Effect of Axle Load Spreading and Support Stiffness on the Dynamic Response of Short Span Railway Bridges

In dynamic analyses of railway bridges, the train axle loads are often modeled as moving point forces. However, these point forces are further distributed to the bridge structures through the ballast, which can lead to large reductions in the bridge response, especially for short span bridges. For this reason, the Eurocode prescribes distribution of the axle loads over three adjacent sleepers. In this paper, the axle load distribution is first studied using a plane finite element analysis, and based on this, a triangular load distribution is proposed. Then, numerical simulations are performed to compare the effect of this load distribution with the one prescribed by the Eurocode. Both simply supported bridges and bridges with integrated backwalls, all with span lengths less than 10 m, are studied. For the latter bridges, the effect of the stiffness of the foundation has been studied by adding springs at the supports.