The rail pad stiffness is one of key design parameters of the track structure, affecting the load distribution along the rail and the dynamic behavior of the track. The rail pad stiffness, however, can be increased under accumulated train load and environmental load, i.e., temperature change, due to the nature of resilient rubber. This study investigates the causes and prediction model of the stiffness increase of the resilient rail pads used in the ballasted and concrete slab track in high-speed railway. For this purpose, in-situ rail pads were taken from several sites, and the static and dynamic stiffness was measured. Also, the repeated load test and accelerated heat aging test on new rail pads in the laboratory have been performed. Based on the test data, proposed is a mathematical model for predicting the increase of the rail pad stiffness according to passing tonnage and elevated temperature.

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