the strength of prestressed concrete girders where the original strands or tendons have been damaged. Strengthening by post-tensioning can also be applied to nonprestressed concrete girders. A variety of successful methods of post-tensioning exist in the literature.

Collision Repair

Collision of overheight vehicles or equipment with a bridge constructed with prestressed concrete girders can result in damage to or severing of the girder tendons. Exposure to water and salt can also cause damage, especially where the concrete cover is damaged or cracked. Because the steel tendons determine the load carrying capacity of the girder, any damage must be repaired.

At a minimum, the following steps apply:

• Conduct an investigation on the extent of damage. • Perform a structural evaluation to determine the extent of repair. • Evaluate the existing diaphragms to ensure the adequacy to support the end anchorage

of the tendons. • Determine the placement of the temporary load to be applied to the bridge before

removal and placement of concrete in prestressed concrete girders, if any, to ensure the proper distribution of loads in the final condition.

Design the post-tensioning system according to the manufacturer’s recommendations. Wedge type anchorages are susceptible to high seating losses for short length tendons. Preferably, use high strength prestressing tendons in the application. The LRFD Specifications require the establishment of resistance at ultimate limit states at which the interaction between the parent and the post-tensioning systems must be investigated.

Because the anchorages are always close to the beam ends, post-tensioning anchorages are vulnerable to salt laden water seeping through imperfectly sealed deck joints. Protect the tendons by corrosion resistant ducts, either grease filled or grouted.



21.5.2.2.3 Compensate for Section Loss

Field welding or bolting additional plates to a steel girder can compensate for the loss of section. Fabricators often use welding for shop fabrication of steel members and for welding pieces in preparation for rehabilitation work. Field welding is often difficult to perform properly. Field welding requires individuals with the appropriate documented qualifications. The proper inspection of field welds is equally difficult. Avoid field welding and, if used, obtain approval from the Structures Design Manager. Bolting additional plates over a corroded section, which has been cleaned and painted to prevent further section loss, is a more reliable long term solution.

21.5.2.2.4 Add Cover Plates

If the deck is deteriorated and removed, adding cover plates to strengthen a beam becomes a viable alternative. The LRFD Specifications place fully welded cover plates into fatigue category E′ at the ends of the cover plates, which is the lowest fatigue designation and, therefore, welded cover plates can be counterproductive from the design perspective. If bolts designed according to LRFD Article 6.10.12.2.3 are used at the end of the cover plates, apply fatigue category B. Because the design requires the presence of drilling equipment and work platforms, consider a fully bolted cover plate construction.

21.5.2.2.5 Introduce Composite Action

Many older steel structures use noncomposite decks. Introducing composite action between the deck and the supporting beams is a cost effective method to increase the strength of the superstructure. The LRFD Specifications require the use of composite action where current technology permits. Welded studs or high strength bolts can achieve composite action. Design shear connectors in accordance with LRFD Article 6.10.10.

Composite action considerably improves the strength of the upper flange in positive moment areas, but the beneficial effect on the beam as a whole is only marginal. The combination of composite action in conjunction with selective cover plating of the lower flange is the most effective method of beam strengthening.

Introducing composite action near joints prevents the deck from separating from the beams, thus increasing the service life of the deck. Provide the treatment on each bridge that has the deck removed for other reasons.

21.5.2.2.6 Add New Girders

If the deck is removed, a new set of girders added to the existing bridge is one alternative to strengthen the superstructure. To ensure proper distribution of live load, stiffness of the new girders must be between 80% and 120% of the stiffness of the adjacent girders.

The old girders could also need rehabilitation, in which case, removing the girders could be more feasible from a structural and economic perspective.



21.5.2.3 Bearing Rehabilitation

Often, the existing bearings only require cleaning or repositioning. Extensive deterioration, or frozen bearings, can indicate that the design requires modification. Evaluate a variety of elastomeric devices for sliding and roller bearing assemblies. If the reason for deterioration is a leak in the expansion joint seal, consider closing the joint or repair or replace the seal.

If the bearing is seriously dislocated, the anchor bolts are badly bent or broken, or the concrete seat or pedestal is structurally cracked, the bridge could have a system wide problem usually caused by temperature or settlement that warrants investigation.

When conditions permit, make the bridge integral and eliminate future bearing maintenance.

See Chapter 19 for more information on bearings.

21.5.2.4 Continuous for Live Load Retrofit

Eliminate joints between simple spans and make the diaphragm integral to reduce the future potential for deterioration due to leaking joints and improve the structure load rating. Providing continuity for live load often requires extensive deck work. The end of the girder could also require strengthening to accommodate the loads due to continuity.

21.5.2.5 Link Slab Retrofit

Use link slabs to eliminate joints between simple spans where integral diaphragms are not feasible. A link slab is constructed by removing the joint and several feet of deck on each side of the joint, and replacing the joint with a concrete slab that is not bonded to the girder. The treatment can eliminate the leaking joint and minimize repair costs and impacts. Refer to the SD drawings and WS sheets for additional information.

21.5.2.6 Fatigue Crack Retrofit

Fatigue damage entails the formation of cracks in base metal or welds. If not repaired in a timely manner, fatigue cracks can lead to brittle fractures. The type of repair and timing depend on many factors including:

• Reason for the cracking (e.g., poor detailing, heavier than anticipated truck traffic, poor notch toughness, load induced or distortion induced fatigue, constraint)

• Location of the crack (e.g., cross frame, stiffener, weld, heat affected zone, main member)

• Depth, length and geometry of the crack • Redundancy

The following sections present retrofit options.



21.5.2.6.1 Hammer Peening

Peening is an inelastic reshaping of the steel at the surface location of cracks, or of potential cracks, by using a mechanical hammer. The procedure smooths and shapes the transition between weld and parent metal, and introduces compressive residual stresses that inhibit the cracking. Peening is most commonly used at the ends of cover plates to reduce fatigue potential. However, the success of hammer peening is highly dependent upon the skill of the operator.

21.5.2.6.2 Ultrasonic Impact Treatment

Ultrasonic peening is a computer controlled peening process using high speed peening. The process removes the dependency of the quality of mechanical hammer peening on the operator’s proficiency. The process promises weld toe enhancement for unavoidable poor fatigue resistance details, such as terminations of longitudinal stiffeners, and involves the deformation of the weld toe by mechanical hammering at a frequency of approximately 200 Hz superimposed by ultrasonic treatment at a frequency of 27 kHz. The treatment introduces beneficial compressive residual stresses at the weld toe by plastic deformation of the surface and reduces stress concentration by smoothing the weld toe profile.

For more information, see “Fatigue Resistance of Welded Details Enhanced by Ultrasonic Impact Treatment (UIT)” by Sougata Roy, John W. Fisher, Ben T. Yen in the International Journal of Fatigue, Volume 25, Issues 9-11, September-December 2003, pp. 1239-1247.

21.5.2.6.3 Grinding

If the penetration of surface cracks is small, the cracked material can be removed by selective grinding without substantial loss in structural material. Grinding is preferably performed parallel to the principal tensile stresses, and surface striations are carefully removed because the striations can initiate future cracking.

The most common application of grinding is to the toe of the fillet weld at the end of cover plates to meet fatigue requirements. Grinding can also be used when girders are nicked while removing old decks.

21.5.2.6.4 Drilled Holes

At the sharp tip of a crack, the tensile stress exceeds the ultimate strength of the metal, causing rapid progression if the crack size attains a critical level. Drilled holes blunt the sharp crack tip. The location of the tip is therefore established by a crack detection method in Section 21.2.2.2. Missing the tip renders the process useless.

Check sections to ensure that the reduced member capacity due to the crack and the drilled hole is still adequate which, however, is typically not a critical concern. The mitigation of the stress concentration at the tip is much more critical than the loss of net section. As such, the hole must be as large as tolerable in terms of net section. Drill bits of 13/16-in. and 1-1/16-in.



diameter are common due to the use for fabricating bolt holes. Hole saws can be used for even larger radii.

If holes overlap, grind the sides of the slots smooth to remove any projecting surfaces, which creates one oblong hole.

21.5.2.6.5 Bolted Splices

Where rivets or bolts in a connection are replaced, or where a new connection is made as part of the rehabilitation effort, the strength of the connection must meet current requirements in the LRFD Specifications. Almost exclusively, the connections are made with high strength bolts (ASTM A325).

Bolted splices can also be used to span a cracked flange or web, if the connection is designed to replace the tension part of the element or component.

21.5.2.6.6 Tungsten Arc Remelt

Tungsten arc remelting uses a gas shielded tungsten electrode moved at a constant speed along the weld toe, just melting the metal without addition of new filler metal. The GTA remelting process can remove slag intrusions and reduce the stress concentration at the weld toe. GTA remelting can also repair cracks up to approximately 3/16 in. deep. GTA remelting requires great operator skill and adequate penetration, both of which may be difficult to attain for a field retrofit.

