Norio Iwata

Semi-active seismic response control of base-isolated building with MR damper

This study deals with a shake table test on a three-story base-isolated steel frame. The frame rests on four roller bearings for isolation and is equipped with four laminated rubbers as shear spring. An MR damper is used in the test to perform semi-active seismic response control. The basic control algorithm applied in the study is to simulate the load-deflection of an origin-restoring friction damper (ORFD) which is a sort of friction damper that looses its resistance when it moves toward the origin, making sure for the base-isolated system to minimize residual displacement even after an extremely strong ground motion. Also attempted is a hybrid type control that superposes viscous damping on the ORFD when the damper moves from the peak displacement toward the origin.

Application of MR damper to base-isolated structures

This paper presents a comprehensive study on the application of the MR damper to base-isolated building structures. It first proposes a simple semi-active control algorithm for a base-isolated structure with an MR damper. The algorithm, in which the MR dampers hysteresis shape is controlled, aims to reduce the isolators displacement without increasing the acceleration responses of the upper structures. The second part of this paper covers the properties of an MR fluid and an MR damper developed for a base-isolated model structure. The damper has a nominal capacity of 40kN, which can be adjusted in accordance with the applied magnetic fields. In the test, the damper is subjected to cyclic sinusoidal displacements with different amplitudes, velocities and magnetic field intensities. The last part describes shaking table tests carried out using the MR damper and the base-isolated model structure. It is confirmed that the proposed semi-active control method is effective in reducing the isolators displacement without increasing the acceleration responses.