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NCHRP 12-92
Proposed LRFD Bridge Design Specifications for Light Rail Transit LoadsYail Jimmy Kim, Ph.D., P.Eng. FACI
Chengyu Li, Ph.D, PE, SEAssociate Professor, Department of Civil Engineering
University of Colorado DenverSenior Group Manager, Structures Group
Atkins North America
Contents
1. Introduction (Overview of Research)
2. Phase III (Guide Specifications)
3. Phases III (Design Examples)
4. Summary
5. Acknowledgments
Introduction
II IVIIIII 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 guide specifications about bridges carrying light rail loading and light rail/highway traffic loadings, including design examples for practitioners
Introduction
Overview of Research
Phase I(Planning)
• Literature review (155 papers)• Research methodologies• Outline of specifications• Interim report 1
Phase II(Implementation)
• Site work and FE modeling• Standard light rail load model• Load effects and forces/load factors• Interim report 2
Phase III(Specifications)
• Guide specifications proposed• Design examples• Interim report 3
Phase IV(Final product)
• Update of specifications• Ballot items• Final report
Completed Completed
6 months(3-month review)
Completed
Introduction
Research TasksTask 1: A critical literature reviewTask 2: A methodology specifying the light rail transit load characteristics Task 3: A detailed outline with annotated description for the developed
specificationsTask 4: Preparation of interim report No. 1Task 5: Execution of the approved work to develop the proposed
methodologyTask 6: Preparation of interim report No. 2Task 7: Development of proposed AASHTO LRFD design specifications
and commentaryTask 8: Development of design examplesTask 9: Preparation of interim report No. 3 (we are here now)Task 10: Update of proposed development to the AASHTO LRFD
SpecificationsTask 11: Preparation of a final report
Phase II (Task 5)
Overview of Technical Subtasks of NCHRP 12-92
Response monitoring of constructed bridges
Finite element modeling and field verification
Development of a standard light rail live load model
Characterization of live load effects
Rail-train-structure interaction and associated forces
A unified approach for bridges carrying light rail or/and highway
traffic loads
Proposal of load factors
Field Testing
Strain gage calibration to measure train loadEmpty train (laboratory)
Empty train (site)
Five light rail bridges in Denver
Broadway Bridge
Wheel load distribution
Typical girder strain
Finite Element Modeling
Validation of Modeling Approach (5 bridges in Denver, CO)
Indiana Bridge
Two articulated trains on Indiana Bridge
Dynamic response
Live load distribution
Finite Element Modeling
Design of Benchmark Bridges4.719.254.71 9.254.71 4.71 4.714.71 9.25
32
9.254.71 4.71
6 4 44 4 4 4 632 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
644444632
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 4 632
4 6 6 6 6 4 4 8 8 8 6 10 10 632 32 32
4
RC girder girder
Phase III (Guide Specifications)
I IVIIIII VII
Phase III
Phase III: Specifications
• Objectives of Phase III are:
• To propose guide specifications that complement AASHTO LRFD BDS (Art. 3.6.1.5: ‘Where a bridge also carries rail-transit vehicles, the owner shall specify the transit load characteristics and the expected interaction between transit and highway traffic’)
• To develop design examples using the specifications
• To submit Interim Report No. 3
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
• Proposed contents
1. General2. Design Philosophy3. Loads4. Structural Analysis5. References
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
1. General• ScopeThese guide specifications (LRT Guide Specifications) are asupplement to the AASHTO LRFD Bridge Design Specifications(AASHTO LRFD BDS) that address the design of bridges subjectedto light rail transit (LRT) loadings or LRT and conventional highwaytraffic loadings.
• Notations: AASHTO LRFD BDS
• Definitions: AASHTO LRFD BDS
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
2. Design Philosophy• General (in conformance with Art. 2.5 of BDS)
• Limit States • Service I, II, III, and IV (2016 interim used)• Strength I, III, IV, and V (2016 interim used)• Extreme Event I and II• Fatigue I and II
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
2. Design Philosophy• Load factors and combinations (light rail only; light rail/highway)
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
2. Design Philosophy• User comfort criteria
• Bridge deflection: deflection vs frequency (CHBDC)• Pedestrian and passenger comfort (UIC- Int. Union of Railways)
UIC Code 776-2 (Art. 5.2)
CHBDC (Art. 3.4.4)
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
3. Loads• Permanent loads (DC, DW, and EV based on BDS)• Earth loads (EH, ES, and DD based on BDS)• Live loads (LL and PL)
• Number of design tracks• Multiple presence of live load• Design light rail transit load (LRT-16):
LRT-16
• 48,256 models• 4 probability levels• 660 load enveloping cases with 33 trains operated in the nation
30 ft to 160 ft (initial)HL-93 up to 150 ft30 ft to 300 ft (T-5)
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
3. Loads• Dynamic load allowance (IM): 30% (25% plus 5% margin)• Derailment load (DE): 100% vertical and 40% horizontal• Centrifugal force (CE):
• Braking force (BR)28 percent of the axle weights of light rail design train or5 percent of the axle weights plus lane load
• Wind loads: WS (on structure) and WL (on trains)• Earthquake effects (EQ): Art. 3.10 of BDS
( )4.12.034 2
+−= ngRvC
Phase III (Task 7)
Task 7: Development of proposed AASHTO LRFD designspecifications and commentary
4. Structural Analysis• Acceptable method of structural analysis (Arts. 4.4/4.5 of BDS)• Structural material behavior (Arts. 4.5.2.2/4.5.2.3 of BDS)• Modeling geometry and boundary conditions (Art. 4.5.3 of BDS)• Influence of plan geometry (Art. 4.6.1 of BDS) • Distribution factor method for moment and shear
• PC box, PC I, Steel box, Steel plate, and RC
• Skewed bridges
Phase III (Design Examples)
I IVIIIII VIII
Phase III (Task 8)
Task 8: Development of design examples: Dr. Tobias/Dr. Wang
1. Simple span composite steel plate girder
Phase III (Task 8)
2. Continuous span composite steel plate girder
Task 8: Development of design examples: Dr. Tobias/Dr. Wang
Phase III (Task 8)
3. Simple span composite prestressed concrete girder
Task 8: Development of design examples: Dr. Tobias/Dr. Wang
Summary
I IVIIIII VIII
Summary
• Tasks 7-9 were completed
• Task 7: guide specifications were proposed in conjunction with BDS to meet the objectives of NCHRP 12-92
• Task 8: comprehensive design examples were developed based on the guide specifications and BDS
• Task 9: Interim Report No. 3 was submitted
• Tasks 10-11 will be completed by Feb. 2017 (6 mths after approval)
• Task 10: Update of proposed guide specifications• Task 11: Preparation of a final report
Phase III (Specifications)
Acknowledgments
• AASHTO
• Transportation Research Board (TRB) and NAS
• Dr. Waseem Dekelbab
• NCHRP 12-92 Panel Members
• AASHTO Sub T-5 (S. Hida and J. Robert)
• Regional Transportation District (RTD) in Denver, CO
• RT Members (Consultants: Dr. Tobias and Dr. Wang)
• Graduate Students Participating in NCHRP 12-92
- Thank-you to: I IVIIIII VV