Research On Soil-structure Interaction And Reliability Of Main Building In Conventional Island Of Nuclear Power Plant Based On Spectral Stochastic Finite Element Method

The seismic safety design of a nuclear power plant faces two major problems.One is the complexity of the soil-structure interaction and the other is the uncertainty in the project.Although the current seismic design has begun to consider soil-structural interaction,the stochastic analysis theory is still in its infancy.It is far less mature than the deterministic analysis theory,which makes random analysis and reliability design less applicable in engineering.Using deterministic analysis methods makes the design of the structure conservative and its economical is relatively poor.As facilities with significant safety and production significance,nuclear power plants should be designed with more precise analysis.For this reason,a reliability analysis method based on spectral stochastic finite element method for the structure of a conventional island main building in nuclear power plants is proposed in this paper.The main research work and conclusion are as follows:A spectral stochastic finite element method considering soil-structure interaction and the randomness of soil parameters was proposed.Based on the mathematical theory of random field,the stationary normal random field and its correlation models of the soil parameters were established.Using the Karhunen-Loève series expansion method to discrete random fields,the discretization error decreases with the increase of the number of expansion variables.For random field with a smaller correlation length,the number of Karhunen-Loève expansion variables should be appropriately increased.Based on the discretization of random fields and Winkler elastic foundation model and Eular beam theory,the beam element on Winkler elastic foundation considering the randomness of soil was constructed.Combined with the polynomial chaos expansion of stochastic responses,the spectral stochastic finite element equations were established considering the soil-structure interaction and the randomness of soil parameters.Based on the spectral stochastic finite element method considering soil-structure interaction,the program SSI-SSFERUM was developed on Matlab platform for soil-structural interaction and reliability analysis.Using the SSI-SSFERUM program,the random displacement response of the conventional island foundation under vertical static load was firstly analyzed.The mean and standard deviation of the maximum settlement are located at the side columns,and the coefficient of variation of the response is greater than the coefficient of variation of the input parameters.Secondly,the influence of variation coefficient and correlation length of soil random field on the reliability of soil settlement was studied.The surpassing probability of soil settlement to the limit value increases linearly with the coefficient of variation of soil random field,and gradually increases with the correlation length.Finally,by comparing with Monte Carlo simulation results based on Latin Hypercube sampling technique,the computational efficiency and calculation error of the spectral stochastic finite element method were analyzed.Taking the steel structure of the conventional island main plant as the analysis object,the influence of the interaction between the superstructure and the soil on the dynamic response of the superstructure was analyzed by using the SSI-SSFERUM program.The analysis results show that the SSI effect increases the displacement response of the superstructure as a whole,with an increase of between 10% and 50%.The SSI effect reduces the acceleration response of the superstructure and the flexible foundation has a certain shock absorption effect.Based on the spectral stochastic finite element method,the random response and reliability of the structure under seismic loading were analyzed.With the goal that the failure probability of the structure does not exceed 0.10,the steel structure of the main building can withstand a rare earthquake with an intensity of about 8.5 degrees.Compared with Monte Carlo simulation results,the error of spectral stochastic finite element calculation is small,and its computational efficiency is higher.