304 鉛配管を用いた振動荷重による崩壊モード実現の試み

After the accident at Fukushima Dai-ichi Nuclear Power Plant in 2011, IAEA requires to consider the design extension conditions (DEC) for the safety management of nuclear power plants (NPP). In considering the 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 mechanisms of piping systems under excessive seismic loads. A lot of preceding studies indicated that the most likely failure mode under the seismic load would be the fatigue failure. But other failure modes, such as collapse, ductile fracture, etc. may occur under the DEC. So it is necessary to clarify the conditions to cause various failure modes. However there are some difficulties to realize such failure mode experimentally with steel pipes due to the limitation of the ability of the test equipment, and the safety problem in conducting the experiment. In order to clarify the failure modes under excessive seismic load in safe manner, shaking table tests on simulation material is proposed. Bend pipes made of Lead (Pb) were used in the shaking table tests, and other failure modes such as ratchet collapse or overall deformation were obtained experimentally. From the experimental results, the gravity affects a lot on the occurrence of the collapse. The experimental method to use simulation material is effective to investigate the macroscopic failure behavior of piping systems.