超长钻孔灌注桩有限元分析.pdf

河北工业大学硕士学位论文超长钻孔灌注桩有限元分析姓名:时长春申请学位级别:硕士专业:岩土工程指导教师:徐东强20061201河北工业大学硕士学位论文i 超长钻孔灌注桩有限元分析摘要随着高层建筑的增多,超长桩因其具有高承载力使其用量日益增多。尽管超长桩已被大量使用,但对这类桩的荷载传递机理到目前为止还不很清楚,超长桩的设计仍按普通桩的计算理论进行,迄今还没有符合实际的计算方法。超长桩的现行规范设计法并非建立在超长桩的承载变形机理深入研究的基础之上,存在理论与实际之间的矛盾,因此,开展超长桩承载性状研究和提出超长桩合理的设计方法不仅是桩基理论自身发展的需要,更是工程界的迫切要求。因此,在前人研究工作的基础上,本文采用三维弹塑性接触非线性有限元法,进一步研究超长桩在竖向荷载下承载变形特征,比较超长桩与一般桩的异同。结合工程实例,基于ANSYS建立了有限元的计算模型,主要分析了桩身模量、桩长和桩径等因素对荷载-沉降关系桩侧摩阻力的发挥性状、桩身轴力的传递性状和桩身压缩量的影响。分析试验结果和有限元计算结果,提出了一些规律性的结论和建议。结论如下:,侧阻先于端阻发挥,侧阻本身在各土层的发挥也是异步的。上部土层首先达到极限摩阻力,随荷载的增加下部土层逐渐再达到极限摩阻力。,桩长在一定长度范围内,接近桩端处,出现桩身侧阻力强化效应。 ,由于在桩顶沉降达到控制值时,桩端沉降量小,远未达到桩端阻力完全发挥所需要的桩端沉降量,使得桩端阻力不能充分发挥。这说明按照传统的设计方法中确定的超长桩的承载力是不准确的,因为在极限荷载下桩端阻力并没有得到充分发挥。,当桩长超过一定长度时,单纯增加桩长,不能有效的提高承载力,因为此时桩顶位移可能已经达到了沉降控制要求。,应取适当的桩径,才能充分发挥其桩长的作用。但增大桩径,会明显增加混凝土的用量,造价提高较多。因此,对超长桩,在设计中应考虑各种因素,合理地选择合适的桩径和桩长。关键词:超长桩,承载性状,静载荷试验,有限单元法大直径超长钻孔灌注桩有限元分析ii FINITE ELEMENT ANALYSIS OF SUPER-LONG BORED PILES ABSTRACT With the development of super-long buildings, it is necessary to massly use super-long piles because of their high bearing capacity. Though a large number of super-long piles have been used, its load-transfer mechanism is not distinct. By now, its design method still adopts that of the ordinary piles, which disagrees with practical situation. The design method of super-long pile in the applicable codes and standards is not based on the mechanism of load-bearing and deformation. Therefore, the research on the load-bearing properties and the reasonable design method of the super-long piles is important to meet the requirements of the theory and the reality. Therefore, in this paper, based on the other research works, the three-dimensional non-linear finite element calculation technology is adopted to study the load-transfer mechanism of super-long piles and find out the different properties between super-long piles and ordinary piles. Furthermore, with a project example,by the ANSYS, the three-dimensional simula