改进的薄层单元在桩-土动力相互作用中的应用

Application of modified thin layer element to the analysis of dynamic pile-soil interaction

在地震荷载作用过程中,由于桩身材料性能与周围土体性质差异较大,土体在桩-土接触面上发生张开或滑移,该强非线性接触行为直接影响接触面附近土体与桩体应力状态,从而影响上部结构地震响应水平。真实桩-土接触面由于桩身表面混凝土约束关系,具有一定厚度且存在相关体变规律的接触带。通过有限元软件ABAQUS用户自定义单元UEL程序编写改进Desai薄层接触单元,在Desai薄层接触单元中加入Rayleigh阻尼项以模拟地震作用时桩-土强非线性接触行为能量耗散过程。接触面法向与两切向本构关系采用双曲线模型。规定了Desai薄层接触单元在桩-土接触面上的行为模式以模拟土体在接触面黏结、滑动、张开、再闭合等接触状态。建立精细三维桩-土-结构体系动力相互作用模型以研究改进Desai单元对上部结构峰值动力响应水平影响,为工程结构抗震设计时程分析提供参考依据。

The material property of soil significantly differs from that of pile, inducing the relative sliding or separation between soil and concrete pile during earthquake. The strong nonlinear contact behavior can directly affect the stress states of pile and soil near the interface, thus affecting the seismic response of superstructure. The real pile-soil interface does have a certain thickness due to the constraint relationship of concrete on pile, and the contact zone of related volumetric law does exist. A user-defined element （UEL） program based on modified Desai thin interface element is developed and then inputted into ABAQUS. In the modification process, Rayleigh damping is added into the interface element to simulate energy dissipation in the process of strong nonlinear contact behavior between soil and pile. Hyperbolic model is adopted in normal and tangential constitutive relation. Certain behavior pattern rules of modified Desai element on pile-soil interface are made to simulate the contact states such as bonding, sliding, separation and reclosing. A fine 3D pile-soil-structure model is developed to improve the effect of the modified Desai’s interface element on the dynamic response of superstructure. The result provides an instructive guideline for engineering design in time-history analysis.