Research On Numerical Model Of Dynamic Stiffness Of Buried Foundation Based On Continued Fraction Method

Seismic projects of nuclear power,hydropower and other major projects have greatly promoted the numerical analysis of soil-structure dynamic interaction.In order to better solve the dynamic stiffness of unbounded foundations,the scaled boundary finite element method(SBFEM)dynamic stiffness numerical model is established based on dimensional transformation.Combined with the finite element method to solve the dynamic stiffness of two-dimensional unbounded foundatiom with complex form in the near-field medium.The method is further applied to solving the dynamic stiffness of three dimensional unbounded domain,which is used to analyze the influence on foundation embedded.Finally,a million-kilowatt nuclear power plant structures has been taken as the research object,the effect of site excavation on the dynamic response of the superstructure is discussed based on the visco-elastic boundary model.(1)The solution of dynamic stiffness of unbounded foundation is an important part of the analysis of soil-structure dynamic interaction.The continued fraction based on SBFEM is one of the effective methods to solve the fundamental dynamic stiffness of an unbounded domain in recent years.However,for practical parameters of the site,the degree of the difference amplifise about the magnitude of the stiffness matrix or flexibility matrix entries as increasing order of the continued-fraction,which leads to the unstable solution of the dynamic stiffness of thr unbounded domain.Aimed at the problem above,The real parameters of the site are converted to nondimensionalized form,based on which the dynamic stiffness matrix is calculated.Then the computational results are reduced to the real dimension.The numerical results show that this method can effectively reduce the error and improve the accuracy of calculation.(2)The finite element was used to simulate the near-field soil,and the improved continued-fraction based on dimensional transformation was used to simulate the unbounded domain.Thus,a solution model based on the above two methods to jointly solve the foundation dynamic stiffness was established.An example is introduced to verify that the above method is feasible and stable,and the fine division of the near field has a certain correction effect on the low frequency section.Furthermore,the influence of the foundation section form on the foundation dynamic stiffness is discussed.Then,based on the fact that the circular section strip foundation is embedded in the unboundded foundation,the influence of the material parameters in the near-field region on the dynamic stiffness in the unbounded domain is discussed.When applied to the solution of the dynamic stiffness of a two-dimensional transversely isotropic unbounded foundation,it is verified that this method can be used to solve the dynamic stiffness of heterogeneous foundation.Finally,the transmission boundary is simulated by the improved continued fraction based on dimensional transformation,and the dynamic response of a certain region under the effect of resonance is calculated.(3)the improved continued-fraction method based on dimensional transformation is applied to the simulation of the three-dimensional unbounded foundation dynamic stiffness.The results obtained from the above method are compared with the numerical results based on the visco-elastic boundary harmonic analysis method and the ASCE4-98 standard.The influence of the foundation embedment on the dynamic stiffness of the unbounded domain is discussed in detail.Taking the lumped mass model of a million-kilowatt nuclear power plant as the research object,the influence of the foundation embedded on the seismic response of the upper factory building was discussed based on the visco-elastic boundary model.The calculation results show both the dynamic stiffness and the earthquake response are affected by the foundation embedment.