manual de diseño de alcantarillas de drenaje transversal

HIGHWAY DESIGN MANUAL

Chapter 19 - Reinforced Concrete BoxCulverts and Similar Structures

Revision 26

January 9, 1996

1/9/96

CHAPTER 19REINFORCED CONCRETE BOX CULVERTS AND SIMILAR STRUCTURES

(SPANS UP TO 12.2 m)

Contents Page

19.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1

19.2 SELECTION CRITERIA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3

19.3 FOUNDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3

19.3.1 Rock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-4 19.3.2 Earth or Granular Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-4

19.4 DESIGN GUIDELINES FOR BOX CULVERTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-5

19.4.1 Design Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-519.4.2 Analysis Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-519.4.3 Load Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-519.4.4 Dead Load and Earth Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-619.4.5 Live Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-619.4.6 Live Load Impact Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-719.4.7 Wall Thickness Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-719.4.8 Concrete Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-719.4.9 Reinforcement Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-819.4.10 Skewed Precast Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-819.4.11 Detailing Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-9

19.5 COMPUTER DESIGN AND ANALYSIS PROGRAM . . . . . . . . . . . . . . . . . . . . . . . . 19-9

19.6 DESIGN AND DETAILS OF CONCRETE CULVERTS . . . . . . . . . . . . . . . . . . . . . . 19-10

19.6.1 Contract Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1019.6.2 Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1119.6.3 Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1819.6.4 Headwalls/Edge Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-20

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19.7 PRECAST CONCRETE CULVERTS (SPECIAL DETAILS AND REQUIREMENTS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-20

19.7.1 Contract Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2119.7.2 Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2619.7.3 Design and Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2619.7.4 Precast Arches and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-2619.7.5 General Notes for Precast Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-28

19.8 GUIDE RAILING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-28

19.9 CUT-OFF WALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-33

19.10 LOW FLOW DISH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-33

19.11 APRONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-34

19.12 SUBBASE DRAINAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-35

19.13 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-36

LIST OF FIGURES

19-1 Typical Cross Sections, Cast-In-Place19-2 Wingwalls Plan and Elevation, Precast or Cast-In-Place19-3 Contraction & Construction Joint, Cast-In-Place19-4 Longitudinal Section, Cast-In-Place19-5 Wingwall Plan, Culvert on Skew, Precast or Cast-In-Place19-6 Wingwall Aprons, Cast-In-Place 19-7 Reinforcement Diagram19-8 Typical Cross Sections - Precast19-9 Typical Cross Section - Precast19-10 Headwall Details - Precast 19-11 Headwall and Wingwall Connection - Precast19-12 Precast Arch and Frame19-13 Approach Railing Details, Transition to Box Beam Guide Railing19-14 Approach Railing Details 19-15 Culvert Railing Details, Cast-In-Place Connection

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19-1CHAPTER 19

REINFORCED CONCRETE BOX CULVERTS AND SIMILAR STRUCTURES

19.1 INTRODUCTION

The purpose of this Chapter is to provide a good working knowledge of the requirements fordesigning and preparing contract plans for reinforced concrete culverts.

This Chapter is intended to provide guidelines, minimum recommendations and the availablereferences needed to complete a design. As with any structural engineering design, alternatedesign methods are available. The designer has the ultimate responsibility to provide an efficient,safe design. It is not possible to provide guidance in this chapter for all conditions. Guidance isprovided for the typical design.

Engineering judgment will need to be used for most projects. The history of the project site mustalways be evaluated and must be factored into the design when appropriate. Each location willusually have some unique character (floods, scour, surroundings etc.). Also, each Region mayhave their own preferences. For example, some Regions only specify heavy stone filling in streambeds and on the side slopes. Other Regions prefer stone gutters instead of sod gutters. In Regions10 and 11, some designs need to consider the effects of salt water. Another potential problem canbe polluted water. Unique environments need to be thoroughly evaluated and all environmentalrequirements satisfied.

The reinforcement and section properties charts in the previous edition of this Chapter have beeneliminated in favor of a Reinforced Concrete Box Culvert Design and Analysis Computer Program(see Section 19.5).

Wingwall alignment is highly dependent on site conditions and should be evaluated on a case bycase basis. Wingwall design is not included in this Chapter. Information on retaining wall designcan be found in Chapter 20. Computer programs available for wall design are BRADD2 andWALLRUN. If assistance is required, contact the Regional Structures Engineer or the StructuresDesign and Construction Division.

In the previous edition of this Chapter, there were references to different designs or details when theskew exceeded 20°. These references have been removed. All culverts, regardless of skew, shallbe individually designed to determine the required reinforcement and segment sizes.

This chapter is entirely in metric units, except the references to bar reinforcement sizes. At thistime, the bar reinforcement manufacturers are not producing bar reinforcement in hard metric sizes.All references to reinforcing bar size in this Chapter are in customary english units. Bar spacingsare in metric units. Should the situation change in the future, the designer should be aware that anarea of reinforcement per spacing length may need to be provided.

CONCRETE CULVERTS19-2

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Definitions (explanations of the terminology used in this chapter) follow:

A culvert is defined in the Standard Specifications as any structure, whether of single or multiplespan construction, with an interior width of 6.1 m or less when the measurement is madehorizontally along the center line of the roadway from face to face of abutments or sidewalls.Structures spanning more than 6.1 m along the center line of the roadway are consideredbridges. Various precast structures spanning up to 12.2 m are covered in this Chapter.

