RESPONSE OF STEEL RAILWAY BRIDGES ON 25T ROUTE DUE TO TRAIN LOADS

Abstract

Dynamic behavior of bridges is a complex phenomenon depending on span and member sections of the bridge, weight of rolling stock and as well as the adopted track geometry. Complete dynamic analysis for bridge-vehicle interaction is adopted to determine response of the bridge to train loads, but it is, to some extent, rigorous and cumbersome. Therefore current codes prescribe a simple multiplication factor which basically gives the fraction of live load to be taken into account for the dynamic effects. In the present study, dynamic analysis has been performed for two plate girder bridges, 12.2 m span & 24.4 m span, and two welded truss bridges, 30.5 m spans & 76.2 m span. The moving load input parameters are defined by the train definitions. There are I 125T loading trains (25T-P1 to 25T-FE2). These trains are classified as freight and passenger trains depending on loads and usage. Trains are modeled as a series of concentrated axle loads moving across the bridge. The analysis is carried out for various speeds. SAP2000 package is used for the analysis. The linear dynamic time history analysis is carried out for various train-bridge combinations. In general, it has been observed that the bridge displacement increases, marginally, with an increase in train speeds. However due to different axle loads and axle spacing in the trains considered and the variation of type and span of bridges including stiffness distribution of constituent elements, no generic trend can be established. The non-resonant response dominates the bridge response as exhibited in both the acceleration and displacement power spectra. The critical speed of the trains consistent with the bridge spans is not likely to be realized with the existing locomotives or the track geometry adopted.