I just did some guy wire length calculations. I used a 100' Rohn 55 tower
with a 12" torque arm at the top and a 80' guy radius. The guy wire length
is 126- 6.28". I then rotated the tower 10 degrees and the guy wire length
increased to 126' - 6.41" or 0.008% longer. If I connect the guy to the
tower leg, I get an increase length of 0.006%. Since in real life the
actual guy wire would not be longer this extra length would have to come
from slack in the guy or stretch. I am not a PE, but it would seem that the
is not enough different to provide much torque resistance with this system.
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: <keith@dutson.net>; "TowerTalk" <towertalk@contesting.com>
Sent: Wednesday, August 04, 2004 01:09
Subject: Re: [TowerTalk] Rohn Torque Bar confusion
But no one is saying they are equal Keith.
I see a serious flaw in the idea a guying system does
nothing to reduce twist. That idea only would be true if the
guyline attached to the center axis of the tower.
Consider a spoked wheel such as on a bicycle or even the
drive wheel of a motorcycle or car with wire wheels. If the
guyline does not resist twist, why do wire wheels resist
huge amounts of torque without serious deflection?
The reason is pretty simple. When the tower twists all three
guylines have to reach a longer distance, tension increases
a large amount. (You could view the tower as a wheel.) All
three guylines, when the tower starts to wrap up, add force
that opposes any twist. That's because the guylines are no
longer in line with the center line of the tower. Each
guyline adds an equal opposing force to any twist.
Now that isn't exactly like a wire wheel with 50 spokes, but
it still is a significant force when the twist tries to pull
the guyline an extra inch or two!
As a matter of fact, this is why tower with heavy insulators
in guylines feel so "twisty". They have more sag to suck up
out of the guyline, so the tower can twist and wobble more
than a guyline with less sag.
If a tower with a radius of one foot is extended to two feet
in radius by the addition of a torque arm, the same increase
in guyline end spacing would cause twice as much resistance
to torque.
The primary difference between a torque arm and a six wire
star bracket is the star bracket already starts with the
wires "deflected" from being in line with the center, so the
initial movement is much less for a given increase in guy
tension. The fact it is six lines doesn't help, because
three are going slack while three are tightening.
That's how it looks to me in my head-cad.
I'm sure there is someone who can put numbers on this. The
problem isn't that complex. I do absolutely know the idea
guylines do nothing to resist twist is wrong, because I
can't twist my tower that sits on a greased ball at the base
insulator and it has NO torque arms of any type.
73 Tom
_______________________________________________
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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_______________________________________________
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.
_______________________________________________
TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk
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