Ed, when multiple guys are connected to an anchor, the resulting forces are
resolved to single angle.
Knowing what this angle might be is another matter though.
There are guidelines in the Rohn catalog that might help. Their
pre-engineered anchor designs assume you have the anchor placed 80% of the
tower
height away from the base. Then depending on the number of guys and where they
are connected to the tower, the anchor rod angle is specified. For 25G, this
varies from a minimum of 37 degrees to a maximum of 50 degrees.
If you are using a different base to anchor distance these numbers would
also be different. You can see that using a mid range number of say 43
degrees you would only be off by about 6 degrees and that seems close enough
to
your 5 degree number.
The Rohn designs have the top guy connected about 5ft below the top of the
tower. If you connect higher then the optimum angle would be a little
higher. If you place the anchor less than 80% of the height, then the optimum
angle would also be higher.
All of this is also based on the prescribed guy wire sizes preloaded to 10%
of the rated breaking strength.
Hope this is helpful.
73,
Gerald K5GW
GM Texas Towers
In a message dated 3/17/2015 12:05:22 P.M. Central Daylight Time,
ed.n3cw@gmail.com writes:
I looked at the Hubbell link Shawn provided on the earth anchors, and
noticed this:
Note: If hand installed, holding capacity may be reduced by as much as 10%
to 20%. Capacity ratings apply to properly installed anchors only. Failure
to install within 5° of alignment with the guy load will significantly
lower
strength.
I always knew the type of soil would affect holding capacity, but now I see
that with hand-installed anchors, and with anchors used to hold 2 or 3 guys
(where I am definitely exceeding the 5 degree load alignment spec)...I may
be way down from what I am estimating holding capacity to be.
So ignoring the lower capacity due to sandy soil here in Florida, I may be
losing 20% of capacity due to hand installing, and losing some unspecified
capacity (Hubbbell says "significantly reduced") because some of my guys
are
pulling outside the 5 degree alignment. I'm starting to wonder how much if
any margin I have. Guess a more formal analysis may be warranted.
--Ed, N3CW--
Message: 2
Date: Tue, 17 Mar 2015 15:57:24 +0000 (UTC)
From: N3AE <n3ae@comcast.net>
To: TowerTalk <towertalk@contesting.com>
Subject: Re: [TowerTalk] Earth Anchors
Message-ID:
<1802192855.8625804.1426607844350.JavaMail.zimbra@comcast.net>
Content-Type: text/plain; charset=utf-8
The product you're looking for is likely on this page:
http://www.hubbellpowersystems.com/anchoring/no-wrench/
Perhaps a call to Hubbell's customer support line would get you info on a
local distributor.
OBTW...I put in three PS816's last year, by hand. What a job! Time of the
year, at least around here in Maryland, makes all the difference. Very
moist
ground after the winter thaw is the best, i.e. NOW. In the summer with dry,
hard earth, forget it.
Good luck
Shawn
N3AE
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