21.5.2.7 Cleaning and Repainting or Overcoating Structural Steel

Cleaning and repainting or overcoating structural steel painting is frequently considered in conjunction with rehabilitation work on steel structures. Consider painting for bridges experiencing corrosion with section loss and for highly visible bridges with rust Grade 4 or more (SSPC Vis 2) where 10% of the surface area is rusted. The 10% level of corrosion is aesthetically unacceptable and often progresses to steel section loss. Consider the following options:

• Full removal of existing paint and repainting • A complete recoat over the top of the existing paint (overcoat) • Zone (spot repair) painting

Virtually all paint applied to bridges before 1988 contains lead and other heavy metals. To remove existing paint, the current state of practice is abrasive blast removal, full enclosure and with environmental and worker monitoring.

The paint industry has developed products that can be successfully applied over existing paints. An overcoat can be an economical alternative to full removal and repainting where a uniform appearance is desired at the conclusion of the project; however, the removal of the lead based paint is deferred until a subsequent rehabilitation or structure replacement. Zone painting



neither provides a uniform appearance nor removes the lead based paint. Zone painting can be appropriate in localized areas where corrosion could cause section loss.

Overcoating lead based paint having extensive rust spots but less than 1% of surface rusted (rust Grade 6) is generally not cost effective. The existing top coat is usually aluminum based and too stiff and brittle to overcoat. Blast cleaning must remove rust spots to bare metal and remove the aluminum top coat. Full containment is required. Overcoating retains the existing lead based paint and removal is merely deferred. Typically, postpone painting until the bridge has reached rust Grade 4 (10% of surface rusted) when complete lead based paint removal and repainting is appropriate.

Overcoating existing zinc based paint for rust Grade 6 extends the service life of the existing coating. The option is only appropriate on bridges that are highly visible to the public where aesthetics is as important as improved protection.

21.5.2.8 Heat Straightening

Restrict the use of heat straightening to hot rolled steels. Steels deriving strength from cold drawing or rolling tend to weaken when heated. The basic idea of heat straightening is that the steel, when heated to an appropriate temperature, loses some elasticity and deforms plastically, which rids the steel of built up stresses.

Heat straightening is as much an art as science. Exercise special care not to overheat the steel; accordingly, experience is required to implement the process. Also, the heating temporarily reduces the resistance of the structure. Apply measures such as vehicular restriction, temporary support, temporary post-tensioning, etc., as appropriate. For additional guidance on heat straightening, see Guide for Heat-Straightening of Damaged Steel Bridge Members, FHWA, 2008, and Heat-Straightening Repair of Damaged Steel Bridge Girders: Fatigue and Fracture Performance, NCHRP, 2008.

21.5.2.9 Pin/Hanger/Hinge Rehabilitation or Replacement

Structural engineers originally used pin and hanger details or in span hinges to facilitate the analysis of bridges by providing pins in otherwise continuous bridges. The use today is not necessary due to modern computer based structural analysis. Pin/hanger/hinge details are particularly susceptible to corrosion. Corrosion can result in the initiation of fatigue cracking in the hangers due to frozen pins and the unseating of the hangers on the pins due to misalignment from the corrosion product.

Typical solutions to address deteriorating pin and hanger details include:

1. Unlock Frozen Pins and Hangers. The pin and hanger detail can be disassembled after providing alternative support to the suspended girder. Then, the various components of the detail can be cleaned of rust and dirt or replaced before reassembly.



2. Provide a Catch Girder. As a safeguard against failure, especially for fracture critical girders, an alternative permanent support system can be fabricated to catch the suspended girder ends if the pin and hanger detail fails.

3. Eliminate the Pin and Hanger Detail. If the girder sections allow, a bolted splice of the web and flanges can be fabricated to replace the pin and hanger. A structural analysis of the resulting continuous structure must verify that the resulting loads do not exceed the resistance of the existing girder section.

21.6 SUBSTRUCTURE PRESERVATION

21.6.1 Evaluation

Chapter 18 provides a detailed discussion on the structural design of substructures for new bridges, and Chapter 17 applies to foundations. Many of the Chapter 17 and Chapter 18 design and detailing practices also apply to the rehabilitation of the substructures of an existing bridge.

21.6.2 Treatments


Repair concrete bent caps, columns, pedestals, wingwalls and abutments using traditional procedures outlined in the UDOT Standard Specifications. Refer to Section 21.5.2.1 for additional information.

Use shotcrete for extensive surface repairs where forming is difficult or expensive. Remove loose or spalling concrete down to or just below the existing reinforcing. Replace corroded reinforcing when required to restore capacity. Place welded wire fabric or replacement stirrups to replace deteriorated or missing stirrups. Place shotcrete and shape the surface to match the original surface or as required to restore capacity. Shotcrete can be plain or fiber reinforced.

Develop a special provision, define the limits of removal and define required reinforcing replacement when specifying repairs using shotcrete.

21.6.2.2 Abutment or Wall Stabilization

21.6.2.2.1 Deadman Anchor

The lateral force exerted by retained earth tends to push forward and rotate abutments and retaining walls. One solution for this problem is the installation of a deadman anchor.

A deadman is a heavy solid mass, usually concrete blocks that are connected to the retaining structure by long steel rods. A deadman is located in a stable earth mass well behind the structure. For wingwalls, or walls located on both sides of the roadway, the anchorage can



simply be connected together by steel tension rods. Protect the rods against corrosion and evaluate the effects of differential settlement.

Because the stabilization technique modifies the wall support from a cantilever to simple span pinned, check the wall reinforcing for the revised moments. The lateral earth pressure diagram can also be changed if more than one level of tension rods and anchors are installed.

21.6.2.2.2 Wingwalls

The wingwalls can break off and separate from the abutment due to earth pressure and differential settlement. If the opening is stable, the do nothing option is often preferable. If not stable, the wall must be stabilized or replaced. Stabilize existing walls with soil nail anchors, supplemental footings or supplemental connections to the abutment.

21.6.2.3 Integral Abutment Retrofit

Correct rotating abutments, deteriorating backwalls, damaged pedestals, out of alignment bearings and seismically vulnerable bearings by making the abutments integral. Evaluate the existing foundation system to ensure that the existing foundation is not damaged due to temperature movements and to ensure that superstructure elements are not overloaded by foundation restraint loads.

21.6.2.4 Semi-Integral Abutment Retrofit

Use a semi-integral abutment retrofit when foundation conditions do not permit an integral abutment retrofit. Use a semi-integral abutment retrofit to correct rotating abutments and deteriorating backwalls. The retrofit replaces or repairs damaged pedestals, out of alignment bearings and seismically vulnerable bearings.


Strengthening substructures is required when the structure shows evidence of overloading or damage caused by inadequate strength or when the strength of the structure has been compromised by other events such as collision impacts, damage from illegal loading, flooding, seismic or other extreme events.

Evaluate the existing structure strength when significant rehabilitation work is being performed and the existing structure shows evidence of significant corrosion. Strengthening activities are cost effective. Significant substructure rehabilitation includes activities that exceed removing and replacing loose concrete in localized areas, such as column wraps used for durability or when the entire cover concrete is planned to be removed and replaced.



21.6.2.5.1 Post-Tensioning

Bent caps can be strengthened by external post-tensioning. Evaluate the existing concrete in the cap. Include tensioning strand or rods externally on the cap to add compression to the cap. Use brackets, distribution plates and other components to transfer the post-tensioning forces to the cap. If aesthetics are a concern, widen the cap with ducts placed internally for the post-tensioning.

Post-tensioning is usually symmetrical to the cap so that an eccentric force is not introduced. Examine the stressing sequence to ensure that the cap is not overloaded eccentrically during post-tensioning operations.

21.6.2.5.2 Pile Repair or Replacement

When corrosion has reduced the section of an exposed steel pile such that it becomes a structural concern, the missing cross section can be rebuilt by adding plates to the flanges and/or web as appropriate by either welding or bolting. Also, consider concrete cast in a stay in place fiberglass form. If the pile has deteriorated such that there is insufficient sound remaining material for the section to be rebuilt, use a new pile; removing the damaged pile is optional.

21.6.2.5.3 Bent Shoring Repair

Use shoring placed adjacent to or under a failing bent or abutment to restore support. Typically, use shoring as a short term repair until a permanent solution is developed.

21.6.2.5.4 Concrete Bridge Seat Repair or Extension

Concrete bridge seats can fail due to deterioration of concrete, corrosion of the reinforcing, friction from the girder or bearing devices sliding directly on the seat or the improper design of the seat, which results in shear failure. Anchoring an extension to the existing cap restores adequate bearing for girders that have deteriorated or sheared at the bearing. Do not expose the extension to any load during curing. Also, repair any damage to the end of the girder.

