Civil Engineering Reference
In-Depth Information
It should also be noted that vortex shedding effects are to some extent dependent on
the Reynolds number (
Re
=⋅
m
2
/s is the kinematic viscosity of
air) and of the turbulence properties in the oncoming flow. Information about these
effects is presented by Simui & Scanlan [4] and by Dyrbye & Hansen [5]. For a tubular
cross section the Reynolds number effect is to change the point of flow separation, thus
changing the Strouhal number as well as the load intensity. The main effect of
turbulence is to broaden the band-width and disturb the size and coherence of the
pressure fluctuations on the surface of the structure. Most structures are more prone to
vortex induced oscillations in smooth flow.
Above, only the effects in the across wind direction and torsion have been included.
In general, vortex shedding will also generate more or less narrow-banded load
fluctuations in the along wind direction, but at a frequency twice that which occurs in the
across wind direction and for most bridges at an insignificant load intensity.
5
VD
/
where
1.5 10
−
=
υ
υ
