【作者】 邹新军；

【导师】 赵明华； 刘光栋；

【作者基本信息】 湖南大学 ， 岩土工程， 2005， 博士

【摘要】 随着山区高墩桥梁及大跨径桥梁的不断发展,超长基桩(特别是自由长度较大的高桥墩基桩)的应用日益广泛,桩身屈曲或纵向挠曲分析已成为一相当复杂而又具有重要理论与工程实际意义的课题。尽管国内外学者对此课题已进行大量研究,并提出了相应的理论解答,但多为基于第一类稳定问题的半解析解;试验方面,除早期国外学者所进行的一些研究外,国内虽已完成了部分工作,但也只是初步;至于国内相关行业的规范中,更因缺少可靠的试验数据与成熟的理论计算方法而仅能推荐一些经验公式。因此,为完善规范及便于工程实用,仍需从理论与试验上对桩身屈曲稳定问题进行更深入的研究。 本文首先基于m法假定,采用最小势能原理和变分法分别导得了桩身在无均布轴向荷载、作用有侧摩阻力、自重等载荷工况下的稳定计算长度与临界荷载解析解,进而导得了桩侧地基土反力系数呈一般幂分布时的桩身屈曲稳定分析能量法统一解,并系统地探讨了桩侧摩阻力、桩身自重及地基反力系数分布模式等对桩身屈曲稳定的影响规律:一般情况下可不考虑桩侧摩阻力的影响,而当桩顶自由长度较大时桩身自重的影响不容忽视;至于地基反力系数分布模式对桩身屈曲稳定的影响则与桩身埋置比例有关,埋置比例越大,则影响愈明显。为了考虑桩身可能初始缺陷等对桩身后屈曲稳定的不利影响,首次采用扰动法对桩身初始后屈曲问题进行探讨,获得了不同桩土刚度比、桩顶自由长度等因素对桩身初始后屈曲平衡路径的影响规律曲线。因基于第一类稳定问题的基桩屈曲分析能量法难以考虑桩土共同工作及非线性等复杂因素的影响,首次将新型的无单元伽辽金法引入桩基工程领域,将桩身屈曲视为第二类稳定问题进行数值分析,并对诸如权函数选取、位移边界条件施加、背景积分网格划分及内部位移不连续处理等基本问题进行了深入研究和探讨,然后采用所给出的两种位移边界处理技术对某理想嵌岩桩进行挠曲变形分析,其结果与解析解、有限元法的对比分析不仅验证了无单元伽辽金法的优越性,也发现了该法暂时存在的计算效率偏低、占用资源大等缺陷。随后,提出了处理桩土接触面上存在的材料与位移不连续问题的两类方法:当假定桩土变形协调时,按可视性准则分别采用修正变分原理与罚函数两种方法进行处理;对非变形协调,则基于线弹性—理想塑性接触模型给出了接触分析的非线性迭代算法。并针对桩身屈曲破坏时可能存在的材料非线性,给出了弹塑性问题的无单元伽辽金法算法。在此基础上,建立了桩身屈曲分析的数值模型,并开发出相应的计算程序PBAP_EFGM,其可近似考虑桩土共同工作、材料与几何非线性及桩身可能初始缺陷等因素的影响。另外,设计并完成了多组室内单桩屈更多还原

【Abstract】 With the continuous development of high-pier and wide-span bridges in mountainous areas, super-long piles (especially those high-pier piles with a major unsupported length at the top) are being widely used. And the buckling analysis of pile shaft has become a complicated problem of important theoretical and engineering significance. Though many scholars at home and abroad have done extensive study work on this problem, the corresponding theoretical solutions are mostly half-analytic and obtained on the basis of the first kind of stability problem. And besides those early buckling tests directed by overseas scholars, only some elementary work has been reported at home. As for the related professional criterions or regulations, some empiric formulas have to be proposed because of the absence of reliable test data and mature computation methods. Therefore, further theoretical and experimental research on the buckling stability of pile shaft has to be performed for the perfect of professional criterions or regulations and convenient engineering application.First, according to the m-method assumption by criterions, analytical solutions for the buckling length and load of pile shaft under no axial stress, side resistance and deadweight are derived respectively by using the minimum potential energy theory and variational method. Then, unified solutions by energy method for the general exponential distribution of subgrade reaction coefficient are obtained. Based on these solutions, influence rules by side resistance, deadweight and distribution model of subgrade reaction coefficient are probed into in detail. The comparative analysis shows that, the influence by side resistance can usually be neglected, while effect by the deadweight of pile shaft can’t be ignored especially when an unsupported length exists at the pile top. And the embedment proportion of pile shaft determines the influence by subgrade reaction coefficient, i.e., a larger embedment proportion causes more obvious effect. In order to consider the disadvantageous effect by those possible initial defects, the perturbation method is applied to discuss the behavior of initial post-buckling of pile shaft. And the influencing curves by the stiffness ratio of pile shaft to the surrounding soil, the length of unsupported part at the pile top, and other factors are presented as well. As the analytical solutions for buckling analysis of pile shaft by energy method are obtained according to the first kind of stability problem and can’t consider some complicated factors such as the pile-soil interaction and nonlinear effect, the newly developed element-free Galerkin method (EFGM) is introduced for the first time into the field of pile foundation for buckling analysis of更多还原