正交异性钢桥面板弧形切口及其CFRP补强的疲劳性能

横隔板弧形切口疲劳裂纹为正交异性钢桥面板的主要疲劳病害之一，为研究该细节的疲劳抗力与裂纹处治技术开展了正交异性钢桥面足尺模型疲劳试验，对横隔板光滑弧形切口、含人工缺陷弧形切口、以及CFRP单面加固含人工缺陷弧形切口的疲劳性能进行了比较研究；结合有限元方法对横隔板光滑弧形切口疲劳评估方法进行了探讨。结果表明：打磨光滑的横隔板弧形切口在标准疲劳车作用下的疲劳寿命超过5 000万次，基本不存在疲劳问题。车轮荷载横隔板弧形切口处存在显著的压应力集中，热残余应力和轮载应力幅的组合效应构成了弧形切口疲劳开裂的外部驱动力。此外，初始几何缺陷是该细节疲劳开裂的重要影响因素。光滑弧形切口的疲劳评估，可采用距切口自由边6 mm处横隔板表面的主应力作为该细节名义应力，其疲劳抗力高于AASHTO规范的疲劳等级A（CAFL为165 MPa）。外贴CFRP补强可有效阻止含缺陷弧形切口处疲劳裂纹的发展。若以裂纹长度6.5 mm作为损伤容限，单面粘贴CFRP加固含缺陷横隔板弧形切口的疲劳寿命为未加固切口的14.5倍以上；若采用双面CFRP加固寿命将提高更多，提高幅度有待进一步研究。

Fatigue Behavior and CFRP Reinforcement of Diaphragm Cutouts in Orthotropic Steel Bridge Decks

Fatigue cracking at the diaphragm cutout is one of the major diseases of orthotropic steel decks (OSDs). Sufficient fatigue tests are needed to validate the fatigue resistance, fatigue evaluation method, and crack treatment techniques of the cutout detail. Fatigue tests on full-scale OSD models were carried out to investigate the fatigue performance of polished cutouts, defective cutouts (with artificial defects), and defective cutouts strengthened with carbon fiber-reinforced polymer (CFRP). Combined with the finite element method, the fatigue assessment methods for the polished cutout details were also studied. The results show that the fatigue lives of polished cutouts exceed 50 million cycles under standard fatigue vehicle loads, indicating that fatigue cracks will not occur during the service period. There is a significant concentration of compressive stresses around the cutout under the effect of wheel load, and the combined effect of the wheel load stress and thermal residual stress constitutes an external driving force of the fatigue cracking. Moreover, the initial geometric defect is also an important reason for this fatigue cracking. For the fatigue evaluation of polished cutouts, the principal stress 6 mm away from the free edge of the cutouts on the surface of the transverse diaphragm can be used as the nominal stress, and the fatigue resistance is proved to be higher than fatigue grade A (with an constant-amplitude fatigue threshold of 165 MPa) in the specification of American Association of State Highway and Transportation Officials (AASHTO). The externally bonded CFRP reinforcement is effective in arresting the fatigue crack propagation at the defective cutouts. If a 6.5-mm-long fatigue crack is taken as the damage tolerance, the fatigue life of the diaphragm cutouts strengthened with CFRP on one side is more than 14.5 times that of the un-strengthened ones. The fatigue life can be further improved if double-side CFRP strengthening is applied, which should be studied in the future.