Abstract:

In order to learn the wind environment and the parameters of the wind environment at the sea-crossing bridge in Guangxi, the characteristics of the mean wind (mean wind velocity and directions, maximum wind velocity and instantaneous maximum wind velocity) and the fluctuation wind (the wind attack angel, turbulence versus , turbulence integral scale and turbulence power spectrum) are presented at site of the bridge, on the basis of the field measurements of the near-ground wind environment using the observation instruments of gradient wind in a wind measurement tower, which is 55m in height, at 10, 33, 38, 48, 53 m and ultrasonic anemometer at the bridge surface height (43 m) during the whole year 2012. The designing wind velocity by using the wind observation data of Fangcheng reference meteorological station is calculated for different reappearing period at site of the bridge. The results show that: 1) The change of horizontal mean wind velocity followed the power exponent law, and the vertical wind shear indexes of complete wind sample and strong wind sample were 0.148 and 0.062, respectively. The observed maximum wind speed and instantaneous maximum wind speed were 26.0 and 29.3 m/s, respectively, and both of them appeared at the height of 53 m. The mean wind velocity in the first half of the year was greater than that in the second half. The annual dominant wind direction of mean wind field was partial to N, and so was in autumn, winter and spring, while it was partial to S in summer. 2) The wind attack angel of Typhoon Kai-tak was almost ±3°, which did not exceed the test range for wind resistance performance in specification. It reflected that the terrain of the site of the bridge was relatively flat. The turbulence variation was even and stable in the observed process of Typhoon Kai-tak. The change of turbulence versus changing in 3D direction had the same trend. The 3D turbulence versus had small fluctuation in strong wind period, and the value was small too. The turbulence integral scales of 3D changed with time slightly, and it was basically in agreement with the assumption of Taylor self-correlation function method. The turbulence power spectrum followed the -5/3 power law of Kolmogrove in inertial subrange, and a decrease trend of that was with the increase of wind speed. 3) The correlation between the maximum wind speed of Fangcheng reference meteorological station and that of the site of bridge was relatively good. The correction coefficient of strong wind speed was 1.398. The designing wind velocity at the bridge surface of 50 years frequency was 39.7 m/s and that of 100 years frequency was 42.7 m/s.

Key words: sea-crossing bridge, field measurement, mean wind field, fluctuating wind field, designing wind velocity, Guangxi