On 4/14/20 3:13 AM, Rob Atkinson wrote:
I've never owned a tower but I would think the guy anchors need to be
set in a relatively deep hole that is filled with concrete. I don't
think I have ever seen a commercial tower that didn't have guy anchors
in concrete.
Lots of big towers and telephone poles are safely anchored by screwing
something into the ground. I'd venture that very, very few wooden poles,
even those giant ones, have any concrete involved at all, and they have
fairly large side loads, both static, and wind driven, from the wires
and line equipment.
It's a well understood technology. Hams tend not to do it, because of
the complexity of properly installing the anchor - commercially, it's
done by a truck with a hydraulic arm and motor to position the anchor at
the right angle and to drive it into the ground.
When I worked in the effects business, we used the screw in anchors
(placed by a company that does this for a business) to hold all sorts of
loads, including things like 50 foot 4x4 foot towers (crane boom
sections) with substantial side loads (i.e. loads supported between the
towers). We also had the same company come out and unscrew the anchors.
I would not trust guying a tower by merely screwing any
kind of anchor into the ground. How tall is your tower? Maybe 60
feet of R25 is okay if you screw the helix deep, like 5 feet or more
but if you live anywhere with high winds, or soft soil, lots of rain,
or huge wind load like a TH7, I'd pour concrete. It's money spent up
front that saves on the replacement cost of a tower and antenna(s).
I note that these particular P46 anchors are rated at about 3000 lbs in
class 2 soil - so I'd allow for a safety factor of 1.5 or 2, and not
plan on having any single anchor have a load of more than 1500 or 2000
lbs. That's something you should be able to get from your tower analysis.
The fact that they are aluminum isn't all that important - 3000 lbs is
nowhere near the failure load of the shaft or the threads in tension.
And being aluminum, they're cheaper to ship and easier to handle.
73
Rob
K5UJ
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