While it is recognized that any structure with a span over 6.1 m is technically not a culvert, forsimplicity, all structures in this Chapter will be referred to as culverts. However, the procedurefor the hydraulic analysis differs based on the span length. For guidance on hydraulic design forstructures with spans of 6.1 m or less, see Chapter 8. Any structure with a span greater than6.1 m will require a more detailed analysis. The procedures for structures with a span greaterthan 6.1 m is outlined in the AASHTO Model Drainage Manual with NYSDOT modifications. TheNYSDOT modifications for the AASHTO Model Drainage Manual and assistance in hydraulicdesign procedures for structures greater than 6.1 m may be obtained from the Structures Designand Construction Division or the Regional Hydraulics Engineer.

The largest culverts are typically not boxes, rather they are frames or arches and are discussedin Section 19.7.4.

Concrete box culverts have prismatic members, i.e., the wall and slab thickness dimensions areuniform. They have top slabs, sidewalls and usually bottom slabs and cutoff walls if there is abottom slab. Frames and arches typically have varying wall and/or slab thicknesses.

There are two types of concrete culverts: open and closed.

Open concrete culverts do not have bottom slabs and are typically used at locations where thefootings can be founded on rock at or near the stream bed. Use of open concrete culverts whererock is not at stream bed would require piles under the footings or some other form of scourprotection. Open concrete culverts on spread footings may be used for cattle passes,bicycle/pedestrian paths and other uses that do not convey water, i.e., they do not have scourvulnerability.

Closed concrete culverts have bottom slabs (invert slabs) of either cast-in-place or precastconcrete. Closed concrete culverts are typically used where the stream bed is earth or granularsoil and rock is not close enough to the stream bed.

The clear span is the perpendicular distance between the inside of the sidewalls. The maximumclear span recommended for a concrete box culvert is 7.3 m.

The design span is the perpendicular distance between the center of the sidewalls. A designspan for a concrete box culvert in excess of 7.5 m may prove to be uneconomical. For culvertswith skewed ends, the distance controlling design will be between the center of the sidewallsparallel to the highway. If an extreme skew (e.g., >30E) is necessary, squaring the ends shouldbe considered if site conditions will allow. Squaring the ends will reduce the required top slab

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thickness, the reinforcement and edge beam requirements. Under certain conditions (e.g., stageconstruction, R.O.W. problems, utility conflicts, detour conflicts, etc.) the sections may need tobe skewed.

19.2 SELECTION CRITERIA

The most appropriate type of short span structure must be determined. The choices are acorrugated metal structure, concrete box culvert, concrete frame or arch and a short spanbridge. While the site conditions should be the primary deciding factor for structure selection,economics are also very important.

Precast and cast-in-place concrete culverts are usually more expensive in first cost than acorrugated metal structure. However, concrete culverts should not be rejected as an alternativewithout making an engineering analysis that includes suitability to the site and life cycle costestimates. The advantages of concrete culverts are superior durability for most environmentalconditions, greater resistance to corrosion and damage due to debris, greater hydraulic efficiencyand typically longer life spans (i.e. potentially lower life cycle costs).

At sites with limited headroom, concrete culverts may be the least expensive option. Corrugatedmetal structures may not fit the site conditions without appreciable changes to the roadwayprofile. Corrugated metal structures typically require a minimum height of cover of 600 mm ormore. Concrete culverts can have asphalt pavement placed directly on the top slab. Corrugatedmetal structures will also typically require taller structures to provide adequate waterway areabelow design high water than concrete culverts. If a corrugated metal structure is a viable option,an engineering and cost analysis should be done. Hydraulics may dictate the need for a concreteculvert because of excessive back water, excessive water velocity or ice and debris.

When a concrete culvert is selected, a precast option should be considered whenever possible.Speed of erection, maintenance of traffic, stream diversion problems and site constraints canbe minimized when this option is chosen.

Before a final determination is made to use a large concrete culvert, the use of a short spanbridge with laid back slopes and integral abutments should be investigated. Possible advantagesof a bridge may be: minimized work in the stream, speed of erection, no interference with existingstructure foundation and easier construction when there is staged construction.

Information on corrugated metal structures (steel and aluminum) is available in Chapter 8.

19.3 FOUNDATIONS

At this time, all structures discussed in this chapter, regardless of span and height of cover, areconsidered buried structures in regard to foundation design, thus there is no requirement forseismic analysis. This may change in the future as more research is completed. For culvertswith spans


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greater than 6.1 m, questions should be directed to the Structures Design and ConstructionDivision.

19.3.1 Rock

When sound rock is at or near the surface of a stream bed, no invert slab will be required.Concrete footings are either keyed or doweled into rock based on a consultation with anEngineering Geologist from the Geotechnical Engineering Bureau.

If the elevation of the rock surface varies by 600 mm or less, the wall height should be constantand the footing height varied. If the variation in rock surface elevation exceeds 600 mm, theheight of the culvert wall may be varied at a construction joint or at a precast segment joint. Insome cases, it may be required to use walls of unequal heights in the same segment, but thisshould be avoided if possible.

19.3.2 Earth or Granular Soil

When a concrete culvert cannot be founded on rock, an invert slab is typically required.However, in areas of compact soil and low stream velocities, open concrete culverts may beused if they have scour protection (piles, sheeting, stone lined invert or deeper footings).

In areas with a significant potential for cobbles and boulders to move with the bed load, an openculvert with a strip footing on piles should be investigated. The movement of cobbles andboulders may damage a concrete invert.

To avoid differential settlement, closed concrete culverts should never be founded partially onrock and partially on earth. If rock is encountered in a limited area, it should be removed to aminimum depth of 300 mm below the bottom of the bottom slab and backfilled with either selectgranular material or crushed stone. Concrete culverts are rigid frames and do not perform wellwhen subjected to differential settlement. If differential settlement cannot be avoided, a concreteculvert should not be used.

