[TowerTalk] Screw Anchor Experience

[K0DAN]

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 at 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