This paper provides a part of series of “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities”. Paper is focused on the seismic evaluation method of the multiply supported systems, as the one of the design methodology adopted in the equipment and piping system of the seismic isolated nuclear power plant in Japan. Many of the piping systems are multiply supported over different floor levels in the reactor building, and some of the piping systems are carried over to the adjacent building. Although Independent Support Motion (ISM) method has been widely applied in such a multiply supported seismic design of nuclear power plant, it is noted that the shortcoming of ignoring correlations between each excitations is frequently misleaded to the over-estimated design. Application of Cross-oscillator, Cross-Floor response Spectrum (CCFS) method, proposed by A. Asfura and A. D. Kiureghian[1] shall be considered to be the excellent solution to the problems as mentioned above. So, we have introduced the algorithm of CCFS method to the FEM program. The seismic responses of the benchmark model of multiply supported piping system are evaluated under various combination methods of ISM and CCFS, comparing to the exact solutions of Time History analysis method. As the result, it is demonstrated that the CCFS method shows excellent agreement to the responses of Time History analysis, and the CCFS method shall be one of the effective and practical design method of multiply supported systems.

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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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