For a train traveling over a bridge, the moving train will result in sequential moving loads on the bridge, while the bridge in oscillation will feedback its motion to the train as well. The vehicle-bridge interaction (VBI) takes places in such a coupling system (see Fig. 1). To solve for the two sets of equations of motion each written for the running train cars and bridge, which are coupled, the VBI system matrices must be updated and factorized at each time step in the time-history analysis [1]. This is a rather complicated procedure for a high speed train that consists of a number of vehicles running on a bridge. To overcome this computational drawback, this study proposed a two-stage technique for simplifying the complicated computational process by considering the fact that the self-weight of a train car is usually much larger than its vertical inertial force. First, we let the bridge subjected to only the moving static loads of the train (see Fig. 2). Then, the dynamic response of the bridge sustaining the train cars will be used as the source of excitation for the moving train cars. From the numerical parametric studies, the proposed two-stage technique can be reliably applied to the dynamic analysis of the VBI system for conventional HSR trains if the mass ratio of the train car to the bridge is smaller than 0.05.
