Numerical investigations into the behavior of light rail bridges

Abstract

This paper presents various technical aspects related to bridges under light rail gravity loadings, including flexural and shear responses, deflection, serviceability, and dynamic load allowance. Unlike highway and conventional rail bridges, the behavior of light rail bridges has scarcely been reported; thus, limited information is available. Five types of benchmark bridges are designed with steel plate girders, prestressed concrete boxes, reinforced concrete T-girders, prestressed concrete I-girders, and closed steel box girders. Three-dimensional finite element models are developed to predict the behavior of these bridges when loaded by four representative light rail trains operated in the United States (Colorado, Massachusetts, Minnesota, and Utah), which results in 4,932 cases. Parameters for investigations involve structural configurations (simply-supported and continuous spans), geometries (girder spacing, span length, curvature, and skew), and loading characteristics (one-track-loaded and two-track-loaded with one to four articulated trains). A comparative study is conducted to evaluate the applicability of existing design specifications (highway and heavy-haul train loadings) that are frequently referenced in light rail bridge design. The flexural moment of the bridges is controlled by span length, the number of loaded tracks, and the axle spacing of the articulated trains. Contrary to the implications of horizontal curvature, those of skew angles are significant in altering the responses of the bridges concerning moments and fundamental frequencies. The deflection criteria of the existing specifications are not applicable to the light rail bridges; consequently, an alternative approach is suggested. Regarding dynamic load allowance, the predicted values are generally lower than those used in practice.