Comparative analysis of different types of damage indexes of coastal bridges based on time-varying seismic fragility

When bridge is constructed in a seismic-prone area, different damage index analysis methods will cause errors in seismic performance evaluation of bridge. Focusing on time-varying chloride erosion, time-varying bond–slip, and time-varying damage indexes, this paper presents a methodology to carry out fragility analysis of bridge under earthquake, which can incorporate the various existing analytical methods of damage index of pier in a coastal environment. First, the mechanical properties of concrete and steel in the entire life cycle considering chloride erosion and the repair of damaged concrete of piers are introduced. Then, ground motion input, fragility analysis method, and time-varying attenuation analysis of the varies exiting damage indexes of piers are constructed. After that, a methodology to carry out the fragility analysis of bridges under earthquake is proposed. According to the proposed flowchart of the computational procedure, using a coastal bridge as an example to investigate the seismic performance of bridges. Results show that fragility analysis based on security is significantly more conserved than economy-based methods. The maximum difference between them appears on the side with smaller seismic intensity when damage degree is small, while it appears on the side with larger seismic intensity when damage degree is large.