A CM/GC Approach for the Design of a Two-Girder Horizontally Curved Pedestrian Bridge

Irvin J. Lopez, P.E., Senior Bridge Engineer

Ken D. Price, PE, SE, PEng, Manager Complex Bridge Group

2

Project Overview

— Purpose and Challenges

— Concept Development and Acceptance

— CM/GC Procurement

— Design and Analysis

— Global stability and redundancy

— Lessons learned

3

Project Location

UVU is located approx. 39 miles south of Salt Lake City.

North

4

— Destination of choice for many students in Utah

— Current enrollment is over 37,000

— Largest university in Utah

— Campus growth and expansion

Purpose and Challenges

5

Challenging Site Conditions and Constraints

MSE Walls

UPRR & UTA Private Property I-15 Interstate College Dr.

6

Concept Development and Acceptance

How did we get here?

Original DesignInverted Fink Truss

Re-design Concept

Three Plate GirdersConstant Depth

I I I OptimizeTwo Plate Girders

Constant Depth

I I

NTP

Final ConceptTwo Plate Girders

Haunched

Cost Reduction

Notice to Proceed

D-B-B CM/GC

80

% D

esig

n

7

Original (Complex) Fink Truss Concept

Original Design - Inverted Fink Truss Superstructure

Overall Length: 1022.5 ft.S-Curve Alignment

Pylon

Tower Bents = 4

Rods

Steel Box Chord

Anchor Bents = 2

8

Final Accepted Concept

Re-designed Bridge – Two Plate Girder Superstructure

Overall Length: 965 ft.Single Radial Curve Alignment

Roof Post

Steel Girder Outriggers & Floorbeams

Concrete Bents = 5

57.5 ft. Reduction (~6%)

9

CM/GC Project Team

UDOT

Client

WSP USA

Lead Designer

Design Sub Consultants

Architects, Environmental, Survey, Geotechnical

Kraemer North America

Lead Contractor

Stanton Construction Services

Cost Estimator

Innovating Contracting Consultant

CM/GC Lead for UDOT

Utah Valley University

(UVU)Stakeholder

Utah Transit Authority (UTA)

Stakeholder

10

CM/GC Project Schedule

Aw

arde

d to

Kra

emer

Feb.

201

9

Concept DevelopmentSteel Plate Girder

Bridge

Preliminary Design

30% Design Plans

Early Steel Package

Plans, Specs, & Estimate

Full Package Final DesignPlans, Specs, &

Estimate

Construction 12 month for substantial completion

Com

plet

e Co

nstr

ucti

onby

Nov

. 202

0

Aw

arde

d to

Kra

emer

Aug

. 201

9

Sept 1 8 Nov 1 9

S&L Plans

Nov 1 8

Jan 1 9

Feb 1 9

VE Efforts

11

Bridge Aesthetics

Aesthetic Elements— Roof Profile— Haunched Girders— Perforated Metal Enclosure— Materials— Lighting

12

Span Configuration

Site constraints resulted in unbalanced span arrangement

Sp. 1 / Sp. 2 = 1.15Sp. 4 / Sp. 3 = 0.56 (Uplift at Bent 5?)

226’Span 2

Ideal Ratio = 0.70

13

Bridge Elevation

UPRR & UTA Private Property I-15 Interstate College Dr.

14

Typical Sections

Section at End Bents

Typical Section

Section at Interior Bents

15

Design Loads

Project Design Criteria

UDOT SDDM

ASCE 7

AASHTO

Bridge Loads (AASHTO, UDOT SSDM)— Pedestrian Live Load & H5 Truck— Temperature— Wind— Earthquake— Fatigue (Wind AASHTO LTS)

Roof Loads (ASCE 7)— Snow = 30.5 psf.— Maintenance Live Load = 20 psf.— Wind

16

Pedestrian Live Load

Similar to AW3 “Crush” Load

Project Design Criteria → PL = 90 psf (no dynamic load allowance) → Load Factor (Strength) = 1.75→ 90 psf. x 1.75 = 157.5 psf.

AASHTO LRFD Guide Specification for the Design of Pedestrian Bridges

17

3D Analysis Model

SuperstructureDesign

Global Effects

Substructure Design

Foundation Design

Seismic Design

• Thermal• Wind• Stability

Lateral Bracing Other Analyses:• Staging• Dynamic• Redundancy

Roof Structure

18

Support Conditions

— Due to Seismic Demands, interior bent bearings were fixed.

Exp.(Guided)

Fix Fix Fix Exp.(Guided)

Theoretical point of “zero” movement

L/3L

19

Load Patterns for Maximum Demands

— “Patch” load cases were defined for PL, SN, and LLr.

M+ M+ M+ M+

M- M-

M-

Max. TotalLoad

20

Wind Load and Vibration Analysis

— RDWI conducted wind and pedestrian-vibration study

21

Wind Tunnel Testing

22

Fracture Critical and Redundancy Analysis

Reference Documents and Specifications

What about Pedestrian Bridges?

23

Pedestrian Bridges?

— Pedestrian bridges are not governed by fatigue

— Minimal guidance FCM requirements

— All referenced studies are based on vehicle loads

— Pedestrian loads and factors are calibrated differently than vehicular loads and factors

24

Damage Criteria

Complete failure of one girder at a critical location on the bridge with concurrent live load overload

Lateral bracing, floorbeams, deck, and composite action all contributed to load path redundancy (system redundancy).

Collapse Limit State

The bridge does not collapse under the above condition, and remains functional (deflection criteria)

How?

A Common Sense Approach

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-25000

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

0 200 400 600 800 1000

M3

(k-

ft)

DC-Girder 1 Combined

Unfractured

Fracture

Dynamic

-20000

-15000

-10000

-5000

0

5000

10000

15000

20000

0 200 400 600 800 1000

M3

(k-

ft)

DC-Girder 2 Combined

Unfractured

Fracture

Dynamic

Redundancy AnalysisTwo Girder System is redundant – will not collapseAn event scaling approach was adopted to prove redundancy of bridge superstructure.

26

Fabrication and Weight Efficiency

Weight efficiency does not always result in most economical design.

Fabrication costs must also be considered when detailing bridges.

Field Splices 1 2 3 4 5 6 7

I-15 Interstate

27

Fabrication and Construction

— Large Field Sections (driven by site)

— Max. girder segment length (over RR) = 183 feet

— Max. weight = 70 tons.

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— CM/GC worked well for this project.

— Two-girder bridges can be redundant

— Refined analysis was utilized to identify system redundancy

Lessons Learned

Thank you!

wsp.com

Marshall Railway Consulting