All closed precast concrete box culverts should have a designed undercut and backfill. TheRegional Geotechnical Engineer or the Geotechnical Engineering Bureau should be consultedto determine the depth of the undercut and type of backfill material required.

A closed concrete culvert can be considered if settlement is expected and the foundation materialis fairly uniform. However, the culvert should be designed to accommodate additional wearingsurface(s) which may be needed to accommodate the settlement of the box.

If the foundation material is extremely poor and it is desirable to limit settlement, the problemshould be referred to the Regional Geotechnical Engineer or the Geotechnical EngineeringBureau to determine the best course of action. A typical remedy might be removal of unsuitableor unstable material and replacement with suitable material.


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19.4 DESIGN GUIDELINES FOR BOX CULVERTS

Reinforced concrete box culverts (precast or cast-in-place) subjected to either earth fill and/orhighway vehicle loading shall be designed in accordance with the guidelines in Sections 19.4 -19.4.11.

The following Sections and Articles of the AASHTO Standard Specifications for Highway Bridges- Fifteenth Edition have been used to develop these guidelines:

Article 3.24 Distribution of Loads and Design of Concrete SlabsSection 6 CulvertsSection 8 Reinforced ConcreteArticle 17.6 Reinforced Concrete Box, Cast-In-PlaceArticle 17.7 Reinforced Concrete Box, Precast

19.4.1 Design Method

The design method shall be either the Service Load Design Method (Allowable Stress Design)or the Strength Design Method (Load Factor Design) as described in Articles 8.15 and 8.16 ofthe AASHTO Standard Specifications for Highway Bridges - Fifteenth Edition (AASHTO) withNYSDOT modifications described in Sections 19.4.2 - 19.4.11.

19.4.2 Analysis Method

The analysis of reinforced concrete box culverts shall be in accordance with AASHTO Article8.8.2 and modified as follows:

In analysis, distance to the geometric centers of members shall be used in thedetermination of moments. Moments at faces of support, however, may be usedfor member design. Face of support shall be defined as the inside face of anexterior or interior wall. When a fillet is built monolithic with the member andsupport, no portion of the fillet shall be considered as adding to the shear andmoment capacity of the member.

19.4.3 Load Factors

The product of the load factors [gamma (() x beta ($)] for the Strength Design Method (LoadFactor Design) shall be equal to 1.3 for Dead and Earth Loads and 2.17 for Live Loads inaccordance with AASHTO Article 3.22 and Table 3.22.1A Group X.


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19.4.4 Dead Load and Earth Pressure

The dead load on the top slab shall consist of the mass densities of the pavement, soil and theconcrete slab. For simplicity, the computer program assumes the pavement as soil.

The following mass densities, as given in AASHTO Articles 3.3.6 and 6.2, shall be used indetermining dead load and earth pressures for design:

Soil mass density = 1925 kg/m3

Concrete mass density = 2400 kg/m3

Lateral earth pressure = 960 kg/m3 max., 480 kg/m3 min.

Maximum and minimum values of lateral earth pressure shall be investigated in accordance withAASHTO Articles 3.20.2 and 6.2.1.B.

Soil mass density shall be modified when using the Strength Design Method (Load FactorDesign) in accordance with AASHTO Articles 17.6.4.2 and 17.7.4.2 Modification of Earth Loadsfor Soil Structure Interaction (Embankment Installations).

19.4.5 Live Load

Reinforced concrete box culverts shall be designed for MS-23 vehicle live load.

When the depth of fill is less than 600 mm, wheel loads shall be distributed in accordance withAASHTO Article 3.24.3.2, Case B and modified as follows:

Wheel loads shall be distributed over a distribution slab width, E (measured inmeters), equal to 1.22 + 0.06S, where S is the perpendicular distance in metersbetween wall centerlines.

When the culvert is skewed relative to the over roadway, the distribution width, E,shall be reduced by multiplying E by the cosine of the skew angle. In no instanceshall the distribution width exceed 2.13 m nor the section length of precast units.

A live load surcharge pressure equivalent to 600 mm of earth fill shall be addedto the lateral earth pressure.


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When the depth of fill is 600 mm or more, wheel loads shall be distributed in accordance withAASHTO Articles 6.4.1 and 6.4.2:

Wheel loads shall be considered as uniformly distributed over a square with sidesequal to 1.75 times the depth of fill. When such areas from severalconcentrations overlap, the total load shall be uniformly distributed over the areadefined by the outside limits of the individual areas, but the total width ofdistribution shall not exceed the total width of the supporting slab.

19.4.6 Live Load Impact Factor

The Live Load Impact Factor, I, described in AASHTO Article 3.8.2 shall be modified as follows:

For fill heights < 900 mm, the Impact Factor, I, shall be equal to 1.3 for S #12.2 m, where S is the perpendicular distance in meters between wallcenterlines.

For fill heights $ 900 mm, the Impact Factor shall be equal to 1.0.

19.4.7 Wall Thickness Requirements

Exterior wall thickness requirements for reinforced concrete box culverts shall be controlled bydesign, except that minimum exterior wall thickness requirements have been established to allowfor a better distribution of negative moment corner reinforcement as follows:

MINIMUMCLEAR SPAN WALL THICKNESS<2.45 m 150 mm$2.45 m & <4.25 m 200 mm$4.25 m & <6.10 m 250 mm$6.10 m 300 mm

Interior wall thickness, in multi-cell applications, shall be controlled by design but shall not be lessthan 150 mm in any instance.

