## 2 Wind Tunnel Test Setup
### Model Setup  
A streamlined box girder from a certain cable-stayed bridge was selected as the research object. The main beam has a width of 34.0 m, a height of 3.5 m, and a wind nozzle angle of 56\({}^{\circ}\). Considering the wind tunnel test section dimensions and blockage ratio requirements, the scale ratio was set to 1:30. The scaled model has a length of 2.140 m, a width of 1.070 m, and a height of 0.117 m, with a width-to-length ratio of 2:1 and a width-to-height ratio of 9.15:1. The maximum blockage ratio is less than 4.48%. The sectional model parameters are shown in Table 1. The model is constructed with a steel tube and rib plates as the framework and covered with ABS panels to ensure sufficient strength and stiffness.  
A ring of pressure measurement holes was arranged at the midspan of the model, with a total of 180 pressure holes on both the upper and lower surfaces. Figure 1 shows the sectional model of the main beam and the layout of its surface pressure measurement holes. The wind pressure was measured using the micro ESP pressure scanning valve and data acquisition system, with a measurement range of \(\pm\)20 in H\({}_{2}\)O, a sampling frequency of 330 Hz, and a static accuracy of \(\pm\)0.05%FS. To facilitate the representation of each measurement point, the dimensionless distance \(D_{\text{d}}\) is defined as  
\[D_{\text{d}}=\frac{d_{\text{i}}}{D} \tag{1}\]  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter Name** & **Prototype Value** & **Similitude Ratio** & **Model Value** \\ \hline Length, \(L\) [m] & 96.8 & \(-\) & 2.140 \\ Width, \(B\) [m] & 32.0 & 1:30 & 1.070 \\ Height, \(H\) [m] & 3.5 & 1:30 & 0.117 \\ Mass, \(m\) [kg\(\cdot\)m\({}^{-1}\)] & 2.56 \(\times\) 10\({}^{4}\) & 1:30\({}^{2}\) & 28.545 \\ Frequency, \(f\) [Hz] & 0.245 & 1:7.837 & 1.920 \\ Damping ratio, \(\zeta\) & \(-\) & \(-\) & 0.22\% \\ \hline \hline \end{tabular}
\end{table}
Table 1: Test parameters of the main beam sectional model.  
where \(d_{i}\) is the distance from the \(i\)-th pressure measurement point on the upper or lower surface to point A along the surface and \(D\) is the distance along the surface on which the \(i\)-th point is located between points A and B, with both \(d_{i}\) and \(D\) measured in meters. Points A and B are the end points on both sides of the main beam section. Figure 2 shows the dimensionless distance diagram for the sectional model of the main beam.  
The model is supported by eight vertical springs. The influence of the end plate on the flow pattern and the aerodynamic characteristics of the test models are complicated. Many researchers have carried out numerous experimental and numerical studies. Many valuable conclusions were obtained [41; 42; 43; 44]. Generally, the end plate can suppress the end effect. The suppression effect is dependent on the shape and dimension of the end plate. The end plates used in wind tunnel tests for a streamlined beam section model were usually rectangular plates with round corners. The width of rectangular plates was around 1.4-5.5 times the beam width, and the height was around 3-5 times the beam height [1; 36; 44]. Thus, the rounded rectangular end plates with a width of \(1.5B\) and a height of \(3.5H\) were employed to eliminate the end effects in the current study. The wind speed was measured using the Series 100 Cobra Probe (Turbulent Flow Instrumentation Pty Ltd., Tallangatta, VIC, Australia), with a measurement range of 2-100 m/s, a sampling frequency of 625 Hz, and a measurement accuracy of \(\pm 0.5\) m/s. The vibration displacement was measured using the HL-G112-A-C5 laser displacement sensor (Panasonic Holdings Corporation, Kadoma, Japan), with a distance of 120 mm between the laser emission point and the measurement center, a measurement range of 120 \(\pm\) 60 mm, a sampling frequency of 1000 Hz, and a resolution of 8 \(\upmu\)m. The installation diagram of the model is shown in Figure 3.  
Figure 1: Diagram of the model and measuring points (unit: mm).  
Figure 2: Schematic diagram of the dimensionless distance.