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Fw: [wind_haz_mit] Fw: Wind loading

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Another response on wind loading from the wind_haz_mit egroup.

James Cohen
Website: http://u2.expertpages.com/jccpc

-----Original Message-----
From: Ernie Jones <ernie(--nospam--at)eriinc.com>
To: JCohen <jccpc(--nospam--at)email.msn.com>
Date: Sunday, October 17, 1999 15:27
Subject: RE: [wind_haz_mit] Fw: Wind loading



To whom it may concern;

I am unaware of any testing on combined wind effects for such a situation.
Actually, outside of the three and four sided trussed tower force
coefficients,
based of wind tunnel testing, and latice framework coefficients, I'm unaware
of
any other published references.

We have a similar problem in the EIA/TIA TR 14.7 committee I work on.
This committee writes the ANSI/TIA/EIA-222 Broadcast Tower Standard.

We only give wind sheilding if the feedlines, climbing ladders,  or other
members are fastened
directly, and not beyond a face of the tower.  The idea is that these
members play the same role
as structural members in the faces, and the face with the highest "e" (Af +
Ar / Ag) governs.  The
Ae and Cf are taken from the "e" of this face.   However, if the feed lines,
ladder, etc. are inside the
triangular or square tower, then they have to be taken as seperate members
in free space, with
the highest applicable shape factor used.  We certainly know that some wind
sheilding exists,
however, without a proven method to calculate this we cannot put a realistic
number to it,
so we take the conservative route.

There is some limted information on interference effects in a reference
titled "Wind Forces in
Engineering" by Peter Sachs (Pergamom Press).  They summed up their limited
work by
saying a body which is windward of another will affect the wind forces on
the second one,
if they are within 6 diameters (widths) of each other.  If greater, then
consider them to have
no wind sheilding effect.  They give a shape factor for both bodies together
based on their separation.

Hope this can be of some help, although I know it does not provide specific
data to keep from
using somewhat of a conservative combined calculation method.

Regard,

Ernie Jones, P.E.  ERI at (812) 925-6000 Phone