Seismic Performance Assessment of Highway Bridges Under Scour Effects

Bridge scour is a common cause of highway bridge failure. To make sure that a highway bridge is capable of resisting structural degradation due to scour in addition to other natural hazards, development of a multi-hazard approach is necessary. Towards this goal, the current paper studies the combined effects of scouring and earthquake on the performance of reinforced concrete (RC) bridges. The extent of scour represented by scour depth is estimated and its associated uncertainties are considered. Based on the probability distribution of scour depths obtained from Monte Carlo simulations, risk curves are developed to find the probability of occurrence of scour at the location of bridge. To evaluate the effects of scouring on seismic performance of bridges, detailed models of two- and three-span case study bridges are generated. From the nonlinear time-history analysis of bridges, maximum structural responses and ductility ratios are calculated and bridge fragility parameters are estimated for a range of scour depths. The developed fragility curves clearly show that the lateral load bearing capacity of bridge decreases with the increase in the scour depth. This makes the bridge more vulnerable to the future earthquakes and increase the probability of exceeding any specified damage state.