Optimum base-isolation system control using force restricted viscous mass dampers

As a result of recent development of an apparent mass damper in which the actual mass of a cylindrical flywheel can be amplified several thousand times by a ball screw mechanism, seismic control systems using an apparent mass damper are being actively investigated in Japan. The authors have already succeeded at putting an apparent mass damper system, referred to as a tuned viscous mass damper seismic control system, into practical use. Although researchers have attempted to apply the apparent mass damper to baseisolation, they were confronted by large floor response accelerations induced by the large mass and the finite stiffness of the damper supporting element. Against this backdrop, a damper force restriction mechanism and a buffer spring are proposed to improve floor accelerations in a base-isolated building containing the apparent mass damper. The objective of this paper is to present a closed form solution of an optimum parameter that is useful to design an appropriate maximum friction force for the force restriction mechanism in the proposed damper.