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Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads (2017)

Chapter: Chapter 4 - LRFD Guide Specifications for Bridges Carrying Light Rail Transit Loads

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Page 191
Suggested Citation:"Chapter 4 - LRFD Guide Specifications for Bridges Carrying Light Rail Transit Loads." National Academies of Sciences, Engineering, and Medicine. 2017. Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads. Washington, DC: The National Academies Press. doi: 10.17226/24840.
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Page 191
Page 192
Suggested Citation:"Chapter 4 - LRFD Guide Specifications for Bridges Carrying Light Rail Transit Loads." National Academies of Sciences, Engineering, and Medicine. 2017. Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads. Washington, DC: The National Academies Press. doi: 10.17226/24840.
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Page 192

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191 C h a p t e r 4 All technical findings from this research are integrated to develop guide specifications for bridges carrying light rail loading and light rail and highway traffic loadings. A holistic summary of the specifications is briefed in this section, while detailed contents are available in a separately published AASHTO document. 4.1 General The scope of the guide specifications is introduced along with notations and definitions. It is noted that the specifications are a supplement to AASHTO LRFD BDS providing comprehensive technical information necessary for bridge design. 4.2 Design Philosophy In compliance with AASHTO LRFD BDS, the design methodology of the specifications is based on LRFD. Various limit states are defined for service, strength, extreme events, and fatigue. Load factors and their combinations for bridge design are listed, depending upon loading con- figurations. To address the comfort of users, design criteria are specified from pedestrian and passenger standpoints. 4.3 Loads A variety of loads and associated forces to be considered in design of light rail bridges are discussed, including permanent loads and live loads. A standard live load model is presented to facilitate design processes, leading to uniform design outcomes. The DLA of light rail trains is stipulated, in conjunction with additional considerations on derailment events. Provisions on centrifugal force and braking force are followed. Several design articles are taken from AASHTO LRFD BDS, because these are both applicable to light rail and highway bridges (e.g., wind load on structures, earthquake effects, and thermal loading). This section concludes with articles related to rail–structure interaction and rail break. 4.4 Structural Analysis Analysis methods are concisely provided, followed by material behavior, modeling geometry, and boundary conditions. The contents of the approximate method of analysis encompass bridge decks, live load distribution for moment and shear, skew correction, and curved bridges. LRFD Guide Specifications for Bridges Carrying Light Rail Transit Loads

192 proposed aaShtO LrFD Bridge Design Specifications for Light rail transit Loads General discussions on the refined method of analysis, dynamic analysis, and analysis by physical models are given in accordance of AASHTO LRFD BDS. 4.5 Design Examples Six design examples are illustrated to help design professionals understand the use of the specification articles. Specifically, the following examples are worked: (1) simple span com- posite steel plate girder—Strength I moment, (2) continuous span composite steel plate girder—Strength I moment, (3) simple span composite precast prestressed girder—service stress checks and Strength I moment, (4) simple span composite steel plate girder—Strength I moment subjected to both light rail and highway traffic loadings, (5) simple span composite steel plate girder—other considerations, and (6) simple span composite steel plate girder— interior deck design

Next: Chapter 5 - Summary and Conclusions »
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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 851: Proposed AASHTO LRFD Bridge Design Specifications for Light Rail Transit Loads provides proposed specifications for bridges carrying light rail transit loading, including those subjected to both light rail and highway traffic loading. The proposed specifications and design examples are based on comprehensive response monitoring of five bridges carrying light rail transit vehicles in Denver, Colorado, and analytical programs for investigating the behavior of light rail bridges, live loads and associated forces, rail–train–structure interaction, and load factor calibration to implement the Load and Resistance Factor Design (LRFD) method. A standard live load model generates uniform design outcomes for any transit agency. Load factors are calibrated, particularly for the strength and fatigue limit states of light rail bridges.

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