基于WIM数据和断裂力学方法的钢桥疲劳强度评估

Evaluation of Fatigue Strength of Steel Bridge Based on WIM Data and Fracture Mechanics Method

为了准确评估钢桥焊接结构的疲劳强度,基于断裂力学K判据对于高周疲劳的适用性分析,采用Pairs公式并结合有限元方法和G*积分理论,计算获得了钢桥典型构造细节的应力强度因子表达式。结果表明:钢桥棱角焊缝构造细节和T形接头对接焊缝构造细节的应力强度因子均与结构裂纹尺寸密切相关,其表示式可以由裂纹尺寸、工作应力及结构尺寸等参数联合表达。以构造细节的应力强度因子为基础,计算得到了典型构造细节的等效200万次疲劳强度,并与各国规范及疲劳试验结果进行了对比分析。结果表明:采用断裂力学方法获得的疲劳强度结果与规范值及试验值均吻合良好,对应棱角焊缝构造细节的计算偏差基本在10%以内;对应T形接头对接焊缝细节的计算偏差在20%以内,且T形接头构造细节的疲劳强度远低于棱角焊缝构造细节的疲劳强度,设计和施工中需引起重视。基于坝陵河大桥动态称重系统实测数据,计算获得了钢桁梁节点构造的等效应力幅,并采用上述断裂力学方法评估了该节点构造的疲劳强度和寿命。通过坝陵河大桥节点疲劳模型试验,进一步验证了该方法在钢桥疲劳强度评估上的适用性,研究成果可为钢结构桥梁的强度评估提供借鉴和参考。

For exactly evaluating the fatigue strength of welded structure in steel bridge, based on the analysis the applicability of the K criterion of fracture mechanics to high cycle fatigue, the expressions of stress intensity factor for typical structure details of steel bridges are obtained by using Paris formula combining with finite element method and G＊ integral theory. The result shows that the stress intensity factors of the arris weld structure detail and the butt weld of T-joint structure detail for steel bridges are closely related to the crack size of welded structures, and the expressions can be expressed by the parameters of crack size, working stress and structure size. Based on the stress intensity factor of structure details, the equivalent 2 million times fatigue strength of the typical structure details are calculated and comparatively analysed with the specified values of many countries and fatigue test results. The result shows that （1） the calculation values using the method of fracture mechanics are in good agreement with the specified and experimental values, the calculation deviation is about less than 10% for the arris weld structure detail, the calculation deviation is less than 20% for the butt weld of T-joint structure detail, and the fatigue strength of T -joint structure detail is far lower than that of the arris weld structure detail, which must be paid attention in design and construction. Based on the measured WIM data of Baling River Bridge, the equivalent stress amplitudes of the steel truss girder joints are obtained by calculation, and the above fracture mechanics method is applied to evaluate the fatigue strength and lifetime of the welded joint structure. By the joint fatigue model test of Baling River Bridge, the applicability of this method in fatigue strength evaluation for steel bridges is further verified. The research result can provide a reference for strength evaluation of steel structure bridges.