Study on Characteristics and Effects of Seismic Isolation System of Vertically Utilized Coiled Springs

In recent years many structures employing seismic isolation systems have been constructed in Japan, the practical concern on the cost of seismic isolation systems has heightened. This paper describes the research and development of a new seismic isolation system using vertically utilized elastic and elasto-plastic coiled spring, and discusses analytical model for coiled spring. The basic concept of the earthquake isolation system that was constituted of bearing, restoration and damping elements is to realize cost effective design without any reduction in isolation performance. The restoration and damping elements of the isolation system were constituted by two types of coiled springs. The horizontal static tests were performed to evaluate the restoring characteristic and the mechanical model of elastic and elasto-plastic coiled spring. The restoration element of elastic coiled springs was made of using the two types of materials JIS SUP9 steel and JIS SUS 304 stainless steel. The elasto-plastic coiled springs of damping element also was made of using the two types of JIS SS 400 steel and JIS SWRM 17 steel. The characteristics of these coiled springs such as transverse stiffness and hysteretic damping and the validity of the analytical model were clarified through the static tests. Furthermore the response analyses based on the restoring force characteristics of experimental results were carried out to assess the isolation performance of this system.