In a message dated 96-12-13 13:34:40 EST, you write:
> I have the torque bars on the top two guy locations of my 100' 25G,
>and I can't see that they do any good at all. One of the guys on the
>reflector (sorry, I can't recall right now who it was), told me he achieves
>much better torque stiffness by attaching a horizontal 6 foot piece of angle
>iron to his tower just below the top, and running a guy from each end of it
>to a single guy point, in lieu of the top guy on that side. It's easy to
>see how that would be much more effective, just from the geometry of the
>thing.
Hi, Pete --
To cut to the chase, you're right - they don't do much. When Rohn went
to one of the new past revisions of TIA-222, they re-calculated the torsion
resistance of the (let's call them the old) bar torque arms. They found that
the old torque arms simply provided additional torque resistance "when it was
being climbed" and didn't really do anything for tower twisting. As a
result, they quit making them and introduced a new "guy assembly" that didn't
have the long bars on them but really did add some torsional resistance and
allowed them to meet the new TIA spec.
BTW, hams went up in arms because the old torque arms were discontinued.
They raised such a ruckus that Rohn put them back into production - despite
the fact that they really didn't do anything. A case of "that's the way I've
always done it".
Since the post I was responding to had to do with the owner's wish to
make the tower safer for climbing, I recommended them for that reason.
In regard to the homebrewed angle iron arms, yes, they probably add a
little bit of additional torque resistance but in light of the above
comments, probably little if any. But, no, I wouldn't recommend that anyone
take this approach. Unless you have calculated the forces on the new
appurtenances and had them fabricated by a qualified person, DO NOT do this.
A much better approach is to use the hardware designed by the manufacturer.
In the case of Rohn, they make a 'star bracket' where each guy point has two
guy wires attached to it. This approach is guaranteed to eliminate any
twisting of a tower in the wind.
BTW, in the case of 25G and the aforementioned home brew arms, a six
foot piece of angle means that 2.5 feet sticks out on either side of the
tower where the guy wire attaches to it. Any wind pressure on the tower will
result in 2.5 times the force on the sidearm (force times distance,
remember). And since it sticks out horizontally instead of inline with the
guys like the Rohn guy assemblies, it's even MORE likely to bend. Get my
drift?
73, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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