Guy tension ??

[Stan Griffiths]

>My concern in tensioning guys is never the EXACT calibrated tension, but
>rather that all guys are tensioned the same at whatever in-exact amount that
>may be.

I have heard this advice several times but I am not sure how important it is
either.  When you say "tension all guys the same amount", you must be saying
tension the set at 30 feet the same as the set at 60 feet and the same as
the set at 90 feet.  The tension in all three guys at any one level will
pretty much equal each other since the tower will flex to make it so.  So
why is it important to have all the sets equal to each other?  In fact, on
further reflection, that advice conflicts with the advice to tension guys to
"10% of their breaking strength" since the Rohn book often shows guys of
different breaking strength used at different levels on the same tower.

>And finally a question for the experts.  The 10% rule has been around forever
>it seems.  Why?  Why 10% as compared (e.g.) 5% or 15%?

And what should happen if you decide to use the next size larger guy wire
than Rohn calls out for?  Should you increase the tension according to the
guy wire size or leave it as it should be for the smaller wire?

My guess on "why 10%" is that you don't want them sloppy loose since the
tower tends to move around in the wind that way.  You don't want them too
tight since they tend to pull the tower down or break if they are too tight.
So somewhere in the middle is where you want to be.  If you have gone with
Rohn's recommended guy wire size, 10% should put you in about the right
place and I'll bet the range of 5% to 15% would be just fine.  But as I said
up front, this is my guess.  I would like to hear other opinions on this.

>And finally, finally .... ever watched the pros check guy tension with a pc
>and a stop watch by giving the guy a "twang" and counting the oscillations per
>unit time (or something to that effect...been 10yrs since I watched it done on
>commercial towers)....then knowing temperature, humidity et al, let the pc
>calculate the tension?  Maybe someone ought to get that software and method
>distributed.......

I have a friend who developed a variation of this technique.  He has 100
feet of Rohn 45 up and guyed like Rohn suggests TO THE LETTER.  This is one
of the most conservative engineers I have ever met and I would trust him
with my life.  What he did was install an "in line" tension measuring device
(dynamometer) and crank the tension to the prescribed amount.  He then set
the guy wire into oscillation by gently pushing it sideways with his
fingers.  It takes a dozen or so pushes to get it moving.  He carefully
observed that it was not oscillating in more than one section meaning that
it was oscillating at its fundamental frequency rather than a harmonic.  The
oscillations are slow, like one per second or so.  He counted them for one
minute, timed with a stop watch, and recorded the number of oscillations.
The frequency will be different for each level of guy since it depends on
guy length, wire size, and tension so you have to install the dynamometer at
each level to determine the correct frequency for that set.  He then removed
the dynamometer, reattached the guy to the tower and tensioned it until its
oscillation frequency was the same as before.  To check guy tension now, all
he has to do is check the oscillation frequency with his stop watch against
the numbers recorded originally.  No computer.  No software.  The key, of
course, is owning (or borrowing) a dynamometer to calibrate against.  These
things are expensive, like one or two thousand dollars in the 100-2000 lb
range.  Tom found his in an estate sale . . . cheap.  BTW, you can check the
accuracy of the dynomometer by hanging known weights from it.

Stan  w7ni@teleport.com