【作者】 徐腾飞；

【导师】 赵人达；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2010， 博士

【摘要】 由于具有良好的力学性能,特别是良好的抗压性能,钢管混凝土已广泛应用于建筑结构中,并在桥梁结构中多用作拱桥拱肋。雅泸高速公路中首次采用劲性骨架钢管混凝土做为桥墩。本论文以腊八斤连续刚构桥为研究背景,开展钢管混凝土桥墩稳定性研究,其中最高桥墩达182米,为亚洲第一高墩。本文内容主要包括以下三个部分：论文的第一部分,在阅读大量国内外文献基础上,综述了钢管混凝土承载能力与可靠度研究现状。并提出了进行钢管混凝土稳定承载能力分析与可靠度研究的课题。论文的第二部分,主要解决钢管混凝土非线性稳定极限承载能力的问题。首先建议了考虑偏心影响的约束混凝土应力—应变关系,利用退化梁理论编制了钢管混凝土材料非线性分析的有限元程序,并利用弧长法求解钢管混凝土非线性问题。采用钢管混凝土轴压与偏压试验,验证本文非线性有限元程序的正确性。利用非线性分析程序与既有钢管混凝土短柱偏压试验,研究钢管混凝土偏压柱的受力机理。研究结果表明在偏心荷载作用下,核心混凝土部分受拉开裂,开裂程度与偏心率有关。核心混凝土开裂后,混凝土体积膨胀受到抑制,导致套箍效应削弱。钢管混凝土构件在轴向荷载与小偏心荷载作用下,破坏时以混凝土受压破坏为主；大偏心与纯弯构件破坏时,核心混凝土大量开裂,构件破坏形式为钢材受拉屈服,其承载能力主要取决于钢管强度与含钢率；介于小偏心与大偏心之间的构件,其破坏时混凝土部分受拉开裂,钢管混凝土的套箍效应受到削弱。为了解决钢管混凝土稳定极限承载能力的求解,在考虑材料非线性的有限元分析基础上,应考虑几何非线性分析。论文利用U.L列式推导了退化梁单元的几何刚度矩阵。利用已有的钢管混凝土长柱,钢管混凝土拱试验与本文开展的超高墩模型试验,验证了本文的非线性有限元程序的正确性。利用参数分析,考察几何非线性对承载能力的影响。以腊八斤大桥中的钢管混凝土桥墩为例,对混凝土强度等级,钢材型号,轴向荷载偏心距展开参数分析。论文的第三部分,主要解决钢管混凝土非线性稳定极限承载能力的可靠度分析问题。首先利用蒙特卡罗方法,考察了钢管混凝土短柱轴压极限承载能力概率分布,并得到钢管混凝土轴压短柱可靠度的简化计算公式。其次,介绍了钢管混凝土结构初始几何缺陷的一致缺陷模态法与随机场缺陷法描述两种方法。讨论了随机网格划分数目的上限问题,提出了采用插值技术的随机场网格离散方法,并研究该方法的离散精度。利用已有的文献中的可靠度分析结果,验证了该方法的正确性与有效性。最后,利用响应面理论,建议了钢管混凝结构稳定极限承载能力的可靠度计算方法。利用优化原理,采用序列无约束极小化技术,解决由于非线性引起的FORM验算点搜索困难。利用钢管混凝土柱,钢管混凝土拱与钢管混凝土超高墩的可靠度分析实例,对几何非线性与初始缺陷的影响,稳定系数的取值,钢材、混凝土材料特性与径厚比对可靠度影响等问题展开讨论。更多还原

【Abstract】 Because of the good mechanical performance, the concrete-filled tube (CFT) is widely applied in the structure. CFT usually is demonstrated as a suitable structural element for arch ribs through bridge engineering practices, for the CFT element exhibits excellent compressive resistance capacity. Rigid framework with CFT was in service as super high pier in Ya Lu High Way. The stability of CFT piers are studied, relying on the LaBaJin and HeiShiGou continuous rigid frame bridge in this thesis, of which is the highest pier in Asia (182m). The dissertation includes three parts mainly:In the first part, based on a large number of literatures, the overviews of CFT structures and reliability are undertaken. The research project to study the ultimate resistance and reliability of CFT structures is put forward.In the second part, the nonlinear analysis of ultimate stability resistance is solved. First, a modified stress-strain relation for confined concrete which involves the influence of load eccentricity on confining pressure is proposed. The nonlinear finite element software of CFT is presented, adopting in formulation of degenerated beam element. To study the whole-process behavior of the CFT structure, the arc-length method is introduced in the nonlinear analysis program. The nonlinear behaviors of experimental CFT short columns are investigated, and the accuracy of the proposed constitutive model for confined concrete is mainly concerned. The results demonstrate that because of the crack of confining concrete with increment of eccentricity, the volume expansion of core concrete may decrease gradually, which leads the steel tube to provide weaker confining pressure on core concrete. It can be found that the core concrete is under whole-section compression, for the small eccentrically loaded column. On the contrary, as large eccentrically loaded column, a large portion of core concrete has been tensile cracked, and trivial confining pressure can be predicted. The case can be viewed as an intermediate state between small and large eccentrically loaded column, and a reduction of confining pressure may be an appropriate way to reflect the actual behavior. To solve the ultimate stability resistance of CFT, the geometrical nonlinearity should be considered as well as material nonlinearity. Second, geometrical stiffness matrix induced by large deformation is derived by updated Lagrange formulation. The behaviors of CFT slender test columns and test arch are simulated by the program developed in this part. The numerical data are suitable for the test results well. The effect of geometrical nonlinearity is studied by parametric analysis. In additional, the effects of concrete strength, steel strength and eccentricity to the ultimate resistance of high pier in LaBaJin Bridge are investigated. A model experiment of CFT high pier is accomplished. The accuracy of the nonlinear analysis program is proved by the experimental results.In the third part, the main propose is to present a reliability analysis method of nonlinear ultimate stability resistance of CFT. Probability distributions of ultimate resistance capacity of axial loaded short CFT column are investigated by Monte Carlo method. Means and mean-square deviations of those are presented by regression analysis. The distributions don’t refuse normal distributions through K-S method. The reliability index can be calculated easily with the suggested probability distribution model. Next, consistent mode imperfection method and random field imperfection method are introduced to deal with the initial imperfection of CFT structures. The upper limit of random variables of exponential decay model and square exponential decay model are induced, considering the range of variables in person computer. Based on the interpolating technology, a new method is suggested to mesh random field, verified by exiting literature. Finally, a general and versatile reliability analysis program of nonlinear ultimate bearing capacity of CFT is developed by response surface method. The difficult of searching designing point induced by nonlinear is solved through Sequential Unconstrained Minimization Technique (SUMT). The stability coefficient and influences of geometrical, initial imperfection, concrete strength, steel strength and D/t to reliability index are discussed in the numerical examples.更多还原