Rick:
I believe all you have to do is transfer the Moment from the point in
question to the point of reference on the tower. The windload area of
the antennas must be converted to pounds force by multiplying
the sq. ft. by either 30, 40, or 50 pounds per square foot wind pressure
factor as determined by the Uniform Building Code charts. The correct
factor is selected as a function of your location and the height of the
antennae in question.
Then multiply the force by the height of the antenna(s). These are the
individual moments of each antenna. Add these together, divide be the
height of the tower (or 2 feet below as you wish) and again divide by
the wind pressure factor previously used. This will give you an equiv-
alent wind load area at any height you select.
I think the limiting parameter used in figuring tower loading is the
longitudinal crushing of a tower leg by the moment converted to a
compressive force. This is what I remember from the US tower calcs.
that I received when I applied for my permit.
All the above is from memory - I'm a graduate EE (UC DAVIS) not a
structural type. So I suggest consultation with a CE with a structural
registration if you're really concerned.
I use a US tower rated at 18 sq ft loading and have a 204BA, 15-4,
105BA and a single KLM 40 ele. all stacked on a 21 ft. mast. No
problems yet?????
Eric, NV6O
EDWOODS@PACBELL.COM
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