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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