## 4 Results and Discussion
### Fluctuating Wind Characteristics
#### 4.2.1 Turbulence Intensity  
Turbulence intensity (\(I_{i}\)) is a dimensionless parameter that characterizes the intensity of fluid motion. It is expressed as the ratio of the standard deviation of the fluctuating wind speed to the mean wind speed, as indicated in Equation (5). An intuitive reflection of the strength of the turbulent flow field relative to the mean flow field is provided by the turbulence intensity [26]. \[I_{i}=\frac{\sigma_{i}}{U},(i=u,v,w) \tag{5}\]  
where \(u\), \(v\), and \(w\) represent the fluctuating wind speed components in the longitudinal, transverse, and vertical directions, respectively; \(\sigma\) denotes the standard deviation of the fluctuating wind speed; and \(U\) is the mean wind speed at the monitoring point. In wind engineering, the dominant flow direction is typically represented by the longitudinal wind. Consequently, the turbulence characteristics of the longitudinal wind have the most significant influence on wind flow behavior. Thus, an analysis of the longitudinal wind turbulence intensity at various locations on the bridge is conducted in this study. The turbulence intensity on the southwest bridge tower is shown in Figures 24 and 25. The results indicate that when the oncoming wind is uniform, the turbulence intensity decreases with increasing height. This is due to the primary influence factor of turbulence intensity in uniform flow being the undulations of the terrain. The higher the location, the less the blocking effect of the terrain, which leads to a lower turbulence intensity. Additionally, the turbulence intensity continuously decreases with the increase in oncoming wind speed. This may be attributed to a more uniform airflow at high wind speeds, resulting in a reduction in turbulent fluctuation components. When the oncoming wind is ABL inflow, the degree of variation in turbulence intensity with height and oncoming wind speed is relatively small. Due to the presence of rough elements and wedges in front of the terrain, the ABL inflow inherently possesses a certain level of turbulence intensity, whereas the uniform inflow lacks any turbulence components. Consequently, after passing through the same terrain disturbance, the turbulence intensity at the bridge site of ABL inflow is higher than that of uniform inflow. Figure 23: Wind attack angles of the main beam under ABL inflow with different wind speeds and directions. The turbulence intensity on the northeast bridge tower is presented in Figures 26 and 27. When the oncoming wind is uniform, the turbulence intensity decreases with the increase in oncoming wind speed, which is consistent with the pattern observed on the southwest bridge tower. When the wind direction is \(180^{\circ}\), the turbulence intensity first increases and then decreases with the increase in height, reaching a maximum at \(y/H=0.25\), which is approximately \(40\%\), as shown in Figure 26c. This phenomenon is caused by the northeast bridge being located on the leeward side of the mountain, where the mean wind speed is low (as shown in Figure 8c), resulting in a higher turbulence intensity. When the wind is ABL inflow, the turbulence intensity for the \(0^{\circ}\) and \(30^{\circ}\) wind directions shows no significant variation with oncoming wind speed, while for the \(180^{\circ}\) direction, the turbulence intensity decreases with the increase in oncoming wind speed. Figure 26: Turbulence intensity of the northeast tower under uniform inflow with different wind speeds and directions. Figure 24: Turbulence intensity of the southwest tower under uniform inflow with different wind speeds and directions. Figure 25: Turbulence intensity of the southwest tower under ABL inflow with different wind speeds and directions. The turbulence intensity on the main beam is depicted in Figures 28 and 29. The variation in turbulence intensity with wind speed on the main beam is consistent with the patterns observed on the two towers, showing a decrease as the wind speed increases.