To obtain ultimate characteristics under various loading conditions for 1600mm diameter of large scale lead rubber bearing (LRB) which was designed as a seismic isolation device for nuclear power facilities in Japan, a series of break tests (i.e. horizontal loading break test under various vertical pressure and tensile loading test under various offset shear strain) were planned and performed as a part of the project “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities” of Ministry of Economy, Trade and Industry. Because of determination of the safety margin of seismic isolated structures against beyond design earthquake ground motion level, ultimate characteristics of isolators should be evaluated.
As a result of those tests, some new knowledge was obtained. For example, while vertical pressure dependence for break shear strain is small, however offset shear strain dependence for break tensile strain is large and its dependence is non-linear.
In this paper, for the purpose of clarifying the non-linearity of offset shear strain dependence for break tensile strain, new analysis method which can predict a break tensile strain under various offset shear strain was examined. Generally, in the case of predicting break strain, break criteria and its threshold value must be defined. In this study, we proposed the break criteria and its limit value for LRB. As a result, we could find stretch ratio λ1 as a one representation of break criteria. By taking the criteria, we clarified the reason of non-linearity of offset shear dependence for break tensile strain and performed parameter study by using proposed analysis method for the purpose of examining various parameters dependence (i.e. stiffness variability of LRB, break strain variability of rubber and lead plug diameter).
In addition, we proposed two other break criteria. One is linear sum of maximum principal stretch ration λ1 and minimum principal stretch ratio λ3 and the other is strain energy density function.
Construction of this paper is as follows;
In chapter 1, outline of this study is explained. In chapter 2, outline of proposed analysis model is explained. In chapter 3, validity of analysis model is shown by comparing test results. In chapter 4, using proposed analysis model, analytical prediction method based on FEA is proposed and analysis of break test result is performed. In chapter 5, based on proposed analytical prediction method, various parameter dependences for break characteristics of LRB were examined. In chapter 6, probability of other break criteria is considered. In chapter 7, conclusions of this study are described.
