Variation in Seismic Performance of Bridges Caused By Riverbed Scour

Abstract eng:
This paper applies the capacity spectrum approach to evaluate the seismic performance of a bridge at different scour depths. The capacity spectrum is constructed based on the lateral pushover curve obtained from finite element analysis. During the pushover process, the forces applied on the superstructure and the pile-cap are assessed by the modal analysis of a bridge bent; these forces are adjusted after reaching the yield limit states of the structure to account for the effect of stiffness change. The performance limit of the bridge is identified in the capacity spectrum, and the seismic demand required to reach this performance limit is determined accordingly. The influence of riverbed scour on the seismic performance of a bridge is assessed by comparing the seismic demands correlated to the performance limit at different scour depths. Results highlight that for a bridge originally equipped with sufficient foundation strength, the seismic demand correlated to its performance limit first increases with increasing scour depth. This result indicates an improved seismic performance when the scour depth is shallow. Once the scour depth exceeds a critical level, the seismic performance of the bridge is controlled by the unexpected damages in the foundation. The seismic demand correlated to the performance limit of the bridge decreases, and the seismic performance declines rapidly when the scour depth increases.

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