Study of Secondary Effects of Fatigue Cracks in Cross Partitions of Steel Plate Reinforced Steel Box Girders

In order to investigate the effect of optimized reinforcement of cross-section of steel box girders with fatigue cracks on other vulnerable parts (cross-section, U-rib and deck slab, etc.) under wheel load, and to reveal the stress distribution law of critical parts after the optimization of steel plate reinforcement or arc notch. In this work, a suspension bridge with fatigue cracks in the curved notch of the cross-sectional plate is considered as the research object, two types of curved notch optimization reinforcement solutions are considered and finite element analysis is performed. Longitudinal and transverse moving loading tests were conducted with a test vehicle to test the stresses in the critical parts of the curved cutout of the cross-section. Furthermore, the effects of the two optimized strengthening solutions on the stresses in the curved cutout, the sides of the diaphragm, the sides of the U-rib and the deck slab were analyzed, and the effects of the changes in the diaphragm stiffness on other critical vulnerable structures were analyzed. The study shows that when the “arc notch optimization” strengthening scheme is adopted for crack-free or short cracks, although it can effectively improve the stress transfer path of the arc notch of the diaphragm, it also weakens the cross-sectional area of the diaphragm and has little effect on the diaphragm side, U-rib and deck plate. When the long crack is reinforced by “arc notch optimization + steel plate reinforcement”, it is easy to cause a reaction to the diaphragm sides arranged at the junction area of the diaphragm arc notch and U-rib without steel plate coverage, and the stress will be slightly higher than that when the diaphragm is not optimized. The steel plate reinforcement hurts the lateral stress of the U-rib, but the reinforcement effect will not have any effect on the deck plate.