Seismic fragility analysis of coastal bridges considering different corrosion damage modes among multiple RC bridge columns

In a typical coastal bridge structure, the multiple reinforced concrete (RC) bridge columns possess different distributions of the atmospheric, splash-tidal, and submerged zone along the elevation, owing to the seabed topography and depth difference. Thereby, the corrosion damages are different among the multiple bridge columns. This phenomenon affects the bridge seismic fragility but has seldom been studied. Two main novelty of this study on the bridge seismic fragility are as follows. First, the variable corrosion deterioration rate along the height of one bridge column is considered. Second, the differences of the corrosion damages among multiple bridge columns are considered. Three sequential parts of research were conducted in this paper to bridge the research gap. (1) The bridge columns in one bridge were categorized into three types according to the corrosion damage characteristics. For each type of column, the life-cycle possible seismic failure modes were analyzed. (2) The corrosion processes of the coastal bridge columns in the three types were divided into two stages. The initial corrosion time and the time-dependent mechanical properties of the reinforcement were studied. (3) The seismic fragility of coastal bridges incorporating multiple bridge columns with different corrosion damages was analyzed by a case study. Research results indicate that for the multiple bridge columns in one coastal bridge, the time-dependent seismic failure modes are different due to different corrosion positions. Such differences should be considered when estimating the bridge’s seismic fragility in the service life. This paper provides the method to this complicated problem and also a case study to illustrate the method.