Research On Design Wind Load Of Large-span Rectangular Flat Roof Structure

Large-span flat roof is a kind of widely used structure,which has the characteristics of light weight,large flexibility and small damping,and wind-induced vibration effect is significant.Wind load is one of the most important factors in structure design.However],there is no wind-resistant design method for long-span roof structures,the method in "Load Code for the Design of Building Structures" is widely used at present,but the method is mainly used for high-rise structure,not fitting for large-span roof structure.Therefore the calculation method of the wind load of the long-span roof structure design,with the application in the flat roof,is the problem solved in this paper.In this paper,the wind load characteristics of flat roofs with different aspect ratio,span-depth ratio,geomorphological type and model scale ratio are systematically studied,and the design wind load of long-span flat roof structure is given based on wind load characteristics,providing the basis and suggestion for the relevant part of "the code of wind-resistant design in roof structure".The main work of this paper is as follows:1.A series of wind tunnel tests for flat roof are designed and completed,including variables of aspect ratio,span-depth ratio,geomorphological type and model scale ratio,discussing the effects of these variables on mean wind load,fluctuating wind load and extreme wind load.The coefficient of mean and fluctuating wind pressure on the long windward side is greater than that on the short windward side;coefficient of wind pressure increases as the increase of span-depth ratio with the same aspect ratio;when the geomorphological type changes from A category to C category,the coefficient of mean wind pressure of the flat roof gradually decreases,the coefficient of fluctuating pressure increases gradually,and the coefficient of extreme wind pressure increases gradually.2.Based on wind-induced vibration calculation examples,combining form of Equivalent Static Wind Load(ESWL)in mean and fluctuating wind pressure,the changing laws of background effect and resonant effect are investigated,calculating ESWL factor.The major influencing factor for resonant factor is fundamental frequency of grid-pyramid structure,and the major influencing factor for background factor is correlating length factor.3.According to the zones of the main structure in China and abroad,using well-shaped division for main structure,calculated zone values of mean and RMS wind pressure coefficients are applied to wind-resistant design of main structure concerning variables of aspect ratio,span-depth ratio,geomorphological type and wind direction.The formula of the equivalent RMS factor is obtained by fitting the fundamental frequency of the grid-pyramid structure as variable.96.9% of calculation results could be envelope by ESWL calculation results,which tends to be conservative,and validate the applicability of the conclusions in truss structures.4.Zoning method in the code of building envelope in United States is improved by new reasonable zone method concerning the variables of aspect ratio,span-depth ratio and geomorphological type,and corresponding coefficients of extreme wind pressure are applied to the structure wind-resistant design of building envelope.