American Concrete Institute ACI Structural Journal January 2019
Evaluation of Prestressed Concrete Bridges under Light Rail Loading
by Yail J. Kim and Yongcheng Ji
Newswise — A field work study of four bridges in Denver, Colorado was conducted to assess the behavior of prestressed concrete bridges carrying light rail transit loadings. Light rail systems are a salient transportation component in urban communities, and have been adopted by most major cities in the U.S. owing to their convenient operation and environmental friendliness.
The behavior of light rail bridges, however, is significantly unexplored relative to bridges subjected to conventional heavy-haul and high-speed trains and, consequently, practice is based on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specification, the American Railway Engineering and Maintenance-of-Way Association (AREMA) manual, and other agency-specific design guidelines.
The four bridges were selected to investigate static and dynamic responses when loaded, including flexural behavior, passenger occupancy, statistical properties, live load distributions, natural frequencies, and user comfort (Figs. 1 and 2). Three-dimensional finite element models are developed to complement in-situ findings.
Results of the study indicated that the measured train loadings were statistically stable and their probability distribution was Gaussian. Live load distributions estimated by the Lever Rule and the equations specified in the AASHTO LRFD Bridge Design Specification were conservative (overly conservative for interior girders) when compared with site-based distributions. To facilitate bridge design, live load distribution factors for light rail trains should be developed or the AASHTO equations recalibrated to meet their loading characteristics. Existing criteria for deflection control were not usable for light rail bridges. An assessment on the serviceability of the bridges clarified that user comfort (pedestrians and passengers) was not a concern for light rail transit systems. Nonetheless, if a light rail bridge accommodates frequent pedestrians, a refined analysis appears to be necessary to avoid serviceability problems.
The research can be found in a paper titled “Evaluation of Prestressed Concrete Bridges under Light Rail Load,” published by ACI Structural Journal.
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