Seismic Response Analysis Of Nuclear Power Structure-pile Group-soil System

The dynamic interaction between nuclear power structure and pile group layered soil system is extremely complex,which is closely related to the dynamic stiffness of pile group foundation,the free field response of layered site,the layout form of pile foundation and the nonlinear dynamic characteristics of soil,nuclear island superstructure system and other factors.It is an important technical problem to be solved in the design of nuclear power structure under the condition of non-lithologic soft soil foundation.In this paper,a three-dimensional finite element model of nuclear power structure,pile group and soil structure is established by ANSYS software for an AP1000 nuclear island structure-pile foundation system.The direct stiffness method of viscoelastic artificial boundary conditions is applied to analyze the dynamic stiffness and ground motion input of the pile group foundation.At the same time,different pile foundation models are considered to reflect the influence of soil-structure dynamic interaction on the dynamic response of the superstructure and the internal force of the pile foundation.The main research contents and results of the thesis include the following aspects.(1)Research on site ground motion input.The equivalent linear constitutive model is used to reflect the nonlinear and hysteretic behavior of soil dynamic deformation.The viscoelastic artificial boundary is used to simulate the radiation damping effect of the infinite foundation.The free field response analysis is performed by NPSSI software.The effects of different foundation conditions on ground motion input are analyzed by comparing the acceleration response spectra of the bottom surface of the raft in three conditions: undisturbed soil field,raft-original soil site and raft-pile foundation treatment site.(2)Study on dynamic stiffness of pile group.By applying viscoelastic artificial boundary to the outer surface of near-field foundation,the dynamic stiffness of pile group foundation under different foundation conditions is calculated and analyzed.(3)Dynamic response analysis of nuclear power structure,pile group and layered soil system.The dynamic response analysis of soil-structure is carried out systematically,the acceleration response spectrum of superstructure is extracted,the results of pile foundation treatment site and undisturbed soil site are compared,and the influence of different foundation model conditions on the internal force of superstructure and pile foundation is discussed.(4)Comparative study on the calculation model of pile-soil interaction.The effects of pile-soil interaction model on the response of the superstructure were studied according to three different foundation models: undisturbed soil site,pile-soil complete bond,and soft layer around the pile.