Seismic risk analysis over the entire service life of a sea-crossing cable-stayed bridge based on fragility

Cable-stayed bridges located in seismic-prone regions face durability-related degradation from environmental corrosion throughout their service life and seismic hazards from sudden earthquakes. To investigate this issue, this study uses the Hong Kong-Zhuhai-Macau Bridge as a case study. Nonlinear finite element models for cable-stayed bridges are established at different stages of their service life using OpenSees. The models consider material degradation over time and analyze the time-dependent seismic fragility and earthquake risk of primary components and systems within the cable-stayed bridge. The research findings show that the fragility of diverse components and systems gradually increases as the service life of cable-stayed bridges progresses, although the overall escalation is relatively modest. In extremely rare earthquake, the probability of severe damage and complete failure in seismically-damped cable-stayed bridge systems is significantly lower compared to non-seismically-damped counterparts (48.5% and 24% lower, respectively). Throughout the entire service life, the seismic risk of cable-stayed bridge towers and piers remains below 5%, while the seismic risk of the bridge system is mainly influenced by components with higher seismic risks, such as the bearings. On the other hand, components with lower seismic risks, like the towers and piers, exert minimal influence on the overall risk of the cable-stayed bridge system. The seismic risk of the cable-stayed bridge system remains relatively stable over the full duration of service. Taking the initial service time as an example, the implementation of seismic damping measures results in a reduction of earthquake risk for slight damage by 58.45%, moderate damage by 14.41%, severe damage by 2.52%, and complete failure by 0.32%. It should be noted that these reported risk reductions are relative to the non-damped system and are based on the first-order method, which may overestimate absolute risk. Nevertheless, the comparative effectiveness of dampers is clearly demonstrated. Seismic damping measures significantly enhance the overall seismic performance of the cable-stayed bridge, reducing both its fragility and earthquake risk.