Seismic fragility analysis of corroded reinforced concrete bridges in Bandar Abbas, Iran

The seismic performance of reinforced concrete (RC) bridges in the coastal environment of Bandar Abbas, Iran, was investigated. Probabilistic seismic hazard analysis results of the region, covering a radius of 150 km keeping Bandar Abbas as the centre, are first presented. To determine the dominant earthquake scenario characterised by magnitude and source-to-site distance, disaggregation of peak ground acceleration (PGA) hazards corresponding to mean return periods of 475 and 2475 years was carried out. Results of the disaggregation analysis were then used to select a ground motion set for non-linear dynamic time history analysis of a bridge. In the next step, the effects of chloride-induced corrosion of the bridge columns, including degradation of steel bars, cover concrete and core concrete properties, were considered at different time steps in the bridge's service life. Finally, seismic fragility curves of the corroded bridge at selected time steps were developed based on multiple-stripe analysis results and the maximum likelihood approach. Based on these analyses, to ensure the appropriate seismic performance of a RC bridge over its service life, it is proposed that the design PGA should be increased approximately by 37%.