This paper investigates the derailment of trains moving on multi-span simply supported bridges with foundation settlements or rotations. Rail irregularities, train-track-bridge interactions, and wheel/rail separations were considered in the three-dimensional nonlinear finite element analysis. A moving spring-mass with separation and contact modes was used to validate the proposed finite element model. In the parametric study, finite element results indicate that foundation settlements or rotations cause sharp displacements between two simply supported girders, which generate large train derailment coefficients. The train derailment coefficients rise with increased train speed, and they greatly increase at a critical speed. The time history displacements of a train obviously contain a jump when it passes a location with foundation settlements or rotations, so a warning system can be established using this measurement.
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