考虑多裂纹耦合扩展的钢桥面顶板焊缝疲劳可靠度研究

A large number of penetrating fatigue cracks have been detected in the welded joints of steel bridge decks. The size and density of cracks increase with the aging of the steel bridge. These phenomena initiate the coupling expansion and fusion penetration behaviors, which significantly reduce the local stiffness and fatigue life of steel bridge decks. Conventional single-crack analysis method is difficult to capture the coupling expansion and correlation of multiple cracks. Thus, it is infeasible to evaluate the fatigue reliability of in-service steel bridge decks from the aspect of welding system level. In this respect, this project conducts the following researches based on the coupled propagation behavior of the penetrating multiple cracks on steel bridge deck and fracture probability analysis. Firstly, the coupling expansion behaviors of penetrating multiple cracks in steel bridge deck are revealed, and the dynamic response surface of the crack tip coupling stress intensity factor is established. Secondly, the fusion fracture probability of multi-crack body is analyzed based on the ligament connectivity criterion, and the transmission mechanism of the fracture probability in the deck welding system is investigated. Finally, the research results are applied to reliability assessment of multiple cracks fusion fracture of existing steel bridge deck based on traffic flow and crack measured data, and the dominant fusion path of multi-crack body is identified. The purpose of this project is to explore the influence of the coupling propagation behavior of the penetrating multi-crack body at the steel bridge deck on the fusion fracture probability and the fatigue reliability of the roof system. The research results can lay a theoretical foundation for the fatigue safe assessment and maintenance of existing steel bridge decks.

既有钢桥面顶板焊缝处已检测到大量贯穿型疲劳裂纹，且裂纹尺寸与密度随桥梁老龄化而增加，引发多裂纹耦合扩展与融合现象，从而显著降低钢桥面局部刚度与疲劳寿命。常规单裂纹方法难以考虑多裂纹体耦合扩展及概率相关性特征，因而无法从焊缝体系层面评估既有钢桥面板的疲劳可靠性。鉴于此，本项目围绕钢桥面顶板多贯穿裂纹的耦合扩展行为与断裂失效概率分析的关键问题，开展以下研究：捕捉钢桥面顶板多裂纹耦合扩展行为，建立共线裂纹应力强度因子耦合系数的动态响应面；基于韧带连通准则分析多裂纹体融合失效概率，并表征该失效概率在钢桥面顶板焊缝体系层面的传递模式；应用研究成果至基于车流与裂纹实测数据的既有钢桥面顶板疲劳可靠性评估，并识别多裂纹体的主导融合路径。本项目旨在探究多裂纹耦合扩展效应对钢桥面顶板局部断裂失效概率的影响，进而评估焊缝体系的疲劳可靠度，研究成果可为既有钢桥面板的疲劳安全评定及新型抗疲劳设计优化奠定理论基础。

随着既有钢桥面板老龄化进程的加剧，焊缝处疲劳裂纹大量萌生并持续扩展，裂纹尺寸与密度迅速增加，导致多裂纹耦合扩展并连通融合，大大降低了钢桥面板局部刚度，影响桥梁服役安全。本项目围绕钢桥面顶板多疲劳裂纹耦合扩展行为与断裂失效概率分析的关键问题，结合断裂力学理论、扩展有限元方法及节段足尺模型试验，开展了钢桥面顶板焊缝多疲劳裂纹数值模拟与疲劳试验研究，并应用于实桥评估。通过本项目研究，揭示了钢桥面顶板-纵肋焊缝处双裂纹耦合扩展过程中的应力强度因子变化规律，表征了多裂纹体相互融合形成长裂纹体的演化过程，提出了一种基于韧带连通准则的多裂纹体融合过程简化分析方法，提出了随机车流作用下钢桥面板疲劳可靠度分析方法。本项目重视研究成果的转化与应用，以南溪长江大桥钢桥面板为工程实例，现场调研了焊缝疲劳裂纹的分布及车辆荷载数据，并开展室内足尺模型疲劳试验研究，分析了车轮横向分布和超载作用下钢桥面板焊缝处疲劳裂纹随机扩展特性，评估了实测车流作用下钢桥面板的疲劳可靠度，基于分析结果制定了重载车辆的管控措施。本项目的研究成果可从焊缝体系层面表征老化钢桥面板焊缝的疲劳可靠性，可用于既有钢桥面板的疲劳性能评估与维护，也为新型抗疲劳设计方案的优化奠定理论基础。