This paper deals a seismic isolation system with nonlinear characteristics mechanism for a vertical seismic oscillation. The seismic isolation system consists of a rhombus shape link, horizontal coil springs and vertical coil springs. Restoring force of the system can be calculated by the geometric calculation. The authors propose a design principle of the system, using that natural period of the seismic isolation system can be calculated from its restoring force characteristics. A Seismic isolator using the nonlinear characteristics was actually made, and its restoring force characteristics were measured by static loading test From this experiment results, it revealed that the characteristics of the device can be accurately predicted from the design principle.