21.6.2.5.5 Micropile Underpinning

Micropiles, also known as minipiles and pin piles, are small diameter reinforced piles that are drilled and grouted to support structures. The piles can reach service loads up to 300 tons, can be installed to depths of approximately 200 ft and usually use some type of steel bar, or bars and/or steel casing pipe. The bars are grouted into the ground and/or the casing pipe is filled with grout. Although a conventional pile is generally quite large and requires heavy equipment and large staging areas for installation, micropiles can be used where conventional piling is not convenient or possible, such as for underpinning or retrofitting existing bridges or structures. Micropiles have proven effective in many ground improvement applications by increasing the bearing capacity and reducing settlement, especially when strengthening the existing foundations.



21.6.2.6 Scour Mitigation

Scour is the erosion of streambed or bank material due to flowing water. Based on an assessment of potential scour provided by the hydraulics engineer, the structural engineer can incorporate design features that prevent or minimize scour. Typical measures to minimize scour include armoring the banks, bents and abutments. FHWA HEC-23 Bridge Scour and Stream Instability Countermeasures provides design guidance for scour mitigation. Figure 21.3 lists potential scour countermeasures from HEC-23.

Scour Countermeasures Described in HEC-23

Articulating concrete block systems at bents

Grout filled mattresses at bents

Gabion mattresses at bents

Rock riprap at bents

Partially grouted riprap at bents

Grout/cement filled bags (primarily abutments)

Rock riprap at abutments

Guide banks (abutments/embankments)

Figure 21.3 — HYDRAULIC SCOUR COUNTERMEASURES

Several scour mitigation methods are discussed below. The hydraulics engineer is responsible for determining appropriate countermeasures. The structural engineer is responsible for assuring that the countermeasures are incorporated into the project plan set. Scour countermeasure details can be on structures plan sheets, roadway plan sheets or hydraulics plan sheets. Coordinate with the roadway designer and hydraulics engineer to determine an appropriate countermeasure and to determine how the information is best incorporated into the plan set.

21.6.2.6.1 Design Countermeasures

Based on an assessment of potential scour provided by the hydraulics engineer, the structural engineer can incorporate design features that prevent or minimize scour damage at bents. Circular piers or elongated piers with circular noses and an alignment parallel to the flood flow direction help minimize scour. Provide protection against general streambed degradation by drop structures or grade control structures in, or downstream of, the bridge opening.

Designing for roadway overtopping can provide relief from pressure flow scour at the bridge. Streams with wide floodplains are often good candidates for incorporating roadway overtopping adjustments into the design because flow is less likely to be diverted into another drainage conveyance.



21.6.2.6.2 Guide Banks

For large drainage areas with adverse channel skew angles or encroachments, or both, that empty into wide floodplains, guide banks are recommended to align the approach flow with the bridge opening and to prevent scour around the abutments.

21.6.2.6.3 Riprap

Where stone of sufficient size is available, rock riprap is often used to armor abutment fill slopes and the area around the base of existing bents.

21.6.2.6.4 Monitoring

For existing scour critical bridges, monitoring and closing a bridge during high flows and subsequent inspections after the flood can be an effective countermeasure. If monitoring is selected as the countermeasure, the POA lists the appropriate actions to be taken when the target flood elevations are reached.

21.7 CULVERT PRESERVATION

21.7.1 Evaluation

Section 22.1 discusses the structural design of new culverts. Many of the Section 22.1 design and detailing practices also apply to the rehabilitation of an existing culvert.

21.7.2 Treatments


Repair concrete culverts using the requirements in the UDOT Standard Specifications. Refer to Section 21.5.2.1 for additional information.

Use shotcrete for extensive surface repairs where forming is difficult or expensive. Remove loose or spalling concrete down to or just below the existing reinforcing. Replace corroded reinforcing when required to restore capacity. Place welded wire fabric or replacement stirrups to replace deteriorated or missing stirrups. Place shotcrete and shape the surface to match the original surface or as required to restore capacity. Shotcrete can be plain or fiber reinforced.

Develop a special provision, define the limits of removal and define required reinforcing replacement when specifying repairs using shotcrete.




Strengthening culverts is required when the structure shows evidence of overloading or damage caused by inadequate strength or when the strength of the structure has been compromised by other events such as collision impacts, damage from illegal loading, flooding, seismic or other extreme events.

Evaluate the existing structure strength when significant rehabilitation work is being performed and the existing structure shows evidence of significant corrosion or overloading. Significant culvert rehabilitation includes activities that exceed removing and replacing loose concrete in localized areas or when the entire cover concrete is planned to be removed and replaced.

Evaluate the cost of replacing the culvert versus the cost of repairs when planning significant repair work. Typically, strengthening activities are cost effective.

21.7.2.3 Scour Mitigation

Refer to Section 21.6.2.6 for a discussion on scour mitigation.

21.8 SEISMIC RETROFIT

21.8.1 Evaluation

Coordinate with the Structures Design Manager and Project Manager to determine the appropriate seismic design criteria. Seismic design criteria for rehabilitations vary based on anticipated future life span, available funding and importance of the structure. Refer to Chapter 13 for seismic design and modeling information.

Bridge failures induced by seismic displacements are typically attributed to the lack of adequate connections between segments of a bridge, lack of support length or inadequate confinement reinforcing. Other deficiencies include inadequately reinforced footings, rocker bearings and nonductile connections.

Tying the segments of an existing bridge together is an effective means of preventing unseating. Bridges with single column bents are particularly vulnerable where segments are not connected.

Column failures are typically caused by inadequate confinement, shear and anchorage reinforcing. Confinement and shear deficiencies occur where too few and/or improperly detailed ties and spirals are present. Short lapped splices in longitudinal column reinforcing also result in anchorage failures. The failure modes are especially critical in single column bents.

Determining the preferred retrofit involves the following considerations:

• Anticipated failure mode • Influence on other parts of the bridge under seismic and normal loadings



• Interference with traffic • Fabrication and installation cost

Some retrofits are designed to correct bridge inadequacies related to seismic resistance. The procedures can be categorized by the function the retrofit serves, including:

• Restraining uplift • Restraining longitudinal motion • Restraining hinges • Widening bearing seats • Isolating/modifying seismic forces between the superstructures and substructures

(seismic isolation bearings) • Strengthening columns and footings • Restraining transverse motion

21.8.2 Seismic Retrofits

21.8.2.1 Column Jacketing

Jacketing consists of adding confinement to columns by covering with a grout filled steel shell, fiberglass wrap or carbon fiber wrap. The steel jacket consists of structural steel welded over the column and grouted. The fiberglass and carbon fiber wraps are glued to the column in multiple layers. The wraps are proprietary products. Noncircular columns can be retrofitted by jacketing, but the increased rigidity must be evaluated. A circular steel casing can be placed around the noncircular column and grouted.

Locate jacketing only at the points of potential column hinge formations. However, if more than half the total height of the column requires a jacket, typically extend the jacket to full height for improved aesthetics. Jacketing increases column rigidity, amplifying global seismic forces and attracting more load to the column. Evaluate the increased rigidity.

Refer to ACI 440.2R-08 “Guide for Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures” for additional information on fiber wraps.

21.8.2.2 Seat Width Extension

Seat width extensions allow larger relative displacements to occur between the superstructure and substructure before support is lost and the span collapses. Consider the seat width extension strategy at bents when the bent has inadequate strength to resist the forces from restrainer cables connecting the superstructure to the bent. The extensions are likely to be exposed to large impact forces due to the dropping span. Refer to the FHWA Seismic Retrofitting Manual for Highway Structures: Part I – Bridges for design guidance. Follow the provisions in the LRFD Specifications relative to the design of seat widths.

Use a combination of post-tensioning rods and coated dowels for bent cap widenings. Post-tensioning rods are generally impractical at abutments because excavating behind the backwall



is necessary, which disrupts traffic. Seat width dimensions are frequently controlled by the development length of the coated dowels.

21.8.2.3 Structural Continuity

Some older bridges were constructed with multiple simple spans, which lack longitudinal continuity. The older bridges frequently have minimal support lengths under the ends of the girders and limited restraining devices (e.g., anchor bolts). Historically, limited support lengths, inadequate restraining devices and lack of superstructure continuity contribute to spans collapsing during earthquakes. Typically, retrofitting a superstructure to make the structure continuous for full dead and live loads is not feasible, unless the deck is being replaced; however, steel plate girder bridges can sometimes have web continuity plates added over the bents. Refer to the FHWA Seismic Retrofitting Manual for Highway Structures: Part I – Bridges for design guidance.

21.8.2.4 Restrainers and Ties

In general, restrainers are add on structural devices that do not participate in resisting forces other than seismic force effects. Typically, the components are made of steel; design the components to remain elastic during seismic action, and protect the components against corrosion.

Three types of restrainers exist — longitudinal, transverse and vertical. The two former types prevent unseating the superstructure. The third type precludes secondary dynamic (impact) forces that can result from the vertical separation of the superstructure. Design the restraint devices to be compatible with the geometry, strength and detailing of the existing structure.

Ties are restrainers that connect only components of the superstructure together. The ties are activated only by seismic excitation.

Shear keys or blocks allow in service movements of the bridge, without applying significant loads to the substructure. During an earthquake, the shear keys transmit the seismic force to the substructure.

