Field and numerical investigation of the effect of under-sleeper pads on the dynamic behavior of railway bridges

There is a growing need to minimise vibrations of railway structures, especially the railway bridges, due to the increasing speed of trains. Various methods are used to reduce the effects of vibration on bridges. One of the methods is using under-sleeper pads. In this study, a real railway bridge – located in the northern district of Iran – with two spans and a free span length of 7 m was selected for the investigation of the effect of under-sleeper pads on the reduction of vibrations imposed on railway bridges. Field experiments – including the installation of an accelerometer to measure the accelerations beneath bridge decks, on the rail web, and next to the sleeper, and also the installation of Linear variable differential transformers (LVDTs) to measure the displacements of midspan point of bridge decks – were conducted. The effect of under-sleeper pads on the reduction of vibration accelerations, displacements, and moments of bridge midspan was investigated by developing numerical models of the bridge and validating its results through experimental outputs. The modeling predicts that the reduction of acceleration imposed on the deck in the first and second spans was different; the reduction effects in the first span were higher, where there was 58% reduction after using under-sleeper pads beneath the sleepers. There was a 15% decrease in the displacement of the bridge deck when under-sleeper pads are used. Similar results were obtained for the midspan moment of the bridge which reduced by 16%.