19.4.8 Concrete Strength

Reinforced concrete box culverts shall be designed for the following concrete strengths:

Precast f'c = 35 MPa

Cast-in-place f'c = 25 MPa


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19.4.9 Reinforcement Requirements

Reinforcement shall be either bar reinforcement, welded wire fabric (plain), or welded wire fabric(deformed). Designs shall use a yield strength of 415 MPa for bar reinforcement and 450 MPafor welded wire fabric in accordance with AASHTO Articles 17.6.2.2 and 17.7.2.2.

When the fill height over the box culvert is less than 600 mm, all reinforcing steel in the top matof the top slab shall be epoxy coated.

The maximum service load stress in the design reinforcing steel for crack control shall be inaccordance with AASHTO Articles 17.6.4.7 and 17.7.4.7.

Design reinforcement stresses at service loads shall be limited to satisfy the requirements forfatigue in accordance with AASHTO Article 8.16.8.3.

Minimum reinforcement shall be provided in accordance with AASHTO Article 8.17.1 at all crosssections subject to flexural tension, including the inside face of walls.

Distribution reinforcement as described in AASHTO Article 3.24.10 shall be modified as follows:

To provide for the lateral distribution of loads, steel reinforcement shall be placedtransverse to the main design steel in both the top and bottom slabs of reinforcedconcrete box culverts for fill heights less than 600 mm.

The amount of distribution reinforcement required shall be in accordance withAASHTO Article 3.24.10.2 Equation (3-21).

All faces of reinforced concrete box culverts not requiring design or distribution steel shall bereinforced with the equivalent of #4 bar reinforcement at 300 mm centers in each direction.Under no circumstances shall any reinforcement be spaced greater than 300 mm.

Shear reinforcement shall not be used in reinforced concrete box culverts. Slab and wallthickness shall be designed to have adequate shear capacity in accordance with AASHTOArticles 8.15.5 or 8.16.6.

19.4.10 Skewed Precast Sections

Skewed precast culvert sections should be avoided if practical. Precast concrete culverts shouldhave square ends whenever possible. Skewed sections are sometimes required to satisfyright-of-way constraints and/or stage construction requirements for skewed alignments. In theevent they are necessary, skewed precast culvert sections shall be designed for the skewed endclear span. Large skews may lead to sections that require additional reinforcement and/orgreater wall and slab thickness than typical square sections with the same clear opening.Fabricators should be contacted for information on maximum skews available.


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19.4.11 Detailing Requirements

The minimum reinforcing bar cover requirements for precast box culverts shall be as follows:

Exterior concrete cover top slab 50 mm (Fill < 610 mm)25 mm (Fill $ 610 mm)

Exterior concrete cover bottom slab 25 mmExterior concrete cover walls 25 mmInterior concrete cover 25 mm

The minimum reinforcing bar cover requirements for cast-in-place box culverts shall be asfollows:

Exterior concrete cover top slab 50 mmExterior concrete cover bottom slab 75 mmExterior concrete cover walls 50 mmInterior concrete cover 50 mm

The minimum bending radius of negative moment reinforcing steel (outside corners top andbottom slabs) shall be in accordance with AASHTO Article 8.23.2 Minimum Bend Diameters.

Top and bottom slab outside face transverse steel shall be full length bars unless spliced to topand bottom slab corner reinforcing steel.

19.5 COMPUTER DESIGN AND ANALYSIS PROGRAM

A Reinforced Concrete Box Culvert Design and Analysis Program is used by the StructuresDesign and Construction Division. It has been distributed to NYSDOT Regional Structurespersonnel and the Precast Concrete Association of New York (PCANY). Questions regardingthe use of this program or how to obtain a copy and/or a Users Manual should be addressed tothe Structures Design and Construction Division.

This program will design and/or analyze a one, two, three or four cell reinforced concrete boxculvert with prismatic members (precast or cast-in-place) with or without bottom slab inaccordance with the design criteria in Section 19.4. All cells are assumed to be the same sizefor any one culvert and the clear opening dimensions remain constant. By knowing the span,rise, and fill height, the program will design the box culvert by either Service Load Design or LoadFactor Design. The program will design wall and slab thickness and required reinforcement.The bar schedule will be displayed for the entire length of a cast-in-place box culvert or one unitof a precast box culvert.


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19.6 DESIGN AND DETAILS OF CONCRETE CULVERTS

Standard details for concrete culverts are shown in Figures 19-1 through 19-11.

When a cast-in-place concrete culvert is proposed for a site, the designer is required to providea complete design for the contract plans. If a precast concrete culvert is proposed, thecontractor/fabricator will be required to submit the design and fabrication details to the State forapproval. This shall typically be done within 45 days of the contract award date.

If alternate designs (i.e., cast-in-place vs. precast) are proposed for a site, the bar list table forthe cast-in-place culvert unit may be omitted from the contract plans. Once the contract hasbeen awarded and an alternate is chosen, the designer must provide a complete design if thecast-in-place alternate is selected. This shall typically be done within 45 days of the contractaward date.

19.6.1 Contract Plans

The contract plans shall include these minimum design details:

1. Live Loading Requirements: MS-23 unless another loading is required.

2. A Plan View showing the alignment, skew angle of the culvert relative to a perpendicularto the centerline of roadway, stationing along the culvert centerline, the equality stationsfor the intersection with the highway centerline, and wingwall orientation.

3. An Elevation View indicating the culvert clear span and rise, slope protection,general foundation treatment and any clearance requirements.

4. For culverts that are categorized by definition as bridges, a table of hydraulic data and theminimum hydraulic area perpendicular to flow below Design High Water .

5. A Longitudinal Section showing the slope of the culvert, a typical highway section, culvertend treatments, foundation treatment (footing on rock or piles, 4-sided box with cut-offwalls), type of apron, and any utilities attached, in the embankment or sidewalk.

