The Fragility Analysis Of Shield Building Of Nuclear Power Plant Subjected To Mainshock-aftershock Seismic Sequences Based On Nonlinear Damage

In order to “do a good job of carbon peak and carbon neutral”,the development of nuclear power industry is the need of the continuous development of China’s social economy and the continuous improvement of people’s living standards,as well as the need to optimize China’s energy structure,alleviate environmental pollution and ensure energy security.AP1000 nuclear power plant is widely used,but the research on its seismic performance is still insufficient.As an important building to protect the safety of nuclear power plant,it is very necessary to study whether the shield building can protect the safety of nuclear power system under the action of earthquake.In addition,strong earthquakes are often accompanied by many aftershocks,the main shock will cause a certain degree of damage to the structure,and the aftershocks may further aggravate the damage.Therefore,it is of great significance to further study the seismic performance and aseismic design of nuclear power plants to study the performance and failure mechanism of shield plant structure to continue to withstand aftershocks on the basis of initial damage caused by the main earthquake.Based on the damage factors of nonlinear materials in shielded building,this paper focuses on studying the fragility of the structure after main-aftershocks considering the intensity and duration of aftershocks as well as the the initial damage.The main research contents are as follows:(1)A finite element model was established to simulate the dynamic performance of the shield building,and the damage factor under tension and compression was defined as the damage index of the structural nonlinear material.The appropriate ground motion sequence is selected according to the target spectrum.Then,based on the acceleration of the response spectrum of ground motion,the main-aftershock sequence suitable for the dynamic analysis of the shield building structure was obtained by adjusting the ground motion sequence with the single-point amplitude modulation method.(2)Using the incremental dynamic analysis method,the effect of the acceleration ratio of the main and aftershock spectrum on the fragility of the shield building structure under the main-aftershock is analyzed.The relative strength of aftershocks has a significant effect on the probability of tensile and compressive failure of the structure under the action of main-aftershocks.(3)The cumulative damage caused by the main-aftershock sequence was quantified based on the damage ratio of tension and compression damage.The cracking mode of the structure under the action of main-aftershocks was studied.And the fragility curve considering the influence of the aftershock duration was plotted.The results show that longer aftershocks will cause more severe cumulative damage and increase the probability of tensile and compressive failure of the shield building structure.The additional damage of the structure after the aftershock is obviously affected by the initial damage.