Nonlionear Dynamic Analysis Of Bases Isolated Structure

Seismic isolated structure system is a passive active control system, which is different from traditional anti-seismic structure system. Through setting isolation layer, earthquake energy is absorbed and dissipated and earthquake response of structure is reduced, so that the safe of structure is ensured. Studies and applies of isolated structure technology is done through these twenty years. Effective of isolated structure is proofed through lots of earthquake reactions.From the theoretical analysis of single and two-degree-of-freedom base-isolated structure, influence factors and influence degree can achieved. The analysis results show that:ω/ωnmust greater than 2 , the greater theω/ωnthe better the bases isolation result;The greater ratio of upper and isolation layer's stiffness the greater response of the upper layer, the smaller response of the isolation layer;when the effective mass coefficient of whole isolation structure arrive to 0.9, the effective mass coefficient of upper structure will greater than 0.9 .That means effective mass coefficient must increase when design upper structure.From the analysis of multiple-degree-of-freedom base-isolated structure, congsidering nolionear of upper structure and isolation layer,using wilsion-θworke out nonlinear dynamic time history analysis program(NA-BA),effectiveness of the program was proved from the shaking table experiment.From the analysis of structure instance, using the programe(NA-BA), the influence degree will get from bases isolated structure's difference influence——different layer,eathquake intensity isolation layer stiffness,damping ratio. Layer shearing and bilinear restoring force modal are used to describe the character of isolated structure, to analysis different response of different site's seismic wave. The analysis results show that: the more stiffness of isolation layer the smaller layer displacement response of the isolation layer; the greater layer displacement response of the superstructure; the greater acceleration of the whole structure. The greater damping ratio the greater the acceleration, the smaller the displacement. So, the influence of structure response depends on isolation layer stiffness and damping ratio.The isolated structure design is more complex than traditional anti-seismic structure. Displacement restrictive condition of the iaolation layer in the seismic code is studied in this paper。To keep the displacement of isolation layer lower than the limit, the frequency ratio must in definite range, rational stiffness of the iaolation layer will woke out. Damping coefficient in horizontal direction formulas and rational equal stiffness of the upper structure are derived from theoretical analysis of double particle mode.