## 5 Conclusions  
To investigate the influence of oncoming wind speed on the wind characteristics at a bridge site in a mountain valley, a wind tunnel test of a terrain model with a scaling  
Figure 52: Probability density function of the main beam under uniform inflow with different wind speeds and directions. Figure 53: Probability density function of the main beam under ABL inflow with different wind speeds and directions. ratio of 1:1000, where a long-span bridge would be built in the V-shaped canyon, was conducted. Uniform and ABL inflows were both applied in the wind tunnel test. The mean and fluctuating wind characteristics at locations of the main beam and two bridge towers under different oncoming wind speeds were comprehensively studied. The main conclusions are as follows:  
(1) The trend in mean wind characteristics at the bridge site in the V-shaped canyon with the variation in wind speed is consistent under uniform and ABL oncoming wind, while the influence of oncoming wind speed is more pronounced under the ABL inflow. Wind profiles and wind speed amplification factors decrease as wind speed increases, while the wind yaw angles remain largely unchanged. Moreover, an increase in oncoming wind speed leads to an increase in wind attack angles, and all values are positive. Therefore, a significant upward air current is present across the entire bridge site, which typically increases the lift component of the bridge and affects the stability of the structure. Special attention should be paid to the influence of large attack angles on bridges in engineering projects. (2) Under uniform inflow conditions, the fluctuating wind characteristics exhibit a significant variation with the oncoming wind speed: increasing oncoming wind speed decreased the turbulence intensity, reduced the peak frequency of the power spectrum, and slowed down the high-frequency decay rate. The variation in the turbulent integral scale with oncoming wind speed is greatly influenced by the terrain. The turbulent integral scale at the southwest tower increases with the oncoming wind speed, whereas at the northeast tower, it decreases with the increase in wind speed. When the oncoming wind is ABL, the turbulence intensity and the turbulent integral scale remain unchanged with variations in oncoming wind speed, and the power spectrum curves are essentially coincident. In additional, the power spectra at various locations of the bridge align well with the von Karman wind spectrum, and the turbulent integral scale derived from fitting with the von Karman wind spectrum is sufficiently accurate. (3) As wind speed increases, the value of K gradually increases, and the value of C also increases, leading to an enhancement of the coherence between the two points. At high wind speeds, different locations of the bridge may simultaneously be affected by wind loads, resulting in a more significant overall structural response, which is highly unfavorable for bridge safety and necessitates the implementation of protective measures in engineering. Additionally, the coherence function is only influenced by the spacing between two points. When two points are at different locations but with the same spacing, the coherence function remains roughly the same. (4) Locations with higher kurtosis and skewness values exhibit steeper probability density functions. When the main beam or bridge tower is on the leeward side of a mountain, the kurtosis and skewness coefficients tend to be larger. Furthermore, the kurtosis and skewness coefficients increased with the oncoming wind speed increases, causing the probability density function to deviate more from the Gaussian distribution. Appropriate preventive measures should be taken in advance in engineering to cope with strong gust conditions at high wind speeds. Unfortunately, due to the bridge not yet being constructed, there are no field measurement data available. In future work, we will make every effort to conduct comparative studies between wind tunnel tests and field measurements. W.L.