Performance Verification of Vertical Seismic Isolation Equipment Using Negative Rigidity Mechanism

Abstract

In recent years, various seismic isolation devices have been developed to prevent earthquake damage to valuable art works. The purpose of this study is to develop a vertical seismic isolation system that both reduces the natural frequency and solves the problems of vertical seismic isolation systems in previous studies. In this study, we developed a vertical seismic isolator that supports the load with inclined springs without using vertical springs. A motor is mounted on the ball screw that constitutes the central axis of each crank mechanism. The vertical stiffness of this seismic isolator can be changed using the motor. In this study, the seismic isolation performance was improved by using the negative stiffness property to set the natural frequency lower. The vertical seismic isolation system was modeled using SimulationX. The characteristics of the vertical seismic isolation system were verified and its performance was evaluated by various experiments and simulations. The MBS model of the newly developed device was used to accurately simulate the loading characteristics of the vertical isolator such as negative stiffness characteristics. The performance of this vertical isolator was verified by vibration experiments and simulations assuming typical seismic waves in Japan. The average response factor of acceleration in the experiment was 17.8%, and the average response factor in the simulation was 15.9%, which exceeded the performance of the device in the previous study. Finally, in the resonance avoidance test, the acceleration of the top plate of the vertical base isolation system was reduced by 57% by using the vertical natural frequency adjustment mechanism to avoid resonance.