| Title | Bi-directional Characterization of Seismic Isolation Bearings |
| Authors | Whittaker, Andrew; Thompson, Andrew C. T.; Huang, Wei-Hsi; Fenves, Gregory L. |
| Publication | PEER Report in publication |
| Objectives | To characterize the bi-directional response of elastomeric and sliding seismic isolators and to investigate strain-history, path-history, scragging, and recovery effects. |
| Abstract | There is a large amount of data on the unidirectional behavior of seismic isolation hardware. Design of structural systems incorporating such hardware is primarily based on unidirectional test data. Few tests have been performed to investigate the bi-directional response of isolators: Kajima corporation has tested elastomeric bearings and SUNY-Buffalo has tested sliding bearings. An ongoing coordinated experimental and analytical research program at UC Berkeley, sponsored by the California Department of Transportation, is actively addressing bi-directional characterization of both elastomeric and sliding bearings. The bearings are subjected to bi-directional displacement-history orbits, traced by UC Berkeley's earthquake simulator at the Earthquake Engineering Research Center. The orbits are selected to investigate unidirectional and bi-directional response, strain-history, and path-history effects. The amplitudes and sequences of the orbits are selected to investigate scragging and recovery effects. To date, both DIS lead rubber (LR) bearings and Bridgestone high-damping rubber (HDR) bearings have been tested. Friction-pendulum bearings and Andre HDR bearings will be tested in May 1999. Results from sixty tests performed on the Bridgestone HDR and DIS LR bearings are presented. There is much evidence of scragging in the HDR bearings. It is found that the greatest percentage in shear-modulus reduction occurs during the first half-cycle. Also, scragging the bearing in one direction will likely scrag the bearing in the orthogonal direction. The virgin properties of the tested HDR bearing recovered with time. There is little evidence of scragging in the tested LR bearing. Path-history is found to affect the force response of both the tested HDR and LR bearings. |
