Finite Element Model For Earthquake Response Analysis Based On Viscous-spring Boundary And Its Application

This dissertation establishes the earthquake response analysis models based on the single-phase and saturated viscous-spring boundaries by using the general finite element software ABAQUS,and applies them to the study of local topography and soil-structure problems in engineering.1.Single-phase partThis dissertation combines the three-dimensional(3D)single-phase viscous-spring boundary and its corresponding equivalent nodal force method for seismic wave input with the equivalent linear approach for nonlinear analysis of soil.Firstly,a 3D frequency-domain finite element model for earthquake response analysis is established by using the Fourier transform and steady-state dynamic analysis methods.Then,a 3D time-domain finite element model for earthquake response analysis is established by employing the implicit dynamic analysis method.Applying the 3D frequency-domain and time-domain model,this dissertation studies the problem of local topography in single-phase site.The study emphasis is on the influence of soil nonlinearity on the earthquake response of local topography of sedimentary basin and canyon.It is found that there are significant differences between the nonlinear and linear earthquake response of 3D local topography,and there may be a noticeable phenomenon that the nonlinear response is greater than the linear response near the local topography center.For the 3D sedimentary basin,the peak values of nonlinear acceleration and response spectrum can be as high as 1.30 and 1.31 times of the linear results respectively.For the 3D canyon,the peak value of nonlinear acceleration can be as high as 1.17 times of the linear result.Applying the 3D time-domain model,this dissertation studies the problem of soil-structure in single-phase site under nonlinear condition.The study emphasis is on the change of nonlinear earthquake response of the beyond-code-specification tall building structure(BCTS)after considering the dynamic soil-BCTS interaction,which rests on a deep soft soil and has a structural type of frame-core wall with outriggers.It is found that the dynamic soil-BCTS interaction enlarges the lateral displacement,inter-storey drift and frame column base shear of BCTS,and the results show that the above responses of the soil-BCTS system can be as high as 1.79,1.22 and 1.76 times of those of the fixed-base BCTS model.2.Saturated partThe commonly used finite element software does not provide a two-phase element that can be adopted for dynamic analysis.This dissertation develops a two-dimensional(2D)element for time-domain dynamic analysis of saturated media in ABAQUS.On the other hand,in the derivation of the saturated viscous-spring boundary,it is assumed that the permeability coefficient is extreme,so the boundary is approximate and needs to be far enough from the area of concern.This dissertation studies the reasonable location of the 2D saturated viscous-spring boundary.It is suggested that,in the analysis of earthquake displacement or acceleration responses,the boundary should be located at an appropriate distance from the scattering source according to the situation,while in the analysis of earthquake stress response,the distance from the left-right-side boundary to the outer edge of local topography or structure should not be less than 12 times of the effective size of local topography or structure.This dissertation combines the 2D saturated viscous-spring boundary and its corresponding equivalent nodal force method for seismic wave input with the equivalent linear approach for nonlinear analysis of soil.By calling the developed element and employing the implicit dynamic analysis method,a 2D time-domain finite element model for earthquake response analysis is established.Applying the 2D time-domain model,this dissertation studies the problem of soil-sturcture in saturated site under nonlinear condition.The study emphasis is on the dynamic solid-fluid coupling effect on the earthquake response of tunnel structure in the case of considering nonlinearity and interaction.It is found that the overall distribution of the earthquake response of tunnel at the single-phase site is similar to that at the saturated site.However,from the results of this dissertation,the earthquake response of tunnel at the single-phase site is found to be more conservative than that at the saturated site.Ignoring the dynamic solid-fluid coupling effect can cause the maximum diametric deformation,internal force,and principal stress of the tunnel to be overestimated by up to 21%,38%,and 18%,respectively,and may cause the locations of the maximum internal force and principal stress to be misjudged.