钢桥面板焊缝疲劳裂纹扩展规律与开裂失效机理研究

China's long span steel bridges are at the leading position in the world considering either scale or amount. As the prolong of service life of the domestic built steel bridges, the fatigue problems of the steel bridge deck become increasingly prominent, which also being one of the difficult issues for the safe operation of the bridges. And failure evaluation of the fatigue crack is the theoretical foundation of the fatigue maintenance of steel bridge. Bt it mainly based on experiences at present. By experiments and theoretical analysis, the propagation law of the fatigue crack will be studied. The deterioration of the partial bearing capacity of the structure will be analyzed, considering the interference effect of several cracks. The failure evaluation method for the fatigue crack will be put forward. First, fatigue experiments will be carried out on specimens with a new type of fatigue testing machine. Combining residual stress analysis and metallurgical analysis, the pattern of crack propagation and failure will be analyzed, and developed fatigue crack propagation law will be studied. Second, numerical simulation will be carried out toward the specimens stress regarding to the fatigue crack propagation process. Considering the test results, the deterioration law of the bearing capacity will be studied during the crack propagation process.Third, the specimens will be tested and analyzed considering multiple fatigue cracks, the interference effect of multiple fatigue cracks will be studied toward bearing capacity. Last, based on deterioration law of the bearing capacity, the evaluation criteria of the fatigue crack failure of the steel bridge deck will be proposed considering the demand of the actual project. The study can support and provide a theoretical background for the failure of the fatigue crack and determination of the appropriate repairing opportunity.

我国大跨径钢桥规模和数量已处于世界前列，随着已建钢桥服役年限的增长，钢桥面板疲劳问题日益突出，成为钢桥运营安全亟需解决的难题之一。疲劳开裂失效判定是钢桥疲劳维护的理论基础，而目前失效判定主要依赖经验。本研究通过试验和理论分析，探究钢桥面板疲劳开裂扩展规律，考虑裂纹干涉效应对承载力退化规律影响，提出疲劳开裂后失效评判方法。首先，应用新型振动疲劳试验机进行构件疲劳试验，结合残余应力和金相特征，分析裂纹扩展和失效模式，研究疲劳裂纹扩展规律。其次，对疲劳裂纹扩展过程中构件受力进行数值模拟，结合试验结果，研究开裂扩展过程中构件承载性能退化规律。再次，考虑多裂纹的共同作用，进行多裂纹试件试验和数值分析，研究多裂纹间的干涉效应对承载性能的影响。最后，基于承载性能的退化规律，考虑实际工程的承载需求，提出钢桥面板疲劳焊缝失效评判标准。本研究可为疲劳开裂结构局部失效以及合理修复时机评判提供理论依据。

钢桥因其受力性能优越、跨越能力强以及经济合理等优点，在国内外桥梁建设中得到了广泛应用。随着已建钢桥服役年限的增长，钢桥面板疲劳损伤问题日益突出，已成为目前钢桥运营养护中的关键技术难题。疲劳裂纹扩展规律的确定及失效准则的制定是有效开展钢桥疲劳研究及开裂维护的重要基础。目前已有的研究工作主要侧重简单构件的疲劳试验研究，对钢桥面板的复杂构造细节的裂纹萌生及扩展的研究较少，并且在疲劳试验中对疲劳失效的判定更多依赖主观判断和相关经验，缺少统一的评判标准。. 本研究在大量国内外调研的基础上，采用理论、数值和试验等手段，重点围绕顶板与竖向加劲肋、顶板与U肋构造细节、横隔板弧形缺口部位开展疲劳实验，研究典型构造细节的疲劳裂纹扩展规律和疲劳失效机理。项目首先采用振动型疲劳实验机对近100个构件施加弯曲疲劳荷载，利用人工目视、磁粉探伤、气泡指示法等多种手段研究了典型构造细节疲劳裂纹萌生位置,测量了裂纹的扩展路径，计算了扩展速率，分析了开裂前后应力幅的变化规律，探讨了构件疲劳性能的退化规律。利用数值模拟手段，重点针对顶板与U肋焊缝裂纹，建立了钢桥面板多裂纹分布模型，对比了单裂纹和多裂纹情况下裂纹尖端的应力场，评估了多裂纹干涉行为对钢桥面板局部承载性能的影响。在疲劳试验基础上，进一步采用线弹性断裂力学，对二维裂纹尺寸进行数值积分，考虑相互作用准则下的裂纹合并，模拟裂纹扩展，讨论了板件尺寸、初始缺陷、材料参数、应力幅等因素对裂纹扩展的影响，建议了疲劳失效指标及取值范围。最后，采用钻孔法、补焊法对疲劳裂纹实施维修，对比研究了维修前后的裂纹扩展规律，评价了技术的修复效果。研究成果揭示了钢桥面板典型构造细节疲劳裂纹的扩展规律，建议了疲劳失效指标及其取值范围，积累了丰富的疲劳试验经验，为钢桥面板抗疲劳设计、疲劳裂纹检测和开裂维护提供了重要的借鉴和参考。