Cyclic and Fragility Analysis of a Corroded Bridge Reinforced by Steel Plates under Mainshock and Aftershock Sequences

The corrosion of steel bars embedded in concrete structures results in the degradation of their structural capacity. In earthquake-prone zones, the corroded structure may be considerably vulnerable under mainshock–aftershock sequences relative to a single mainshock. Therefore, it is necessary to reinforce corroded structures to resist potential natural hazards. In this study, the effects of both pitting and uniform corrosion on the structural capacity of a bridge pier before and after strengthening were studied. Subsequently, the failure probability of a corroded bridge was calculated, which is conditional on the corrosion level, steel plate thickness, and ground-motion intensity. The findings implied that both pitting and uniform corrosions significantly reduced the capacity of the bridge pier, particularly pitting corrosion. The fragility curves showed that with an increased thickness of the steel plate, the probability of failure decreases if the intensity of the mainshock–aftershock sequences is higher than the threshold value. In addition, the threshold value has a high correlation with the thickness of the steel plate and the corrosion ratio.