Laboratory Study to Determine the Effects of Tie Pad Stiffness on Attenuation of Strain in Concrete Ties


The effect of tie pad stiffness on the bending moments produced by impact loading of concrete railroad ties was investigated in laboratory tests. Controlled impact loads were applied to a one-tie test arrangement in which the pads were interchanged. Beginning with a rigid plastic pad currently in use on the Northeast Corridor track, the test loads reproduced the time history of bending strain which had been previously measured in track. It was also found that the initiation of bending cracks and their subsequent propagation closely matched crack development observed in track.
Using the rigid plastic pad as a reference, the ability of a variety of tie pads to attenuate impact response was measured at load levels below the cracking limit. The stiffness of each pad was measured statically and at load rates of 9-10 Hz. It was found that major reductions in pad stiffness can significantly reduce the effect of impact loading, but that the stiffness measurements of flexible pads do not provide a reliable measure of impact attenuation properties.