After the accident at Fukushima Dai-ichi Nuclear Power Plant in the 2011 Great East Japan Earthquake, the International Atomic Energy Agency (IAEA) requires to consider the design extension conditions (DEC) for the safety management of nuclear power plants (NPPs). In considering DEC, it is necessary to clarify the possible failure modes of the structures and their mechanism under the extreme loadings. Because piping systems are one of the representative components of NPP, and there is a possibility to failure at seismic events, the authors conducted an experimental investigation on failure modes and their mechanisms of piping systems under excessive seismic loads.

The experiments are categorized into the fundamental plate tests and pipe component tests. In this paper, the results of the pipe component tests would be described. In the pipe component tests, the authors used piping specimens constituted with one steel elbow and a weight. Though the input acceleration level was much over the allowable level to prevent collapse failure by the seismic design, the failure mode obtained by the excitation tests were mainly the fatigue failure. The reduction of the dominant frequency and the increase of the hysteresis damping were clearly observed in the high-level input acceleration due to the plastic deformation, and they affected the specimens’ vibration response greatly.

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