| Due to the special safety requirement of the nuclear power plant,the seismic analysis and design standard of the nuclear power plant is more stringent than the ordinary civil facility.The nuclear power plant has the characteristics of high rigidity and heavy weight.Therefore,the soil-structure interaction(SSI)has significant influence to the seismic response of nuclear power plant built on non-bedrock site,which is directly related to reactor safety.SSI has become an important issue in the seismic analysis of nuclear power plant as an important factor affecting the seismic performance.In the present paper,investigations on the finite element SSI analysis method adopting artificial boundary are conducted.The three-dimensional coupled model of soil and structure is established in the general-purpose commercial finite element software.The simulation of the seismic wave propagation in the infinite domain is achieved by constructing artificial boundary.Moreover,a specific method of applying seismic input on the artificial boundary is proposed,which makes it easy and straightforward to apply the seismic excitation on the artificial boundary in universal software.This finite element method is adopted to analyze the seismic dynamic response.Through the analyses of the SSI seismic response of a simplified nuclear power plant using artificial boundary and detailed model considering full-size soil domain,the artificial boundary method is verified by comparison of the results.The influences of calculation domain dimension/shape and artificial boundary type on the calculation results are compared.Reasonable modeling parameters for the SSI finite element analysis of the nuclear power plant using the artificial boundary method are proposed.The results show that the simple viscous boundary is suitable for the artificial boundary method.And more accurate results can be obtained when the size of the calculation domain in the direction of excitation is about three times the size of the structure,and the ratio of the calculation domain is 2:1.Using the aforementioned modelling parameter,the SSI effect of 10 MW high-temperature gas-cooled reactor(HTR-10)on non-bedrock sites(Changping,Beijing)is analyzed and evaluated.The floor response spectra at different floor levels of the HTR-10 reactor building under three-dimensional seismic input are calculated,and the influence of the SSI effect on the response is discussed.In the horizontal direction,the response spectra of each floor are similar.The influence of SSI at different floors are similar.In the vertical direction,the response characteristics of each floor are obviously related to the vertical frequency characteristics of the floor itself,and the responses of different floors are quite different.To investigate SSI effects on different type of soil,analysis of the HTR-10 plant is then performed on a softer site,and the floor response spectra under the three-dimensional seismic input are calculated.Since the soil property affects the SSI seismic response,the dynamic response of the HTR-10 plant on the softer site is quite different from that on the Beijing site in China.The differences in SSI seismic responses of two soil-structure model is summarized,and the factors leading to these differences in seismic response is discussed.The response spectrum of the soft-soil model increases slightly in the low-frequency range and decreases in the high-frequency range.The differences of shear wave velocity and the damping ratio between different soils are the main factors that affect the seismic response of structure on different sites.Moreover,the sway motion caused by the horizontal excitation on the soft soil has significant effects on the vertical response spectrum. |
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