Study On Wind Load For Roof Cladding Of Building With Large Aspect Ratio

With the improvement of technology and industrial functions,more and more large-aspect buildings have arisen.Meanwhile,due to global climate change,disastrous wind is more frequent,which leads to more serious losses.Previous wind disaster surveys show that even though the overall damages of large-aspect buildings are not common,the failures of roof cladding occur frequently.One main reason for this is that the calculation methods for design wind load of roof cladding have not been established systematically.Aiming at the deficiencies of existing research,combined with wind tunnel tests,a study on wind load calculation methods for roof cladding design is done,based on Vortex theory,Classical extreme value theory,Multivariate analysis theory,Unsupervised learning method and Multivariate extreme value distribution theory.The main research contents and methods are as follows:(1)Study on distribution characteristics and formation mechanism of wind pressure on roof of building with large-aspect ratioBased on the results of wind tunnel tests,the reasons for different distributions in small and large aspect ratio buildings and the formation mechanism of wind pressure in them are analyzed with Vortex theory.Then combined with the physical distribution characteristics of wind pressure,through statistical theory,the correlation of fluctuating wind and non-Gauss characteristic of wind pressure are studied.(2)Estimation method of extreme wind pressure by using short time history samplesUsing short time history samples to estimate the extreme wind pressure is a practical method.It is common to estimate wind pressure based on extreme value theory by blocking time histories and extracting extreme values from each block time history as sub extreme samples.But this method is effective only when the block time histories are independent with each other as well as the extreme samples,which have not been handled well.To ensure the independence of the block time histories,the rescaled range is used to determine the long-term correlation vanishing point and the length of block time histories.To obtain mutually independent sub extreme samples,declustering method has been used to eliminate the possible extreme values contained in the same cluster.After the above work,the method for extreme wind pressure with sub extreme sample is established based on the interval maximum value model and the effectiveness and practicability of the method are verified by the wind tunnel test data of the rigid roof model.(3)A zoning method for the wind pressure based on improved K-means clusteringK-means clustering has limitations in wind pressure coefficient zoning applications,which requires K values(cluster number)in advance.Two measures have been taken to improve the method.One is to limit the K value in advance to realize fast clustering under all K values.Another is to use the validity index to determine the best K value.About 20 effectiveness cluster indexes have been compared and summarized.Flat roof under two working conditions are chosen as examples to illustrate and verify this zoning method.(4)Estimation method of zoning extreme wind pressure by considering the correlation of multipoint extreme wind pressureBased on the multivariate extreme value distribution theory,two calculation methods for zoning extreme wind pressure of a large area are put forward.They are direct method and combination method.These methods can not only calculate the extreme wind pressure of an area where the measure point locates according to the distribution of wind pressure on this point and the arbitrary correlation of extreme wind pressure,but also give the extreme failure probability of the corresponding area.By using the direct average method,moving average method and the multivariate extreme value method,the zoning extreme wind pressure including the most unfavorable pressure and suction of the single wind direction and the full wind direction is calculated.The results show that the combination method has better security.(5)Study on wind pressure area reduction effect of roof claddingThe variation of area extreme wind pressure in different positions on the roof is studied.Combined with the physical characteristics of wind pressure distribution and zoning results,wind pressure,including the most unfavorable pressure and suction on the angle,edge and center of the roof surface are selected for analysis.Area average pressure method is used to calculate area extreme wind pressure with different area.The area curves of different parts of roof are described with unified logarithmic linear form formulas.