Wind Effects on Buildings and Design of Wind-Sensitive Structures
The articles in this book, written by seven internationally known experts, present the fundamentals and practical applications of comtemporary wind engineering dealing with wind-building interaction complex problems from the perspective of a structural de
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CISM COURSES AND LECTURES
Series Editors: The Rectors Giulio Maier - Milan Jean Salençon - Palaiseau Wilhelm Schneider - Wien
The Secretary General %HUQKDUG6FKUHÁHU3DGXD
Executive Editor 3DROR6HUDÀQL8GLQH
The series presents lecture notes, monographs, edited works and SURFHHGLQJVLQWKHÀHOGRI0HFKDQLFV(QJLQHHULQJ&RPSXWHU6FLHQFH and Applied Mathematics. 3XUSRVHRIWKHVHULHVLVWRPDNHNQRZQLQWKHLQWHUQDWLRQDOVFLHQWLÀF DQGWHFKQLFDOFRPPXQLW\UHVXOWVREWDLQHGLQVRPHRIWKHDFWLYLWLHV RUJDQL]HGE\&,60WKH,QWHUQDWLRQDO&HQWUHIRU0HFKDQLFDO6FLHQFHV
,17(51$7,21$/&(175()250(&+$1,&$/6&,(1&(6 &2856(6$1'/(&785(61R
:,1'())(&7621%8,/',1*6 $1''(6,*12):,1'6(16,7,9( 6758&785(6 (',7('%< 7('67$7+2328/26 &21&25',$81,9(56,7 Vo. Negative values of CP are observed on roofs and sides of building. 7KH ZDNH UHJLRQ LQ )LJXUH LV FKDUDFWHUL]HG E\ OLWWOH SUHVVXUH JUDGLHQW %HUQRXOOL¶V equation is not applicable but pressure coefficients can also be expressed in dimensionless form:
CP
w
Pw Po
(13)
1 / 2 UVo 2
Pressure coefficients in wake are invariably negative. Typical time series of pressure coefficients along with variation of wind speed and their statistics are shown in Figure 13. Definitions of Cpmean and Cppeak are: Mean pressure coefficient: Cpmean = CP
Peak pressure coefficient: Cppeak = GC P
'Pmean 1 / 2 UVmean 2 'Ppeak 1 / 2 UVmean 2
(14)
(15)
The location of separation points and the geometry of the wake have a substantial influence on the pressure distribution and the total forces on the bluff obstacle. In the case of rectangular cylinder the separation points were dictated by the geometry of the prism. The boundary layer, which builds up on the front surface, fails to flow around the sharp corners boundary layer, which builds up on the front surface, fails to flow around the sharp corners and separates. For other bluff shapes particularly for those with curved surfaces such as wires, chimneys, and circular tanks the separation points are not easy to predict. For a circular cylinder, for example, separation takes place at different positions depending on the magnitude of the viscous forces, which dominate the flow within the boundary layer. The relative magnitude of these viscous forces can be expressed in the form of a dimensionless parameter known as the Reynolds number Re:
Re
UVo 2 D 2 in ertia forces v V viscous forces P o D2 D
(16)
T. Stathopoulos
Thus R
e
Vo D
(17)
Q
in which ȡ is the density, µ is the dynamic viscosity, and Ȟ is the kinematic viscosity of the air. Figure 14 shows the variation of pressure coefficients on the surface of a circular cylinder for different values of Re. Clearly the influence on the side face and the leeward side is significant.
Figure 13. Wind pressure and wind speed traces indicating mean and peak values The time-averaged aerodynamic forces on structures can be expressed as along wind or drag forces (FD) and across wind or lift forces (FL). The latter should not be confused with the upward
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