21.8.2.5 Bearing Replacement

Bearings not adequately designed for seismic movements and damaged or malfunctioning bearings can fail during an earthquake. In addition, steel rocker and roller bearings can perform poorly in seismic events. One option is to replace the bearings with steel reinforced elastomeric bearings. To maintain the existing girder elevation, either insert a steel assembly between the girder and the elastomeric bearing, or seat the elastomeric bearing on a new concrete pedestal. Existing anchor bolts can assist in resisting shear between the pedestal and the bent.



21.8.2.6 Seismic Isolation Bearings

Replacing exiting bearings with isolation bearings can be a cost effective alternative to substructure strengthening or reduce the extent of substructure strengthening required. Although isolation bearings can significantly reduce the seismic load demands, the bearings can still transmit a significant load (15% to 30%) of dead load to the substructure. The substructure could require additional strengthening to accommodate forces transmitted through the isolation bearing.

Refer to the WS sheets for isolation bearing sheet requirements and to Section 19.2.2.4 for design information.

21.8.2.7 Modifying Seismic Response

Use the following techniques to modify the seismic response of a bridge:

1. Reduce Flexural Reinforcing. Concrete columns are often over reinforced. Over reinforcing means that the flexural steel is not expected to yield during the design event, resulting in both higher compressive and shear forces on the concrete. In addition, more load is transferred to footings. If other design criteria permit, some of the flexural steel can be cut to reduce the plastic moment and associated shear demand.

2. Increase Flexural Reinforcing. Increase the flexural reinforcing to attract more load and/or to decrease displacements. Locate the vertical reinforcing in a concrete jacket that is shear connected to the column by means of drilled and grouted dowels. Additional reinforcing increases the rigidity of the column, increases the demand on the column and increases the demand on the foundation system. Verify that the foundation system accommodates the increased demands.

3. Infill Shear Wall. A concrete shear wall can be added between the individual columns of a bent. Connect the wall to the columns with drilled and bonded dowels. The method substantially changes the seismic response characteristics of the structure, requiring a complete reanalysis. The more rigid infill wall can attract more load.

21.9 BRIDGE WIDENING

21.9.1 Evaluation

Bridge widening presents a multitude of challenges during the planning and design stages, during construction and throughout the bridge service life. Consider construction and future maintenance when planning the overall design and detailing of the widening.

The following briefly summarizes the basic objectives in bridge widening:

• Match the structural components of the existing structure, including splice locations. • Match the existing bearing types in terms of fixity.



• Do not perpetuate fatigue prone details. • Evaluate the need to replace the bearings and joints in the existing structure. • Evaluate the load carrying capacity of the existing structure. • Evaluate the seismic resistance of the existing and widened structure. Incorporate

retrofit measures if appropriate. • Use the same structure frame on the widened portion as on the existing bridge. • Match the flexibility/stiffness of the existing and new superstructures. • Match the top and bottom of concrete deck elevations at the interface between the new

deck and the existing deck. • Match the top deck overlay elevations at the interface between the new deck overlay

and the existing deck overlay.

21.9.2 Design

Modifying the existing structure solely because the structure was designed to AASHTO specifications before the adoption of the LRFD Specifications is not necessary.

When preparing plans to modify existing structures, determine the live load and design criteria used in the original design. With few exceptions, structures on the state highway system have been designed for loads and stresses specified by AASHTO. Coordinate with the Structures Design Manager to determine the appropriate design criteria and goals when the existing structure does not meet current loading requirements. Structures with Inventory Ratings less than 1.0 based on the original design methodology (LFD or LRFD) are candidates for strengthening. Structures with Operating Ratings less than 1.0 are strong candidates for strengthening. Also, consider strengthening any structure with posted load restrictions. Consider the historical perspective of the design criteria, such as live loads, allowable stresses, etc., when analyzing a rehabilitated structure. For accurate and complete information on specific structures, see the as built plans, special provisions and appropriate editions of the AASHTO specifications.

Design all widened portions to current AASHTO requirements or according to requirements defined by the Structures Design Manager.

Coordinate with the Structures Design Manager to determine the appropriate seismic design criteria.

21.9.3 Details of Existing Structures

21.9.3.1 Load Carrying Capacity

Existing structures were often designed for either live loads or seismic loads less than those currently used for new bridges. Consult the data available in the bridge record for information on the condition of the existing structure. Determine the legal load rating for the existing bridge to quantify the capacity of the existing bridge (see Chapter 4 of the BMM). Based on the information, determine whether the existing structure should be strengthened to increase load carrying capacity. For the evaluation, consider the following:



• Cost of strengthening existing structure • Physical condition, operating characteristics and remaining service life of the structure • Seismic resistance of structure • Other site specific conditions • System conditions (is the bridge the only structure on the route with load restrictions?) • Width of widening • Traffic accommodation during construction

Document the results in the Structure TSR.

21.9.3.2 Materials

For material properties of older structures, check the as built bridge plans, if available, or plans of comparable bridges of the day. Also, reference the bridge record for historical properties of materials.

Sometimes, the grade of reinforcing steel is indicated as intermediate grade, which means Grade 40.

Up to approximately 1960, ASTM A7 was the primary structural steel used in bridge construction. The yield and tensile strengths of A7 can be taken as 33 ksi and 66 ksi, respectively.

Use the concrete strengths listed on the plans. Where concrete strength controls the design and an increase in concrete design strength can significantly improve the structure rating, coordinate with the Structures Design Manager to determine if concrete cores should be taken and tested to support the use of a higher concrete strength in the calculations.

21.9.3.3 Substructures/Foundations

Investigate foundation capacities of existing structures if additional loads are imposed by the widening. Newly constructed footings under a widened portion of a structure can settle. The new substructure can be tied to the existing substructure to reduce the potential for differential foundation settlements, provided that the treatment does not adversely affect the existing substructure. If the new substructure is not tied to the existing substructure, make suitable provisions to prevent possible damage where such movements are anticipated. Coordinate with the Geotechnical Design Division to assess the compatibility of new and existing foundations and the potential for differential settlement.

21.9.4 Details of Widened Structures

21.9.4.1 Girder Type Selection

In selecting the girder type for a structure widening, use a construction type and material type consistent with the existing structure. Proportion the widening to ensure that the structural



response is similar to the existing bridge. Provide design live load deflections that are between 80% and 120% of the adjacent girders design live load deflections.

21.9.4.2 Deck Closure Pour

Consider the use of a closure pour to complete the attachment to the existing structure. Refer to Section 16.2.12 for additional information on closure pours. When closure pours are not used, consider the effects of the existing bridge on the deck pour screed deflections.

FEBRUARY 2015

MISCELLANEOUS STRUCTURES



Miscellaneous Structures 22-i

TABLE OF CONTENTS

22.1 CULVERTS AND DRAINAGE STRUCTURES ........................................................... 22-1

22.1.1 Design Considerations .................................................................................. 22-1 22.1.2 Design Requirements for Culverts and Drainage Structures ......................... 22-1

22.1.2.1 Design Specifications .................................................................. 22-2 22.1.2.2 Loads and Loadings .................................................................... 22-2

22.1.3 Precast Three-Sided Culvert Structures ........................................................ 22-2

22.2 OVERHEAD SIGN STRUCTURES ............................................................................. 22-2

22.2.1 Design Requirements for Overhead Signs .................................................... 22-3

22.2.1.1 Guidelines .................................................................................... 22-3 22.2.1.2 Design Process ............................................................................ 22-4 22.2.1.3 Design Specifications .................................................................. 22-5 22.2.1.4 Loads and Loadings .................................................................... 22-5 22.2.1.5 Materials ...................................................................................... 22-5 22.2.1.6 Minimum Clearances and Geometry ........................................... 22-5 22.2.1.7 Foundations ................................................................................. 22-6 22.2.1.8 Overhead Sign Structure Type Selection and Layout .................. 22-6 22.2.1.9 Miscellaneous .............................................................................. 22-7 22.2.1.10 Luminaire Support Tubes ............................................................ 22-7 22.2.1.11 Sign Panel Bracing ...................................................................... 22-7

22.2.2 Design Requirements for VMS Signs ............................................................ 22-7

22.2.2.1 Design Specifications .................................................................. 22-7 22.2.2.2 Loads and Loadings .................................................................... 22-8 22.2.2.3 Materials ...................................................................................... 22-8 22.2.2.4 Minimum Clearances and Geometry ........................................... 22-8 22.2.2.5 Foundations ................................................................................. 22-8 22.2.2.6 VMS Requirements ...................................................................... 22-8

22.2.3 Overhead Sign Structures and VMS Working Standards .............................. 22-9

22.3 TRAFFIC SIGNALS, LIGHTING AND CAMERA SUPPORTS ................................... 22-10 22.4 RETAINING WALLS .................................................................................................... 22-10

22.4.1 Design Considerations .................................................................................. 22-11 22.4.2 Design Requirements for Retaining Walls ..................................................... 22-11

