Experimental Study on the Bidirectional Behavior of a Lead-Rubber Bearing

Abstract eng:
There has been an increasing demand for introducing a base isolation system to secure the seismic safety of structures and equipment. Most of the guidelines for the seismically isolated structures require the production test to verify the mechanical properties of isolation devices. When the risk and performance based design concept is applied, the prototype test under the beyond design basis seismic loading also required to make sure that the base isolation system have enough seismic margin. However, the behavior of isolators with elastomeric rubber material under the large displacement is not very well understood. In this study, the full scale lead-rubber bearings which have 1,500 mm diameter of rubber and 320 mm diameter of lead core were tested. The displacement controlled horizontal motions were applied to the specimens with a constant vertical load. These horizontal input motions were determined by the response analysis of an earthquake motion or used as simplified sinusoidal motion. For the input displacement of two orthogonal horizontal directions, the maximum directional response of ground motions was considered. As an experimental results, the behaviors of isolators in the design displacement range and the beyond design displacement ware investigated. The difference between unidirectional and bidirectional force-displacement curve were compared and the fracture test were also accomplished in each cases. Finally, the considerations for the test protocol of isolation devices and the limit state under seismic loading were discussed.

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