Dynamic Analysis of Steel Bridges Under Moving Train Loads

In this paper, dynamic analytical model of train-bridge system is established, with the vehicle wheel hunting as the self excitation of the system. The train-bridge system equilibrium equations are derived and a computer software for solving the problem is worked out. Whole histories of the train passing through the bridge are simulated on computer. Dynamic responses of the truss and their distributions versus train speeds are calculated, and are compared with those from field measurements. Discussions are concentrated on spatial coupling problems occurring in a real double track truss bridge acted on by a train running at speeds of 100km/h – 300 km/h.Results of calculations and measurements show that the hunting movement of train wheel-sets and the deflection of truss stringer play important roles in the train-truss system vibration. At certain train speeds, the excitation a case either the lateral or the vertical responses or both of them are amplified. Also, as for a double track truss bridge, the lateral and the vertical vibrations are coupled with each other when a train runs on one track. The torsional vibration induced by eccentric loading makes the lateral displacements and the amplitude greater. This should be taken into account in dynamic analysis and design of high speed railway bridge.