Multi-hazard fragility analysis of cross-sea cable-stayed bridges cable bent tower under seismic-wind combined action

Cable-stayed bridges are one of the primary bridge types for large-span cross-sea bridges, especially in earthquake-prone regions. These bridges face not only the threat of seismic disasters but are also continuously exposed to the adverse effects of strong winds. Under the combined influence of both earthquakes and wind loads, the safety of cable-stayed bridges has become a key focus in disaster-resilience research. However, research on the disaster-resilient performance of cable-stayed bridges under multi-hazard interactions remains relatively limited. Therefore, this study focuses on the multi-hazard fragility of cross-sea cable-stayed bridges' main load-bearing component, the towers. First, a finite element model of the entire cable-stayed bridge is developed, followed by the construction of a cable-stayed bridge tower model through static and dynamic equivalence. Based on the Pacific Earthquake Engineering Research Center (PEER) database, seismic wave data is selected. Different heights of fluctuating wind speeds for the tower are simulated and converted into concentrated force time-history curves. Through nonlinear time-history analysis, the multi-hazard fragility of the tower in cable-stayed bridges under seismic-wind combined action is studied. The results show that seismic-wind combined action leads to increased dynamic responses of the tower of cable-stayed bridges. Taking the case of slight damage to the tower under the combined action of rare seismic and different wind speeds (30, 40, 50 m/s) as an example, the probabilities are 15.9 %, 17.0 %, and 20.1 %, respectively. Compared with the seismic action alone, there was an increase of 1.3 %, 2.4 %, and 5.5 % respectively. Under seismic-wind combined action, the fragility of the tower significantly increases. However, as the seismic intensity increases, the influence of wind speed on tower damage gradually decreases, and the extensive damage degree of the tower is mainly controlled by seismic action.