Active isolation of structures under seismic vibrations

Seismic isolation of structures is very important to prevent serious damage in buildings due to earthquake, and to protect equipment during transportation. Several passive or semi-active devices exist for protecting structures from secondary seismic waves, but few solutions are present to avoid damage due to primary waves. Usually, primary waves are considered less dangerous than secondary waves, nonetheless they can produce serious damage close to the epicentre. In order to protect structures from vertical oscillations, in this paper an active vibration control system is proposed. In the present formulation, active vibration control is based upon varying foundation stiffness during the seismic movement. In the paper, it will be shown how such kind of vibration control is effective in suppressing vibrations for the case of a measured earthquake signal.