For introducing the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, benchmark analyses on a static in-plane bending test on an elbow (the pipe element test) and a piping system test under one-directional excitation (the piping system test) were conducted. As for the benchmark analyses on the pipe element test, 14 groups participated in the benchmark analysis. The variation of the elastic-plastic analyses and the factors which affect the analytical results are examined by comparing the analytical results with the experimental results. From the examination of analytical results, it is shown that the decision of the yield stress for the analysis rather than the secondary gradient affects a lot on the load deflection curve or the strain behavior, when the stress-strain relationship is simulated by bi-linear approximation. The strain ranges are well simulated by the analyses, though the residual strains scatter a lot. The failure mode in the experiment was the fatigue failure at the flank of the elbow, and it was well predicted by the participants’ analyses. As for the benchmark analyses on the piping system test, ten groups participated in the benchmark analysis. The eigenvalue analyses are well estimated by the all participants, but the dynamic response and strain behavior of pipes under random input waves vary widely. The findings from the benchmark analyses would be reflected to the inelastic analysis guideline for the seismic safety estimation of nuclear piping systems under beyond design seismic input.

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