Multi-objective Optimization of Semi-active Control of Seismically Exited Buildings Using Variable Damper and Genetic Algorithms

Semi-active fluid viscous dampers as a subset of control systems have shown their ability to reduce seismic responses of tall buildings. In this paper, multi-objective optimization of the performance of this group of dampers in reducing the seismic responses of buildings is studied using multi-objective genetic algorithms. For numerical example, two 7 and 18 stories buildings are chosen and modeled as 3D frames. The equation of motion for each building, subjected to earthquake accelerations, is written in presence of semi-active fluid dampers and resolved in state-space. The optimal number and position of dampers are considered as decision variables while the structural responses such as displacement of top floor, base shear and etc. are considered as the objective functions to be minimized. The objective functions are taken part in multi-objective optimization as a group of three functions, and the goal is finding so called Pareto-optimal solutions that are non-dominated to each other and can optimize whole objectives as best as possible, simultaneously. In this case, any Pareto-optimal solution will be in fact, a certain configuration of some dampers in specific places of the structure. In this study, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) has been used.