Study On Extreme Statistical Method,Distribution Characteristics And Dynamic Mechanism Of Random Wind Pressure Field On Large-span Roof

Compared with the main structure of the building,the failure phenomenon of the cladding structure under the action of wind load is more common.And due to the characteristics of the large-span roof structure and the irregular movement of the flow field near the ground,the wind pressure field around it is more complex than that around the highrise building structure.Therefore,more attention will be paid to the wind field distribution characteristics,wind resistance safety and reliability of large-span roof cladding structures.Based on the requirements of wind load research and wind resistance design of large-span roof structures,several key problems related to the wind load of large-span roof structures are studied in detail.The research results have important theoretical reference significance and practical application value for promoting the research of wind resistance theory,technical progress and improving the accuracy of wind effect estimation of large-span roof structures.The main research contents and achievements of the thesis are as follows:(1)Refined simulation of the atmospheric boundary layer wind field.Through debugging and combining the flow field test devices,the effects of the shape,size and placement of the trapezoidal spire,baffle,rough element on the flow field parameters are studied.First of all,the similar simulations of the mean wind speed profile and turbulence profile of the test flow field with three geometric scaling ratios(1:150,1:300,1:500)under the same landform are realized.Secondly,three kinds of wind fields with the same mean wind speed profile but significant difference in turbulence distribution at the same scale ratio are simulated.The above experimental wind field lays a reliable foundation for the follow-up quantitative study of the influence of geometric scale ratio and flow field turbulence on the wind pressure distribution of roof structure.(2)The estimation method of extreme wind pressure of building cladding structures.A method for estimating the extreme wind pressure of a short-term building envelope is proposed and is granted a national invention patent.Firstly,the nonlinear characteristics of wind pressure series are analyzed based on mutual information technology.The results show that the mutual information can analyze the nonlinear information in the turbulent structure and reflect the turbulent structure indirectly.And the reasonable time intervals of independent segments are determined from the theoretical level and probability sense.Then the peak segment average method is used to estimate the extreme wind pressure of the sample under the independent observation duration.Finally,the extreme wind pressure under the target observation duration is obtained by converting the extreme conversion relation of different observation time duration.The accurate estimation of the extreme wind pressure of different types of buildings is realized with less sample cost.compared with the existing methods,it shows that the proposed method has better effectiveness and numerical stability.Furthermore,the envelope statistics are carried out for the independent segment duration of multiple wind tunnel test projects with different scale ratios and types.Then the modified peak segment average method is used for extreme value verification to determine the minimum sample length that can be used for extreme value analysis.And a simplified formula of modified peak segment average method is given.(3)Analysis of wind load characteristic parameters of large-span flat roofs.Based on the basic work of content(1),the wind tunnel tests of three different scale ratios on largespan flat roof are carried out and the effects of different turbulence on the wind load of the roof are investigated.Under the condition that the wind field parameters are similar,the wind pressure distribution on the roof of the model with different scale ratio has a good consistency.The difference of turbulence integral scale is the main reason that leads to the difference between the roof test results of scale 1: 150 and that of the other two scales.Then the influence of turbulence on the roof wind pressure is studied.The overall variation trend of standard deviation wind pressure coefficient increases with the increase of turbulence,and the overall variation trend of minimum wind pressure decreases with the increase of turbulence.For the mean wind pressure coefficient: when the incoming flow blows to the flat roof,the mean wind pressure coefficient is less affected;when the incoming flow blows obliquely to the flat roof at a certain angle,the mean wind pressure coefficient is suppressed with the increase of turbulence.(4)Aerodynamic wind resistance measures for large-span roof structures.The overall wind resistance and mitigation effects of different forms of parapet and eaves on the local high negative pressure area of long-span flat roof are studied.The research shows that the wind resistance effect of perforated parapet and perforated eave is better than that of nonperforated parapet and non-perforated eave.And the wind resistance of the perforated parapets is better than that of the perforated eaves.Comparing the results of parapet with different opening conditions,the wind resistance effect of 3mm high parapet with 40%opening ratio is the best,and the mitigation effects are 14.2%.(5)Mechanical mechanism analysis of random wind pressure field on building surface.The dynamical modal decomposition(DMD)method is used to analyze the dynamic mechanism of the random wind pressure field on the surface of a large-span roof.Based on the Takens embedding theorem,the time delay coordinate is introduced to increase the spatial dimension of the original snapshot matrix to improve the standard DMD method,which can discover the fuzzy dynamic features hidden in the wind pressure test data.The DMD method and the proper orthogonal decomposition(POD)method are applied to analyze the random wind pressure field on flat roof,and the spatial mode,time mode and reconstruction effect of the two methods are compared.The spatial modes of the two methods can reflect the main characteristics of the typical vortex in the fluctuating pressure field.POD time mode contains multiple frequency coupling information.On the other hand,the DMD time mode is a singlefrequency mode and the attenuation rate of each mode can be obtained,which can better explain the dynamic characteristics of the random wind pressure field.When the same proportion of modes are used to reconstruct the fluctuating wind pressure field,the reconstruction results of the DMD method can better describe and fit the local characteristics of the original fluctuating pressure field than those of the POD method.Therefore,the DMD method has more advantages in revealing the spatio-temporal evolution characteristics of random wind pressure field.