Evaluating the Effectiveness and Optimal Design of Isolation Bearings and Fluid Dampers for a Highway Bridge Using a Fragility Function Method and Genetic Optimization

Modern seismic protection technologies in the forms of isolation bearings and fluid dampers can be used to improve the seismic responses of highway bridges. This paper aims to use the performance-based evaluation approach to investigate the seismic performances of a newly constructed highway over-crossing in California that is equipped with isolation bearings and fluid dampers. A simplified 2D bridge model representing the transverse response of the bridge is adopted that take into account of nonlinear behavior in bridge, isolation devices and fluid dampers as well as soil-structure interaction effects. Fragility curves are derived by PSDA for pier columns and base isolators first then combined into a composite system curve based on the repair cost ratio of these two components for each damage state. The efficiency of using isolation bearings and fluid dampers is investigated by comparing system fragility curves of three different cases, i.e., the as-built bridge, the isolated bridge, and the bridge installed with both base isolators and fluid dampers. Furthermore, utilizing a multi-objective genetic algorithm, the optimum combination of mechanical parameters of isolation bearings and fluid dampers are identified. The study shows that the optimum design of isolation bearings and fluid dampers are able to reduce the bearing deformation and deck acceleration simultaneously and minimize the overall damaging potential of the bridge.