Time-varying seismic fragility analysis of bridges under the condition of the scour and freeze–thaw cycles

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This article proposes a seismic fragility analysis framework of bridges, which considers the freeze–thaw cycles and scour comprehensively. The time-varying seismic fragility analysis method is used to analyse the bridge system based on the degradation law of mechanical properties of concrete under the freeze–thaw cycles, combined with the uncertainty of earthquake, scour depth and freeze–thaw cycles. Under the condition of the scour, with the growth of service time, the seismic fragility of piers and bearings increased and the exceeding probability of bearing is higher than the pier, which makes the bearing more easily damaged than the pier in the case of an earthquake, thus reduces the seismic damage of the pier. The plastic hinge of the bridge pier transfers from the immersion zone to the freeze–thaw zone in freeze–thaw cycles. In this process, the curvature in the freeze–thaw zone grows up, dissipates seismic energy and leads the pier’s fragility to decrease before the plastic hinge transfer. When combined with the scours and freeze–thaw cycles, the failure probability of the pier is slightly lower than that of only the scour action due to the phenomenon of plastic hinge transfer.