22.4.2.1 Design Specifications .................................................................. 22-11 22.4.2.2 Loads and Loadings .................................................................... 22-11


22-ii Miscellaneous Structures

22.4.3 Approved Retaining Wall Types .................................................................... 22-12 22.4.4 CIP Concrete Retaining Walls ....................................................................... 22-12 22.4.5 Precast Concrete Retaining Walls ................................................................. 22-13 22.4.6 MSE Retaining Walls ..................................................................................... 22-13

22.4.6.1 Piles Within MSE Walls................................................................ 22-13 22.4.6.2 Moment Slab for Barrier Rails ...................................................... 22-13 22.4.6.3 Copings ........................................................................................ 22-14

22.4.7 Prefabricated Modular Retaining Walls ......................................................... 22-14 22.4.8 Tieback Walls ................................................................................................ 22-14 22.4.9 Soil Nail Walls ................................................................................................ 22-14 22.4.10 Wire Enclosed Riprap (Gabion) Walls ........................................................... 22-15 22.4.11 Permanent Wire Face Walls .......................................................................... 22-15 22.4.12 Soldier Pile and Lagging Walls ...................................................................... 22-15 22.4.13 Concrete Crib Walls ....................................................................................... 22-15 22.4.14 Temporary Retaining Walls ........................................................................... 22-16 22.4.15 Responsibilities .............................................................................................. 22-16

22.4.15.1 Shop Drawings ............................................................................ 22-16 22.4.15.2 Geotechnical Design Division ...................................................... 22-16 22.4.15.3 Wall Supplier ................................................................................ 22-16 22.4.15.4 Structural Engineer ...................................................................... 22-17

22.5 SOUND WALLS .......................................................................................................... 22-17 22.6 PEDESTRIAN/BICYCLE BRIDGES ............................................................................ 22-17

22.6.1 Safety/Americans with Disabilities Act ........................................................... 22-17 22.6.2 Design Requirements .................................................................................... 22-18

22.6.2.1 Geometrics .................................................................................. 22-18 22.6.2.2 Structure Type ............................................................................. 22-18 22.6.2.3 Seismic ........................................................................................ 22-18 22.6.2.4 Fatigue ......................................................................................... 22-19 22.6.2.5 Prefabricated Steel Truss Bridges ............................................... 22-19 22.6.2.6 Pedestrian Bridge Decks ............................................................. 22-19

LIST OF FIGURES

Figure 22.1 — WORKING STANDARDS FOR OVERHEAD SIGN STRUCTURES ............. 22-10


Miscellaneous Structures 22-1

Chapter 22 MISCELLANEOUS STRUCTURES

The transportation system includes a wide variety of structure types other than highway bridges. Chapter 22 presents the applicable practices and criteria for the structural design of miscellaneous structures. This chapter supplements a variety of AASHTO publications that apply to the miscellaneous structure types.

22.1 CULVERTS AND DRAINAGE STRUCTURES

Culverts are buried structures that transport water or traffic (pedestrian, wildlife or vehicle) under roadways, railways or embankments. Drainage structures include any structure required to control, direct, process or retain drainage.

22.1.1 Design Considerations

The Hydraulics Division determines the size of culverts based on the required design flood. The roadway designer is responsible for sizing pedestrian culverts. Verify that the sizes provided are reasonable for the location. Information on sizing pedestrian facilities is available in the AASHTO Guide for the Planning, Design, and Operations of Pedestrian Facilities.

Drainage structures are sized and located by hydraulics engineers and roadway designers. Coordinate with drainage and roadway designers when preparing structure plan sheets. Verify locations of drainage structures with the roadway and drainage plans.

22.1.2 Design Requirements for Culverts and Drainage Structures

Use the WS sheets for typical culvert and drainage structure designs and details. Do not use the WS sheets, and provide a site specific design if any of the following conditions exist:

• The geometry or loadings exceed the values in the working standards. • Other structures impose loads on the culvert or drainage structure. • The sequence of backfilling the sides of the reinforced concrete box does not allow

equal loading. • A special inlet, outlet, confluence or another special hydraulic structure is required. • No WS sheet exists that addresses the project requirements. Use the WS sheets as a guide for developing designs not covered by the WS sheets. Culverts with traffic directly on the top slab require an approach slab. Refer to the WS sheets for additional information.


22-2 Miscellaneous Structures

22.1.2.1 Design Specifications

Use the LRFD Specifications for the design of culverts and drainage structures. The LRFD Specifications do not require seismic design unless a fault transverses the structure. Coordinate with the Structures Design Manager to determine the seismic design requirements when all of the following are true:

• The structure crosses a fault. • The structure span is greater than 30 ft. • The structure is used as a pedestrian or vehicle undercrossing. NCHRP 12-70, Final Report, Volume II, presents recommended specifications, commentaries and example problems for the design of buried structures.

The UDOT Standard Specifications define design requirements for precast concrete box and three-sided culvert structures.

Refer to Chapter 4 of the BMM for load rating requirements.

22.1.2.2 Loads and Loadings

Use loads and loadings defined in the LRFD Specifications except as modified below:

• Do not design for fatigue according to LRFD Articles 5.5.3.1 and C12.5.3. • Do not design for Extreme Event I except as specified above. • Use a 10-in. future wearing surface and a unit weight = 0.160 kcf. • Use an exposure factor (γe) of 1.00. 22.1.3 Precast Three-Sided Culvert Structures

The Structures Design Manager and the Hydraulics Engineer must approve the use of precast three-sided culvert structures when the culvert conveys water.

Precast concrete arch culverts are a type of three-sided culvert. The manufacturer designs precast concrete arch culverts based on the size and geometry specified in the structure drawings and the project specifications.

22.2 OVERHEAD SIGN STRUCTURES

An overhead sign is a sign over any portion of the roadway (including shoulders) requiring vertical clearance for vehicles to pass underneath. Overhead signs provide the traveling public with clear messages under a variety of conditions directly over the roadway. Overhead sign structures support overhead signs. VMS signs are a specific type of overhead sign and have specific design requirements. See the following sections for specific requirements. Use the WS



sheets and SD drawings to prepare overhead sign structure plan sheets. Use the procedures in this section to design all overhead sign structures.

The WS sheets detail seven types of overhead sign structures:

• Cantilever • Butterfly • Span type (single and double mast) • Dual cantilever • Span type VMS • Cantilever VMS • Roadside VMS The SD drawings illustrate the types of overhead sign structures. The Traffic and Safety Engineer determines the size and location of signs and if an overhead sign is required. The Traffic Management Division determines the required size and location of VMS. All overhead sign structures are tubular steel structures.

22.2.1 Design Requirements for Overhead Signs

Design sign structures for overhead signs based on the following requirements. The design requirements apply to the standard designs and to project specific designs not covered by WS sheets. Section 22.2.2 presents specific requirements for VMS signs. Section 10.4.5 presents vertical clearance requirements.

22.2.1.1 Guidelines

Use the following guidelines:

• Do not locate signs on bridge structures without prior approval from the Structures Design Manager. See Section 2.2.3.

• Avoid placing an overhead sign structure on a bridge. See Section 2.2.3. Overhead sign structures attached to bridges require specially designed post supports and connections. In addition, bridge vibrations affect the overhead structure. If there is no alternative to an overhead structure on a bridge, use a span type sign structure supported on the bent cap or abutments. Do not use cantilever sign structures supported on bridges.

• Use cantilever sign structures to support signs over the shoulder and/or the travel lane nearest the post. Cantilever sign structures are generally less costly to construct and inspect than span type sign structures. Consider two smaller cantilever sign structures in lieu of one span type sign structure.

• Use a span type sign structure when the span of a cantilever sign structure exceeds 42′-6″ or 40% of the roadway cross section or when the span to height ratio exceeds 1.5.



• Use single mast span type sign structures to support sign panels with a maximum sign panel height of 17′-6″, including any auxiliary sign panel tabs. When the sign panel height exceeds 17′-6″, use a double mast span type sign structure.

• In most cases, use a span type sign structure to support Type 1 VMS due to the eccentricity of the VMS dead load and the magnitude of fatigue forces. On some projects, the Traffic Management Division can approve the use of a Type 2 VMS centered over the shoulder or outside travel lane and supported by a cantilever sign structure as a low cost alternative.

• Refer to Chapter 2 for the sign panel replacement policy. • Use the UDOT Standard Drawings for sign structure foundations encased in a 42-in.

single slope median barrier. Other median installations could require protection as a fixed object.

22.2.1.2 Design Process

The following outlines the general design procedures when designing an overhead sign structure or VMS sign structure. The outline applies designs addressed by the WS sheets and project specific designs not covered by WS sheets:

• Determine the size, type and location (with respect to the roadway) of sign panels or VMS assemblies supported by the sign structure. Ensure that the Traffic and Safety Division has approved the sign panel configuration before beginning final design.

