Seismic fragility analysis of single‐pylon double‐plane highway cable‐stayed bridge

Abstract Single‐pylon double‐plane separated cable‐stayed bridges have aesthetic and economic benefits. Nonetheless, its single‐pylon load‐bearing attribute leads to seismic behavior that markedly diverges from that of twin‐pylon structures. This paper examines the West Fourth Ring Olympic Sports Bridge in a city as an engineering case study. A sophisticated nonlinear finite element model was developed utilizing the OpenSees platform. Comprehensive application of incremental dynamic analysis (IDA) and probabilistic seismic demand models (PSDMs) facilitated systematic seismic fragility evaluations at both the component and system levels. The findings demonstrate that bearings are the most susceptible components. In the event of infrequent seismic activity, the probability of moderate damage to the mid‐pier bearings is 20.36%; damage to the pylon and piers is predominantly concentrated toward their bases. In the event of exceedingly rare earthquakes, the likelihood of minor damage at the pylon base is 45.29%, whereas at the pier base under PGA = 1.0 g, the probability of minor damage escalates to 99.74%, although the probability of severe damage remains exceedingly low; the overall system risk surpasses that of any singular component. In the context of unusual earthquake intensity, the upper‐bound probabilities for moderate damage, substantial damage, and total collapse of the system are 67.50%, 23.66%, and 4.73%, respectively, underscoring the imperative for probability‐based evaluation at the system level. The analysis reveals a distinctive seismic performance pattern for this single‐pylon system, characterized by ‘vulnerable bearings, ductile pylon and piers, and concentrated system risk,’ which fundamentally differs from twin‐pylon configurations offering a quantitative foundation for the robust seismic design of analogous single‐pylon cable‐stayed bridges.