Optimization research for base-isolated structures with fluid viscous dampers

For the base-isolated structure with fluid viscous dampers in isolation layer, a parametric multi-objective optimization method of fluid viscous damper using non-dominated sorting genetic algorithm (NSGA-Ⅱ) was proposed. Bouc-Wen model was applied to simulate the isolation layer's force-deformation behavior. The motion equation was established for time-history analysis. The total displacement of the isolation layer and superstructure were selected as the optimization objective. The Pareto optimal front can be gained through algorithm. A six-storey base-isolated structure was selected as an example of numerical analysis. The vibration responses of the isolation layer were selected for FFT spectrum analysis and response spectrum analysis. By adjusting the constraint of optimization target and the optimization range of the parameters, NSGA -Ⅱ was also used to obtain a more concentrated parameter distribution, and the effectiveness of the damper was verified by other earthquake. The results show that the optimal dampers can effectively reduce the displacement of isolation layer; for some earthquake, the optimal dampers may be detrimental to the seismic response of the superstructure. However, the seismic response of the superstructure can be kept in acceptable range by reducing the effectiveness of fluid viscous damper; the damper effectiveness depends on the type of earthquake. When the main excitation frequency of the isolation layer tends to be lower in the range of first mode frequency, the damper has better effectiveness in controlling the displacement of isolation layer; the damper effectiveness is correlated with the acceptable supplemental damping of isolation layer; the excessive supplemental damping is not favorable to the dynamic response of the superstructure; according to the threshold of the displacement of the isolation layer and the reduced optimal range of the damper parameters, the damper parameters that can be applied to actual projects could be obtained.