Currently, research on wind fields of U-shaped valleys is rarely reported, and anemometers or wind observation towers are usually used for field measurement, but the measured position is limited and the cost is high. In order to study the wind characteristics in a mountainous U-shaped valley, a long-range, all-weather, high-precision Wind3D 6000 lidar was placed at a bridge site located in a U-shaped valley. Then, according to the data effective ratio and wind speed, nearly 6 months of original data ranging from 0 m to 810 m were analyzed statistically. It was found that the spatio-temporal distribution of wind speed and direction is obviously not uniform, and the wind parameters are correlated among different virtual wind towers (VWTs). By classification, the effective data of midspan position is taken as the research object, and the wind speed profile is divided into three categories. Type-1 shows disorderly characteristics; Type-2 shows a linear relationship; and Type-3 shows a nonlinear relationship. The wind direction is consistent with the main wind direction at the bridge site and the average wind direction of different VWTs has a high consistency. The concept of wind-direction deflection rate is put forward to describe the variation of wind direction with height. These measured wind parameters could be used as a reference for bridge wind-resistant design.

This paper investigated the aerodynamic response features of an asymmetric cable-stayed bridge. The wind resistance design parameters for judging the response were first determined, afterwards the bridge dynamic characteristics were analyzed for subsequent aerodynamic analysis. The vortex-induced vibrations (VIV) and flutter response at various wind fairing angles were then examined by using a 1:50 sectional model in the wind tunnel test. Finally, a 1:150 full bridge aeroelastic model was employed to explore the aerodynamic stability and characteristics of the whole asymmetric bridge under different wind attack angles in various flow fields. The results show that the sharp wind fairings could reduce the VIV amplitude of the steel box girder cable-stayed bridge to some extent, and the example bridge has examined to have enough flutter stability through sectional and full bridge aeroelastic model wind tunnel tests. Unlike symmetric bridges, the bridge’s maximum displacement of first torsion mode shape is at the closure rather than the mid-span, which is the essential reason to lead this unique vibration feature. The results from the present study could highlight the important effect of structural asymmetry and fairing shape to the wind-induced bridge vibration and hence may facilitate more appropriate wind design of asymmetric cable-stayed bridges.

The wind parameter distribution law at a bridge midspan in a U-shaped valley has important influence on the wind strength of this bridges. In this paper, the wind characteristics were researched by computational fluid dynamics (CFD). The surface roughness, the inlet wind speed, the wind speed profile, and the oncoming wind direction were selected as the initial conditions; the wind speed, the wind attack angle, and the wind azimuth angle were set as wind parameters; and the effect of the four initial conditions on the wind parameters was comprehensively analyzed. An innovative quantification model used to connect the coefficient of sensitivity factors with scale values was established, and the influence of initial conditions on wind parameters was studied by analytic hierarchy process (AHP) for the first time. The results show that the spatial distribution of wind characteristics in a U-shaped valley is complex and obviously affected by the initial conditions. The established quantification model has certain practicability. The AHP evaluation results showed that the influence of the oncoming wind direction on wind parameters was the most obvious. The influence degree of oncoming wind direction and wind speed profile on wind speed was just as important, accounting for 77.4%. The sensitivity of wind attack angle to oncoming wind direction was 60.8%, which was much higher than the surface roughness, inlet wind speed, and wind speed profile. The influence degree of oncoming wind direction on wind azimuth angle was the sum of the other three initial conditions.

In order to study the wind characteristics in inland cities, a Wind3D 6000 Lidar which has many advantages in measuring wind parameters was placed on a campus in Xi’an city. Then, through filtering the original measurement data, the wind speed, wind direction, wind attack angle and turbulence intensity were analyzed using the data of nearly four months ranging from 64m to 610m. It is found that during the field measurement period, there is a linear correlation and Lorentz density function distribution between wind speed and height, but the power index law is not obvious. The wind direction changes obviously with the time and season but less along the height. The probability density of wind attack angle presents Gauss distribution, with an average value of about 1.35°, which is negatively linear correlated with height and wind speed. The probability density of turbulence shows the distribution characteristic of LogNormal density function, which increases first and then decreases with the height, and has a positive linear correlation with the wind attack angle.