Application of Micro-GA for optimal cost base isolation design of bridges subject to transient earthquake loads

Seismic isolation and energy dissipation systems are innovative strategies for seismic design and upgrade or retrofit of bridges. In a retrofit design, base isolation devices can be easily incorporated into existing bridges to replace conventional bearings and to improve the overall structural performance. In this paper, an optimal cost base isolation design or retrofit design method for bridges subject to transient earthquake loads is studied. The goal of this study is to push forward the concept of retrofit design optimization of structures using this isolation design as an example. This is achieved by combining nonlinear time history analyses with an optimization procedure to select base isolators that minimize the cost of the isolation system while satisfying certain design requirements. An improved genetic algorithm (GA), Micro-GA, is employed to search for the optimal solutions for such discrete optimization problems. An example of the optimal design of a highway bridge is presented and the minimum cost expense of the isolation system is achieved with improved structural response under multiple transient earthquake loads.