Hank,
> Using TIA/EIA 222-F wind loading criteria and 70 mph wind
> velocity (min. recommended) a 40 foot section of Rohn, 25g
> un-guyed and cantilevered will develop a moment at the base
> of 7200 ft-lbs at the base. This is without an antenna load,
> just the tower itself. The published allowable moment for 25g
> ,by Rohn, with a 1/3 increase for wind loading duration is
> 6,720 ft-lbs. At 40 feet it is clearly overstressed. How do
> you say that this is ok and that Rohn fully supports this?
"Self-Supporting Towers - Allowable Antenna Areas (Sq. Ft.)
Drawing A871266RI dated 9/24/1987 and found in the Rohn
Commercial Products Catalog (mine is copyright 1993).
For 70 MPH w/no ice the maximums are:
#25 40' @ 1.5 sq. ft. (1 x 5/8" line per face)
#45 45' @ 2.3 sq. ft. (1 x 7/8" & 1 x 1/" line per face)
#55 60' @ 0.8 sq. ft. (2 x 7/8" lines per face)
" 55' @ 4.0 sq. ft. (2 x 7/8" lines per face)
#65 80' @ 0.9 sq. ft. (2 x 7/8" lines per face)
" 70' @ 8.7 sq. ft. (2 x 7/8" lines per face)
The chart also shows self-supporting heights for 80 and 90 MPH
as well as the data for the same heights with 1/2" of ice.
Surface areas assume round antenna members.
73,
... Joe, K4IK
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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