INVESTIGATION OF ULTIMATE BEHAVIOR OF ELBOW PIPES BY TENSILE LOADING TEST IN THE DIRECTION OF IN-PLANE BENDING

Probabilistic risk assessment is useful in considering the safety of nuclear power plants. To recognize the weaknesses of structures, a realistic fragility assessment must be conducted. Furthermore, it is important to set the failure mode appropriately for a realistic fragility assessment. However, few experimental data for the ultimate state of elbow piping with ductile rupture compared to fatigue exist. In this study, tensile loading tests of full-scale elbow pipes were conducted to enrich the knowledge of failure modes of piping systems. 150A Sch80 and 200A Sch40 elbow pipes made of carbon steel (JIS STPT410S) did not rupture despite the ductility factor exceeding 30. Therefore, the possibility of ductile rupture of elbow pipe under earthquakes is extremely low. Aiming at a realistic fragility assessment of ductile rupture, analytical models that precisely predict the test results were investigated. For a 150A Sch80 pipe, which did not show buckling deformation in the test, the FEM model using shell elements was able to predict with good accuracy. For a 200A Sch40 pipe, even one that buckled at the top of the elbow, the behavior, including buckling, was able to be predicted with good accuracy.