I live on a hilltop location which has many benefits, but weather is not one
of them!
In North Texas, I believe that self supporting towers will eventually fail and
only those with very broad bases actually survive, although many of them do
not. I am in a 70 mph zone, 400 feet above Ft. Worth with Exposure Category C
(nothing to break the wind to the horizon) but I see 70 mph wind speed several
times a year.
The published data on guyed Rohn Towers has been adequate for all of my
installations, but I would never say they are grossly over designed. The only
variables that I have had to calculate have been based on my installations and
include the guying points, number of guys, load at the top of the tower and
account for local soil, slope, and wind loading conditions for the base and
guy anchors. Don't forget the feed lines and other cables (they are not
insignificant).
Rohn Pre-Engineered Drawings have always been adequate for me and they
accommodate from 70 mph to 110 mph wind speed and resulting wind pressures. I
prepared a set of drawings for Rohn 25 from 40 feet to 150 feet, paid a PE to
check all my calculations (and Rohns), and obtained blanket approval for all
of these tower heights based on the Southern California Soil conditions.
Several amateurs used these same drawings through the San Diego DX Club to
obtain the required building permits. The PE cost was minimal ($250) and
included several types of guy posts and ground anchors. Rohn uses the basic
assumption that at the time of the strongest wind speed (fastest mile and 50
year probability) the ground will have little holding strength due to water
saturation of the soil.
Why would anyone put their life and their families lives at risk with an
improperly engineered or installed structure?
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