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RE: WIND DESIGN-Buffeting?

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As usual, the definition depends on who you are
talking to and what sort of structure you are talking
about...

According to "Wind Loading and Wind-Induced Structural
Response," ASCE, 1987, in the section on bridges,
"Buffeting typically is defined as the randomly forced
vibration of a structure due to velocity flucuations
in the oncoming wind....it is a pure forced vibration
where the forcing function is totally independent of
the struture motion."

It is distinctly different than torsional divergence
(monotonically increasing rotation to failure), 
vortex shedding (interactive aeroelastic phenomenon
resulting in periodic motion transverse to wind
direction), flutter (vertical/torsional oscillation
due to motion-dependent variation in aerodynamic
action),  and galloping (large-amplitude vertical
oscillation, again due to aeroelastic interaction.)

d a v e e v a n s 


-----Original Message-----
From: Wontae Kim [mailto:Wontae.Kim(--nospam--at)unistresscorp.com]

Sent: Thursday, June 02, 2005 2:46 PM
To: seaint(--nospam--at)seaint.org 
Subject: WIND DESIGN-Buffeting?

Hi!
What is the exact definition of 'buffeting'?

-----Original Message-----

"Buffeting" is the result of the forces applied on a
structure due to
wind TURBULENCE effects. The most prominent example of
a turbulence
effect is "vortex shedding."

"Buffeting" is more pronounced at higher wind
speeds--which results in
greater turbulence at the "boundary layer" near the
ground where
structurally significant winds will occur. It
generally results in
oscillation roughly transverse to the wind direction.

At low wind speeds wind exhibits "laminar" flow.

(Note that "buffeting" is really the EFFECT of wind
turbulence, and is
NOT the same thing as the wind GUSTING, the effects of
which typically
cause structure movement parallel to the wind
direction. However both
effects will be more pronounced for flexible
structures).



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