Ultimate Strength of Seismic Isolation System Using High Damping Rubber Bearing for Buildings. 1st Report. Analytical Mehtod for Ultimate Strength.

Abstract

This paper proposes an analytical method to estimate the ultimate strength of seismic isolation systems using high damping rubber bearings against excessively strong earthquakes. In the method, responses of each rubber bearing of the system in horizontal deflection and vertical force are analyzed, and are compared with a breaking limit curve of the rubber bearing represented in a plane with axes of shear strain and tensile/compressive stress to judge whether or not the trajectory of the rubber bearing responses crosses the limit curve. For the rubber bearing response analysis, analytical models for horizontal and vertical restoring force characteristics of the bearing were proposed considering properties in large deformations up to the breaking region. Excitation tests were carried out for an about 0.3 scale model of a base-isolated building supported by four high damping rubber bearings using large acceleration inputs, showing that the analytical results agree well with the experimental results. The tests and analyses showed that the vertical force acting on the bearing was considerably varied according to the horizontal deflection increase, and when a large tensile force acted on the bearing, the rocking motion of the building excited its vertical vibration which caused a fluctuation in the vertical force.