The Earthquake Engineering Online Archive

Testing of a natural rubber base isolation system by an explosively simulated earthquake

Kelly, James M.

UCB/EERC-80/25, Earthquake Engineering Research Center, University of California, Berkeley, 1980-08, 58 pages (530/K38/1980T)

This report describes the base isolation experiment of the SIMQUAKE II test. The experiment used a 1/24-scale model of a containment structure. The model was mounted on a base isolation system which incorporated multilayered natural rubber bearings and a newly designed fail-safe system. The base isolation system was designed to produce a very low natural frequency of vibration in horizontal motion and much higher natural frequencies for the vertical and rocking motions. During the SIMQUAKE II experiment, the isolation system was subjected to two distinct ground motions. The first had peak ground accelerations of plus or minus 0.75 g horizontally and plus 1.25 g, minus 0.94 g vertically; the second had ground accelerations of plus or minus 3.0 g horizontally and plus 4.4 g, minus 5.6 g vertically. The isolation system easily overrode the effects of the first ground motion; but the second, having an upward acceleration greatly in excess of any possible earthquake and much higher than anticipated in the design of the bearings, caused them to fail in tension. The fail-safe system was then activated, preventing collapse of the structure. The outcome of the SIMQUAKE II test was highly successful for the base isolation system. It demonstrated that multilayered natural rubber bearings could be designed to provide protection for containment structures during earthquakes of reasonably probable intensity during the lifetime of the structure. For an earthquake of anticipated intensity, the fail-safe system prevented overall collapse of the structure.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-80-25.pdf (3 MB)