Development of cyclic hardening/degradation soil model for analysis of wave propagation characteristics during earthquake

Abstract

In the dissertation, the cyclic soil behavior model, which can accommodate the cyclic hardening and degradation, was developed by modifying the original parallel IWAN model and the applicability of the developed model was verified by performing torsional shear tests on sands. Nonlinear 1-D site response analysis program was developed using the proposed model and the effects of cyclic hardening and degradation behaviors on site responses were evaluated. The cyclic hardening and degradation behaviors under cyclic loading conditions may be attributed, mainly, to volume change or particle rearrangement of soil. In order to consider these behaviors, the cyclic threshold strain, above which the backbone curve deviates from the original curve, was defined and the accumulated strain was determined by summation of the strains above the cyclic threshold in the stress?strain curve with applying Masing rule on unloading and reloading curves. The isotropic hardening or softening elements are attached to the original parallel IWAN model. The slip stresses in the isotropic hardening and softening elements are shown to increase and decrease respectively according to the hardening and degradation functions. The hardening and softening functions have a single parameter to account for the cyclic hardening and degradation and defined by the symmetric limit cyclic loading test in forms of accumulated shear strain which incorporates the characteristics of cyclic threshold strain. Two types of torsional simple shear tests were performed on two dry sands. Symmetric limit cyclic loading tests were performed to evaluate the model parameters and to investigate the model behavior under different relative densities and confining pressures. Irregular loading tests were performed to verify the applicability of proposed model on transient loading condition. The comparison between model estimation and experimental result provides an opportunity to understand the capability of the proposed mo...