Keywords: train-track-bridge interaction, transition zones, substructuring model.

In this paper, the dynamic response of a high speed train-track-bridge system is analyzed for different transition zone configurations. Transition zones appear in railway track sections that present abrupt changes in the vertical track stiffness. These sections require usual maintenance works due to the wear of track components or to ensure track geometry. The use of transition wedges and under sleeper pads (USP) on the bridge are two usual solutions used in order to smooth the apparent track stiffness between the track on the terrain and the track on the bridge.

The current work presents the train-track-bridge system studied and the different transition wedge configurations that are analyzed. The paper attempts to clarify the effect of the number and dimensions of the material layers of the transition wedges. Also the influence of the bridge flexibility and the use of USP in the dynamic response of the system is analyzed.

A substructuring model, which combines physical (vehicle) and modal substructures (rails, sleepers and bridge), is used to obtain the dynamic response of the coupled system. The modular feature of the system model allows the building of the train-track-bridge system for different transition zone configurations in an easy way.

The results show that the flexibility of the bridge should be taken into account when a study of a transition zone would be performed. For the system studied, the dynamic response considering a flexible bridge is greater than the response for the rigid bridge.

The dynamic response of a train running on a transition zone greatly depends on the train velocity, except for a resonance behaviour of the train-bridge system. This resonance behaviour, that appears at a given train velocity, depends on the train-track-bridge system properties; mainly, the bridge flexibility and the USP stiffness. Lower values of USP stiffness greatly reduce the magnitude of the wheel-rail contact force.

The system dynamic response is slightly influenced by the transition wedge configuration. In that sense, the contact force response depends basically on the apparent track stiffness.

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