Characterization of high damping bearings and their responses to earthquake motions

An isolation system consisting of six (6) laminated high-damping rubber bearings has been installed in a test facility on the Tohoku University site in Sendai, Japan. The isolation system is designed to have a frequency of 0.75 Hz. This frequency, however, is obtained only when there is a strong earthquake, resulting in significant horizontal displacements. After the installation of this system, in April 1989, static and dynamic tests were performed to obtained fundamental dynamic response properties of the system. The day after these tests were completed, an earthquake of magnitude M = 4.9 occurred in the area. The maximum acceleration experienced by the building was only about 0.03 g. Several other earthquakes have occurred since then, all of which resulted in low input acceleration at the Tohoku facility. Analytical investigations for the building have been carried out using a model with stiffness and damping of the isolation system obtained from the in-situ tests. Response of the simulated model to this earthquake show good agreement with the recorded data at each floor of the isolated building. Both the recorded data and the analytical results indicate that the bearings installed in this building are stiff enough to prevent drift of the superstructuremore » under minor tremors or wind loads. Results of all in-situ tests are presented. 5 refs., 10 figs., 1 tab.« less