基于初始缺陷的钢桥面板疲劳性能退化机理研究

The structure of steel bridge deck is complex, and many weld joints are designed to connect the different components. The lack of consideration about initial defects in the anti-fatigue design and fatigue assessment, is one of the important factors for early fatigue cracking and the deviation between assessment result and actual state, including welding defect, residual stress, manufacture error and so on. This proposal takes fatigue performance degeneration mechanism of steel bridge decks as research object, full-scale fatigue tests will be carried out to explore the fatigue crack initiation and propagation rules for typical details. Numerical models for three-dimension (3D) fatigue crack propagation are built through eXtended Finite Element Method (XFEM), and realize the trans-scale propagation numerical simulation for mix-mode cracks, revealing the initial defect evolution rules and fatigue failure modes for typical details. Determining method for initial crack and critical crack parameter is proposed when it is used in fracture mechanical analysis. Based on fracture parameters change trend, the influence rules of fatigue crack propagation state on remaining fatigue strength are analyzed. Fatigue performance degeneration mechanism is revealed for typical details under different cracking modes, fatigue performance degeneration models are built, and initial defects control indices are proposed for steel bridge decks. Research achievements of this proposal have important theoretical significance and engineering value for fatigue safety control of steel bridge decks, which provide new scientific basis for anti-fatigue design and fatigue safety assessment for steel bridges, and offer beneficial references for relevant specification revises.

正交异性钢桥面板构造复杂、焊缝较多，在抗疲劳设计和疲劳评估时对焊接缺陷、残余应力、制造偏差等初始缺陷考虑的不足，是钢桥面板疲劳开裂过早、评估结果与实际存在偏差的重要原因之一。本项目以钢桥面板疲劳性能退化机理为研究对象，拟开展足尺模型疲劳试验，研究典型细节疲劳裂纹萌生与扩展规律；采用扩展有限元方法建立疲劳裂纹扩展三维数值模型，实现复合型疲劳裂纹跨尺度数值模拟，揭示典型细节初始缺陷演化机制及疲劳失效模式，提出断裂力学分析时初始裂纹及临界裂纹尺寸的确定方法；基于断裂力学参数变化特征，分析疲劳裂纹扩展状态对剩余疲劳强度的影响规律，确定不同开裂模式下典型细节的疲劳性能退化机理，建立基于初始缺陷的钢桥面板疲劳性能退化模型，提出初始缺陷控制指标。项目研究成果对钢桥面板疲劳安全控制具有重要的理论意义与工程价值，为钢桥抗疲劳设计和疲劳安全评估提供新的科学依据，同时对修编相关规范提供有益参考。

正交异性钢桥面板构造复杂、焊缝较多，在抗疲劳设计和疲劳评估时对焊接缺陷、残余应力、制造偏差等初始缺陷考虑的不足，是钢桥面板疲劳开裂过早、评估结果与实际存在偏差的重要原因之一。针对正交异性钢桥面板疲劳安全问题，采用模型试验、数值模拟和实桥应用等方法，系统开展基于制造缺陷的钢桥面板疲劳性能退化机理研究。基于5000余吨钢箱梁无损检测结果，明确了钢桥面板初始缺陷类型、尺寸与分布位置等参数。通过钢桥面板足尺节段模型疲劳试验，揭示了典型细节疲劳裂纹萌生位置及疲劳荷载作用下裂纹扩展规律，为初始缺陷演化机理研究奠定试验基础。建立基于扩展有限元方法（XFEM）的钢桥面板多尺度有限元模型，采用足尺模型试验数据进行有限元模型验证，进一步研究基于初始缺陷的典型细节疲劳裂纹萌生、扩展规律与疲劳失效机理。对初始缺陷中的残余应力、微裂纹、夹渣和气孔进行变参数分析，包括残余应力大小、微裂纹方向、气孔尺寸、夹渣尺寸，研究初始缺陷对正交异性钢桥面板抗疲劳性能的影响规律。基于累计应变能释放率指标，揭示了钢桥面板初始缺陷和疲劳裂纹扩展行为演化规律，建立基于制造缺陷的典型细节疲劳性能退化模型。以某跨海大桥钢箱梁桥面板为工程背景，开展交通荷载监测、疲劳裂纹检测，建立钢桥面板跨尺度有限元模型，基于当前运营荷载和疲劳裂纹状态预测疲劳裂纹扩展趋势与钢桥面板疲劳寿命，并给出实桥钢桥面板疲劳安全检测与维护间隔的确定方法，进一步验证了提出的初始缺陷对钢桥面板疲劳性能的影响规律及疲劳损伤容限控制指标。项目研究成果可为钢桥面板抗疲劳设计和疲劳评估提供理论依据与技术支撑，对修编相关规范亦可提供参考。