Experimental Evaluation of Seismic Isolation of a 9-Story Braced Steel Frame Subject to Uplift

摘要

In the second phase of an experimental study of base isolation of medium-rise buildings subject to column uplift, earthquake simulator tests were performed on a 1/4-scale 9-story braced steel frame structure with height to width ratio of 1.59, for two types of base isolation bearings, neoprene and natural rubber with lead plug, against a wide range of earthquake ground motions. The study found that base isolation of medium-rise structures provides significant reductions in base shear and story accelerations. Both the neoprene and lead-plug bearings proved to be effective isolators. The neoprene bearings did not provide as much damping as the lead-plug bearings, but did not experience any significant change in stiffness while the lead-plug bearing shear stiffness decreased by 50% after many cycles of displacement. The lead-plug bearings also tended to excite more higher mode response in the structure than the neoprene bearing isolators. Comparison of the test results with response spectrum analysis showed that the latter is an effective technique for determining the maximum responses of a base-isolated structure.