Seismic MainShock-AfterShock response assessment of reinforced concrete bridges pre-exposed to flood induced local scouring

Flood may cause the removal of bed material or local scour before seismic activity for bridges located at seismically active as well as flood-prone sites. That, in turn, causes loss of lateral support at the foundation level and this phenomenon effectively reduces the lateral stiffness of the bridge system. These events may take bridge structure to a relatively higher vulnerability state during sequential MainShock-AfterShock action. The present study aims to assess the vulnerability of reinforced concrete bridges (2-span and 3-span) under a multi-hazard scenario of flood-induced scour and sequential seismic events. For this investigation, an appropriate bridge site flood hazard curve derived-local scour depths and ground motion records that come under different hazard levels are adopted. Two-dimensional nonlinear bridge models are developed in suitable finite element platform incorporating soil-pile interaction of bridge sub-structure using recommended nonlinear P-Y springs. To simulate local scour conditions, P-Y springs have been removed up to scour-affected depth to depict the loss of all-around lateral support. Nonlinear time-history analyses are carried out for MainShock alone case and MainShock-AfterShock sequential occurrence for no scour condition as well as for various scour cases. The probabilistic seismic demand model regression fits are established, and associated fragility curves are developed corresponding to different damage states.