• Verify that the sign structure is behind a roadside barrier or outside the clear zone. • Verify that the location matches the roadway plan sheet location. • Determine the appropriate sign structure type. • Determine the span length and sign panel height based upon the required horizontal and

vertical clearances. • Determine if a single or double mast sign structure is needed on span type structures. • Determine post heights. Measure the post height from the bottom of base plate to the

centerline of the horizontal mast arm (the lowest mast arm for a double mast sign structure).

• Determine if a working standard applies: ○ When a working standard applies, select design data from the data tables for the

applicable sign structure type. The data includes pipe diameter, pipe wall thickness, splice plate connection data, base plate requirements, foundation data, etc. Refer to Section 22.2.3 for additional information on the WS sheets.

○ When the working standards do not apply, design the structure according to the requirements listed in this chapter. Detail the structure using the working standards as a model, updating design data, general notes, etc.

• Complete the overhead sign structure plan sheets using the WS sheets and SD drawings or calculated design data. Include roadway typical sections and geometric calculations as part of the final structure acceptance package.




Use the current version of the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, as modified in Section 22.2, for the design of overhead sign structures. Sign structures covered by the WS sheets use the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, 6th Edition, 2013 and do not require rechecking unless directed otherwise by the Structures Design Manager.


Determine loads on overhead sign structures as specified in the current version of the AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, as modified below:

• Dead load ○ Steel: 490 pcf ○ Sign panels, including attachments: 15 psf ○ Concrete in foundation design: 150 pcf ○ Soil in foundation design: 120 pcf

• Fatigue design ○ Use Fatigue Category I

22.2.1.5 Materials

Use material requirements defined on the WS sheets for overhead sign structures.

22.2.1.6 Minimum Clearances and Geometry

• Provide the required minimum vertical clearance defined in Section 10.4.5 across the width of the entire roadway section, plus the clear zone or barrier deflection distance, beneath the sign structure. The vertical clearance envelope extends from the highest elevation of the roadway beneath the sign structure to the bottom of the sign panel(s) and all points on the sign structure including sign attachments, lighting, pipe elbow radius and, if applicable, future anticipated sign panels and attachments.

• Protect sign structure foundations with a barrier or locate the foundation outside of the roadway clear zone. If protected with a roadside barrier, provide the required deflection distance (see below): ○ Provide a minimum clear distance of 1′-0″ between the back of the barrier and

the sign structure foundation when a pinned barrier protects the sign structure foundation.

○ Provide a minimum clear distance of 3′-0″ between the back of the barrier and the sign structure foundation when an unpinned concrete barrier protects the sign structure foundation.



○ Provide a minimum clear distance of 2′-0″ between the back of the barrier and the sign structure foundation when guardrail protects the sign structure foundation.

• Use the applicable SD drawings when a sign structure foundation is encased in a median barrier. Alternatively, locate the sign structure post at least 1′-0″ behind the traffic face of a rigid barrier measured at the top of barrier, or provide at least 6 in. of concrete cover from barrier face to anchor bolts, whichever is greater.

• Accommodate planned future roadway widening so that the sign structure does not require replacement, when feasible.

22.2.1.7 Foundations

Use drilled shaft foundations for all overhead sign structures. For drilled shaft designs not covered by the SD drawings, at a minimum use the following parameters:

• Analyze drilled shaft foundations for lateral resistance and overturning using the p-y analysis method and using a computer program such as LPILE or equivalent.

• Use ½ in. for the maximum allowable lateral deflection at the top of the drilled shaft. • Design the foundation using the site specific design parameters when available. In the

absence of site specific geotechnical recommendations, design the drilled shaft foundation based on the following soil parameters: ○ Soil type: soft clay ○ Moist unit weight: 110 pcf ○ Water table depth: 3′-0″ ○ Undrained shear strength, c:

+ 500 psf (3.5 psi) at depths of 0 ft to 20 ft + 1000 psf (7.0 psi) at depths greater than 20 ft

○ Modulus, k: + 30 lb/in3 at depths of 0 ft to 20 ft + 100 lb/in3 at depths greater than 20 ft

○ Strain, E50: + 0.02 at depths of 0 ft to 20 ft + 0.01 at depths greater than 20 ft

22.2.1.8 Overhead Sign Structure Type Selection and Layout

Determine the size, type and location of sign panels supported by the sign structure. Center the sign panels on the mast length regardless of the total length of the mast or actual sign location when performing design checks on the mast. Evaluate whether future sign panel size increases are likely. If changes are expected, design the sign structure to accommodate the larger of either the current or future sign area and indicate on the plan sheets the future sign configuration used to design the support. Determine the total sign area supported by the sign structure by summing all sign panel areas. Design span type sign structures supporting traffic signs for at least 50% of the mast arm length covered by signs.



Based on the sign location and sign area, determine the sign structure type needed.

22.2.1.9 Miscellaneous

Design all overhead sign structures to support lighting, allowing for an illuminated structure in the future if lights are not initially installed. Overhead sign layout sheets specify whether the sign structure is illuminated.

Comply with the deflection and camber requirements in AASHTO.

22.2.1.10 Luminaire Support Tubes

The luminaire support tubes in the working standards are applicable for the conditions listed below. Prepare a project specific design if any of the following conditions are exceeded:

• 54-lb maximum luminaire weight • 6′-0″ maximum horizontal offset from sign panel face to the end of the luminaire support • 1′-11″ maximum vertical offset from the top of the luminaire support to the centerline of

bolts for the top mounting clamp • Fatigue loading from truck induced gusts consistent with AASHTO • Wind and ice loadings consistent with AASHTO • All luminaire support tubes are HSS 1½″ × 1½″ × ¼″ 22.2.1.11 Sign Panel Bracing

Secure and brace sign panels to mast arms using the details shown in the working standards. Sign panel bracing as detailed in the working standards is limited to a maximum total sign height of 17′-6″ for single mast sign structures (8′-9″ maximum dimension from mast arm centerline to sign panel edge) and a maximum total sign height of 24′-0″ for double mast sign structures (6′-0″ maximum dimension from mast arm centerline to sign panel edge). The dimensions specified include the auxiliary panel tab height.

All vertical supports are HSS 3″ × 3″ × 5/16″ with a maximum spacing of 60 in. for single mast sign panels and a maximum spacing of 72 in. for double mast sign panels.

22.2.2 Design Requirements for VMS Signs

Design sign structures for VMS signs based on the following requirements.


Use the current AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, as modified herein for the design of VMS sign structures.




Determine loads on VMS sign structures as specified in the current AASHTO Standard Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, as modified below and in Section 22.2.1.4:

• Wind load (frontal area): ○ Type 1: Maximum frontal area of 194 sq ft (24′-9″ × 7′-10″) ○ Type 2: Maximum frontal area of 39 sq ft (11′-8″ × 3′-4″)

• VMS assemblies: ○ Type 1 VMS: 3450 lb maximum (including access platform) ○ Type 2 VMS: 580 lb maximum

22.2.2.3 Materials

Use material requirements defined on the WS sheets for overhead sign structures.

22.2.2.4 Minimum Clearances and Geometry

Use the overhead sign structure requirements except as modified below.

Provide the minimum vertical clearance defined in Section 10.4.5 across the width of the entire roadway section beneath the sign structure. The vertical clearance envelope extends from the highest elevation of the roadway beneath the sign structure to the bottom of the sign panel(s) and all points on the sign structure including sign attachments, lighting, catwalks, pipe elbow radius and, if applicable, future anticipated sign panels and attachments. The larger clearance reduces the effects of truck induced gusts experienced by maintenance workers.

22.2.2.5 Foundations

Use drilled shaft foundations for VMS sign structures. For drilled shaft designs not covered by the SD drawings, use the parameters listed for overhead sign structures.

22.2.2.6 VMS Requirements

The Traffic Management Division selects the VMS assembly type based on the number of approach lanes and the posted speed. Obtain documentation of the configuration and VMS type approval from the Traffic Management Division before pursuing final design.

Additional layout requirements in the preparation of VMS structure plans are:

• Center span type and cantilever VMS over the traffic lanes. • Locate the catwalk access over the shoulder to minimize the impact to traffic, requiring

shoulder closures only. Accommodate access via a scissor lift vehicle.



• Consider aesthetics by ensuring that the VMS and frame span centers are as consistent as possible without sacrificing functionality or safety.

22.2.3 Overhead Sign Structures and VMS Working Standards

Use the WS sheets and SD drawings for overhead sign structures and VMS sign structures to minimize design effort, expedite plan preparation and promote consistency in design. Use the WS sheets on all projects where the sign geometry fits within the limitations of the SD drawings. Sign structures that do not fit within the limitations require a design conforming to the design requirements in Section 22.2.1 (overhead) or Section 22.2.2 (VMS).

The PE stamping the plans based on the working standards certifies that the submitted plan sheets meet the requirements defined on the WS sheets and SD drawings. The EOR also certifies that the geometry shown on all sign structure plan sheets is correct. UDOT certifies the working standards in the SDDM and accepts the associated liability. If a new design is required, the EOR assumes liability for both the design and the plan sheets.

