Experimental investigation of the modal response of a rail span during and after wheel passage

This paper examines the vibrations of a rail span (rail section between two consecutive sleepers) during and after the passage of a rail car’s wheel as well as under impact hammer excitation. In literature, the dynamic response of railway tracks under moving loads has been studied extensively. Many of these studies focus on the responses in relation to displacement/force-time histories and wave propagation parameters. These responses are investigated for the time instants when rail car wheels transverse over the rail spans of interest. In this context, an investigation of responses in relation to modal parameters during and after moving loads might provide additional information. Such information can be used to examine how the loading and additional masses induced by the moving wheels affect the dynamic responses. To this end, field tests were carried out at Transportation Technology Center Inc. (TTCI) facility in Colorado, U.S. First, to find the flexural modes of a rail span under no loading, data was collected from three accelerometers placed on the span under vertical impact hammer excitation. Next, the accelerometers were placed underneath the rail span, and data was collected while a rail car traveled over the span. The signal segments corresponding to during and after a wheel passage were analyzed for the identification of modal parameters. The comparison of the results demonstrated that the frequencies of the rail span increased as the loading induced by the wheel increased.