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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