# Fatigue Performance of Different Rib-To-Deck Connections Using Traction Structural Stress Method
## 3 Fatigue Performance of Rib-To-Deck Connection Types in Orthotropic Steel Bridges
### Comparative Results of Three Typical Connections and Discussions
The normal tensile stress and compressive stress of Large-Weldline1 decreased from the side of the weld seam and the stress of the side was more significant than the stress of the middle of the weld seam. The trend of structural stress of the Large-Weldline2 was similar to the trend of the Trad-Weldline2. Compared to the structural stress of Large-Weldline2, the maximum bending stress of the Trad-Weldline2 increased by 16.4%. The normal compressive stress increased by 14.9% and the normal tensile stress increased by 16.7%. Figure 9: Mises stress of the bottom side of the bridge deck of a traditional weld seam. (**a**) Mises stress diagram of the bottom side of the bridge deck (Pa). (**b**) Fatigue cyclic life of the connection of the rib-to-deck, 1 the number in the contours is the base 10 log of the contour line. Figure 11: Mises stress of the bottom side of the top flange of the weld seam of a large root. (**a**) Mises stress diagram of the bottom side of the bridge deck (Pa) (**b**) fatigue cyclic life of the connection of the rib-to-deck, 1 the number in the contours is the base 10 log of the contour line. Figure 10: Equivalent structural stress of the weld root and weld toe of a traditional weld seam. (**a**) Equivalent structural stress of Trad-Weldline1, (**b**) equivalent structural stress of Trad-Weldline2. The comparative results showed that the equivalent structural stress of the bridge deck with the weld seam of a large root was much more significant than that of the bridge deck with a traditional weld seam. The fatigue performance of the bridge deck with a traditional weld seam was better than that of the bridge deck with the weld seam of a large root. Therefore, it is not recommended to apply the weld seam of a large root with relatively larger seam area. Furthermore, the weld seam size should be controlled crucially for better fatigue resistance. Four types of the weld lines of the double-sided weld seams of the bridge deck were considered. The weld seam called Double-Weldline1 is the weld seam of the outer weld toe and bridge deck. The weld seam called Double-Weldline2 is the weld seam of the weld root and bridge deck. The weld seam called Double-Weldline3 is the weld seam of the inner weld root and bridge deck. The weld seam called Double-Weldline4 is the weld seam of the inner weld toe and the bridge deck. Compared to the bridge deck with the traditional weld seam and the weld seam of the large root, the location of the maximum Mises stress (Figure 13) and the lowest fatigue cyclic life in the bottom of the bridge deck was shifted from the weld root of the outer weld seam to the weld toe of the inner weld seam. In addition, the location of the minimum cyclic life was shifted to the weld toe of the inner weld seam instead. Figure 12: Equivalent structural stress of the weld root and weld toe of the weld seam of a large root. (**a**) Equivalent structural stress of Large-Weldline1, (**b**) equivalent structural stress of Large-Weldline2. Figure 14 shows the equivalent structural stress for the four weld lines from Double-Weldline1 to Double-Weldline4. The stress trends of Double-Weldline1 to Double-Weldline4 were similar to the other weld seams. The bottom of the bridge deck was mainly subjected to normal tensile stress with little normal shear stress. The normal stress was mostly tensile stress with significant structural stress value. Comparison of the in-plane shear structural stress showed that the effect of the shear structural stress could be ignored when considering the fatigue behavior of the connection of the rib-to-deck. The maximum normal stress at both ends of the Double-Weldline1 was 30 MPa. The normal stress gradually decreased from the end to the middle of the weld seam and the minimum normal stress in the middle section was 25.21 MPa. However, the structural stress increased in the reverse direction in the connection between the weld toe and crossbeam when compared to the traditional seam. The stiffness of the bridge deck was changed due to the presence of the crossbeam.