6. Construction Staging Information (determines lengths of segments and potential need for

skewed segments).

7. Earth Cover: measured from the top of the top slab to the top of pavement.


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8. Headwall, Cut-off Wall, Wingwall, Apron Slab and Nosing Information: Provide geometry,reinforcement, location on culvert and connection details.

9. End Section Treatment: Provide details for square, skewed, beveled or open endsections, if applicable.

10. Railing Details: Locate the railing on the culvert and indicate how it is to beattached. See Section 19.8 and Figures 19-13, 19-14 and 19-15.

11. Chamfers: Indicate chamfer size and locations.

12. Foundation: All pertinent foundation details.

13. Installation of Draw Connectors: If Draw Connectors are to be left in place they shouldbe galvanized in accordance with §719-01 of the Standard Specifications and a note muststate they are being left in place. (Precast only)

19.6.2 Design Procedure

Determine the clear span and rise of the culvert using proper design procedures for the featurecrossed. See Chapter 8 for information on designing the opening of structures with spans of6.1 m or less crossing water features.

Determine the height of the fill, which is the distance from the top of the roadway to the top of thetop slab of the culvert.

For a cast-in-place culvert, use the Reinforced Concrete Box Culvert Design and AnalysisProgram or manual calculations to determine the wall and slab thickness and requiredreinforcement.

For precast design requirements, see Section 19.7.

Standard details for cast-in-place culverts are shown in Figures 19-1 to 19-6. Standard detailsfor precast culverts are shown in Figures 19-2, 19-5 and 19-8 to 19-11.


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Figure 19-1 Typical Cross Sections, Cast-In-Place.


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Figure 19-2 Wingwalls Plan and Elevation, Precast or Cast-In-Place


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Figure 19-3 Contraction and Construction Joint, Cast-In-Place


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Figure 19-4 Longitudinal Section, Cast-In-Place


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Figure 19-5 Wingwall Plan, Culvert on Skew, Precast or Cast-In-Place


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Figure 19-6 Wingwall Aprons, Cast-In-Place


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19.6.3 Reinforcement

The main reinforcement in the top and bottom slabs shall be perpendicular to the sidewalls incast-in-place culverts and non skewed sections of precast culverts. In a cast-in-place concreteculvert with a skewed end section, the top and bottom slab reinforcement will be "cut" to lengthto fit the skewed ends. The "cut" transverse bars have the support of only one culvert sidewalland must be supported at the other end by the edge beam or cut-off wall. See Figure 19-7. Forreinforcement requirements of skewed precast culverts, see Section 19.7.2.

When the fill height over the culvert is less than 600 mm, all reinforcing steel in the top mat of thetop slab shall be epoxy coated.

All reinforcement contained within the headwall or edge beam including the reinforcement thatextends into the top slab of the culvert shall be epoxy coated and shall meet the requirements of§ 709-04 of the Standard Specifications. If the headwall or edge beam is a significant distancefrom the highway where it is not in danger from chlorides, the epoxy coating can be eliminated.

The following bar label criteria shall be used:

Bar Identification Schedule(see Figures 19-1 and 19-8)

A1 Top Corner Bars (design steel)A2 Bottom Corner Bars (design steel)A100 Top Slab, inside face transverse bars (design steel)A200 Bottom Slab, inside face transverse bars (design steel)A300 Top Slab, outside face transverse bars (design steel for multiple cells)A400 Bottom Slab, outside face transverse bars (design steel for multiple cells)B1 Exterior wall, inside face vertical bars (design steel)B2 Exterior wall, outside face vertical bars (design steel)B3 Interior wall, vertical bars both faces (design steel)C1 Top Slab, bottom slab and wall longitudinal bars (temperature reinforcement)C100 Top Slab, inside face longitudinal bars (design distribution steel)C200 Bottom Slab, inside face longitudinal bars (design distribution steel)

See the Computer Program Users Manual for bars used less frequently. This bar schedule isalso valid for precast culverts.


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Figure 19-7 Reinforcement Diagram


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19.6.4 Headwalls/Edge Beams

Headwalls are normally used on all culverts. A headwall helps retain the embankment in deepfills. In shallow fills, the headwall may retain the subbase and/or highway pavement and providethe anchorage area for the railing system.

Headwalls that are over 300 mm in height or have a railing attachment should be cast-in-place.Headwalls 300 mm or less in height with no railing attachment may be either precast orcast-in-place.

If possible the maximum height of the headwall should not exceed 900 mm. Greater heights areattainable but should only be used in special cases.

Cast-in-Place culverts with skewed ends may require additional stiffening of the top and bottomslabs by what is most commonly called an "edge beam" in the top slab and a "cut-off wall" in thebottom slab. An edge beam is very similar to a headwall in that it may be used to anchor guiderailing posts or retain earth fill. Its main purpose, however, is to stiffen the top slab ofcast-in-place culverts that lose their rigid frame action as a result of having a skewed end. Acut-off wall will stiffen the bottom slab as well as prevent water from undermining the culvert (seeSection 19.9).

When additional strength is required in the concrete edge beam, the following criteria shall beused:

If there is a 1 on 2 slope to the edge beam, it will be more economical to increasethe depth of the edge beam in order to meet the required design.

When the edge beam is at shoulder elevation, the edge beam height should bemaintained and the width of the edge beam should be increased.

Assistance in edge beam and cut-off wall design may be obtained from the Structures Designand Construction Division.

19.7 PRECAST CONCRETE CULVERTS (SPECIAL DETAILS AND REQUIREMENTS)

Precast concrete culverts are fabricated in a plant where the ability to control placement andcuring conditions typically results in higher strength and more durable concrete. Precastingpermits efficient mass production of concrete units. The advantages usually more than offsetthe cost of handling and transporting the units to the site. The majority of concrete culvertsinstalled are precast.


