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概要

Preparation for DEC (design extension condition) is one of the lessons learned from Fukushima Daiichi nuclear accident. Best estimation is required for DEC. For best estimation of structural strength against seismic load, it is needed to know the failure modes of the piping to make adequate preparation against excessive seismic loading. Ratcheting, collapse and fatigue are the probable failure modes of piping due to seismic loading. But the occurrence conditions of these failure modes under seismic loading are still not clear. Due to seismic loading from the cyclic seismic acceleration, structure undergoes progressive distortion and can cause ratcheting or collapse. Also low cycle fatigue is one of the major failure modes observed at seismic events and experiments. The current study investigates the ratcheting and collapse failure modes at various seismic loading by numeric analyses. The results show us some basic understanding on ratcheting and collapse occurrence condition under excessive seismic loading.

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