SUMMARYA recently developed hybrid mass damper (HMD) system and its application to a 36-storey high-rise building with a bi-axial eccentricity, located in Tokyo, are presented. This new HMD system utilizes a gear-type pendulum and a linear actuator. Here, the gear-type pendulum is employed to make the natural period of the auxiliary mass comparatively long while minimizing the height of the device, and the linear actuator, on the other hand, ensures smooth and noiseless operation of the system. There are several special features in the control method as well; two HMD systems are applied to control the transverse-torsional coupled vibration of the building, and also variable gain feedback (VGF) control technique has been developed to fully utilize the capacity of the HMD system from weaker to stronger external excitations.Free vibration tests as well as control of wind vibrations of the building induced by the Typhoon 9810 in 1998 were used to verify the performance of the control system. It was found that the maximum and the root-mean-square acceleration responses of the building were reduced to 63 per cent and 47 per cent of the corresponding uncontrolled accelerations. Finally, the control performance of the system was conÿrmed.

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We have developed a semi-active base-isolation system using semi-active hydraulic dampers that can be switched between two primary damping coefficients. The time lag of the damping force (in other words, the time constant) was measured through triangular wave excitation by means of displacement control, and its dependence on the piston velocity was clarified. Sliding mode control considering the time constant of the damper was developed based on a bilinear optimal control theory and a control law for simultaneous bidirectional control was proposed. It was clarified through shaking table tests that the proposed control reduces the acceleration response of the building, while keeping the deformation of the seismic isolation story relatively small.

A new structural control system using damper-installed shear walls in lower stories with reduced stiffness is proposed for vibration control of high-rise RC buildings. That system has some design variables, i.e., height of shear wall, degree of stiffness reduction at lower stories, and quantity of dampers. In this paper, some parametric studies on the shearbeam model with a stiff beam against two kinds of ground motion, a pulse-type sinusoidal wave and a resonant sinusoidal wave, are conducted to clarify the vibration characteristics of the proposed structural control system. It is shown that the optimal combination of design parameters depends on the input ground motion. It is also shown that it is possible to prevent from increasing the response under the one-cycle sinusoidal input resonant to the lowest mode and reduce the steady-state response under the harmonic input with the resonant fundamental period by reducing the stiffness in the lower structure and increasing the damper deformation.