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Precast units are limited to certain sizes and skews. Transportation and handling limits the sizeof units. Skewed sections may need more reinforcement and larger slab and/or sidewall widths.The use of skewed sections will increase the cost of the culvert due to increased fabricationcosts.

Figures 19-8 and 19-9 show some of the typical section details for precast concrete culverts.Headwall and wingwall connection details are shown in Figures 19-10 and 19-11.

In culverts with end sections squared off, each unit will routinely be square unless the designerhas included special requirements in the Contract documents. Stage construction is oneexample of a special requirement which may require skewed interior sections. The units thatmeet at the division of the stages may need to be skewed to provide adequate width for travellane(s).

In culverts with skewed end sections, the interior sections will routinely be square and the endsections skewed at the outside end. However, this will usually be determined by themanufacturer of the precast units unless the designer has included special requirements in theContract documents.

Concern has been raised about the use of precast culverts on steep grades. No maximum slopeis recommended for closed box culverts because of the need to match the slope of the stream.However, larger open box culverts and the frames and arches discussed in Section 19.7.4should be limited to approximately 2%. Precast fabricators should be contacted for themaximum grade that can be fabricated. If matching a steep stream bed slope is necessary foran open culvert, the footings can be stepped and the length of the sidewall varied. When two or more single cell precast concrete culverts are placed side by side, it is usually notpossible to place the walls of adjacent cells tightly together. It is reasonable to detail a 50 mmto 100 mm gap between the walls of adjacent cells. This gap should be filled with any concreteitem in the project or Class D concrete if no other concrete item is available.

19.7.1 Contract Plans

Dimensions of the sidewalls and top slab and reinforcement size and spacing should not beshown on the plans, unless necessary. If sidewall or top slab dimensions are dictated by siteconditions, show only affected dimensions and indicate if they are minimums, maximums orspecifically required dimensions.

A note in the Contract plans shall require the manufacturer, through the contractor, to provide alldesign details not included in the contract plans for checking by the State. This method shouldresult in the most economical culvert design.


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Figure 19-8 Typical Cross Sections - Precast


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Figure 19-9 Typical Cross Sections - Precast


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Figure 19-10 Headwall Details - Precast


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Figure 19-11 Headwall and Wingwall Connection - Precast


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19.7.2 Reinforcement

The main reinforcement in the top and bottom slabs shall be perpendicular to the sidewallsexcept in skewed sections. Precast concrete culverts with skewed ends are unable to use edgebeams as stiffening members because of forming restrictions. For this reason, transversereinforcement is unable to be "cut" (as in cast-in-place culverts) to fit the skewed end section.

When a precast end section is skewed, the transverse reinforcement must be splayed to fit thegeometry of the skew, (see Figure 19-7). This splaying of the reinforcement will increase thelength of the transverse bars and, more importantly, the clear span of the end section. For smallskews, the splayed reinforcement is usually more than adequate. However, large skews mayrequire more reinforcement and can increase the clear span to the point where increased slabthickness may be necessary.

See Section 19.6.3 for bar identification schedule.

19.7.3 Design and Fabrication

When contract plans do not contain complete design details for the precast concrete culvert thecontractor shall be responsible for providing them. All design submissions from the contractorshall include a complete set of working drawings and a complete set of design calculations. Thedrawings and the design calculations shall be stamped by a Professional Engineer licensed topractice in New York State. If the Reinforced Concrete Box Culvert Design and AnalysisProgram is used to design the culvert, the output shall be substituted for the design calculations.

Fabrication requirements of precast concrete box culverts are contained in Section 706-17 of theStandard Specifications.

19.7.4 Precast Arches and Frames

In addition to box sections, there are various types of proprietary precast concrete arches andframes available. These sections are typically used when larger culverts ($6 m ±) are requiredand are usually founded on footings on rock. They can be considered when hydraulics can beaccommodated and/or aesthetics are a consideration. Where appropriate, they may be placedon a combined invert footing/slab or a pile supported footing.

The advantages of the precast concrete arches and frames are the same as for the precastconcrete box culverts, except that longer spans (up to 12.2 m) are possible. See Figure 19-12.


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Figure 19-12 Precast Arch and Frame


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Fabrication requirements for precast concrete arches and frames can be found in SpecialSpecifications available from the Structures Design and Construction Division. The contractorshall be responsible for providing all design computations and details for these units. Thedrawings and the design calculations shall be stamped by a Professional Engineer licensed topractice in New York State.

19.7.5 General Notes for Precast Culverts

1. For headwalls where H > 1.8 m, specific design information must be provided in thecontract documents. H is the height of the headwall above the top of the top slab. (SeeFigure 19-10.)

2. Reinforcement for headwalls without guide rail shall be the same as shown for headwallswith guide rail. See Figure 19-10, section A-A.

3. Headwalls where 0.3 m # H # 1.8 m are to be attached to the box culvert by use ofmechanical connectors for reinforcing bar splices meeting the requirements of § 709-10(epoxy coated) of the Standard Specifications. The female threaded portion of theconnector is cast into the box culvert.

4. Threaded inserts, where detailed, shall be designed for use with #5 and #6 reinforcingsteel. Inserts shall be non-corrosive and, when used in 35 MPa concrete, able to resistminimum pull out loads of 49 kN for #5 reinforcing and 71 kN for #6 reinforcing.

5. Dowel bars used to attach the cut-off wall to the box culvert shall be drilled and groutedper the requirements of Standard Specification § 586. The keyway shall be grouted withthe same material as the dowels.

