[TowerTalk] Rohn Torque Bar confusion

[Michael Tope]

Offhand I don't know the value of the modulus for a typical
EHS guy wire, but just imagine for a minute how hard you
would have to pull on a guy wire that is already tensioned to
600 lbs in order to get it to yield an additional 0.13 inches.
Also consider that the difference between .008% and .006%
is 33%, or in other words  adding the 12" torque arms to the
Rohn 55 increased the resistance to torsional rotation by a
factor of 1/3. That's nothing to sneeze at.

73 de Mike, W4EF...............................

----- Original Message -----
From: <kk9a at arrl.net>
To: "Tom Rauch" <w8ji at contesting.com>; "TowerTalk"
<towertalk at contesting.com>
Sent: Tuesday, August 03, 2004 8:25 PM
Subject: Re: [TowerTalk] Rohn Torque Bar confusion


> 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 at contesting.com>
> To: <keith at dutson.net>; "TowerTalk" <towertalk at 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
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>