Although the formula P = 0.004 V^2 is nice and simple, and was used for
years, there are newer formulas used by EIA-222-D (effective June 1, 1987)
and the -E version (if I can find my copy of it in the stack somewhere).
2.3.10 The design wind load (Fc) on a discrete appurtenance such as an ice
shield, platform, etc (excluding solid microwave antennas/reflectors) shall
be calculated from the equation:
Fc = qz Gh Ca Ac (lb) [N]
qz is the velocity pressure, calculated based on the centerline height of
the appurtenance, qz = .00256 Kz V^2 (lb/ft^2), where Kz = [z/33]^(2/7)
for z in ft. V is in mph. z is the height above average ground in ft. to
midpoint of section. Kz is the exposure coefficient.
Gh is the gust response factor, calculated based on the total height of the
structure, Gh = .65 + .60/(h/33) ^(1/7) for h in ft, 1.00 <= Gh <= 1.25.
Ca is the force coefficient applied to the projected area (ft^2) of a
discrete appurtenance (Ac). If the aspect ratio <= 7 (member length/member
width), then a cylindrical shape has Ca = 0.8. If the aspect ratio >= 7,
then Ca = 1.2. For flat members, use 1.4 or 2.0.
Ac is the projected area of the appurtenance in ft^2.
As you can see, it is much more complex now. I still like the old formula
best.
73 Roger Cox WB0DGF
Telex Communications, Inc.
http://www.hy-gain.com
800-898-6723 (orders only)
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