Abstract
In normal base-isolated buildings using passive isolation devices, large horizontal displacements between the ground and the superstructures are inevitable to achieve satisfactory reduction in response accelerations of the superstructures. If energy-absorbing devices of large capacities are used to decrease the relative displacements, the seismic isolation performance will be decreased also. To solve this trade-off problem, a semiactive seismic isolation system using a controllable friction damper was developed, in which the damping force was controlled by varying the pressure between the friction elements. Excitation tests were carried out for a base-isolated single-story building model supported by 4 multistage rubber bearings which had a weight of 5250kg and a horizontal natural period of 1.85s. The controllable friction damper equipped with a hydraulic actuator produced a variable damping force of up to 39.2kN and had a time constant of 20 to 30ms. Through the tests, it was confirmed that while achieving satisfactory reduction in the response acceleration equivalent to that of the normal passive systems, the semi-cative system could decrease the displacement to about 1/2 of that of the passive systems. It was also shown that the variable feedback gain control using fuzzy rules was useful to make the displacement remain within an al1owable range against an excessively strong earthquake.
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