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John,

I recommend you look at hard at the vortex-induced vibration conditions you
may encounter.  If the existing building is 300 feet tall also and has not
shown signs of vibration in wind for a seasonal cycle (experienced adequate
wind loads), there may not be an issue.  However, wind tunnel tests are
done precisely to address your concerns, especially on tall slender
structures that have high wind exposure.  You should do some research on
the phenomenon (the web and a book by Robert Blevins is a good place to
start) as well as understand the new buildings (are they shorter than
buildings that surround them, taller, are you in the middle of a barren
field?).  Something to remember is your observation of vapor/smoke flues at
refineries, they have strakes built in to avoid vortex-induced vibration,
other industrial buildings are light with as little surface area present as
acceptable.  Good luck.


Kevin Moore, SE
kmoore(--nospam--at)degenkolb.com


From: "John Holliday" <john.holliday(--nospam--at)chemtex.com>
To: <seaint(--nospam--at)seaint.org>
Subject: Wind loads on twin towers

I am trying to determine the wind loading on two 300 foot steel industrial
buildings spaced at 20 foot clear distance between them using the
requirements of ASCE 7-98. One building (which will be new)  has cross
sectional dimensions of 147'x 38' the second building (which is existing)
measures 87'x 50'. Because they are spaced so close together and
considering
how slender they are (plus I have to design for 120mph winds) I was
wondering about the effects of buffeting and vortex shedding between the
buildings, will these phenomena have any impact on the buildings. Obviously
I would like to use Method 2 and state that there are no special
considerations but if I have to consider buffeting and vortex shedding,
what
is the procedure? Thanks in advance for any info. you guys can supply.


John Holliday, P.E.


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