So the answer, it would seem, is to have any guy anchor (galvanized or not)
to not only be embedded in concrete, but in an elevated pier so that the
entire guy anchor is 100% above ground soil. If I were to do another guyed
tower (which is not my intention) I would do so...the extra labor +
materials to "shield" the anchor from soil is worth it...at least based upon
my circa 1998 tower disaster. YMMV.
There are many very large commercial broadcast and land mobile
communications towers (guyed and self supporting) that have been up for 50+
years. Certainly they are inspected and maintained on better budgets than
most ham installations, altho they beg the question of what techniques make
them successful (even though we know that some of those big boys come down
from time to time).
73
Dan
K0DAN
-----Original Message-----
From: Dick Green WC1M
Sent: June 18, 2013 20:13
To: 'K0DAN' ; N3AE
Cc: towertalk@contesting.com
Subject: RE: [TowerTalk] Screw Anchor Experience
Any anchor that's exposed to soil is at risk of corrosion. Anchors sunk in
concrete are just as vulnerable because typically a good portion of the
anchor rod is not in the concrete -- it's in contract with soil above the
concrete footing. For example, Rohn spec calls for my anchor footings to be
poured in a 6-foot long by 3-foot wide hole that's 4-feet deep. The concrete
footings are only 18" deep, so there's about 2.5 feet of soil that the
anchor rod is in contact with. Since the rod is set at an angle, probably
3-4 feet of the rod is in contact with soil above the footing.
The Rohn concrete anchor rods are very heavy duty, but just in case I
slathered several coats of roofing tar on the portions of the rod that were
above the concrete block.
Regardless of the type of anchor rod you have, it's a really good idea to
inspect them every few years. That means digging down a bit to see if
there's corrosion.
73, Dick WC1M
-----Original Message-----
From: K0DAN [mailto:k0dan@comcast.net]
Sent: Tuesday, June 18, 2013 8:20 PM
To: N3AE
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Screw Anchor Experience
Hi Shawn...
I had screw anchors which I think I purchased from Texas Tower. They
were probably manufactured by Rohn or some other well-known tower mfgr.
IRC they were 4” augers on 4’ 3/4” (or 1”?) rod, all galvanized. They
met the tower mfgr (TriEx) spec. They were installed (with difficulty)
into local soil here near Kansas City. Which is about 2’ of topsoil on
top of packed clay. I do not know the pH of the soil.
The tower was a 72’ crank up (HW series if IIRC) was triple guyed and
was not overloaded. All was fine for 15+ years when one night we had
thunderstorms and 50 MPH wind gusts (the tower was spec’d for 70 MPH), I
was on the air at the time, and suddenly all the signals went down 50dB.
I turned the rotor and it would only turn about 10 degrees. WTF? I went
outside and to my horror, saw the tower lying over in the trees! If you
ever want a gut-wrenching sight, that is it.
Later investigation showed that one guy anchor and failed, causing the
equalizer plate and all attached guywires to slingshot in the direction
of the wires; the remaining two anchors kept tension on the tower,
pulling it in the direction bisecting the angle of the two remaining
guys (50’ trees).
The antennas were destroyed, and the tower sections sufficiently bent
that I did not want to attempt to repair them.
The cause of the anchor failure was long term corrosion (galvanic
action) from soil working on galvanized anchors. The 3/4” anchor rod and
shrunk down to the diameter of a pencil, and probably pulled apart like
soft taffy when then wind load was high enough.
Based on my experience I do not think screw anchors are a good long-term
guy wire anchor at all. For short term, probably fine, but despite what
Texas Towers told me, they are NOT permanent.
However if you drilled and belled footings for the guy anchors, filled
them with concrete, and then inserted the screw anchors, I think you’d
be OK. Ask the tower mfgr or a civil engineer or M.E., not me. With
galvanized encased in concrete, I think there would not be the exposure
to chemical reaction.
It is also possible that your local soil is not reactive and what
happened to me is not a risk at your QTH. You will have to ask people
wiser than I.
I have photos of the crashed tower and failed guy anchor. Someone on
this reflector (maybe the fellow who wrote”Up The Tower”?) was looking
for this stuff a few years ago, and I promised them to him but I lost my
note and never followed through.
Good luck and 73
Dan
K0DAN
From: N3AE
Sent: June 18, 2013 17:16
To: k0dan@comcast.net
Subject: Screw Anchor Experience
Dan,
I was reading your recent post in TowerTalk regarding thoughts on a new
tower for KR5DX. You mentioned a failure you experienced with a screw-
in guy anchor. Wondering if you could share some info on that, like the
type on anchor, auger diameter, depth and a description of your soil
type.
Obviously I'm considering a screw-in anchor here for a tower (EZ-Way).
This tower came from a local who had it guyed using screw anchors and it
held up fine for 15+ years, including hurricanes and tropical storms.
I've been basing my plans on published info from companies like A.B.
Chance and Hubble Power Systems. See
http://www.hubbellpowersystems.com/anchoring/no-wrench/
tnx
Shawn - N3AE
Southern Maryland
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