Civil Engineering Reference
In-Depth Information
Chapter 3
STOCHASTIC DESCRIPTION OF
TURBULENT WIND
The description of the wind field given below is only intended to provide the theoretical
basis that is necessary for the ensuing calculations of structural response. More compre-
hensive descriptions have been presented by Simiu & Scanlan [4] and by Dyrbye &
Hansen [5], where guidelines with respect to the choice of typical input parameters to the
stochastic description of the wind field may be found. Such information has also been
given by Solari & Piccardo [6]. The most comprehensive source of wind engineering
data is provided by Engineering Science Data Unit [7]. Basic theory of turbulence may
be found in many text books, see e.g. Batchelor [8] and Tennekes & Lumley [9]. As
shown in Fig. 1.3.a the wind velocity vector at a certain point is described by its compo-
nents (see Eqs. 1.2 - 1.4) in the Cartesian coordinate system
(
)
x yz
,,
with
x
in the
f
main flow direction and
z
in the vertical direction. It is taken for granted that the wind
field met by the structure is stationary and homogeneous within the time and space that
is considered. A statistical description of the wind field comprises three levels: the long
term variation of the mean wind velocity, the short term single point time domain varia-
tion of the turbulence components, and finally, the short term spatial distribution of the
turbulence components.
3.1 Mean wind velocity
()
The statistical properties of the mean wind velocity
Vz
are required in order to estab-
f
lish a basis for the calculation of structural design load effects during the weather condi-
tions that have been deemed representative for the purpose of obtaining sufficient safety
against structural failure. A design check with respect to ultimate structural strength will
only require information regarding the wind field properties under a characteristic ex-
treme weather condition, but the properties under several representative weather
conditions are required if vortex shedding may occur. If a fatigue design check is