19.8 GUIDE RAILING

The anchorage of the guide railing is determined by the amount of fill over the top of the unit. Ifthere is less than 900 mm of fill, guide railing shall be anchored into the headwall, edge beam orindividual concrete pedestals. If there is more than 900 mm of fill (i.e., enough for standard lengthpost embedment) regular highway guide rail can be used. The offset from the end of culvert tothe back of the guide rail should be considered when choosing the type of highway guide rail, i.e.,the guide rail deflection characteristics should be reviewed.

When the recommended offsets from the back of the posts to the shoulder break can not beachieved or the embankment slopes away from the normal shoulder break steeper than a 1:2slope, extra long posts are required. In these situations, the 900 mm criteria is no longer valid.See Chapter 10 for guidance on the required length of posts.


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When the guide rail is anchored to the headwall, edge beam or pedestal, either culvert rail, bridgerail, or equivalent can be used. Bridge rail is recommended for culvert spans over 6 m. Thechoice may be made on the basis of types of railings being used in the project or Regionalpreference. For example, Region 10 prefers using heavy post blocked-out corrugated beamguide railing. The approach railing details in Figure 19-13 have been modified to match the current BDD sheetfor Steel Bridge Rail-Two Rail. For culvert rail details, see Figures 19-13, 19-14 and 19-15.

The following construction notes, as appropriate, shall be placed on the plans:

Standard Culvert Railing Construction Notes:

After the nuts on the anchor bolts have been tightened to the satisfaction of theEngineer, the anchor bolts shall be flame cut 25 mm above the nut and thethreads above the nut shall be damaged as directed by the Engineer to preventremoval. All other nuts shall be either tack welded in place or have lock washers,as determined by the Engineer. Galvanizing damaged by flame cutting and/ortack welding shall be repaired according to §719-01 of the StandardSpecifications.

Rail terminus details shall be in accordance with the latest approved details. (Forinformation see Figure 19-13 and 19-14 or the latest Bridge Design Data Sheets.)

All railing is to be fabricated and erected so that the rails are parallel to theroadway and the posts are truly vertical.

The box beam rail elements shall be long enough to span the entire culvert or bea minimum of 6 m in length.

For material requirements and construction details, see §568 of the StandardSpecifications.

Anchor rods shall be cast into the concrete or grouted into 40 mm N throughholes made with a core drill. The grout used shall meet the requirements of theStandard Specifications § 701-05, Concrete Grouting Materials, and appear on theDepartment's Approved List.


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Figure 19-13 Approach Railing Details, Transition to Box Beam Guide Railing


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Figure 19-14 Approach Railing Details


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Figure 19-15 Culvert Railing Details, Cast-In-Place Connection


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19.9 CUT-OFF WALL

A minimum 450 mm wide cut-off wall is required in all culverts with invert slabs to preventundermining. The cutoff wall should be 1.2 m deep or to the top of sound rock if the rock iscloser. For culverts with skewed ends, the cut-off wall also provides stiffening to the bottom slab.The 1.2 m is measured from the lowest elevation of the top surface of the invert slab. SeeFigures 19-2, 19-4 and 19-6.

When cut-off walls are required, they shall always be specified at each end of the barrel. Whena concrete apron (Section 19.11) is specified, an additional cut-off wall shall also be specified atthe end of the apron. The bottom of all wingwall footings should be at or below the bottom of thecut-off wall to prevent scour around the edges of the cut-off wall.

When a precast culvert is specified, the cut-off wall may be precast or cast-in-place. Whenprecast concrete cut-off walls are specified, their cost should be included in the cost of theculvert barrel. No separate item is required. When a cast-in-place culvert is specified, the cut-offwall should be cast-in-place.

19.10 LOW FLOW DISH

Closed box culverts shall have a low flow dish whenever the stream is classified as a fishingstream by the Department of Environmental Conservation and a low flow dish is requested. TheRegional Hydraulics Engineer can assist in communications with the Department ofEnvironmental Conservation. The depth of the dish may be as small as 150 mm or as large as300 mm. The depth of the dish depends on the quantity of flow. Lower flows may require adeeper dish to provide adequate depth of flow. A typical dish is shown in Detail E of Figures 19-1and 19-8.

The dish is usually in the center of the invert slab, but there may be times when the dish will beat or near the sidewall. This may happen when the stream is on a curved alignment and the lowflow of the stream is on the outside of the curve.

There are times when the Department of Environmental Conservation may require native streambed material over the top of the bottom slab. The typical requirement is for a 300 mm depth.One problem that may develop is the movement of the native material during high flows.Typically, however, material washed out during the high flow will be replaced with new materialas the water recedes. This periodic movement of material may abrade the surface of theconcrete culvert. The depth of the concrete covering the reinforcing bar should be increased ifthis situation is anticipated. Note that covering the bottom slab with native material will make itvery difficult, if not impossible, to inspect the bottom slab.

The Reinforced Concrete Box Culvert Design and Analysis Program does not design the bottomslab of a culvert with a low flow dish since it is not a prismatic member. The additional triangleof concrete should be considered as not contributing to the strength of the section.


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19.11 APRONS

Box culverts can significantly increase the stream flow velocity because the concrete has aroughness coefficient significantly lower (i.e., smoother) than the stream bed and banks. Thelonger the culvert and the steeper the slope, the more the velocity will be increased. To dissipatethis increase in energy and to prevent scour, a stone apron shall be placed at the outlet of allculverts. In addition, a stone apron should be specified at the inlet of all culverts to prevent scourcaused by the constriction of flow.

