Abstract
In Japan, seismo-free apparatus was proposed by Ryuiti Oka and Yukio Otsuki 20 years ago which was actually applied to a few building in Tokyo. This method may be called as earthquake isolation method by vibration system like pendulum, spring and damper. However, to minimize the transmissibility of ground motion, the natural period of the pendulum or of the springs is required to be sufficiently longer than periods of ground motion (0.1〜5sec.) but is may be very difficult to make the period longer in the case of isolation apparatus by vibration system. This paper proposes the new idea of earthquake isolation method of structure by a high speed electrohydraulic servomechanism and discusses some applications of this idea for the dynamic characteristics, through theoretical calculation. When the ground is displaced by x and the piston of actuator is displaced by y, in the case of ⊿l→x,y minimizes to zero. The motion of the piston in the actuator is controlled by servovalve, electric error detector and by the bob of seismograph to minimize y to zero. Main components of this apparatus are as follows: 1. Hydraulic system 2. Controller of system 3. Electric error detector and amplifier 4. Horizontally supporting member with actuator This isolation method may be suitable for irregular vibration of low frequency about 0.1〜10c/s such as strong ground motion of earthquake.
