| According to the design wind load calculation method stipulated in the load code of China,it can be found that the design wind load made by this method makes the wind resistant design process of the structure conservative.In the boundary layer wind tunnel test,the wind load is calculated using the full wind direction statistical extreme wind speed and the extreme wind pressure coefficient,which also makes the design wind load conservative.In order to accurately carry out the wind resistance design of the main structure of low building,get a more economical and reasonable structural design scheme,and provide reference for the design optimization of wind resistance in the future.It is necessary to consider the wind direction effect in the wind resistance design process.This paper takes the low building model in the wind tunnel test as the research object and the sample of wind speed in Beijing,the wind direction reduction factor of the model roof is systematically studied,including the following aspects:(1)Two kinds of theoretical analysis methods which consider the wind direction effect are introduced,such as Simiu method,Sector-by-sector method and Storm passage method based on directional extreme wind speed data,and the up-crossings method,refined up-crossings method based on continuous wind speed record and wind velocity distribution.(2)Based on the measured wind speed records in the Beijing area,the basic wind speed of the 50 year average recurrence interval is estimated by the mixed distribution of refined up-crossings method and the monthly maximum wind speed distribution.After comparing the calculation results from two kinds of distribution,it find that the mixed distribution of refined up-crossings method is very effective for fitting the annual maximum wind speed distribution.The estimated value of extreme wind speed is also more accurate.In addition,it is found that the essence of the peak over threshold method(POT)based on the small capacity sample and the mixed distribution of refined up-crossings method is same,which leads to the wind speed threshold as the key factor for the effectiveness of the mixed distribution.In addition,based on the annual maximum wind speed data obtained by China Meteorological data network,the extreme value I distribution(Gumbel disribution)is used to estimate the basic wind speed of 50 years.Compared with the analysis results of the two methods,it is found that the extreme wind speed obtained by the improved transcendental probability method is generally smaller.(3)Combined with the wind pressure data on the surface of low building model and extreme wind speed of 50 year average recurrence period in Beijing,the Simiu method is used to solve the wind direction reduction factor,Considering that the mixed distribution of wind velocity distribution is better fitted,the same use of mixed distribution to fit the maximum wind load distribution.Analysing the fitting effect of the Weibull distribution,gumbel distribution and mixed distribution,it is found that the fitting effect of the mixed distribution is the best and the extreme wind load is more accurate.The difference of wind direction reduction factor obtained by the comparison of three kinds of distribution is small,that is to say,any kind of wind direction reduction factor can be used by Simiu method.When considering the reduction factor of the roofs wind direction,it is suggested to reduce the design wind load by using the mean of all buildings towards the wind direction reduction factor. |
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