等截面抗拔桩承载力和变形性状研究

发布时间：2018-03-06 12:00

本文选题：抗拔桩　切入点：有限元　出处：《华南理工大学》2013年硕士论文　论文类型：学位论文

【摘要】：抗拔桩是抗浮工程中经常采用的有效抗拔基础。虽然人们在抗浮工程中广泛的应用了抗拔桩基础并收到了很好的抗浮效果，但是，对于抗拔桩的承载机理、承载力和变形性能的认识，远远落后于工程实践。因此，从桩土相互作用的角度，采用综合方法深入研究等截面抗拔桩承载力和变形性状的问题，既有理论意义，又有工程应用价值。本文在前人研究的基础上，对等截面抗拔桩的基本破坏形态、极限承载力的确定、抗拔桩的变形计算方法以及桩侧摩阻力的发挥特点等作了比较详细的阐述。具体内容为：抗拔桩的破坏形态有沿桩土接触界面的剪破、与桩长等高倒圆锥台形剪破、复合剪切面剪破三种；基于假定的破坏面，推导出相适应的破裂面方程，就可以确定抗拔桩的极限承载力；抗拔桩的变形计算方法包括弹性理论法、理想弹塑性法以及荷载传递法等；土体的剪缩剪胀性、土体单元主应力方向等因素对桩侧摩阻力都具有较明显的影响。通过建立的桩土共同作用模型的有限元模拟研究，较系统地揭示了抗拔桩的桩长、桩径以及桩身弹性模量等因素变化，对抗拔桩承载机理产生的影响。具体表现为，抗拔桩桩长、桩径的变化对抗拔桩的承载和变形能力有较大影响，而抗拔桩桩身材料弹性模量对抗拔桩承载能力的影响不大；相对于抗拔桩承载力和变形能力而言，抗拔桩的桩长、桩径增大到一定程度后，桩长和桩径的增长对抗拔桩的承载变形能力帮助减小。因此可以推断，在确定工作条件下的抗拔桩，存在一个有效桩长与有效桩径，使得抗拔桩能发挥最好的抗拔效果。采用了双曲线荷载传递函数来分析抗拔桩的工作机理。荷载传递法的桩土模型中，桩体视作由多个一维弹性单元组成，桩土间相互作用力则采用非线性弹簧进行模拟。该桩土模型力学概念简单、明了，，很好地解释抗拔桩的荷载传递过程。采用荷载传递法描述荷载传递机理，关键是选取符合抗拔桩实际工作情况桩侧摩阻力-位移函数。通过选取广泛应用的双曲线荷载传递函数，对抗拔桩的荷载传递进行了模拟，得出的模拟计算值与实测值接近，说明荷载传递法能够很好的解释抗拔单桩的荷载传递过程。基于分段配筋原则对抗拔桩的配筋设计进行了优化。根据抗拔桩的桩身轴力变化曲线，在接近桩端部分，抗拔桩的轴力逐渐趋于零。在轴力较小的下半段桩身，仅需少量的钢筋就可以提供足够的拉拔力。因此，可以在桩身的中间某截面裁截去一定数量的纵筋，仅保留部分纵筋伸长至桩底，达到优化配筋的目的。
[Abstract]:Uplift pile is an effective uplift foundation often used in anti-floating engineering. Although the foundation of anti-drawing pile has been widely used in anti-floating engineering and good anti-floating effect has been obtained, the bearing mechanism of anti-uplift pile is studied. The understanding of bearing capacity and deformation performance lags far behind engineering practice. Therefore, it is of theoretical significance to study the bearing capacity and deformation behavior of uplift piles with equal cross-section by comprehensive method from the point of view of pile-soil interaction. Also has the engineering application value. On the basis of previous studies, this paper determines the basic failure form and ultimate bearing capacity of uplift piles with constant cross-section. The calculation method of pile deformation and the characteristics of pile side friction are expounded in detail. The concrete contents are as follows: the failure form of the pile is shear along the interface of pile and soil contact, and the pile length is similar to that of the inverted cone table, and the concrete contents are as follows: the damage form of the pile is shear along the contact interface of the pile and the pile length. There are three kinds of shear failure in composite shear plane: based on the assumed failure surface, the suitable fracture surface equation can be derived to determine the ultimate bearing capacity of the uplift pile, and the deformation calculation method of the uplift pile includes the elastic theory method, Such factors as ideal elastic-plastic method and load transfer method, such as shear-shrinkage and shear-dilatancy of soil mass and principal stress direction of soil element, all have obvious effects on pile side friction. Through the finite element simulation study of the pile-soil interaction model, the changes of pile length, diameter and elastic modulus of pile body are revealed systematically. The bearing capacity and deformation ability of uplift pile are influenced greatly by the length and diameter of the pile, but not by the elastic modulus of the anti-drawing pile body, compared with the bearing capacity and deformation ability of the anti-drawing pile. When the pile length and diameter increase to a certain extent, the increase of pile length and diameter helps to reduce the bearing capacity of the pile, so we can infer that there exists an effective pile length and an effective pile diameter under certain working conditions. So that the anti-drawing pile can play the best anti-drawing effect. The hyperbolic load transfer function is used to analyze the working mechanism of uplift pile. In the pile-soil model of load transfer method, the pile body is regarded as composed of several one-dimensional elastic elements. The pile-soil interaction force is simulated by nonlinear spring. The mechanical concept of the pile-soil model is simple and clear, which can explain the load transfer process of the uplift pile. The load transfer method is used to describe the load transfer mechanism. The key is to select the friction-displacement function according with the actual working conditions of the pile. By selecting the widely used hyperbolic load transfer function, the load transfer of the anti-drawing pile is simulated, and the simulated calculated value is close to the measured value. It shows that the load transfer method can explain the load transfer process of single pile. Based on the principle of sectional reinforcement, the reinforcement design of the pile is optimized. According to the axial force change curve of the pile body, the axial force of the uplift pile tends to be zero in the near end of the pile, and in the lower half of the pile with less axial force, the axial force of the uplift pile tends to be zero. Therefore, a certain number of longitudinal bars can be cut off in the middle section of the pile body, and only a portion of the longitudinal reinforcement can be extended to the bottom of the pile to achieve the purpose of optimizing the reinforcement allocation.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU473.1

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