Experimental studies of the seismic response of structures incorporating base isolation systems

Whereas the concept of base isolating structures from the damaging effects of earthquake motions is not new, implementation of the technique is a relatively new occurrence. This has mainly been due to the need for several important developments in materials science and experimental and analytical modeling before base isolation could evolve into a practical approach for seismic design. One of these developments has been the ability to test large-scale isolation systems using simulated seismic loads. These tests have not only proven the performance and reliability of the isolation systems and hardware, but have enabled correlation studies to be undertaken which have confirmed the accuracy of analytical methods and the acceptability of current design procedures. The Earthquake Engineering Research Center (EERC) at the University of California at Berkeley has been an active participant in this work, and this paper reviews some of the achievements of the Center in the last few years. Component tests on single isolators are described. Tests on plain and high damping natural rubber bearings, lead-rubber bearings, sliding bearings, and bearings incorporating uplift resistance mechanisms have been performed. High-shear strain tests on large (up to full scale) elastomeric bearings have been conducted to determine the stability characteristics and limit states of the isolators