钢桁架桥横梁疲劳性能研究(任务书,开题报告,论文说明书20000字)
摘要
随着钢桥在生活和工程中越来越多的应用，关于钢桥病害问题的研究也显得越发重要。早在上个世纪，国外的桥梁检测报告就指出，钢桥80%—90%的破坏与疲劳断裂有关。本文以某使用多年并且目前出现很严峻的疲劳病害的钢桁架桥为背景，采取有限元软件分析与理论相结合的方法对其横梁节点加固前后的疲劳性能进行了研究。
本文首先对钢桥的疲劳问题进行了介绍，简单叙述了世界上对钢结构疲劳问题研究的历史以及国内外对疲劳问题研究的现状。之后介绍了几种疲劳累积损伤理论及其应用，对其适用条件和应用效果进行了分析讨论。对现在常用的疲劳寿命估算方法（包括S-N疲劳曲线法、断裂力学法、可靠度方法）进行优缺点分析及介绍其工程应用。其中介绍最详细的是S-N疲劳曲线法确定疲劳寿命的方法，主要包括名义应力法和热点应力法。
主要工作是先运用有限元软件ansys进行钢桁架桥的建模，设计要素为某长江大桥公路正桥的连续梁桥段，对其桥梁上部结构（主要包括桥面板、纵梁、横梁和其他支撑结构）建立有限元模型，对整体模型进行结构受力分析，并选取连接纵梁与横梁的典型节点进行局部建模。根据实际情况建立了加固前与加固后两种模型，首先对节点模型进行静力承载分析，选取其中受力不佳部位，之后收集资料编制荷载谱，使用S-N曲线法进行疲劳寿命评估。按照桥梁病害检测报告对加固前模型预制裂纹，使用断裂力学的方法分析其疲劳性能并计算其剩余疲劳寿命。
使用S-N曲线法分别得到在疲劳荷载下的节点模型加固前后的疲劳寿命，加固前由于具有严重的应力集中问题，疲劳寿命计算得到为887743次。加固后的模型应力集中问题得到了极大的改善，在同等疲劳荷载下循环应力幅未能达到结构的疲劳极限强度（即N＞ ），结构的抗疲劳性能得到了很大的提升，因此对节点加固或者可以说改善结构的局部细节构造是提升结构抗疲劳性能的重要措施之一。
接下来在断裂力学法的基础上进行了疲劳裂纹扩展的研究，计算不同裂纹长度对J积分与应力强度因子的影响，并完成了一个例子的计算，并对裂纹初始长度和裂纹扩展速率之间的关系进行了分析讨论。
最后总结本文的研究并对钢结构的设计提出自己的建议。
关键词： 钢桁架桥；疲劳破坏；疲劳寿命；裂纹模拟；有限元建模
Abstract
With more and more applications of steel bridges in life and engineering, the research on steel bridge diseases is becoming more and more important.As early as last century, foreign bridge inspection reports pointed out that 80%-90% of the damage of steel bridges is related to fatigue fracture.Based on a steel truss bridge which has been used for many years and is suffering from severe fatigue diseases, this paper studies the fatigue performance of the beam joints before and after reinforcement by combining finite element software analysis with theory.
Firstly, the fatigue problems of steel bridges are introduced. The history of fatigue research on steel structures in the world and the present situation of fatigue research at home and abroad are briefly described.Then several fatigue cumulative damage theories and their applications are introduced, and their application conditions and effects are analyzed and discussed. The advantages and disadvantages of the commonly used fatigue life estimation methods (including S-N fatigue curve method, fracture mechanics method and reliability method) are analyzed and their engineering applications are introduced.Among them, S-N fatigue curve method is the most detailed method to determine fatigue life, including nominal stress method and hot spot stress method.
The main work is to use the finite element software ANSYS to model the steel truss bridge. The design elements are the continuous beam section of the main highway bridge of a Yangtze River Bridge. The finite element model of the superstructure of the bridge (mainly including bridge deck, longitudinal beam, cross beam and other supporting structures) is established. The whole model is used to analyze the structural forces, and the typical joints connecting the longitudinal beam and the transverse beam are selected for local modeling.According to the actual situation, two kinds of models before and after reinforcement are established. Firstly, the static bearing capacity of the joint model is analyzed, and the parts with poor bearing capacity are selected. Then, the load spectrum is compiled by collecting data, and the fatigue life is evaluated by S-N curve method. According to the bridge disease detection report, the fatigue performance of the pre-reinforced model was analyzed by fracture mechanics and the residual fatigue life was calculated.
The fatigue life of the joint model before and after strengthening under fatigue load was obtained by S-N curve method. Before strengthening, the fatigue life was calculated 887743 times due to the serious stress concentration problem. The problem of stress concentration in the reinforced model has been greatly improved. Under the same fatigue load, the cyclic stress amplitude can not reach the ultimate fatigue strength of the structure (that is, N > ), and the fatigue resistance of the structure has been greatly improved. Therefore, strengthening the joints or improving the local details of the structure is one of the important measures to improve the fatigue resistance of the structure.
Then, based on the fracture mechanics method, the fatigue crack growth is studied. The effects of different crack lengths on J integral and stress intensity factor are calculated. An example is completed to verify that the crack growth rate increases with the crack length.
Finally, this paper summarizes the research and puts forward some suggestions for the design of steel structure.
Keywords:Steel Truss Beam Bridges；Fatigue failure; Fatigue life; Crack simulation; Finite element modeling
目录
学位论文原创性声明 I
学位论文版权使用授权书 I
Abstract II
第1章 绪论 3
1.1 研究背景 3
1.1.1 钢桥节点疲劳问题 3
1.1.2 国内外研究现状 4
1.2 本文主要研究意义及内容 5
1.2.1 研究意义 5
1.2.2 研究内容 6
第2章 钢桥疲劳性能分析理论 7
2.1 结构疲劳破坏的基本概念 7
2.2 疲劳累积损伤理论 7
2.2.1 线性疲劳累积损伤理论 7
2.2.2 非线性疲劳累积损伤理论 8
2.2.3 概率疲劳累积损伤理论 11
2.2.4 对疲劳累积损伤理论的讨论 12
2.3 常用的疲劳寿命估算方法 12
2.3.1 S-N疲劳曲线法 12
2.3.2 局部应力-应变法 20
2.3.3 断裂力学法 21
2.4 本章小结 23
第3章 钢桁梁桥横梁节点建模 24
3.1 钢桁梁桥设计要素及其建模 24
3.1.1 设计要素 24
3.1.2 建模分析 25
3.2 节点模型的建模与静力分析 26
3.2.1 节点模型建模 26
3.2.2 节点模型静力分析 30
3.3 本章小结 35
第4章 节点模型疲劳寿命评估 36
4.1 简单的荷载谱制定 36
4.2 S-N曲线法估算疲劳寿命 36
4.2.1 加固前模型 36
4.2.2 加固后模型 38
4.3 断裂力学法估算剩余疲劳寿命 39
4.4 本章小结 44
第5章 总结与展望 45
5.1 总结 45
5.2 展望 45
参考文献 46
致谢 47 |
