【作者】 王新；

【导师】 毛坚强；

【作者基本信息】 西南交通大学 ， 岩土工程， 2003， 硕士

【摘要】 桩土之间的接触面对桩基的受力特性有着重要的影响，在计算中不应无视它的存在。有限元等数值方法虽然已在桩基特性分析中得到了广泛的应用，但计算中对桩土接触面的处理却仍然是一个并未很好解决的问题。本文的主要目的就是将该类问题作为接触问题进行处理，然后建立一种桩土相互作用的计算方法，并应用于桩基的工程实践之中。 在有限元中计算中，常用的方法是利用节理单元来模拟接触面。本论文对这种方法经过分析之后，发现这种处理方式对接触面的描述并不合理，也无法反映出接触面的主要力学特征。同时指出，将桩土相互作用按接触问题来处理，可以更好地反映出该接触面的主要力学特征，即：(1)接触面具有相应的“抗剪强度”，即当接触面上的某一点处的切向应力小于该点处的抗剪强度时，该处桩土共同变形；达到其抗剪强度时，则沿切向发生滑动；(2)在整个变形过程中，桩与土不能互相侵入。 针对于接触问题的求解，目前已经发展了很多计算方法，如数学规划法、罚函数法等。本文采用的是[2]中提出的“自由度法”，并根据其计算原理建立了轴对称等参数单元的有限元计算公式，并详细介绍了弹塑性接触问题的有限元求解实施过程。“自由度法”涉及到的概念与普通的接触有限元相比，既有同也有异，因此作者在阐述本法相关概念的同时，还与普通接触有限元的处理方式作了对比。 传统的有限元程序采用结构化的语言编写，由于结构化语言本身的缺陷，使有限元程序的更新、扩展功能受到很大的限制，80年代出现的面向对象编程思想为解决这个问题提供了转机。目前，已有学者将面向对象编程思想引入到有限元编程当中，但在接触问题中，却研究较少。本论文中，作者将面向对象编程的思想应用于接触问题有限元程序的编制，并建立起了轴对称接触问题的对象类框架。 完成上述工作后，作者对西昌某工地现场的两根试桩进行了计算分析。通过计算，得到相应的荷载—沉降曲线、轴力图、桩侧阻力图、塑性区、土的竖向位移等值线、桩的滑移过程等结果，并与现场试验结果吻合较好，说明用本文方法计算分析桩基的工作特性是可行和有效的。更多还原

【Abstract】 As the interface between pile and geotechnical media effects the mechanical behaviors of the pile foundation significantly, a reasonable model is critical in the calculation and analysis of pile. So far, though finite element method has been widely used in pile foundation engineering, it still remains an intractable problem to simulate the interface ideally in numerical analysis. The author deems that it is a practical way to treat this problem as contact problem in solid mechanics. The main intension of this paper is to develop a finite element approach for axisymmetric contact problems and apply it to pile foundation.So far, in the FEM analysis, the contact interfaces usually are taken as the joint element, which was introduced by Goodman early in 1968. Nevertheless, in the model, the contact interfaces are charactered simply with stiffness Kn and Ks, whick is not perfect and rigorous in the view of solid mechanics and rather rough for the description of the behavior of the interfaces. In contrast, taken as a contact problem, the principal characters of the interfaces can be reflected: (1) the contact interface is of shear strength which implies that a generic pair of contact points on the interface will displace coincidentally if the tangential force at this point has not reached the limit resistance, else, relative slide between the points will occur along the tangential direction. (2) No matter the relative slide occurs or not, the contact bodies cannot invade each other in any wise.There are considerable numbers of research concerning finite element method on contact problem and a lot of techniques such as mathematics programming, penalty method and so on. The method depends on the ’Freedom Degree’ technique, which was developed in [2], is an effective method to solve contact problems. In this Paper, on basis of the theory, the anisymmetric isoparametric FEM formulae wereconstructed with the principle of virtual work. Moreover, the implementation of these formulae on the computer is also discussed in detail. Also, the similarity and difference between the method and conventional method are compared.Most of the present finite element programs are written in the structural language, such as FORTRAN, C and so on. As the size of programs grows, the defects of the structural language, which are hard to maintain and update, are exposed. The object-oriented programming (OOP) that appeared in 1980’s can solvethis problem well. So far, though OOP has been applied to the field of FEM programming, it rarely be used to solve contact problems. In the paper, the programming of contact FEM code with technique of OOP is discussed and the program frame with object-class is established.Lastly, two axially loaded bored piles in some building site near Xichang city was calculated with the method and some useful data and curves including load-settlement curves and distribution of friction resistance etc. are presented. The accordance between the results of calculation and in-situ test verifies the validity of the method developed in the paper.更多还原