A 3-D dynamic analysis model for a coupled train-bridge system is established. The vehicle subsystem is modeled by multibody dynamics and each 4-axle coach is simulated as a 27-degree-of-freedom model. For the bridge subsystem a 3-D rail-ballast-beam finite element model is created, considering the elasticity and the continuity of the track system. The dynamic interaction between the bridge and the train is realized through the contact forces between the wheels and the track. Track irregularities and wheel hunting are included. The track irregularities are generated with the German high-speed track spectra, whereas the wheel hunting is simulated by a sinusoidal function with a random phase. The equations of motion of the coupled train-bridge system are derived by representing the bridge subsystem through its vibration modes. The proposed formulations are then applied to the Sesia viaduct located on the new Italian high-speed line between Torino and Milano. The dynamic responses of the bridge subjected to an Italian high-speed ETR500Y train are calculated and some results are compared with the measured data. The resonant train speed of the train-bridge system is discussed, and the running safety and the stability of the train vehicles on the bridge are evaluated. The results show that the Sesia viaduct is stiff enough in both vertical and lateral directions, fulfilling the design criteria for high-speed train passage. The numerical method proposed in this paper can be used to predict efficiently the dynamic behavior of coupled train-bridge systems with reasonable computational effort.
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