Calculations on my tower showed that the tower, with a 20 sqf wind load surface
on the top, would resist 85 mph wind without guy wires and 135 mph wind with
the 45° guy wires. (Needless to say, I added guy wires.)
A second note: The guy wires as not attached to the top of the tower but about
70% from the top. The bending momentum will be smaller that way. Yes, I use
four (4) guy wires, about 90° apart.
I don't know where I have the calculations but I can probably regenerate them
if you like.
73 de,
Hans - N2JFS
-----Original Message-----
From: Richard Karlquist <richard@karlquist.com>
To: towertalk <towertalk@contesting.com>
Sent: Mon, Aug 12, 2013 8:22 pm
Subject: [TowerTalk] Adding guys to self supporting towers
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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