Restoring Force Characteristics of Laminated Rubber Bearings Under Various Restraining Conditions

We conducted the measurement of restoring force characteristics of laminated rubber bearings under various restraining conditions. In the experiment, we provided three laminated rubber bearings with various second shape factors $S2=3,4,4.94.$ The restoring force is obtained by using a newly designed combined loading test apparatus. By using this apparatus, the laminated rubber bearing could be subjected to shear, compressive and rotational deformations independently. In this experiment, we defined the degree of restraint as the ratio of the bending moment to the restricting bending moment which was measured when the rotation angle of the laminated rubber bearing was zero radian. This means that the flanges on both sides of the laminated rubber bearings were kept parallel during horizontal deformations. From the experiment, it was confirmed that restoring force characteristics were affected by the degree of restraint. Some reduction in restoring forces was observed when the degree of restraint was small. In particular the laminated rubber bearing with a small second shape factor, namely the rubber bearing, had a slender shape, easily buckling under small horizontal displacement. It was also confirmed that bending stiffness of the laminated rubber bearing had shear strain dependency and vertical load i.e., surface pressure dependency. The results of this experiment reveal that we should consider the reduction of the restoring force if the upper or lower structure of the laminated rubber bearing is not sufficiently rigid.