Shaking-table study of base isolation for masonry buildings

Results ot an experimental study are presented that help illustrate the effectiveness of using base isolators for reducing the lateral-force demand for engineered masonry building structures in areas of high seismicity. Two structures of identical configuration were each subjected to a similar series of three base motions that increased progressively in intensity. One structure was fixed to the platform of an earthquake simulator while the other was mounted on a set of four isolator pads that were attached to the simulator platform. Test structures were constructed at one-quarter scale using model concrete blocks and annealed wire for reinforcement. Measured accelerations of the isolated structure were notably less than that of the fixed-base structure for the same input motion. By isolating the structure, essentially no cracking occurred even for a base motion that caused significant cracking and yielding of reinforcement for the fixed-base structure. Measured response correlated well with estimates computed on the bases of newly proposed Structural Engineers Association of California (SEAOC) design requirements for base isolated structures.