【作者】 宋军；

【导师】 周建庭；

【作者基本信息】 重庆交通大学 ， 桥梁与隧道工程， 2014， 博士

【摘要】 最近几十年，斜拉桥在我国取得了飞速的发展，其中混凝土斜拉桥占据较大比重。在外荷载、温度荷载以及混凝土收缩徐变等因素作用下，混凝土斜拉桥索塔承受着拉索传递的巨大压力，据不完全统计，全国有75%的索塔发生开裂现象，严重影响斜拉桥的寿命甚至威胁人们的生命安全，因而索塔开裂的行为引起越来越多研究人员的关注。本文引入分形损伤理论对斜拉桥高大索塔进行安全性评价，提出了基于裂缝分布状态的高大索塔安全状态评价模式。通过理论分析、模型试验与数值模拟方法，分别从宏观和细观的角度，研究了裂缝的开裂、扩展及结构破坏过程，建立了一套以分形损伤为理论支撑的用于评价索塔开裂后安全状态的新方法，研究了索塔开裂后裂缝分布分形维数与荷载等级之间的关系，为后期实桥应用提供了理论与实践指导。本文的主要研究内容和结论如下：①在研究智能移动视频扫描装置监测高大塔柱裂缝技术的基础上，针对各种滤波算法适用范围和裂缝图像特点的研究，提出中值滤波法，将进行裂纹图像的二值化与提取方法用于裂缝图像分割，并采用图像拼接技术、裂缝矢量化技术及裂缝图像模拟重现技术，实现了裂缝监测信息处理。②把三维裂缝求解问题转换为两个平面的裂缝求解问题，即等效成一个无限大板中心裂纹受到无穷远处的单向拉伸力作用和一个无限大板在单边裂缝受到拉伸荷载作用，采用双悬臂梁理论计算裂缝宽度与深度的关系，推导了裂缝深度的计算公式，为研究三维裂缝问题提供了新思路；根据裂纹分形模型建立混凝土开展裂缝的应力强度因子表达式，结合断裂力学理论，推导了应力强度因子在直线型裂纹和裂纹不规则扩展这两种假设下的关系。③根据斜拉桥索塔的特点，基于子模型技术，采用FRANC3D软件，模拟了索塔裂缝的萌生以及扩展的过程，并计算了索塔结构的应力强度因子与分形维数之间的关系、分形维数与荷载等级之间的关系；建立weibull随机概率分布与材料裂缝分布之间的关系，结合断裂损伤力学与分形理论来评价混凝土索塔表面开裂的严重程度。④建立了基于离散元的颗粒流微观数值模型，采用Fish语言编写程序，模拟混凝土材料的细观破坏过程，并选取了三种不同半径、不同数量团簇研究混凝土开裂性能，当团簇数量越多，对材料性质的提高越显著；当团簇半径越大、结构体系越稳定，则性质增强效果好。团簇材料的破损机理在于随着团簇半径的增加，基质所占比例减小，基质中更容易产生微裂纹，结构表面更容易破坏。⑤基于多尺度均匀化理论，采用有限元法建立了混凝土细观-宏观等效力学性能的多尺度模型，并以索塔表面为例建立有限元模型，对混凝土材料的宏观整体与细观局部化效应进行分析。⑥完成了索塔节段试验模型，验证了上述理论和方法的可靠性，研究了索塔开裂后裂缝分布分形维数与荷载等级之间的关系，为后期实桥应用提供了理论与试验基础。更多还原

【Abstract】 Cable-stayed bridge got rapidly developed in designing and constructing duringthese decades. Concrete cable-stayed bridge occupy larger proportion. Tall cable towers’cracking behavior has aroused more and more attention from the researchers. Under theouter load, temperature load, concrete shrinkage and creep effect, tower of concretecable-stayed bridge suffers huge pressure transmitted by cables. According toincomplete statistics, tower fracture occurs in80%of the Chinese cable bridges, itseriously affects the cable-stayed bridge’s safety and even people’s life. This articleintroduced the fractal damage and the fractal fracture mechanics into safety assessmentof cable-stayed bridge’s cable tower. Then, tall tower’ safety state evaluation model isput forward based on fracture distribution in this paper Beginning and expansion offractures and the structure failure process are analyzed from the macroscopic andmesoscopic point of view through theoretical analysis. This paper set up a new methodsupported by the theory of fractal damage for evaluation of cable tower safety state aftercracking occurs. The relationship between the load level and fractal dimension offracture distribution after the cable tower cracking occurs is researched and it providestheoretical and experimental basis to further application to real bridge. The followingmainly innovative work has been done in this paper.①Tall tower’s crack intelligent mobile video scanning device monitoringtechnology is put forward Median filtering method is put forward according to range ofall kinds of filter algorithm applicable and the crack image characteristics. Crackimage’s binarization and extraction method are used to crack image segmentation.Crack monitoring information processing is realized by image mosaicing, crack vectorquantization and cracks image’s simulation technology.②The solution of the three-dimension crack is equivalent to solutions of twotwo-dimension crack. One is equivalent to solution of center crack of infinite-sized plateunder the uni-axial tensile force from infinity distance, the other is equivalent tosolution of unilateral crack of infinite-sized plate under the tensile load. Relationshipbetween crack height and depth is calculated with double cantilever beam theory, itprovides a brand new method to research three-dimension crack problems. Stressintensity factor expression of tall cable tower’s concrete crack is established based on crack fractal model. The relationship between stress intensity factors under linear crackassumption and irregular crack extension assumption is deduced combined with fracturemechanics theory.③Process of the initiationand propagation of cable tower’s cracks is simulatedbased on the submodel technique and FRANC3D software combined with thecharacteristics of the cable-stayed bridge’s tall tower. The relationships between stressintensity factor of the cable tower structure and the fractal dimension, fractal dimensionand the bearing capacity is calculated out. The relationship between weibull randomprobability distribution and the material cracks’ distribution is established. The severityof the cable tower of concrete surface cracking is evaluated combined with fracturedamage mechanics and fractal theory.④In this paper, the micro particle flow numerical model based on discrete elementis established and the mesoscopic damage process of concrete is simulated with Fishsoftware. Concrete cracking performance is researched with selecting three kinds ofconcrete particle flow with different radius and number of clusters. As a result, thematerial properties improves significantly while the number of clusters increases Thelarger clusters radius is, the greater the stability of the structure system and the betternature of the enhancement effect would be. Mechanism of clusters material’s damagecould be concluded as following. With the increasing of radius of clusters, proportion ofmatrix would decreases, and the matrix of micro cracks occurs more, at the same time,structure surface damages more easily.⑤Based on the theory of multi-scale homogenization. The finite element method isadopted to establish the concrete mesoscopic-macro equivalent mechanical propertiesof multi-scale model. At the same time, as an example, a finite element model of thesurface of the cable tower is established for macro and micro effect analysis to concrete.⑥Cable tower segment model test was done to verify the reliability of thetheoretical system. The relationship between the load level and fractal dimension offracture distribution after the cable tower cracking occurs is researched and it providestheoretical and experimental basis to further application to real bridge.更多还原