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We examined two approaches for predicting the inelastic responses of piping systems. The first enabled us to evaluate accurate responses using nonlinear time-history analysis. We focused on a material model in this approach. Plastic deformation might exhibit a cyclic-hardening effect, which is dependent on the strain ranges, and this hardening affects the dynamic responses of piping systems. Therefore, we improved the hardening model developed by Ohno and Wang (OW model), which is one of the most sophisticated models for producing kinematic hardening behavior. We modified it to produce cyclic-hardening behavior dependent on strain ranges. The second was a simplified approach to evaluate inelastic responses without time-consuming time-history analysis. We developed a tool using equivalent linearization. The tool used analysis techniques including a model of elastic beam elements using flexibility factors for pipe elbows, and modal response spectrum analysis. Equivalent linearization made it possible to apply modal analysis to inelastic analysis. We demonstrated how applicable the approaches were by conducting test simulations.

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In this study, static loading tests were conducted in order to investigate ultimate seismic performance of reinforced concrete foundation (pedestal) for seismic isolated nuclear power plant. Half-scale four test specimens, which consist of Lead Rubber Bearings (LRBs) of 800mm in diameter and reinforced concrete pedestals of 1200mm 1200mm in horizontal view, were used with the parameters of cyclic pattern of axial stress of seismic isolator, existence or non-existence of reinforcing bars at the top of pedestal, and concrete compressive strength. As a result of the study, it was confirmed that the reinforced concrete pedestal shows structural integrity within design level loads. In ultimate level loads, no damage was observed in the case of non-variable axial stress in the area near the center of buildings, and no brittle failure was observed and supporting function of axial loads was retained in the area near the outer edge of buildings, where variable axial stress in ultimate level was extremely large.

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