Conclusion
Seismic retrofit measures tend to focus on individual component response, less research has been carried out on the cable-stayed bridge performance as a system, and the optimal parameters of retrofit devices have not been addressed in the literature. This study presents a methodology to evaluate the optimal parameters of FVD for cable-stayed bridges using the system-level fragility function. JPSDM and Monte Carlo simulation are employed to obtain the system fragility of cablestayed bridges by accounting for the contribution of multi components to the global damage state. Optimal parameters of FVD are derived by directly evaluating the system-level fragility curves of the cable-stayed bridge equipped with these given FVD. A case study bridge, Polonggou cable-stayed bridge, retrofit with varied FVD is employed to exemplify the methodology. Details of the numerical modeling include nonlinear analysis, the uncertainty treatment, limit state capacities, contribution of critical components to the bridge performance as a system, and so on. For illustration purposes, component fragility curves are developed, which indicate that retrofit measures alters the relative vulnerability of the different components. The system-level fragility curves as well as component fragility curves are compared before and after the application of FVD with different parameters. The results indicate that a given parameter of the FVD may have a positive impact on some components, yet lead to a worse performance of the bridge as a system. Thus, in order to obtain comprehensive insight of bridge performance and derive the accurate optimal parameters of FVD, it is necessary to consider the fragility based on bridge system.
