## 3 Wind Load Calculation
### Model Validation  
In order to ensure the accuracy of the simulation results, improve the calculation efficiency and accurately describe the flow characteristics near the wall, the Coupled numerical algorithm is used to study the static three-component force coefficient of the main girder section of the bridge by FLUENT 2022 R1 software. In the simulation process, the air is assumed to be an incompressible fluid that remains unchanged, and the _SST_\(k\)-\(\omega\) model is selected as the turbulence model [26]. In this study, the computational domain is taken as a rectangle of \(16B\times 28B\) (\(B\) is the computed width of the box girder section, \(B=12.75\) m), as shown in Figure 9 boundary conditions of the calculation domain: the inlet is the velocity inlet boundary, the outlet is the pressure outlet boundary, upper and lower boundaries are symmetric boundaries. The maximum wind speed of the most unfavorable wind direction is 30.69 m/s, and the calculation cross-section is modeled by the actual size.  
In the computational domain, the shape of the flow cross-section is established according to the shape and size of the object, and then the computational domain is divided into  
Figure 8: Static three-component force acting on the main beam.  
Figure 9: Calculation domain arrangement of main beam section.  
grids. In order to make the computational grid adapt to the changes in fluency variables, the grid division in places with drastic changes in fluency variables should be denser, while the grid division in places with slow changes should be sparse, and the grid size between the two should gradually transition, as shown in Figure 10.  
Aiming at a concrete rigid frame bridge with a total length of 1010 m, the bridge span arrangement is 105 m + 4 \(\times\) 200 m + 105 m. The bridge is located in the mountainous area, but the terrain is relatively broad and flat. In this paper, the mid-span section of the bridge is selected (see Figure 11 below), and the two-dimensional modeling analysis is carried out at 0\({}^{\circ}\) wind attack angle. In order to verify the reliability of the model, we compare the numerical simulation results with the wind tunnel test results to verify the feasibility of the numerical simulation [27].  
The simulated wind speed U is adopted as 10 m/s. The simulation results include the main beam drag coefficient, lift coefficient and lift moment coefficient. The comparison results are shown in Table 4.  
It can be seen from Table 4 that the simulated three-component coefficient is in good agreement with the experimental data. Although there is a certain error between the lift coefficient and the experimental data, it is within the acceptable range.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Three-Component** & **Experimental Result** & **CFD Simulated** & **Error** \\
**Force Coefficient** & & **Result** & \\ \hline C\({}_{\text{H}}\) & 0.370868 & 0.384444 & 3.66\% \\ C\({}_{\text{V}}\) & 0.558385 & 0.491538 & 11.9\% \\ C\({}_{\text{M}}\) & \(-\)0.129795 & \(-\)0.135794 & 4.62\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of three-component force coefficients between numerical simulation and test.  
Figure 11: Mid-span section of main beam.  
Figure 10: Schematic diagram of structural meshing of the computed cross-section.