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[TowerTalk] More Guy Anchors

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Subject: [TowerTalk] More Guy Anchors
From: gscholten@michamber, (Gale)
Date: Tue, 30 Jun 1998 19:52:16 -0400
Chuck Sudds wrote:
> I am getting ready to install my 80ft of Rohn 45G. I have the base and all
> three of the guy-anchor spots marked off, out in my "North 40." Rather than
> manually digging these holes, I was planning on enlisting the services
> (again) of my Rural Electric Company, and their power pole auger. I plan to
> have them auger down about 8-9 ft and about 18-24" in diameter. Does anyone
> see a problem with round guy anchor bases?? I do plan to have elevated guys,
> about 4-5ft out of the ground.
> Looking forward to ALL replies, mispelled or not ;)
> Chuck Sudds  K0TVD
> Missouri Valley, Iowa USA
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Round guy anchor bases rea OK IF properly designed.  
Example: 80 feet 45G, 90 MPH wind, and 14 sq ft antenna load
Guy anchor pull out force is 2400 # upward and 2600# toward the tower.
The force in line with the guy anchor is approximately 5400 pounds.  If
the concrete and any soil placed on top of the concrete weight more than
2400# the anchor won't lift out of the ground.  BUT  the soil strength
must be great enough to resist the lateral movement.  If your soil has a
load capacity of 1000 PSF (pounds per square foot) than your anchor will
need 2.6 sq ft of projected side surface to resist movement.  Note that
I have not considered any tendency fot the anchor to tip over and pull

This stuff ain't all that simple.  

Check with a local civil engineering company in your area and talk to
someone in their soils or foundation engineering department.  They can
give you a rough idea of the soil strength in your area.  Soil strength
veries greatly.

The Rohn book has a lot of good design info in it but take the time to

Elevated guy anchor points require much larger anchor blocks than in
line guy anchors because of the tipping effect generated by the pole or
pipe acting as a lever that is trying to pry the anchor block out of the

ALSO nearly all of the force at the base of the tower it straight down
and includes the weight of the tower, antennas, rotators and accesories
plus the tension in the guy wires.  It is possible to tighten guy wires
enough that a tower would collapse in a 20 mph breeze.  Get your trig
book out and calculate the down ward pull. or consider that it is equal
to the lifting forse at the guy anchor times 2 because 2 anchors can be
loaded to max if the wind is directly between them.  Doesn't sound right
but its true, get the trig book out and look it up.

I hope this helps.

Willians and Works, Inc
Civil engineers
Grand Rapids, Michigan

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