## 5 Case Study  
Taking the rolling saddle of the Zhanggao River Crossing South Channel Bridge as an example, its mechanical situation in the roller area was investigated. Its different components are constructed, including a cable trough, saddle ribs, saddle base and rollers, as displayed in Figure 5. The length and diameter of the roller are 3500 mm and 800 mm, respectively. The length, width, and thickness are 18,000 mm, 4600 mm, and 1000 mm, respectively. The width of the saddle rib is 120 mm. In this paper, the computational analysis of the part of the saddle, the roller and the top surface of the tower was carried out. The middle longitudinal ribs were symmetrically restrained, and the upper and lower surfaces of the roller were in linear contact with the bottom surface of the saddle and the top surface of the tower, respectively. Under vertical pressure, fixed constraints in all directions were set between the saddle and the grill, fixed constraints in the transverse and longitudinal directions were set on both sides of the upper part of the saddle, transverse fixed constraints were set on the base of the saddle and the rollers, and full fixed constraints were set on the top surface part of the cable tower.  
The loading method chosen was the direct face force method. The rib plates are L1, L2,..., L9, L10 from the left, where L10 is the center rib plate, and the rib plates are loaded symmetrically. Table 1 shows the centripetal pressure of each column of cable strands.  
The whole model rolling saddle and cable tower is established and its Mises stress is calculated, as shown in Figure 6. Because the stress situation around the rollers is the main focus, the Mises stress in both sides of the rollers are further investigated. Its distribution is exhibited in Figure 7. The stress of each roller along the transverse direction is extracted, as shown in Figures 8 and 9.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Rib Plate** & **L1** & **L2** & **L3** & **L4** & **L5** & **L6** & **L7** & **L8** & **L9** & **L10** \\ \hline Centripetal pressure (MPa) & 23.67 & 26.35 & 29.04 & 31.74 & 34.45 & 37.17 & 39.90 & 42.64 & 45.40 & 48.16 \\ \hline \end{tabular}
\end{table}
Table 1: Centripetal pressure of each column of cable strands.  
Figure 5: Different components of the typical rolling saddle: (**A**) cable trough; (**B**) saddle ribs; (**C**) saddle base; (**D**) rollers.  
Figure 6: Whole model rolling saddle and cable tower and its von Mises stress distribution.  
Figure 7: Mises stress in the surface of the rollers: (**A**) upper surface; (**B**) lower surface.  
Figure 8: _Cont._  
It can be seen that the maximum von Mises stress mainly occurs in the contact area of the base of the rope saddle and the roller shaft, which is 1078 MPa. The maximum von Mises stress in the upper structure of the rope saddle is 232 MPa, which occurs at the bottom of the saddle groove. For the Q345 steel, yield damage does not generally occur. The maximum von Mises stress of the roller shaft is 773 MPa, which appears at the ends of the lower surface of the roller shaft. The maximum von Mises stress on the top surface of the tower is 885 MPa, which occurs at both ends of the contact area with the roller shaft. Attention should be paid to the Von Mises stress in the contact area between the saddle base and the roller shaft, the lower surfaces of both ends of the roller shaft, and the top surface of the tower, to avoid material damage.  
Figure 8: Mises stress distribution in the upper surface of the rollers: (**A**) Roller 1–3; (**B**) Roller 4–6; (**C**) Roller 7–9.  
Figure 9: _Cont._