Abstract
This paper describes the coupling effects of horizontal and vertical seismic excitation on the response of a newly developed 3-dimensional base isolation system. This base isolation system achieved very low vertical natural frequency using a velocity reduction mechanism. Therefore, rocking motion will be induced by vertical excitaion as well as by horizontal excitation in the presence of mass eccentricity. And this sysytem employs sliding pads for horizontal isolation and friction dampers for vertical isolation. Thus, the vibrational response of the upper structure depends on the friction forces of the sliding and damping mechanism, and the horizontal friction force varies depending on the vertical seismic response, vice versa. In this study, the coupling effects of the horizontal and vertical seismic excitations are investigated analytically as for the rocking motion, response displacement and response acceleration. The effects of the phase difference between the horizontal and vertical seismic input, etc. are clarified.
