Someone named "Grillo's" must have sent me a huge file on
this but my server won't allow large files to be sent as an
e-mail attachment so it was deleted. Maybe it was something
useful.
Like Pete says, guyline tension changes are a matter of how
much sag the guyline has. It's like the tension problems
using tram lines without sag.
If the guyline doesn't have much sag, a very small change in
end spacing distance results in a large change in tension.
Intuitively I think K1TTT is correct when he says the
largest effect is the torque bar increases the length of the
lever (effective diameter of the tower) at the attachment
point.
One thing we know for certain is if the rigid guy attachment
distance from the center of the tower is doubled we will
more than double resistance to rotation.
This is almost certainly why towers feel noticeably better
when guyed with the torque arms that make no difference.
73, Tom W8JI
----- Original Message -----
From: "Michael Tope" <W4EF@dellroy.com>
To: <kk9a@arrl.net>; "Tom Rauch" <w8ji@contesting.com>;
"TowerTalk" <towertalk@contesting.com>
Sent: Wednesday, August 04, 2004 3:15 AM
Subject: Re: [TowerTalk] Rohn Torque Bar confusion
> 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@arrl.net>
> To: "Tom Rauch" <w8ji@contesting.com>; "TowerTalk"
> <towertalk@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@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.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> >
> > _______________________________________________
> >
> > 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@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
>
> _______________________________________________
>
> 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@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
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@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|