Optimization Of Base-isolation System Based On NSGA-II

Earthquake is one of the natural phenomenon which have serious impact even threaten to human lives. Especially for China, the study of earthquake is so important since it is in the seismic zone. Base isolation system has been widely proved to be one of the most effective ways of reduce the damage of buildings under earthquakes. And genetic algorithm also has been well known as one of the most useful tools of searching for the best combinations for initial values. But the study of combining these two systems together to design base isolation system for certain structures is still in the beginning stage. The work has been done in this paper are as followings:1) In this paper, the responses of one nonlinear base-isolated building undergoing different earthquake acceleration histories are studied. As a simplification, a shear-type structural model, which has one horizontal degree of freedom at each storey, is established. The damping matrix of the structure is set up according to Rayleigh damping theory.2) For considering the nonlinear behaviour of the seismically isolated building, the bilinear hysteretic stiffness model of the lead-rubber bearings is set up by using Newmark's method during calculation of structural response under earthquakes.3) This paper chooses a fast and elitist non-dominated sorting genetic algorithm (NSGA-â…¡) approach to find the optimal values of the stiffness and damping ratio for the base isolation system, which can minimize simultaneously the inter-storey drift and displacement of the base floor.4) A discrete Fourier transformation analysis of the acceleration history of top floor and the earthquake history is done to check the efficiency of the base isolation system.The results show that the applied optimisation technique gave good results, it is useful for us to find the optimal stiffness and damping ratio of the base isolation system to minimize simultaneously the inter-storey drift and displacement of the base floor.