Proposal of Seismic Evaluation Method Using Inelastic Response Analysis

Abstract Ensuring adequate seismic safety margins is crucial for the seismic design of equipment and piping systems in nuclear power plants. There is an increasing need for more precise methods to evaluate these margins, particularly considering the reduction of seismic responses due to inelastic deformation. This study proposes an inelastic seismic evaluation method for nuclear power plant equipment. The proposed method performs an inelastic time history response analysis using the design yield strength in the standard. The inelastic analysis outputs design the seismic loads for calculating the primary stress and the design strains for calculating the cumulative fatigue factor. In this study, the proposed method was validated by comparing the design seismic loads and the design strains from experimental results on a cantilever beam. Since the design seismic loads depend on the yield strength of inelastic analysis model, the load ratios of the design seismic loads to allowable loads were compared. The allowable loads were calculated based on the yield strength and limit analysis using fully plastic material properties. The load ratios from the proposed method exceeded those from the experimental results. Additionally, the design strains from the proposed method exceeded the experimental strains. Therefore, the proposed method provides conservative estimates of seismic loads and strains, making it a practical evaluation method that considers the reduction effect due to inelastic deformation.