## 6 Conclusions  
In this paper, CFRP is used to reinforce the fatigue cracks at the weld of the steel bridge deck and U-rib, and the influence of residual stress is considered in the study of reinforcement performance. The variation of the stress intensity factor of the fatigue crack at the weld of the top plate and the U-rib under the combined load of the vehicle, vehicle-residual stress, and the combined load after CFRP reinforcement is analyzed. The relationship between the crack stress intensity factor and the crack propagation depth under the combined load of vehicle-residual stress and the combined load after CFRP reinforcement is analyzed. The relationship between the crack propagation amount and the number of load cycles before and after reinforcement is compared. The following conclusions can be drawn:  
1. The amplitude of the stress intensity factor of the crack at the weld toe and weld root is less than the threshold value of the stress intensity factor when the vehicle only acts, and the crack will not expand. The initial crack at the welding connection between the deck and the U-rib under the combined load of the vehicle only, considering residual stress, and CFRP reinforcement is a composite crack dominated by Type I. Compared with vehicle only, considering residual stress, the maximum K\({}_{\text{I}}\) value of cracks at the weld toe increased by 6.9 times, and the maximum K\({}_{\text{I}}\) value of cracks at the weld root increased by 10.7 times.  
Figure 24: Comparison of K\({}_{\text{I}}\) before and after reinforcement when the weld toe crack extends to the plate thickness of 7 mm.  
Figure 25: Relationship between cyclic load and crack growth of weld toe before and after reinforcement. (**a**) Depth; (**b**) length.  
2. The reinforcement method of pasting CFRP on the lower side has a reinforcement effect on cracks at the weld toe but no reinforcement effect on cracks at the weld root. The reinforcement effect of weld toe cracks increases with the increase of the number, length, and width of CFRP layers but decreases after exceeding a certain value. Compared with the unreinforced condition, after CFRP reinforcement, the K\({}_{\text{I}}\) at the initial crack tips A and B at the weld toe decreased by 35 MPa\(\cdot\)mm\({}^{1/2}\), and the K\({}_{\text{I}}\) at the deepest crack point C decreased by 33 MPa\(\cdot\)mm\({}^{1/2}\).
3. When the crack at the weld toe was extended, it was found that after reinforcement, when the crack at the weld toe extended to half of the plate thickness by 7 mm, the K\({}_{\text{I}}\) at crack tips A and B decreased by 98 MPa\(\cdot\)mm\({}^{1/2}\) compared to unreinforced ones, and the K\({}_{\text{I}}\) at the deepest crack C decreased by 52 MPa\(\cdot\)mm\({}^{1/2}\). The number of load cycles increased by 43%, and the extension of the crack length decreased by 26%.  
Conceptualization, Y.H. and L.M.; review and editing, L.M.; performance of the finite element simulations and original draft, Y.H.; All authors have read and agreed to the published version of the manuscript.  
The authors are grateful for the funding support from the Graduate Research Innovation Program (KYCX21_3036), the Natural Science Foundation of Jiangsu Province, China (Grant BK20190945), and the National Natural Science Foundation of China (Grant 51608343).  
Not applicable.  
The analysis data used to support the findings of this study are included within the article.  
The authors declare no conflict of interest.