The Research On Earthquake Response And Its Influence Factors For Layered Soil Sites Of Nuclear Power Plants

Considering the nonlinear dynamic characteristics of multi-layered soil,the free field seismic response analysis of nuclear power plant plays an important role in determining the input of seismic motion of the nuclear power plant in the Non-rock sites.Nowadays,one-dimensional frequency domain method is mainly used in the actual engineering,which exist a certain linkup of this method and the three-dimensional analysis model for nonlinear structure-foundation dynamic interaction problem.There are some differences between the model structure of one-dimensional in frequency domain and three-dimensional model structure in time domain during the dynamic analysis of the free field,and the original frequency domain model has some difficulties in the application of the obtained values of displacement frequency spectrum and outputting signal of acceleration time history response.In this paper,the several frequency domain models of soft soil site were conducted a comparison through evaluating calculation results.The expression form of the frequency domain was represented by the form of acceleration transfer function,comparing it with the original analysis methods in frequency domain or time domain.During a real earthquake,the behavior of vertical motion is generally ignored for site response analyses.Moreover,most studies show that the effect of vertical amplification is different from the horizontal part.Therefore,the practice of a single horizontal earthquake load as seismic input of site response analysis,neglecting the other horizontal component and the other vertical one,may result in obvious deficiency of site response.By using three dimensional calculation of element stress state,considering the influence of another horizontal and vertical vibration on the free field response,the relationship between vibration of the vertical and the horizontal direction was measured.And the vibration characteristics were obviously different.The influence factors of the three direction frequency domain were analyzed in layered soil site.Among them,the intensity of ground motion,the water level fluctuation of the layered soil site and the loading mode of the three direction ground motion had great influence on the seismic response of the soil layer.Through the study of the above factors,the new approach is suitable for earthquake resistant design and numerical analysis of the nuclear power engineering structures.The results of numerical examples showed that these calculation models were reasonable and feasible.The seismic settlement of subsoil is considered to be one main reasons of building failure.During an earthquake,the materials of subsoil will be damaged and its modulus will be decreased.The settlement due to earthquake could be evaluated by softening modulus method which deals the seismic settlement as the difference deformation that can be calculated by FEM under gravity loading using the decreasing modulus after earthquake and the initial modulus before earthquake.The seismic settlement of a certain subsoil with five layers was calculated by the softening modulus method,and it shown the results are reasonable and reliable.