Study on Three-Dimensional Seismic Isolation Using Helical Coil Spring

Abstract

Subduction-zone earthquake and local earthquake has been happening for the past several years. A lot of industrial facilities were damaged by them. Seismic isolation structures are receiving a lot of attention these years. Most of seismic isolation structures only act on horizontal earthquake. But because semiconductor producing equipment such as electronic beam exposure equipment is supported by air suspension, it could response to the vertical earthquake easily. To protect those equipment from earthquake, the three-dimensional seismic isolator must be developed. The helical coil spring is one of the seismic structure and it is used for absorbing vibration and shock. General single coil spring has high rigidity in the vertical direction and low rigidity in the horizontal direction. Therefore, it is necessary to lower the rigidity in the vertical direction to achieve three-dimensional isolation using coil spring. In this paper, three-dimensional seismic isolator using multiple coil springs are devised. It is analyzed by the finite element method. Coil springs which is wound circle, triangle, square and pentagon are analyzed. The seismic isolation capability while coil springs in the seismic isolator are inclined has been verified. The paper clarified the winding shape of coils and the inclining angle of springs in the seismic isolator which could lower the three directions of stiffness by performing eigenvalue analysis and time history response analysis on seismic isolator model. As a result, circle is the best shape for coil spring to achieve lowest stiffness and seismic isolation effect. It could reduce the acceleration response to short-period earthquake.