Time-dependent seismic demand and fragility of deteriorating bridges for their residual service life

Coastal bridges that are exposed to marine environments always suffer serious corrosion, which degrades their structural performance during the long-term service period. This paper investigates the time-dependent seismic demand and fragility of coastal bridges for their residual service life. First, the equal exceeding probability method was established to consider the reduction in the seismic hazard level for the residual service life of the structures. A finite element model of sound and aging structures was built by analyzing the different corrosion characteristics of bridge columns in the atmospheric zone, splash and tidal zone and submerged zone due to chloride penetration in concrete. The incremental dynamic analysis method was adopted to analyze the seismic demand and establish the fragility curves of the sound and aging bridges under both the design spectral acceleration and the reduced earthquake inputs for comparison. The results of this analysis indicate that the seismic demand of the structure significantly decreases, and the probability of failure of the structural system does not support the common opinion of increasing in the residual service period, if the shortening of the service period is considered in the analysis.