Field Measurements Of Admospheric Stability And Strong Wind Characteristics Near Ground In Urban Area Of Beijing

Along with the speeding up of construction process in Beijing urban area, buildings are becoming more, denser and higher, so significant changes have taken place in wind characteristics near ground. At the same time, large span and super high-rise buildings are becoming important direction for the development of urban construction, and wind load is one of the important controlled load in the structure design of these two types of buildings. The change of wind field may bring new problems in the aspect of safety in the wind-resistant design of large span and tall building, so it’s very necessary for us to study again on the characteristics of strong wind near ground in urban area of Beijing.On the other hand, wind characteristics are closely related to atmospheric stability and degree of wind stationarity, and people always pay more attention to wind field neutral and statonary in the field of structure wind engineering. Therefore, this paper firstly studied atmospheric stability and stationarity of wind field based on measured data. On the basis of wind data screening, strong wind characteristics and models near ground in Beijing urban area were obtained. The main contents of this paper are as follows:(1) After the preprocessing of measured wind speed data, this paper analysised the interference effect of the tower to ultrasonic anemometer sampling. On the basis of above analysis, this paper statistically analysised the overall wind speed data, yearly wind speed data, monthly wind speed data. Analysis included the probability density distribution, the maximum average wind speed, the maximum instantaneous wind speed, the number of wind speed data in different wind speed ranges, etc.(2) According to the atmospheric stability classification standard of gradient Richardson number Ri and M-O length, atmospheric stability state of Beijing in winter and spring were analyzed based on measured data. Then this paper validated the law that the atmospheric stability near ground tended neutral in strong wind condition and determined selection criteria of measured wind data based on the atmospheric stability.(3) Stationarity inspection was carried out on the basis of measured data respectively through the method of runtest, RHVS and friction velocity ratio method, comparison and analysis showed that the friction velocity ratio method was more suitable for this research project. On this basis, the measured data was further screened. (4) On the basis of measured wind data that satisfied neutral and stationary condition, this paper statistically analyzed the characteristics of mean wind and fluctuating wind. Mean wind features included wind profile, the wind angle, the wind attack angle, etc.And fluctuating wind features included friction velocity, turbulence intensity, gust factor, turbulence integral scale and correlation coefficient of fluctuating wind, etc. According to the characteristics of super-rise buildings and large-span buildings, wind field models suitable for the performance study of wind resistance of these structures were given respectively for the parameters of turbulence, gust factor, turbulence integral scale, etc.