【作者】 周尚猛；

【导师】 李亚东；

【作者基本信息】 西南交通大学 ， 桥梁与隧道工程， 2012， 博士

【摘要】 构造细节的疲劳行为历来是钢桥研究的重点问题之一。近年来,钢桥发展迅速,新型结构形式、构造细节和制造工艺不断涌现。钢桥应用范围的扩大(大跨、高速、跨海、重载),导致结构所承受的外荷载种类和水平逐渐增加；随着钢桥建造水平的不断提高,人们对结构经济和美学性能要求逐渐增强；其必然导致结构构造细节及其结构响应日益复杂,材料的利用效率日益提高。这些因素将导致钢桥疲劳和断裂的可能性逐渐提高。目前,钢桥疲劳强度评定方法是基于名义应力法的构造细节法；该方法以实验结果分类为基本依据,对材料疲劳失效机理体现不足。一方面,该方法不能涵盖所有构造细节,对钢桥典型构造细节和特殊构造细节的估算能力不足。另一方面,从材料疲劳失效机理出发,钢桥构件局部疲劳失效区域处于复杂应力应变状态,仅考虑单轴循环荷载效应无法合理表达钢桥构件的疲劳性能。本文拟从材料多轴疲劳失效理论层面解构钢桥构造细节疲劳问题,以期形成可用于工程实践的钢桥构造细节双(多)轴设计、预测和评定方法。为此,本文展开了以下几个方面的研究工作：(1)分析了影响材料疲劳强度的因素对钢桥疲劳失效的影响,总结出钢桥疲劳失效的主要特征。研究结果表明,在合理抗疲劳设计状态下,钢桥疲劳失效是指,以结构服役过程中所承受的可变荷载(汽车、列车等)为主导因素,桥位处自然环境因素综合影响,导致的材料高周、低频疲劳问题。回顾了材料多轴疲劳强度评定准则,分析了其适用范围,选取应力准则作为钢桥疲劳失效的双(多)轴评定准则。(2)研究了规范中典型构造细节的评估方法,以及特殊构造细节疲劳失效的特征；研究成果表明,特殊构造细节疲劳行为预测失效与现有钢桥单轴疲劳强度评估方法的局限性有关。在探明典型构造细节和特殊构造细节疲劳失效的力学诱导因素和疲劳裂纹分布状态的基础上,结合材料抗疲劳设计理论,发现钢桥构件疲劳失效具有明显的多轴特征。进一步提出了,钢桥多轴疲劳失效需要解决的两个典型问题,形成了“第一类多轴疲劳”和“第二类多轴疲劳”概念。(3)回顾了疲劳强度评定的常用方法,比较分析了名义应力法、热点应力法和局部法的适用范围；结合钢桥材料疲劳特征提出,将局部法应用于钢桥构件疲劳强度预测是求解钢桥多轴疲劳强度的有效途径：从常用的局部法中优选出应力场强法作为钢桥多轴疲劳强度求解的研究对象。(4)分析、研究和阐述了传统应力场强法的局限性。针对于此,建立了改进应力场强法。改进应力场强法,采用临界距离法对疲劳损伤区域的描述建立了新的场径求解方法,采用函数拟合技术更新了传统应力场强法的权函数求解方法。(5)对比分析了求解构件局部应力应变场的解析法和弹塑性有限元方法。根据钢桥构件材料特性及受荷特征,选取合理的弹塑性有限元本构关系模型作为钢桥构件局部应力应变场求解方法。(6)采用钢桥构件疲劳实验分析了传统应力场强法和改进应力场强法的预测性能。研究结果表明,改进应力场强法具有较高的预测精度。(7)采用传统应力场强法和改进应力场强法预测了钢桥节点板的疲劳强度。在此过程中,建立了“等效寿命荷载组”和“等效场径”的概念。二者的计算结果均表明,在疲劳寿命保持不变的情况下,某个方向上循环荷载增大,将导致另外一个方向上的循环荷载减小。传统应力场强法、改进应力场强法计算结果分别呈线性分布、次分布。在此基础上,本文提出了计入双轴疲劳效应的节点板单轴设计公式。更多还原

