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This study was aimed at developing an application technology of magnetorhological (MR) fluid with improving the stability of MR fluid. Variable damper using MR fluid (MR damper) has been expected to control the response of building structures in recent years, because of its large force capacity and variable force characteristics. The MR damper changes the controlling force by adjusting the magnetic field with electric current, and can control the damping forces simply. The semi-active control using MR damper stabilizes the response of the building in earthquake better than the conventional passive control. Authors developed some MR dampers and conducted shaking table tests for the research to improve the performance of building structures against earthquake. A 40kN MR damper with 500mm (+/-250mm) stroke was constructed. Authors conducted a shaking table test of the three-story large-scale structure that has an isolated base using MR damper, and the effectiveness of MR damper was verified. Finally, a 400kN MR damper was constructed and installed in an actual base-isolated residential building in order to improve the performance of the building.

Performance of the super high-rise seismically isolated building during the Great East Japan Earthquake was reported. The response acceleration of the top floor was almost same as that of the 1 st floor. The maximum displacement of the isolation devices was 15 cm, and the cumulative displacement was about 10 m. The dynamic response analysis, considered variation of the characteristic of rubber bearing, ambient temperature and so on, was coincident with observed records.

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The method for evaluation of the building structure response reduction by soil structure interaction (SSI) from the seismographs of soil-structure system is presented. In the proposed method, the simplified SSI model is employed, and the parameter of model is determined by system identification. In the system identification, both the inertial interaction (II) and kinematic interaction (KI) are considered. It is also presented the method to indicate the reduction of structure response by II and KI respectively. The proposed procedures are applied to the observed records of the 2011 off the Pacific coast of Tohoku Earthquake. It is clarified that the reduction effect of II is decreased when the response of super structure enters inelastic range, and the opposite is true. In the building structures with pile foundations the reduction effects of KI is relatively smaller than those of II.