Influence of Rail Pad Stiffness and Axle Loads on Dynamic Responses of Train-track Interaction with Unsupported Sleepers

Increasing the axle load causes track deterioration and permanent settlement of the ballast layer. In the ballasted railway tracks, due to the inevitability of unequal settlements in the ballast layer, part of the rail due to high flexural rigidity will become suspended, which causes the formation of the track with unsupported and partially supported sleepers. This situation increases rail vertical displacement and reactions on adjacent sleepers. Several models have been presented to study the effect of unsupported sleepers on dynamic responses of train-track interaction. In this paper, by applying mathematical model, unsupported and partially supported sleepers have been modeled and equations of motions for train-track interaction were written by assuming nonlinear behavior of rail and wheel contact. Following by solving the equations via numerical integration in the time domain, the effect of axle load and pad stiffness on rail vertical displacement were investigated. Results of the analysis suggested that through increasing the axle load rail displacement increased by 13 % in the unsupported sleeper and from 5 to 10 % in the partially supported sleeper. Also, by increasing the pad stiffness rail displacement decreased from 2 to 13 % in the unsupported sleeper and from 1 to 6 % in the partially supported sleeper.