Influence of Riverbed Scour on the Performance of Bridges Subjected to Lateral Seismic Loads

Many bridges in seismic prone regions suffer from serious foundation exposure caused by scouring of the riverbed. In this study, the seismic performance of a bridge at various scour depths is assessed using a nonlinear static procedure based on the capacity spectrum approach. The performance limit of the bridge is identified in the capacity spectrum. The level of seismic intensity, characterized as peak ground acceleration, 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 intensities correlated to the performance limit at different scour depths. Results emphasize that for a bridge originally equipped with sufficient foundation strength, an improved seismic performance is observed when the scour depth is shallow. Once the scour depth exceeds a critical level, the seismic performance of the bridge is controlled by unexpected damage in the foundation. The seismic intensities correlated to the performance limit of the bridge decreases, and the seismic performance declines rapidly when the scour depth increases. The influence of structural properties and soil profile type on the seismic performance of a bridge at different scour depths is also investigated. The minimum scour depth, which causes the difference in seismic performance limit of a bridge from the original design, reduces with a decrease in the superstructure mass or soil-foundation system strength. The findings of this study help engineers evaluate the need for foundation retrofitting, particularly to ensure satisfactory seismic performance for bridges that undergo riverbed scour.