Determine the sign type and select the design values from the tables on the corresponding SD drawings. Add the design values to the working standards. Do not design or select sign structures by extrapolating beyond the limits of the tables. Provide a project specific design in accordance with Section 22.2.1 (overhead) or Section 22.2.2 (VMS) when the actual sign structure geometry or sign sizes exceed the design limits given for each sign structure type in the working standards.

The working standards are suitable for inclusion in the plan set without modification to the structural design. Use the working standards when possible. Determine whether a working standard is applicable to the sign structure required for the project and prepare and seal the drawings.

Provide one plan set for all overhead sign structures of the same structure type on a project. Select the appropriate working standard based upon the structure type used. Remove details that are not applicable. Use the working standards for the appropriate structure type in Figure 22.1.



Title Working Standard Sheet No.

Cantilever Butterfly Span TypeDual

Cantilever VMS

Cantilever VMS

Roadside VMS

Location plan and notes

WS-201 WS-201 WS-201 WS-201 WS-201 WS-201 WS-201

Sign structure elevation

WS-202A WS-202B WS-202C

or WS-202D

WS-202E WS-202F WS-202G WS-202H

Foundation details

WS-203 WS-203 WS-203 WS-203 WS-203 WS-203 WS-203

Steel details WS-204 WS-204 WS-204 WS-204 WS-204 WS-204 WS-204

Tube connection details

WS-205 WS-205 WS-205 WS-205 WS-205 WS-205 WS-205

VMS and catwalk connection details

N/A N/A N/A N/A WS-206A WS-206A WS-206A

VMS catwalk details

N/A N/A N/A N/A WS-207A WS-207A WS-207A

Sign panel details

WS-206B WS-206B WS-206B

or WS-206C

WS-206B N/A N/A N/A

Luminaire details

WS-207B WS-207B WS-207B WS-207B N/A N/A N/A

Figure 22.1 — WORKING STANDARDS FOR OVERHEAD SIGN STRUCTURES

22.3 TRAFFIC SIGNALS, LIGHTING AND CAMERA SUPPORTS

The UDOT Standard Drawings provide standard designs for traffic signals, lighting and camera supports.

If a traffic signal, highway lighting or camera support size or loading is beyond the limits of the UDOT Standard Drawings, design the structure to meet the current edition of the AASHTO Standards Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals. Obtain specific design requirements from the Traffic and Safety Division and notify the Structures Design Manager to coordinate structural reviews.

The Structures Design Division does not assign structure numbers to these structure types.

22.4 RETAINING WALLS

Numerous styles of retaining walls are permitted. Refer to Section 22.4.3 for approved retaining wall systems.



22.4.1 Design Considerations

Retaining walls not linked to a bridge are normally sized and located by roadway designers. Retaining walls around bridges are sized and located by structural engineers and roadway designers working together. Coordinate with the roadway designer when preparing wall plan sheets. Verify locations of walls with the roadway plans.

22.4.2 Design Requirements for Retaining Walls

Use the standard retaining walls defined in the WS sheets for CIP retaining walls. Use the coping details defined in the WS sheets for MSE or soil nail wall copings. The coping details can also be adapted by the EOR to other styles of retaining walls. Do not use the WS sheets and provide a site specific design if any of the following conditions exist:

• The geometry or loadings exceed the values in the working standards. • Other structures impose loads on the walls. • Special details are required. • No WS sheet exists that addresses the projects requirements. Use the WS sheets as a guide for developing designs not covered by the WS sheets.

Where access is open to the public, provide a pedestrian railing or fencing at the top of the wall. Meet the wall to abutment spacing requirements defined in the UDOT Standard Drawings. Place concrete slope protection between the wall and the abutment or extend the wall concrete coping to the abutment.

Address slope maintenance above and below the wall in the retaining wall layout. Consider surface and subsurface drainage in the wall design. Provide a system to intercept or prevent surface water from entering behind walls.


Use the current LRFD Specifications for the design of retaining walls.


Use loads and loadings defined in the LRFD Specifications except as modified below:

• Neglect passive pressure in front of walls when evaluating sliding resistance using service or strength design load cases.

• Use of passive pressure in front of walls is permitted for extreme event load cases. • Use an exposure factor (γe) of 1.00. • Use the GLE method to determine seismic forces.



• Reduction in design acceleration coefficients based on anticipated wall movement is permitted. Anticipated wall displacements over 2 in. require approval from the Structures Design Manager.

Refer to the following sections for requirements for specific wall types.

22.4.3 Approved Retaining Wall Types

Use the following wall types when project requirements and/or specifications permit:

• CIP concrete retaining walls • Precast concrete retaining walls • Specification approved MSE wall systems • Specification approved prefabricated modular gravity wall systems • Tieback walls • Soil nail walls Use the following wall types only when approved by the Structures Design Manager:

• Wire enclosed riprap (gabions) of limited height • UDOT approved permanent wire face wall systems • Soldier pile and lagging • Concrete crib wall Do not use metal bin walls.

22.4.4 CIP Concrete Retaining Walls

CIP concrete retaining walls that exceed the limits defined in the WS sheets require a site specific design. Account for differential settlement in the construction joint spacing. Account for global stability as described in the UDOT Geotechnical Manual of Instruction.

CIP concrete cantilever walls are best suited for sites characterized by good bearing material and minimal long term settlement. Use pile supported walls if necessary. Piles increase the cost. CIP concrete cantilever walls are often cost effective for short wall lengths.

CIP concrete retaining walls do not require special construction equipment, wall components or specialty contractors. Walls over 30 ft in height are rare and typically use a counterfort to control bending moments in the wall. The footing width for the wall is normally ½ to ⅔ the wall height.

CIP concrete cantilever walls in cut slope locations is possible. For the application, the slope behind the face of the wall requires excavation to provide clearance for the construction of the wall footing. Assume excavation slopes flatter than 1.5H:1V when estimating construction room requirements. If the excavation required is excessive, shored excavation with sheet pile, soil nails or other methods is permitted.



22.4.5 Precast Concrete Retaining Walls

Precast concrete retaining walls require a site specific design. Provide 2 ft of granular backfill underneath the footing, in front of the toe and behind the heel.

22.4.6 MSE Retaining Walls

Refer to the UDOT Geotechnical Manual of Instruction for specification approved MSE retaining wall systems and for design requirements.

MSE walls use reinforced layers of earth fill. The reinforcing is typically nonextensible (metallic) reinforcing. The facing for the walls is concrete panels, modular blocks, geotextile fabrics or exposed welded wire. The heights of MSE walls can extend to over 100 ft. Advantages of MSE walls include:

• Tolerate larger settlements than a CIP concrete cantilever wall • Fast construction • Low cost 22.4.6.1 Piles Within MSE Walls

Place the piles before the construction of the wall. As the wall is constructed, the subsoils beneath the wall and the MSE wall can compress. The piles, however, are rigid. The compression of the soil induces a load into the piles due to friction. Depending on site materials, the downdrag forces can be substantial.

The wall supplier must modify the soil reinforcement when piles are located within the wall. The soil reinforcement must remain linear. Also, do not attach or permit attachment of the soil reinforcement to the piles. A skew of up to 15° from a line perpendicular to the wall face is permitted when the wall supplier accounts for the skew in the design.

22.4.6.2 Moment Slab for Barrier Rails

The top of MSE walls are not sufficiently strong to resist traffic impacts. Transfer traffic impacts from the barrier rail into a moment slab when providing the minimum barrier deflection distance is not possible. A moment slab is a reinforced concrete slab that is part of or located just below the roadway pavement. The concrete slab is sufficiently massive to prevent vehicle impact forces from being transferred into the MSE wall.

Use the WS sheet design unless project specific requirements preclude the use of the WS sheet.

Size the concrete slab to resist sliding and overturning forces due to vehicle impacts as defined in Appendix I, NCHRP Report 663 Design of Roadside Barrier Systems Placed on MSE Retaining Walls.



Design of the MSE reinforcement and panels must also meet the requirements in Appendix I, NCHRP Report 663 Design of Roadside Barrier Systems Placed on MSE Retaining Walls.

Design the reinforcing in the moment slab at the face of the barrier to exceed the capacity of the base of the barrier. The minimum length of a moment slab section is 30 ft.

22.4.6.3 Copings

Use CIP copings at the top of MSE walls. Use the WS sheet design unless project specific requirements preclude the use of the WS sheet.

22.4.7 Prefabricated Modular Retaining Walls

Refer to the UDOT Geotechnical Manual of Instruction for UDOT approved prefabricated modular retaining wall systems and for design requirements.

22.4.8 Tieback Walls

Ground anchored tieback walls typically consist of tensioned ground anchors connected to a concrete wall facing. Ground anchors consist of a high strength steel bar or prestressing strand that is grouted into an inclined borehole and then tensioned to provide a reaction force at the wall face. The anchors are typically located at 8-ft to 10-ft horizontal and vertical spacing, depending on the required anchor capacity. Each anchor is proof tested to confirm the capacity.

