This is an age old tower talk question and I have yet to see a definitive
answer. As a non-engineer, I think that if properly placed, guys would make
for a stronger structure. Self-Supporting towers usually have stronger legs
so the added down force from the guys should not be an issue. I have
installed guys on an aluminum tower to make it more comfortable to climb and
to increase the strength. It held up fine, I no longer own this tower. If
this was a new installation it would not make financial sense to purchase a
self-supporting tower such as a Rohn SSV along with the huge concrete base
and then add guys when you can buy a tower designed for the purpose and only
need a yard or so of base concrete.
John KK9A
To:towertalk@contesting.com
Subject:[TowerTalk] Adding guys to self supporting towers
From:Richard Karlquist <richard@karlquist.com>
Date:Mon, 12 Aug 2013 14:06:29 -0700
List-post:<towertalk@contesting.com">mailto:towertalk@contesting.com>
The topic of adding guys to self supporting towers has been
discussed a number of times on this reflector, but I am
still not clear on exactly why it supposedly won't work.
If I have figured crrectly, the worse case compressive load
on a leg at the bottom of a trianguler tower
is equal to the product of the horizontal windloading
at the top times the factor h/[w*sqrt(3)] where h is
the height and w is the width of a face.
For example, a 100 ft windload at the top of a 50 foot
tower with 18 inch face will induce 1925 lbs of
compressive force. If a the tower is guyed at the top
with the guys at 45 degree angles, the compressive
force is simply equal to the horizontal wind load, or 100 lbs.
Much less than the unguyed 1925 lbs.
It seems to me the guyed tower is much stronger and could
handle a considerably larger wind load based on this
simple analysis.
The only way I can see that this wouldn't work is if a
larger antenna resulted in torque loads that the tower
couldn't handle. For example, the HDBX series, well known
for its poor torque strength, would be a poor candidate
for guying. OTOH, a light weight tower with a large
face width might be able to take a lot of torque. To
facilitate this, you might want to build the tower with
less taper than it typically has in the self supporting
configuration, or maybe no taper. All of this depends
on wind area and boom length.
Comments?
--
Rick Karlquist
N6RK
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