Abstract: To investigate the seismic response evolution of offshore bridges under the coupled effects of main-aftershock sequences and chloride-induced erosion,a time-dependent damage finite element model of a three-span,three-column simply supported bridge was established based on energy dissipation theory and static pushover analysis.Seismic time-history analysis was conducted to obtain key response indicators,including the maximum displacement and residual displacement at the pier top,as well as the proportion of cumulative hysteretic energy generated at the pier bottom during aftershocks.The results show that structural durability degradation significantly affected the seismic responses:under the same seismic excitation,the maximum pier-top displacement of long-term service bridges increased by at least 10%,with a maximum increase of up to 43%,compared with newly built bridges.When subjected to high-intensity earthquakes,the residual displacement at the pier top continuously increased with service time,rising by 66%,121%,and 163% after 50,75,and 100 a of service,respectively,compared with new bridges.Aftershocks induced noticeable cumulative damage at critical locations such as the pier bottom,with the cumulative hysteretic energy accounting for an average of 14.08% of the total energy dissipation during the main-aftershock sequence,reaching a maximum of 25.3%.Therefore,it is recommended that both the energy contribution of aftershocks and the effect of durability degradation be considered in the seismic design of offshore bridges.

Key words: main-aftershock sequences, chloride ion erosion, simply-supported bridge, maximum displacement, residual displacement, hysteresis curve