Experimental Study on the Ultimate Property Diagram of Base Isolators

The guideline for base isolated nuclear power plants is being developed in many countries and several design examples were tried. Because the nuclear facilities must have enough capacity even under the extreme earthquake event, the safety of an isolation system needs to be verified in the design procedure. Therefore, the study on the limit state of an isolator is required prior to the safety evaluation of the isolation system. The type of base isolator appropriate for a nuclear power plant structure is regarded as an elastometric rubber bearing with a lead core. The failure limit of the lead-rubber bearing (LRB) is not easy to be predicted because of its high nonlinearity and complex loading condition by an earthquake excitation. Furthermore, the failure mode of a LRB can be affected by the vertical load, shape factor, material property of rubber, and manufacturing quality etc. Therefore, a simplified and efficient test approach to evaluate the failure state of a base isolator is necessary. From this point of view, the experimental test to determine all possible failure modes and its limit state was performed in this study. This is an experimental study for construction of the UPD to define the ultimate capacity of an isolator