Nonlinear Seismic Response Analysis Of 2-D Soil Based On Multi-yield Surface Constitutive Model

Seismic waves often exhibit significant amplification when they travel in a heterogeneous local site with soft soil layers and complex structure.It's one of the reasons of the serious damage caused by earthquakes.It is important to study the propagation laws of seismic waves in complex soil media.Both the nonlinear characteristics of soils and heterogeneous media are seldom considered at the same time in the previous site response studies.The seismic response prediction results under complex site conditions such as sedimentary didn't match those of observed strong motion records very well.Some differences at some surface points are often observed in previous modelling.It can be seen that the establishment of high dimension soil nonlinear seismic response analysis method is a key problem to be solved reasonably for predicting seismic response.A typical sedimentary basin located on Lower Hutt,New Zealand with deep soft soil layers was selected in this thesis.The geological survey data was provided by New Zealand GNS organization.The two-dimensional multi-yield surface elastoplastic constitutive model proposed by Joyner and Chen is employed in this analysis.A two-dimensional nonlinear seismic analysis model of the basin are established based on the secondary development of ABAQUS software.Based on the New Zealand strong motion observation network,the strong motion records of the basin were obtained.The prediction results are verified by comparing the analysis results with the actual strong motion records.Furthermore,the researches on the basin effect,the influence of two-dimensional topography,the nonlinear characteristics,and the vertical ground motion amplification characteristics of the wave propagation in the basin have obtained some meaningful conclusions.The specific work is summarized as follows:1.The two-dimensional multi-yield surface constitutive model was transplanted to ABAQUS by writing a VUMAT subroutine,and the viscosity of soil was considered in Rayleigh damping based on the constitutive model.By setting up the viscous artificial boundary to simulate the infinite domain,the two-dimensional finite element nonlinear seismic response analysis model is finally established.The correctness of the model is verified by comparing with the literatures.2.A typical basin model was established for nonlinear parameter studies.The selection principles for damping coefficient and the method of the 2D multi-yield surface constitutive model were also studied.3.Based on the 2D nonlinear seismic response analysis model and the selection nonlinear parameters,the model of the LowerHutt basin in New Zealand was established.Based on modelling results,the basin effect,nonlinear characteristics of the basin and the difference between the prediction results of the two-dimensional model and the traditional one-dimensional model are analyzed.4.Based on the nonlinear response model for the LowerHutt basin in New Zealand,the vertical seismic response characteristics for the basin was studied.The effects of different input ground motion intensity on vertical seismic response were also studied.5.This paper summarizes the work of all parts,and puts forward the shortcomings of these work and the future prospects.