Derailment mechanism of trains running over bridges during strong earthquakes

This paper examines the seismic safety of high-speed railway (HSR) trains running over bridges during strong earthquakes. It develops an original seismic vehicle-bridge interaction (SVBI) analysis scheme to investigate the response of both the vehicle system and the bridge system. The study models the train vehicles as three-dimensional (3D) multibody assemblies. All components of a vehicle are assumed rigid bodies connected with springs and dashpots, representing the vehicle suspension system. The 3D bridge is simulated using the finite element method (FEM). To determine the contact point and the direction of the contact forces it considers the practical nonlinear profiles of wheels and rails. The normal contact forces are derived from kinematic constraints as Lagrange multipliers. Detachment occurs when a normal contact force becomes zero. The study formulates the contact-detachment transition along the normal direction of contact as a linear complementarity problem (LCP) and assumes impact follows Newton's law. The calculation of the tangential creep forces due to the rolling contact is based on a nonlinear Shen-Hedrick-Euristic creep model. The proposed wheel-rail contact model can capture directly different contact phenomena, including flange contact, detachment, uplifting, climbing, derailment, and re-contact. The results underline the importance of a realistic analysis of the SVBI during seismic shaking. They show that seismic induced vibration of the bridge reduces both the comfort and the safety of the vehicles travelling over the bridge, compared to same vehicles travelling on the ground. For most examined cases with different wheelsets, the detachment of a wheel happens when the other wheel belonging to the same wheelset is in flange contact. The derailment of the wheel takes place when the wheel rolls over the rail head.