Shake table tests for a base-isolated system containing a rotary inertial damper

The inerter, which brought about new response control strategies for civil engineering structures, is a mechanical device that generates an inertial resistance force proportional to the relative accelerations between its two nodes. One of the most viable ways to implement the idea of the inerter is to utilize a ball screw mechanism; indeed, rotary inertial dampers for seismic control and seismic isolation having apparent masses of 5, 400 and 1, 250T, respectively, have been successfully developed in Japan. Although incorporating a rotary inertial damper is effective for reducing relative displacements, it induces high floor response accelerations, which transmit ground accelerations directly to the superstructure. To mitigate the floor response accelerations without deteriorating the reduction of relative displacements, incorporation of a damping force restriction and buffer spring is proposed. This paper reports the results of shake table tests on a small-scale, base-isolated specimen containing an inerter-like device, namely, a force-restricted viscous mass damper, with the aims to validate the analytical methods and to confirm the effectiveness of the force restriction and buffer spring in reducing floor response accelerations.