Fatigue Crack Repair and Optimization of Cope Holes in Orthotropic Steel Decks

During the process of repairing of cope hole fatigue in orthotropic steel decks (OSD), the fatigue rehabilitation results depend largely on the quality of cutting geometries. An OSD with several cope hole fatigue cracks was investigated, and the cause of stress concentration at the cope holes was analyzed via finite element analysis (FEA) and the structural force flow method. The parameters of cope hole geometry, including the radius of arcs and length and angle of straight lines, were optimized based on four different types of repairing programs. Furthermore, the effects of cutting geometry on the maximum stress were also determined. Several cope holes were selected to conduct an experimental study, before and after the cutting repair process, which relied on the fatigue crack cutting and repair engineering in the OSD. Longitudinal and transversal movement loads were applied via an experimental vehicle, and the stress distribution and the relationship between wheel load positions and stresses were tested at the normal section of the cope holes and on both sides of the diaphragms. Finally, the modified nominal stress method was employed to estimate the fatigue life of the cope holes. The study indicates that the stress flow, generated by wheel loads, passes through the U ribs and then spreads to the diaphragms in the form of shear stress. However, the stress flow is obstructed by the cope hole, which results in stress concentration surrounding the cope hole. The size of the cope hole should be small, while the radius of the cope hole should be larger, and the path of stress flow should be unobstructed. After the cope hole was optimized, the stress reduction proportion attained a value of 58. 4%, and the equivalent stress amplitude, which considered the lateral probability distribution, reduced to 55. 2%. Enlarging the size of the cope holes leads to the reduction in the section area and thereby results in a slight increase in the average compressive stress in the diaphragms. Based on FEA and experimental stress, the fatigue life of the cope hole before repair are respectively 3. 8 years and 7. 2 years, and the fatigue life increases respectively to 58. 5 years and 184. 4 years after repair, which indicates that the cutting repair method exerts a positive effect. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.