<Rohn isn't necessarily the last word on guy grips, of course, not like
>PLP. However, I was told (with straight face, I think), that water sliding
>down guy wires and freezing inside the ends of guy grips could cause them
>to unravel gradually. I drove what are locally called "ice sleeves" on all
>my upward-facing grips with a hammer and vise grips, and there they've
>stayed. I didn't think about the vandalism case then, but am doubly glad I
>did it now
>Pete N4ZR
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Hi all;
Let's get one thing out of the way first, Rohn isnt the definitive word on
anything! Among respected large tower manufatcturers however, they are the
only ones that even remotely support the amateur market with lines of towers,
hardware, accessories etc. Because of this, most hams naturally think they
are the biggest, best, etc etc. Nothing could be further from the truth. In
the microwave industry I see much more Pirod, Andrews, Microflect etc than I
do Rohn. In fact, Rohns largest products (Rohn 80 up....minus the 7500
serious biggies) are about the smallest I see in serious microwave use. (Yes,
I realize they, like all the others, will fabricate to any design standard,
but I am talking standard catalog product here.)
Now, regarding Pete's comments about icing being a potential problem to guy
grips. He is correct. Although RARE, through the years, there have been
industry reports (dont even ask, I dont have them anymore) of guy grip
failure due to ice sliding down guy wires. If I recall, these reports are all
from broadcast or very high two-way/microwave towers with, of course, very
long guy lengths. We're talking 500' and UP here folks!
What appears to happen is, because guy wire conducts heat fairly rapidly,
after the ice storm when temperatures begin to climb the ice cylinders dont
melt uniformly but in "sections". These "sections" travel down the guy wire,
and with great force if the guy wire is long enough. This force can be strong
enough to strip the grip from the guy wire, provided the "section" is long
enough/heavy enough and travels a long distance (long guy wire = high tower).
Again folks, this is RARE stuff I am talking about here. I have been in the
telecom industry (two way-microwave) going on 30 yrs now and I doubt I have
heard about more than 5 cases of this (and some were not DEFINITIVELY due to
grip failure) and they were all tower heights way beyond what a ham ever
uses, in fact the majority were 1000'+. (There may be more cases, I have
never done the research, these are just the ones I recall reading about thru
the years. Still rare at any rate, considering the amount of installed
guy-feet in climates that support icing!).
One of the soultions Pete talks about are "ice sleeves". They look like
"cones" installed just above the guy grip above each preformed deadend (guy
grip). There are several sources of those devices and they do their job. Let
me quote from one of those sources, ERI, Electronics Research Inc in Chandler
IN http://www.eriantennas.com/guygnf.htm
"During the warming process ice cylinders will spiral effortlessly down the
guy wire with great velocity and force. For example, a cylindrical ten foot
long segment of ice formed by 1/2" of radial-ice accumulation on a guy wire
could weigh approximately 10 pounds. This ice cylinder falling 200 feet and
then striking the guy wire grip will generate a force of approximately 800 g
or 8,000 pounds. Any impact of this magnitude could strip the grip from the
guy wire, release the support and result in tower failure. Any tower
accesories in the path of the ice could also be destroyed including ground
wire attachment or guy wire dampeners. Another effect of the ice impact is a
surge increase in guy wire stress." (Quote from ERI website).
Now I havent done the math to support their claims of force magnitudes etc or
even if that magnitude would do the damage claimed. My input here is strictly
to point out the hardware available, and to elaborate a bit on the potential
for the problem. I do admit there a lot more towers without those things here
than with them. Towers that have been up 30+ years with no problems, in an
environment where 1-2 substantial ice stroms a year is the norm. Its a risk
assessment decision folks, and with ham tower heights I believe that risk is
pretty low.
73, Bob K8IA
R.D. Epstein, PE
Consulting Engineer - Wireless
West Bloomfield, MI
USA
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