Modeling and experimental verification of a variable-stiffness isolation system using a leverage mechanism

Recent studies have discovered that conventional isolation systems may incur excessive isolator displacement in a near-fault earthquake with strong long-period wave components. To overcome this problem without jeopardizing isolation efficiency, a novel semi-active isolation system called a Leverage-type Variable Stiffness Isolation System (LVSIS) is realized in this study. By utilizing a simple leverage mechanism, the isolation stiffness of the LVSIS can be easily controlled by adjusting the position of the pivot point on the leverage arm. For accurate analysis, the dynamic equation based on a mathematical model that considers the actual situation of all friction forces within the LVSIS is derived in the study. The mathematical model is then verified experimentally by using a prototype LVSIS tested dynamically on a shaking table. Furthermore, to determine the on-line pivot position of the LVSIS, this study also proposes a semi-active control law whose feedback gain is decided by utilizing a linear active control algorithm, such as the LQR or modal control. By comparing the isolation performance of its uncontrolled passive counterpart, the test results also demonstrate that the LVSIS with the proposed control law is especially effective in suppressing the excessive base displacement induced by a near-fault earthquake.