Natural Rubber Foundation Bearings for Earthquake Protection—Experimental Results

Abstract

Abstract The concept of earthquake protection of civil engineering structures by the use of rubber mountings of low shear stiffness has been discussed by Derham, Wootton, and Learoyd. Figure 1, taken from these references, shows the predicted response of a five-story shear-wall structure to an earthquake having a peak ground acceleration of 0.3 g. The accelerations shown at the various mass levels have been computed both for the building with its foundation fixed conventionally, and for the building “floating” on natural rubber bearings. The bearing stiffness was such as to make the horizontal natural frequency of the mounted structure 0.5 Hz. The basis of computation was the response spectrum of Housner. The results were later confirmed further by using a time-history analysis. The basic conclusion from these computer studies was that the use of rubber mountings leads the building to behave in an earthquake essentially as a rigid body. The rigid body accelerations, and hence the forces, are very much smaller than the accelerations experienced by a fixed-foundation structure, particularly in upper storys. For the case studied the overall maximum acceleration of the rubber-mounted structure was calculated to be one-tenth the maximum acceleration experienced by the fixed-foundation structure.