Prediction of the required support length at expansion bearings in the context of assessing the seismic vulnerability of existing bridges

Loss of bridge deck supports is one of the major failures observed during past earthquakes. Deck collapse due to loss of support has been observed mainly on simply supported bridge structures with insufficient support length at expansion bearings. To accommodate the large displacements induced by seismic movements and to avoid bridge collapse, modern seismic standards and regulations require a minimum support length at expansion deck bearings. This paper presents the state of knowledge on the empirical support length equation and the main geometric parameters influencing the required support length at deck expansion bearings. It also presents the results of the parametric study performed on typical existing single and multi-span simply supported bridges subjected to seismic loads typical of Eastern Canada. The results allowed to identify and describe the key geometric parameters influencing the nonlinear responses of existing bridges, evaluate their relative influence in terms of displacements and ductility associated with the loss of deck supports. It also compares the current empirical equation with predicted displacements and proposes an equation more suitable for predicting expected displacements (lower than code values) in an evaluation framework for judging the seismic vulnerability of existing such as the bridge models considered in this study.