Seismic Response and Fragility Analysis of a Single-Pylon Cable-Stayed Bridge Considering the Construction Process

The structural system, construction stage, and damper parameters have significant influences on the seismic performance of single-pylon cable-stayed bridges. To investigate the seismic responses of the bridge under various construction stages, nonlinear finite-element models were established in OpenSees for the pylon stage, large cantilever stage and completed bridge stage. Parametric analysis was carried out to investigate the effect of pylon-to-girder connection and viscous dampers. Incremental dynamic analysis, parametric analysis and fragility analysis were carried out with the finite element model. The results indicate that, compared with the semi-floating system, the pylon–girder rigid-connection system provides stronger longitudinal restraint, leading to smaller pylon-top displacement, girder displacement, and bearing displacements, but results in a higher bending moment and curvature demand at the pylon base. Installing viscous dampers in the longitudinal direction can reduce bearing displacements. The probabilities of girder unseating damage and pylon-base bending failure continuously increase as construction progresses from the pylon stage to the large cantilever stage and finally to the completed-bridge stage. The fragility analysis further shows that the rigid-connection and semi-floating systems exhibit different vulnerability characteristics at both the component and system levels.