超大跨径斜拉桥钢桥面板疲劳损伤监测与断裂力学研究

为研究超大跨径斜拉桥钢桥面板的疲劳损伤问题,本文以某斜拉桥为工程背景,对实桥进行了现场疲劳损伤监测与分析,并基于断裂力学的三维裂纹扩展模型,对钢箱梁顶板-U肋和横隔板-U肋等焊接细节进行了数值仿真与研究。结果表明：实桥顶板-U肋焊缝细节高应力幅(大于10MPa)循环次数与疲劳损伤度明显低于横隔板-U肋细节,横隔板-U肋焊缝最大应力幅达到75~90MPa,顶板-U肋焊缝最大应力幅为15~30MPa,横隔板-U肋焊缝细节处裂纹数量远大于顶板-U肋焊缝细节处裂纹数量；顶板-U肋焊缝裂纹在扩展过程中基本保持平面,裂纹扩展有先沿焊缝方向纵向扩展,再向深度方向扩展的趋势；横隔板-U肋焊缝焊趾处裂纹先沿初始裂纹深度方向在横隔板扩展,再向横隔板厚度方向扩展,焊趾处裂纹先向U肋厚度方向扩展,后沿初始裂纹长度方向顺桥向扩展；在初始裂纹尺寸与荷载条件相同的情况下,顶板-U肋焊缝焊趾处裂纹扩展速度大于焊根处裂纹扩展速度,横隔板-U肋焊缝焊趾处裂纹扩展速率大于横隔板焊趾处裂纹扩展速率。

Study on Fatigue Damage Monitoring and Fracture Mechanics of Steel Bridge Decks in Super-long-span Cable-stayed Bridges

To study the fatigue damage of steel bridge decks in super-long-span cable-stayed bridges, taking a cable-stayed bridge as the engineering background, the on-site fatigue damage monitoring and analysis of an actual bridge are carried out. Based on the 3D crack propagation model of fracture mechanics, the welding details of the roof-U ribs and the transverse diaphragm-U ribs of the steel box girder are numerically simulated and studied. The results indicate that the high-stress amplitude (greater than 10 MPa) cycles and fatigue damage level of the welding details in the roof-U ribs of the actual bridge are significantly lower than the welding details in the transverse diaphragm-U ribs. The maximum stress amplitude in the welding details of the transverse diaphragm-U ribs reaches 75~90 MPa, while the maximum stress amplitude in the welding details of the roof-U ribs is 15~30 MPa. Moreover, the number of cracks in the welding details of the transverse diaphragm-U ribs is much greater than that in the welding details of the roof-U ribs. The cracks in the welding details of the roof-U ribs tend to remain essentially planar in the propagation process. The cracks propagate longitudinally along the weld direction and then extend in the depth direction. The cracks in the welding details of the transverse diaphragm-U ribs initially propagate within the transverse diaphragm and then extend in the direction of the diaphragm thickness. The cracks at the weld toe initially propagate in the direction of the U-rib thickness and later extend longitudinally along the initial crack length direction of bridge. Under the same condition of the initial crack size and the load, the cracks at the welding toe of roof-U rib extend quicker than the cracks at the welding root. And the cracks at the welding toe of transverse diaphragm-U rib extend quicker than the cracks at the welding toe of transverse diaphragm.