NecessityIn the past, predicting the probable behavior of building componentsunder extreme winds has been difficult.Of all the environmental loads on buildings and structures, wind load isperhaps one of the most damaging load.Source:www.lsuagcenter.com
Contd… Scientists classify wind intensity and damage potential differently forhurricanes, tornados, and general wind storms.Types of storms -(1). Wind storms(2). Dust Storm(3). Sand Storm(4). Cyclones (South Pacific and Indian Ocean )(5). Hurricane (Atlantic and Northeast Pacific)(6). Typhoon (Northwest Pacific )etc. Follows IS:875 (Part # 3)
Experimental setup Wind load on overhangs in a low gable building in presence of freestanding wall. Building model was made on a geometry scale of 1:25 and a study wasconducted in an open circuit wind tunnel. Plan dimension 280mmx156mm and wall height 156mmwith roof slope 25 degrees, with an overhang eaves lengthof and 60mm free standing wall of height 66mm. Effects on pressure variation have been studied on both upper and lowersides of the overhang.
Contd…Free Standing wall(Boundary wall)280 mm=LOverhang wallFig. 2: Lay out of pressure taps in overhang
Analytical study Wind pressure measured on the roof of building models areexpressed in the form of a non dimensional pressure coefficientdefined as –Cp(i) = 2( Pi – Po)/ρU2Instantaneous surfacepressure Static (ambient, atmospheric)reference pressureAir densityMean velocitymeasured Mean Value = (Cp(1) + Cp(2) + Cp(3)+……..)/NTotal No. Of samples
Contd…Cp(min) =Min. of Cp(i) ; Cp(max) = Max. of Cp(i)
Graphical study Individual local pressure coefficients on eaves at various zones(1).For mean pressure coefficients-At upper surface(3>4>1>2)At lower surface
Contd…(2).For maximum pressure coefficients-At upper surface(3>1>4>2)At lower surface
Conclusions Commonly used roof angle of 25o was considered, andcorner, edge and center load on overhangs have been evaluated Net peak upward pressure shows maximum positive value in thepresence of free standing wall, located at a distance of 3h.
References Stathopoulos, T., Luchian, H. (1994) .Wind-induced forces on eaves of lowbuilding. J. wind Eng. Ind. Aerodynamic, vol 52, pp 249-261. Stathopoulos, T., (1981) .Wind load on eaves of low buildings., J. Struct.Div., ASCE, 107, ST10, Proc. Paper 16543: 1921-1934. Journal of Wind & Engineering, Vol. 5, No. 1, Jan 2008, pp. 39-46“Alok David John, Ajay Gairola, Prem Krishna”(Indian Institute of Technology, Roorkee )