To control base displacement in seismic isolation structures subjected to large input level earthquake, variable oil damper (VOD) has beenproposed and developed. Damping force of the VOD is changed automatically by internal mechanism without computer and power supply, whenbase displacement becomes large. In this study, the mechanical properties of the VOD and its application for seismic isolation structures areinvestigated. Results of experimental and analytical studies shows that the response displacement of isolated story is decreased, while response acceleration and story drift of superstructure are slightly increased by the VOD effect.
