Seismic isolators of variable stiffness for earthquakes with strong long-period components

In order to mitigate the excessive isolator displacement that is usually induced by a near-fault earthquake, two new types of seismic isolators with variable stiffness (SIVS) are introduced and investigated experimentally in this study. By properly choosing the geometric parameters of the two SIVS isolators, the isolation stiffness of the isolators becomes a function of the isolator displacement, rather than a fixed value. The geometries of both isolators are defined by using six-order polynomials, so that the stiffness of the isolators has a softening behavior followed by a hardening behavior when the isolator displacement increases. The softening and hardening behaviors aim to reduce the structural acceleration and isolator drift, respectively. In order to verify the feasibility and effectiveness of the proposed SIVS isolators, a shaking table test was conducted on the prototypes of both SIVS isolators. The test results are highlighted and alsocompared with the theoretical ones in this paper.