City tram collisions are simulated using multi-body dynamics. The aim of this paper is to investigate the collision-induced derailment. Simulation results demonstrate that the corner obstacle collision scenario defined in EN 15227 is mainly focused on the energy absorption process. Due to the large impact angle (45 • ), it is unlikely for a city tram to comply with this scenario without derailment. In order to avoid derailment, the maximum impact angle between city tram and oblique obstacle should be reduced to 25 • . Moreover, some influence factors are analysed, such as mass of loaded passengers, friction coefficient, impact angle, etc. Derailment phenomenon is shown to be significantly dependent on these parameters. Two measures are proposed to prevent the collided city tram from derailment. One is using secondary lateral dampers to absorb collision energy. Another is increasing the lateral stiffness of secondary springs as well as the lateral clearance, so that more collision energy can be stored in the suspension. With these measures, the safety against derailment can be improved.
Uneven subgrade settlement associated with rail deflection occurs mainly in the bridge–embankment transition zones of high-speed railways. An iterative method of computation is proposed for studying such uneven settlement in these zones. A vehicle–track–subgrade model is used to investigate the vehicle–track interactions and the deviator stress field of the transition zone, and a soil cumulative plastic strain model is used to obtain the deterioration process of uneven settlement in the transition zone. Results indicate that uneven settlement caused by train loads in the transition zone tends to plateau at 40,000 repeated load applications. Sub-grade settlement changes abruptly in the first measured 5 m, as well as from 25 to 30 m from the abutment; these two regions should be adequately strengthened and should receive more attention for track maintenance.
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