钢桁架桥的疲劳验算

钢桁架桥的疲劳验算(任务书,论文15000字)
摘要
近几年来，我国在钢桥建设方面飞速发展，钢桁架桥发展迅速，在这种情况下，一些问题无法回避地出现在我们面前：20世纪初修建的公路钢桥已经服役了一个世纪，这些钢桥属于老龄化钢桥。在服役期间，公路钢桥由于受到环境侵蚀、材料老化等因素，结构不断地损伤、承载力逐渐减弱，其剩余使用寿命已经达不到预期的要求，并且有些服役时间较长的钢桥由于设计之初考虑的因素较少，早年的设计标准、荷载等级较低，已经不适应目前的交通状况。如何准确地评估这些钢桁架桥，对这些老龄化钢桥进行疲劳验算成为了一大难题。本文具体研究内容如下：
（1）介绍了疲劳的基本概念，S-N疲劳曲线，钢桥疲劳问题的重要性以及疲劳问题的研究现状。
（2）用ANSYS软件建立了一个钢桁架桥模型，在模型上施加荷载（包括一期恒载，二期恒载以及活载），分析全桥的受力分布，计算各个杆件的应力幅并找出了其中的最大值。
（3）介绍了我国公路钢桥抗疲劳设计的规范和方法，详细介绍了无限寿命设计法以及安全寿命设计法。对疲劳寿命理论进行了研究，介绍了传统疲劳寿命评估方法中的名义应力法，疲劳损伤累计理论，基于断裂力学的疲劳寿命评估方法以及可靠度方法，给出了用名义应力法对钢桥进行疲劳寿命评估的具体步骤。
（4）结合平阴黄河公路大桥各个杆件的应力谱，对平阴黄河公路大桥进行了疲劳验算，得出了各个杆件的疲劳损伤度以及使用寿命。
关键字：钢桁架桥；疲劳；名义应力；Miner准则；S-N曲线；应力谱
Abstract
In recent years,China has made rapid progress in the construction of steel bridges,and steel truss bridges have developed rapidly. Under such circumstances,some problems cannot be avoided. The road steel bridges constructed in the early 20th century have been in service for a century. These steel bridges are aged steel bridges.During service,due to factors such as environmental erosion and material aging,the steel bridges of highways are constantly damaged and the bearing capacity is gradually weakened. The remaining service life of the highway steel bridges has not reached the expected requirements.Some of the steel bridges with longer service periods have fewer considerations for the design. The early design standards and the lower load levels have not been adapted to the current traffic conditions.How to accurately evaluate these steel truss bridges has become a major problem for fatigue checking of these aging steel bridges.The specific research content is as follows:
(1)The basic concepts of fatigue,S-N fatigue curves,the importance of fatigue problems in steel bridges and the research status of fatigue problems are introduced.
(2)A steel truss bridge model was established using ANSYS software. Loads were applied to the model (including one-stage dead load,two-stage dead load,and lane load) to analyze the stress distribution of the full-bridge.
(3)The specification and method of anti-fatigue design for highway steel bridges in China are introduced. The infinite life design method and safe life design method are introduced in detail. The fatigue life theory was studied. The nominal stress method,the cumulative fatigue damage theory,the fatigue life assessment method based on fracture mechanics and the reliability method were introduced. The steel bridges were given by the nominal stress method. Fatigue life assessment specific steps.
(4) Check the fatigue of Pingyin Yellow River Highway Bridge,and obtain the fatigue damage degree and service life of each member.
Key words: steel truss bridge; fatigue; nominal stress; Miner criterion; S-N curve; stress spectrum 
目录
摘要    I
Abstract    II
第1章绪论    1
1.1疲劳问题的研究背景及意义    1
1.2疲劳的概念    2
1.2.1疲劳    2
1.2.2疲劳破坏的特点    2
1.2.3 S-N疲劳曲线    2
1.3钢桥疲劳问题研究现状    3
1.4本文的工作内容    3
第2章某钢桁架桥的ANSYS建模    5
2.1钢桁架桥节点ANSYS三维实体建模    5
2.1.1主桁结构形式的选择    5
2.1.2 ANSYS建模流程图    5
2.1.3定义材料特性    6
2.1.4定义截面尺寸    7
2.1.5输入节点    8
2.1.6连接节点建立单元    9
2.1.7单元分群    12
2.1.8添加约束    14
2.1.9添加荷载    14
2.2模型结果分析    16
2.2.1钢桁架桥杆件的强度验算    16
2.2.2杆件受力分析    25
2.2.3杆件应力幅计算    28
2.3本章小结    29
第3章疲劳寿命理论    30
3.1我国公路钢桥抗疲劳设计规范    30
3.2公路钢桥抗疲劳设计方法    30
3.2.1无限寿命设计    30
3.2.2安全寿命设计    31
3.3疲劳寿命评估方法    31
3.3.1传统疲劳寿命评估方法    31
3.3.2基于断裂力学的疲劳寿命评估方法    34
3.3.3可靠度方法    34
3.4本章小结    35
第4章疲劳验算实例    36
4.1应力谱    36
4.2疲劳损伤以及使用寿命计算    38
4.2.1疲劳强度曲线    38
4.2.2损伤度以及使用寿命计算    39
4.3结果分析    41
4.4本章小结    41
第5章结论与展望    42
5.1结论    42
5.2展望    42
参考文献    43
致谢    44