细微观初始缺陷对钢桥焊接节点疲劳抗力的跨尺度劣化机制与量化方法

不可避免的初始缺陷显著劣化并控制焊接节点的疲劳抗力，揭示细微观初始缺陷对焊接节点的疲劳抗力劣化机制并量化其效应，是保障钢桥运维质量和服役安全的基本前提。本项目根据问题的基本属性，引入跨尺度理论分析方法，就细微观初始缺陷致焊接节点疲劳抗力劣化问题进行理论和试验研究：（1）确定钢桥焊接节点细微观初始缺陷特征化参数的概率统计特征，推导钢桥焊接节点疲劳损伤全过程应变能耗散控制方程，建立细微观初始缺陷对于焊接节点疲劳致损和劣化过程的跨尺度理论模型；（2）阐明典型初始缺陷关键特征化参数与疲劳抗力劣化效应的内在联系，由多初始缺陷干涉和融合对疲劳裂纹扩展速率的影响入手，揭示多初始缺陷耦合作用条件下的疲劳抗力劣化机制；（3）建立含随机初始缺陷的钢桥焊接节点疲劳失效概率密度演化方程和疲劳抗力概率预测模型，提出随机初始缺陷致疲劳抗力劣化效应的量化方法。研究成果可为钢桥的疲劳抗力评估和维护决策提供理论和方法支撑。

The fatigue resistance of welded joints in steel bridge is considerably reduced and dominated by the inevitable initial defects. Elucidating the microscale initial defects-induced fatigue resistance degradation of welded joints and quantifying their degradation effects on fatigue resistance of welded joints are the basic prerequisites to ensure the service quality and structural safety of steel bridges. According to the essential attributes of the problem, a multiscale analysis method is adopted in this proposal, and the theoretical and experimental researches on the initial defects-induced fatigue resistance degradation are conducted: (1) The probabilistic statistical characteristics of characteristic parameters of microscale initial defects in welded joints of steel bridge are determined. The governing equations of fatigue damage-induced cyclic strain energy dissipation at the welded joint of steel bridges are derived. A multiscale theoretical model for the fatigue damage and degradation of welded joints caused by microscale initial defects is established. (2) The relationship between the critical characteristic parameters of typical initial defects and the fatigue resistance degradation effect is clarified. The fatigue resistance degradation mechanism under the coupling effects of multiple initial defects is revealed, considering the influence of multiple initial defects interference and mergence on the fatigue crack growth rate. (3) The fatigue failure probabilistic density evolution equation and fatigue resistance probabilistic prediction model of welded joints in steel bridge with random initial defects are established, and the quantitative method of fatigue resistance degradation caused by random initial defects is proposed. The research results can provide theoretical and methodological support for fatigue resistance evaluation and maintenance decision of steel bridges.