【Abstract】 Fatigue behavior of structure details is one of the key problems in the field of research of the steel bridge. In recent years, the steel bridge has developed rapidly, and new structure form, structure details and manufacturing technology of steel bridge are continuously emerging. The expansion of application scope of the steel bridge results in the increases of the kinds and level of load which the structures bear, such as long span, high speed, cross-sea, heavy load. With the increasing of construction level of steel bridge, the demand of economic performance and aesthetic properties is enhanced gradually, which will lead to the complexity of the structure and its mechanical response, correspondingly improve the utilization efficiency of materials. In this situation, the probability of fatigue and fracture of steel bridge will be significantly increased.At present, the classical assessment method of steel bridge fatigue strength is the structure detail method based on nominal stress method. This method is the evidence for the categorization of the fatigue tests of structure details, thus fatigue failure mechanism of materials is not reflected reasonably. On the one hand, this method can not include all kinds of structure details, and the ability of computational estimation of classical and special structure details of steel bridge is insufficient. On the other hand, the local fatigue failure region of steel bridge is in the complex stress-strain state. According to the fatigue failure mechanism of materials, so fatigue behavior of steel bridge component will not be estimated reasonably if the effect is only considered under the uniaxial load. The fatigue failure of steel bridge component is analyzed and discussed according with multiaxial fatigue method of materials in order to establish the multiaxial assessment method of steel bridge structure details which can be used in the engineering practice. Therefore, a series of research work is carried out as follows:(1) Factors influencing the material fatigue strength, which have an effect on the fatigue failure of steel bridge component, are analyzed, and main features of fatigue failure of steel bridge are summarized. Research results indicated that in the reasonable design state, fatigue failure of steel bridge refers to the high-cycle and low frequency fatigue problem which is caused by taking the variable load as dominant factors and comprehensive factors of the natural environment in the bridge position. Assessing criterion of multiaxial material fatigue strength is reviewed, and their scopes of application are discussed. And then the stress criterion is selected to evaluate steel bridge component fatigue strength.(2) The dissertation investigated assessment methods of classical steel structure details in the codes and the fatigue failure features of the special steel structure details. The research results showed that the prediction failure of special steel structure details is related to the limitation of the uniaxial assessment method in the code. From the perspective of the anti-fatigue design, based on the mechanical factors inducing the fatigue failure for classical and special steel bridge structure details and the distribution of the fatigue cracks, the research found that the fatigue failure has the significant multiaxial feature. According to this, two classical problems of fatigue failure are put forward, therefore the first kind and the second kind multiaxial fatigue problems are established.(3) The commonly used fatigue strength assessment methods are reviewed. And the application scope of nominal stress method, hot spot stress method, and local method are analyzed and discussed. Combined with the feature of steel bridge fatigue behavior, the dissertation proposed that the application of the local method to predicating the fatigue strength of steel bridge component is an effective approach to assess the multiaxial fatigue strength of the steel bridge. Stress field intensity method is selected as the research object of the steel bridge multiaxial fatigue strength assessment method.(4) Limitations of the traditional stress field intensity method are analyzed and expounded. The model of the stress field intensity method is improved to overcome limitations. The improved stress field intensity method established the new method of calculating field diameter by using the fatigue damage area of critical distance method, and the new approach to solving weight function by using function fitting technology.(5) Analytical method and elastic-plastic finite element method of solution to local stress-strain field are compared and analyzed. According to material properties and bearing loads feature of steel bridge, proper elastic-plastic finite element constitutive relationship model is selected to solve the local stress-strain field of steel bridge component.(6) The predictability of the traditional stress field intensity method and the improved stress field intensity method are verified by employing the fatigue strength of steel bridge fatigue tests. The research results show that the prediction precision of the improved stress field intensity method is significantly higher.(7) Fatigue strength of steel bridge gusset plate is predicted by using the traditional stress field intensity method and the improved stress field intensity method. In the solving process, equivalent life load group and equivalent field diameter models are established. The results show that when fatigue life is not changed, if the cyclic load of some direction increases, the cyclic load of another one will decrease. The steel bridge gusset plate predictions of traditional stress field intensity method points out the relation of cyclic load appear linear, and the relations of improved stress field intensity method appear parabolic. Based on this, the design formula of uniaxial load of steel bridge gusset plate is established.更多还原