The recommended minimum length of the stone apron is 7.5 m. The stone apron should coverthe full width of the stream bed. In addition, stone filling should be placed on the side slopes toan elevation 300 mm± above Design High Water. A 1.5 m wide by 1.2 m deep key of stone fillingshould be placed in the stream bed at the end of the apron away from the culvert. Stone fillingshould also be required to stabilize all disturbed slopes to an elevation 300 mm± above DesignHigh Water.

The Regional Hydraulics Engineer or the Structures Design and Construction Division HydraulicsUnit should be consulted to determine an appropriate length apron for special situations such aslocations where excessive scour has occurred.

The stone apron will begin at the end of the barrel if no concrete apron is specified. If a concreteapron is specified, the stone apron will begin at the end of the concrete apron. The size of thestone filling shall be determined by the design velocity or Regional preference, whichever islarger. For design velocities of 3 m/s or higher, heavy stone filling should be specified. Fordesign velocities less than 3 m/s, medium stone filling may be used.

When stream velocities are very high (>5 m/s), where special site conditions exist or where theexisting soils are very poor, a concrete apron may be used. It should extend to the end of thewingwalls. See Figure 19-6. A cut-off wall (section 19.9) is required at the end of the concreteapron and at the end of the culvert barrel. The cut-off wall at the end of the culvert barrel is addedprotection if the apron fails or separates from the barrel. Concrete aprons may fail from frostheaves, bed load material abrading the apron or other unique situations.

Where there is significant movement of cobbles and boulders in the bed load, an open culverton a strip footing on piles should be investigated. The movement of cobbles and boulders maydamage a concrete invert.

For some unique situations with very high velocities, steep profiles, or special circumstances,energy dissipators (baffles) may be required to reduce the velocity. Baffles are concrete sectionsthat extend 300 mm to 750 mm above the bottom slab. The Regional Hydraulics Engineer or theStructures Design and Construction Division Hydraulics Unit should be consulted to determinethe need for and the design of energy dissipators.

When a precast culvert is specified, the concrete apron and wingwalls may be precast orcast-in-place. When precast concrete aprons and/or wingwalls are specified, their cost should


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be included in the cost of the culvert barrel. No separate item is required. When a cast-in-placeculvert is specified, the concrete apron and wingwalls should be cast-in-place.

19.12 SUBBASE DRAINAGE

Draining surface and ground water away from the culvert through the subbase is just asimportant as the conveyance of water through the culvert. All culverts should have a minimumlongitudinal slope of approximately 1%, if possible, to drain the water that permeates through thepavement and subbase away from the top of the culvert. The slope is very important, insituations where there is low fill (0.3 m±) or asphalt directly on the culvert, to limit the likelihoodthat water will not pond, freeze and cause potholes or other problems.

If a longitudinal slope is not possible, a 1% slope (wash), perpendicular to the centerline of theculvert, can be used. The wash can be from the centerline to each side or all in one direction.The wash can be formed into a cast-in-place culvert but is difficult to form on precast culverts.On precast culverts, the wash can be added after the culvert is in place by placing a shim courseof asphalt or concrete.

In some instances, culverts will be used to allow the passage of things other than water such aspedestrians, bicycles, trains, golf carts or farm animals. In cases where it is desirable to havea dry environment, a waterproof membrane should be used to cover the joints between precastculvert sections or to cover the construction joints in cast-in-place culverts. Even though a jointsealer is always placed between individual precast concrete culvert sections and the sectionsare pulled tightly together, water may seep through the joint. The minimum requirement forwaterproofing these joints is to provide a membrane strip, having a minimum width of 600 mm,centered on the joints, covering the top slab, and then extending down the sidewalls to the footing.In this application, the membrane is not intended to protect the concrete.

A waterproof membrane may be used to cover the joints of precast concrete culverts that conveywater through the culvert. The Designer must understand that the purpose of the waterproofingmembrane is to restrict seepage of water or migration of backfill material through the joints in theculverts and it is not intended to protect the concrete.

When watertight joints are required, contact the Materials Bureau for the proper waterproofmembrane item to be included in the contract. This item contains all the material andconstruction details necessary for the application of the system.


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19.13 REFERENCES

1. Standard Specifications for Highway Bridges 15th Edition (1992) as amended by theInterim Specifications - Bridges - 1993, American Association of State Highway andTransportation Officials, 444 North Capital Street, N. W. Suite 249, Washington, D. C.20001.

2. Reinforced Concrete Box Culvert Design and Analysis Program Users Manual, January1995, Structures Design and Construction Division, New York State Department ofTransportation, State Campus, Albany, NY 12232.

3. Standard Specifications of Construction and Materials, January 2, 1995, Design QualityAssurance Bureau, New York State Department of Transportation, State Campus,Albany, NY 12232.

4. Model Drainage Manual - 1991, American Association of State Highway andTransportation Officials, 444 North Capital Street, N. W. Suite 225, Washington, D. C.20001.


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CHAPTER 19INDEX

SUBJECT SECTION

Apron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.9, 19.11Box Culvert Computer Design Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.5Cast-In-Place Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.2, 19.6Clear Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.1Contract Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6, 19.6.1, 19.7.1Corrugated Metal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.2Culvert Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.4.9, 19.4.11, 19.6.3, 19.7.2Culvert Railing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.8Culvert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.1 - 19.13Cutoff Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6.3, 19.9, 19.11Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.1Design Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.1Edge Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6.3, 19.6.4, 19.8Energy Dissipators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.11Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.3Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.3Headwall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.6.3, 19.6.4, 19.8Low Flow Dish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.10Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.12Precast Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.2, 19.6, 19.7Precast Arches and Frames . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7.4Skewed Culverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.4.10, 19.6.3, 19.6.4, 19.7, 19.7.2Stone Filling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.11Two-Cell Culvert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.7Waterproof Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19.12

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