Considerations for the evaluation of floor response spectra of a seismically isolated structure

In this study, the analysis of the effects on the floor response spectra by the nonlinear behavior of a seismic base isolation system was performed. The nonlinear behavior was defined as the ratio of stiffness and the effect of bi-direction. FRS(The floor response spectra) depends on the characteristics of the seismic base isolation system such as the natural frequency and damping ratio. An evaluation of the seismic isolated structural integrity, using the equivalent stiffness of the seismic base isolation system was satisfied. However, a FRS of seismic isolated structure is greatly changed because of the nonlinear behavior of seismic isolation system. Therefore the generating of FRS for seismic isolated structure, more researches are needed about nonlinear behavior of seismic isolation system. In this study, the analysis of the effects on the floor response spectra by the nonlinear behavior of a seismic base isolation system was performed. The FRS was increased in hi-frequency domain because the influence by the nonlinear behavior of isolation system. In addition, each floor exhibited a more different of responses compared with the equivalent linear model of the seismic isolated structure. The nonlinear behavior of the seismic isolation system was considered, because of a more reliable assessment of integrity about equipment at each floor of seismic isolated structure