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NCHRP 12-92

Proposed LRFD Bridge Design Specifications

for Light Rail Transit Loads

Dr. Yail Jimmy Kim, PEng, University of Colorado Denver

Dr. Chengyu Li, PE, SE, Atkins North America

Dr. Waseem Dekelbab, PE, PMP, NCHRP

Program manager

Principal investigators

Contents

1. Introduction

2. Field Testing

3. Finite Element Modeling

4. Summary

5. Acknowledgments

2/20

Introduction

I I IV III II V

Introduction

The objectives of NCHRP 12-92 are:

• To characterize light rail transit load effects on the behavior of

bridge superstructure (e.g., standard train load, dynamic load

allowance, load distribution, and design factors for LRFD)

• To examine the interaction between the light rail load and

supporting structures, which can generate various forces to

consider in design and practice

• To propose a unified design approach for light rail transit and

highway traffic, and corresponding design articles and

commentaries for the AASHTO LRFD Specifications, including

design examples for practitioners

4/20

Overview of Research

Introduction

Phase I

(Planning)

• Literature review

• Proposal of research methodology

• Description of alternative specifications

• Interim report 1

Phase II

(Methodology)

• Refined FE analysis

• Standard light rail train load model

• Load effects and forces


Phase III

(Specifications)

• Proposal of design articles

• Development of design examples


Phase IV

(Final products)

• Update of specifications

• Ballot items

• Final report

Completed To be completed in July 2015

5/20

Introduction

Research Tasks Task 1: A critical literature review

Task 2: A methodology specifying the light rail transit load characteristics

Task 3: A detailed outline with annotated description for the developed

specifications

Task 4: Preparation of interim report No. 1

Task 5: Execution of the approved work to develop the proposed

methodology (we are here now)


Task 7: Development of proposed AASHTO LRFD design specifications

and commentary

Task 8: Development of design examples


Task 10: Update of proposed development to the AASHTO LRFD

Specifications

Task 11: Preparation of a final report

6/20

Field Testing

I IV III II V II

Field Testing

Strain gage calibration to measure train load

Empty train (laboratory)

Empty train (site)

Five light rail bridges in Denver

Broadway Bridge

Wheel load distribution

Typical girder strain

8/20

Finite Element Modeling

I IV III II V III


Validation of Modeling Approach (5 bridges in Denver, CO)

Indiana Bridge

Two articulated trains on Indiana Bridge Dynamic response 10/20

Live load distribution


Design of Benchmark Bridges 4.719.254.71 9.254.71 4.71 4.714.71 9.25

32

9.254.71 4.71

6 4 44 4 4 4 6

32 32 32

4 6 6 6 6 4 4 8 8 8 6 10 10 6Steel plate girder

4 6 6 66 4

4.71 9.25 4.71

4 4

9.254.71 4.71

32

6

4.714.71 9.25

8 8 8 10 10 6

3232

Steel box girder

4.719.254.71 4.719.254.71 4.71 4.71 9.25 9.254.71 4.71

6444446

32

6101068884466664 4

32 32 32

PC I girder

4

32

84 88

4.714.71 9.25

32

6 1010 6

4.719.254.71

32

4 4

4.714.71 9.25

12 12

PC box girder

4.714.71 9.25 4.719.254.71 4.71 9.254.71 9.254.71 4.71

6 4 4 4 4 4 6

32

4 6 6 6 6 4 4 8 8 8 6 10 10 6

32 32 32

4

RC girder girder

11/20


Modeling of Benchmark Bridges (5 types)

Four representative light

rail trains

(MN, UT, MA, and CO)

• Response monitoring:

3828 static/dynamic models

(116 models for HL93 and 3,712 models

for light rail trains)

RC

PC Box

PC I

Steel Box

Steel Plate

12/20


Modeling of Benchmark Bridges (flexural moment)

Typical maximum moment

(Steel plate girder bridges)

Light rail trains vs. HL-93

(Steel plate girder bridges)

13/20


Modeling of Benchmark Bridges (serviceability)

Deflection requirements

(Prestressed concrete I

girder bridges)

Passenger comfort criteria

(Prestressed concrete I

girder bridges)

14/20


Modeling of Benchmark Bridges (dynamic load allowance)

Dynamic load allowance

Probability-based inference

Mean DLA (simply-supported span)

Mean DLA (multiple span)

DLA = 25% suggested

for light rail trains

(2960 FE models and

associated probability-

based inference)

15/20


Standard live load model for light rail transit (development)

46,400 load cases analyzed

Decomposition of lane and

concentrated loads

Probability-based

load inference

Comparison to HL-93

w

Uniformly distributed load

P P P

Concentrated loads

P P P

Proposed live load model

w

(Magnitude to be determined) (Magnitude, spacing, and

number of concentrated loads

to be determined)

Proposed load configuration

16/20


Standard live load model for light rail transit (assessment)

Bending moment

Shear force

30 kips 30 kips 30 kips

0.90 kip/ft

14 ft 14 ft 14 ft14 ft

0.96 kip/ft

34 kips 34 kips 34 kips

14 ft14 ft

0.82 kip/ft

27 kips27 kips 27 kips

L > 100 ft L < 100 ft

Proposed

standard live

load model

Alternative live load models

Site-based inference vs.

candidate load model

17/20

Summary

I IV III II V IV

Summary

● The behavior of five light rail bridges was examined on site:

modeling approach validated and statistical properties acquired

● Five benchmark bridges were designed and modeled:

3828 static/dynamic models were used (simply-supported and

multiple spans)

● Dynamic load allowance was proposed to be 25% based on 2960

load cases and four risk levels

● A standard live load model was proposed and assessed against

site-based load inference and existing light rail train loads

19/20

Acknowledgements

• NCHRP staff and panel

• AASHTO

• Regional Transportation District (RTD) in Denver

• TRB AR055

- Thank-you to: I IV III II V V

20/20