Dynamic Amplification of Transit Loads due to Derailment Impact

This work presents the results of a study on the amplification of live load in the vertical direction due to derailment of a train, i.e. derailment impact. The study was performed using numerical models based on a single span precast prestressed concrete girder bridge, with a range of typical stiffness values. Two representative transit vehicles were considered. The transit vehicles were modeled in LS-DYNA, accounting for all geometry, stiffness and damping of the car body and suspension system. The bridge was idealized as a spring-supported rigid surface, with the spring stiffness related to the computed stiffness of the full composite bridge structure. The model simulated the condition of the vehicle derailing and falling vertically through the height of rail and supporting plinth to impact the deck of the bridge. Two different drops were considered, representing the height of rail only and height of rail plus plinth structure. Derailment impact was estimated as the difference between effects of the static load applied to the rails and the dynamic force due to the derailed vehicle impacting the deck. The study also examined the effects of structure stiffness by considering two additional values of stiffness values, representing the range of stiffness expected in typical transit structures. The results showed that the peak amplification of live load due to derailment varied from 300% to 625% over the range of stiffness and vertical train drop considered. The results are based on simplified conditions and compare only peak amplification but are high enough to warrant a more detailed examination of and approach to the derailment forces currently used in North American codes to determine more accurate loads.