Specialized equipment is required to install and test the anchors, resulting in a higher cost relative to conventional walls. An important consideration for tieback walls is the subsurface easement requirements for the anchoring system. The upper row of anchors can extend a distance equal to the wall height plus up to 40 ft behind the face of the wall.

Coordinate with the geotechnical engineer to determine loads.

22.4.9 Soil Nail Walls

A soil nail wall involves drilling and grouting soil nails at 4-ft to 6-ft spacing vertically and horizontally. The length of the soil nail typically ranges from 0.7 to 1.0 times the wall height. The soil nails are large diameter steel bars or strands. Soil nail walls use top down construction. The typical construction methodology includes:

• Provide a vertical cut of approximately 4 ft • Drill, insert and grout soil nails • Expose shotcrete cut surface • Repeat operation until total height of wall is complete • For permanent applications, cast a reinforced concrete wall over the entire surface



Soil nail walls can be difficult to construct in certain soil and groundwater conditions. For example, where seeps occur within the wall profile or in relatively clean sands and gravels, the soil sometimes does not stand at an exposed height for a sufficient time to install nails and apply shotcrete.

Refer to the UDOT Geotechnical Manual of Instruction for design requirements, and coordinate with the geotechnical engineer to determine loads.

Refer to the SS sheets for sample soil nail wall sheets and details.

22.4.10 Wire Enclosed Riprap (Gabion) Walls

Use only when approved by the Structures Design Manager. Use is discouraged and generally limited to ditches, stream banks or other waterways. Limit heights to 15 ft unless approved by the Geotechnical Design Division.

22.4.11 Permanent Wire Face Walls

Use only when approved by the Structures Design Manager and when the walls comply with the project aesthetics plan. Refer to the UDOT Geotechnical Manual of Instruction for design requirements.

22.4.12 Soldier Pile and Lagging Walls

Use only when approved by the Structures Design Manager and when the walls comply with the project aesthetics plan. Refer to the UDOT Geotechnical Manual of Instruction for design requirements, and coordinate with the geotechnical engineer to determine loads.

Soldier pile walls involve installing H-piles every 8 ft to 10 ft and spanning the space between the H-piles with lagging. The H-piles are driven in place or installed by grouting the H-pile into a drilled hole. Installing the H-pile by drilling avoids vibrations and provides better geometry control. The depth of a soldier pile is similar to a sheet pile wall; i.e., approximately two times the exposed height. Lagging can be either timber or concrete panels.

Permanent soldier pile walls typically include a concrete facing in front of the soldier piles and lagging after the wall is at full height.

22.4.13 Concrete Crib Walls

Use only when approved by the Structures Design Manager and when the walls comply with the project aesthetics plan. Do not use within 50 ft of bridges. Provide a concrete coping at the top of the wall. Refer to the UDOT Geotechnical Manual of Instruction for design requirements, and coordinate with the geotechnical engineer to determine loads.



22.4.14 Temporary Retaining Walls

A temporary wall is a wall that is only required during the construction period and the construction period is less than five years. Design all temporary retaining walls to meet the requirements in the current edition of the AASHTO LRFD Bridge Construction Specifications. The contractor designs temporary retaining walls. The Geotechnical Design Manager and Structures Design Manager must approve the design before construction. Seismic design is not required for temporary walls.

22.4.15 Responsibilities

22.4.15.1 Shop Drawings

The wall supplier prepares the shop drawings and supportive calculations. Review the submittals according to requirements in the project specifications and as required in Chapter 6.

22.4.15.2 Geotechnical Design Division

The geotechnical engineer conducts global stability analyses and provides design recommendations including depth of embedment and width of reinforcement. The geotechnical engineer conducts external stability analyses with respect to sliding, overturning, slope stability and bearing pressure failures.

Typical information and details provided by the geotechnical engineer to the structural engineer include the following:

• Depth of embedment of leveling pad • Magnitude of anticipated total and differential settlement • Recommended waiting period before the construction of barrier rails, copings, concrete

anchor slabs and roadway surface • Minimum required reinforcement lengths for the entire length of the wall • Surcharges 22.4.15.3 Wall Supplier

The approved wall supplier checks the external stability with respect to sliding, overturning and bearing pressure to confirm the proposed minimum reinforcement lengths. The geotechnical engineer determines the need for any changes indicated by the contractor’s external stability analysis.

The wall supplier is responsible for internal stability. The wall supplier/contractor is responsible for all costs associated with modifications to the overall wall geometry due to internal stability design or construction convenience.



22.4.15.4 Structural Engineer

The structural engineer is responsible for preparing the retaining wall layout sheets and coping details in conjunction with the roadway designer.

22.5 SOUND WALLS

The standard sound wall is a precast concrete post and panel wall system. All sound walls have architectural treatments. Refer to the UDOT Standard Drawings for standard details and architectural treatments. The Structures Design Manager must approve the use of other sound wall systems.

Sound walls that exceed the dimensional limits of the UDOT Standard Drawings require a structural design. When a structural design is required, design sound walls according to the LRFD Specifications. Comply with the LRFD Specifications for the design of all structural members.

When a sound wall must be placed on a bridge barrier, consider lightweight concrete for the sound wall to reduce dead load. Use the WS sheets unless project specific requirements preclude the use of the working standard.

22.6 PEDESTRIAN/BICYCLE BRIDGES

22.6.1 Safety/Americans with Disabilities Act

Comply with all applicable requirements in the ADA Accessibility Guidelines for Buildings and Facilities. The following requirements apply to all pedestrian bridges to ensure that they are accessible, safe and durable and comply with ADA guidelines:

• Minimum width from face of handrail to face of handrail is 8′-0″. • Maximum grade is 8.33% (12:1). A grade flatter than the maximum is preferable. When

the grade is steeper than 5%, provide a 5′-0″ platform for each 2′-6″ change in elevation. • Provide a platform at each abrupt change in horizontal direction (minimum 5′-0″ × 5′-0″). • Provide a 6′-0″ minimum clear platform at the bottom of each ramp. • Design the profile grade such that there are no abrupt grade breaks at expansion

devices. • Place a protective screening, preferably a chain link fence system or a railing system, on

both sides of the bridge. • The minimum fence height above the top of sidewalk is 8′-0″. 10′-0″ is required over

railroads. • Detail the rails as follows:

○ Minimum height for pedestrian railing is 3′-6″. ○ Bicycle railings must be at least 4′-6″ in height.



○ For pedestrian bridges over roadways, the opening between elements of a pedestrian railing must not permit a 4-in. sphere to pass through.

○ For pedestrian bridges that are not over roadways, the opening between elements of a pedestrian railing must not permit a 4-in. sphere to pass through any opening above 27 in.

• Provide a cover plate over pedestrian bridge expansion joint openings to protect pedestrians from a tripping hazard.

• Provide details that are watertight or designed such that moisture is not trapped in or on the primary and secondary structural members such as girders, bracing, truss members, and arch members. Trapped moisture accelerates corrosion. Detail auxiliary members such as fence members, handrails, lighting elements, etc., to minimize the chance of corrosion due to trapped moisture.

22.6.2 Design Requirements

Use the AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges, except as modified below.

22.6.2.1 Geometrics

The geometrics of the bridge and the approach transitions must meet the requirements of the AASHTO LRFD Guide Specifications for Design of Pedestrian Bridges. Meet the minimum vertical clearance over roads defined in Section 10.4.5. For pedestrian/bicycle bridges over waterways, the Hydraulics Engineer determines the necessary hydraulic opening.

22.6.2.2 Structure Type

Generally accepted structure types for pedestrian and bicycle bridges include:

• Precast, prestressed concrete girders with a CIP concrete deck • CIP concrete slabs • Steel girders with a CIP concrete deck • Tubular steel trusses Consider other structure types as deemed appropriate for the given site. An evaluation of structure types must include a consideration of constructability, aesthetics, use of falsework, construction costs, etc.

22.6.2.3 Seismic

Design pedestrian bridges to meet the same seismic requirements as vehicular traffic. Refer to Chapter 13 for additional information.



22.6.2.4 Fatigue

All tension members must meet minimum V-notch toughness requirements for Zone 2.

22.6.2.5 Prefabricated Steel Truss Bridges

Prefabricated steel truss bridges are typically designed and fabricated by a specialized company. When the design is provided by the fabricator, a generic detail of the truss in the contract documents is sufficient. Coordinate with the Structures Design Manager to determine if a complete truss design is warranted. Identify all applicable design standards in the project specifications or on the plan sheets.

Design prefabricated steel truss bridges according to the LRFD Specifications, AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges and AASHTO Guide Specifications for LRFD Seismic Bridge Design. Design and detail the bridge to accommodate a cold climate temperature differential.

22.6.2.6 Pedestrian Bridge Decks

The minimum pedestrian bridge deck thickness is 6 in. No integral wearing surface is required and the minimum cover is 2 in. The deck must be composite with support members.

