Fragility Analysis Of A Nuclear Power Plant Containment Building Subjected To Mainshock-Aftershock Sequences

The containment building of a nuclear power plant as the last security barrier plays an irreplaceable role in ensuring the safety of nuclear power systems. Seismic performance of the containment building under a single earthquake has been studied by many scholars. Due to the randomness of earthquakes and frequently occurring of beyond-design-basis earthquakes, there may be some damage on the containment building after a single earthquake and the damage may be significantly increased during an aftershock. Therefore, it is very important to investigate whether it will resist the aftershock for mastering the damage mechanisim during multiple earthquakes and for seismic design of nuclear power plants.This paper focuses on the aftershock fragility analysis of the containment building of a nuclear power plant which has been damaged after the mainshock. Specific contents are as follows:(1) The ground motion parameter and the spectral matching period range which are suitable for the dynamic analysis of the containment building have been studied. Based on the location and the earthquake information specified for the nuclear power plant, and combined with seismic hazard analysis and seismic attenuation relationship, the target spectrum has been drawn to select the ground motions. On the basis of the above research, a procedure of selecting the mainshock-aftershock sequences used in the dynamic analysis of the nuclear power plant has been proposed.(2) The dynamic analysis of the containment building has been carried out by using the finite element model and the mainshock-aftershock sequences. The damage of the containment building subjected to mainshock-aftershock sequences has been analyzed, then the parameters and limits of different damage states have been determined. Finally, the relationship between the global and local responses has been studied.(3) The incremental dynamic analysis by scaling the aftershocks has been performed on the structures which have different damage states induced by the mainshocks. The aftershock fragility curves based on different damage states have been obtained and the influences of damage on fragility curves have been researched. Finally, the effects of the spectral shape differences of the aftershocks on the damage states of the structure have been studied.