Wind Loads And Analytic Method Of Equivalent Static Wind Load On Flat Roofs

Long span flat roof,a typical kind of long span roof,is widely used in application.The structures are strongly sensitive to the wind load.The provisions of wind vibration coefficient ?z in GB-50009 only apply to high-level structures and high-rise structures,whose first vibration mode is only considered when calculating wind-induced response.However,the vibration coefficient for long span flat roof is not given.Present studies on equivalent static wind loads little investigated the effects of the terrain categories and building shapes.Wind load on long span flat roofs with three length-width ratios in three terrain categories were studied in order to obtain generalized force spectra.The analytic formula of equivalent static loads was obtained through derivation based on generalized force and the effects of the terrain categories and length-width ratios on the analytic equivalent static wind loads were investigated.Main works are finished in the paper as follows:(1)The characteristics of wind loads on long span flat roofs,which are affected by terrain categories and length-width ratios,including mean pressure,fluctuating wind pressure,peak pressure and the spectrum of wind pressure,are researched.The relationship between them was also discussed.(2)The characteristic of pressure spectra of measure points on the roof and generalized spectra with three length-width ratios in three terrain categories were investigated.Morever,matching equations of generalized spectra were obtained.(3)Based on the matching equation for wind pressure spectra,the analytic formula of wind-induced response of long span flat roof structures was obtained through the method in frequency domain.It was investigated how the background and resonant response were respectively affected by terrain categories and length-width ratios.(4)According to the characteristics of the wind-induced response of long span flat roof structures,the inertial force of the first vibration mode was chosen to obtain the equivalent static wind load.It was divided into mean pressure coefficient and fluctuating pressure coefficient of the equivalent static wind load.The analytic formula of equivalent static wind load was given and how the equivalent static wind load was affected by terrain categories and length-width ratios is investigated.With the analytic formula of equivalent static wind load,it is convenient to obtain the wind load for structural design.