中文摘要：

在主应力方向的旋转过程中，主应力方向与塑性主应变增量方向之间存在着非共轴现象。基于屈服角点结构非共轴理论，建立了一种非共轴本构模型，通过有限元软件ABAQUS的二次开发子程序UMAT，将该模型运用到有限元数值计算中。首先，对中密砂单剪试验进行数值模拟，研究了非共轴现象及其对应力一应变关系的影响。然后，针对偏心荷载作用下条形浅基础荷载一变形特性进行数值分析，研究了非共轴现象对荷载一位移关系的影响。研究结果表明：非共轴模型计算得到的荷载增长速度滞后于共轴模型计算结果的增长速度；在地基变形的初期，非共轴现象比较明显，主应力方向的减小速度要滞后于塑性主应变增量方向的减小速度；随着地基沉降的增加，非共轴现象逐渐减弱；非共轴模型与共轴模型计算结果之间的差异在应变硬化情况下更加明显。

英文摘要：

During the process of the rotation of the direction of soil principal stress, there is a non-coaxial phenomenon between the di- rections of the principal strain rate and the principal stress. A non-coaxial constitutive model is suggested based on the yield vertex the- ory, which is applied to the FEM analysis by the user-defined subroutine UMAT in ABAQUS. Firstly, the simple shear test of medium dense sand is simulated to study the non-coaxial phenomenon and its influence on the relationship between stress and strain. Secondly, the non-coaxial model is applied to the numerical analysis of the load-deformation characteristics of shallow foundation under eccentric loading, and the non-coaxial phenomenon＇ s influence on the load-settlement relationship is studied. The results show that： the increas- ing trend of the load obtained by the non-coaxial model is behind that obtained by the coaxial model; at the early stage of deformation, the non-coaxial phenomenon is obvious, and the decreasing trend of the directions of the principal stress is behind that of the directions of the principal strain rate; non-coaxial phenomenon decreases with increasing of settlement; and the difference between the results of the coaxial and non-coaxial models is more obvious in the case of strain hardening.