On 4/14/20 9:12 AM, Grant Saviers wrote:
I have to wonder if a permitting authority would allow these for
permanent structures without a soils test and engineering, and costs.
(Utilities run on different rules). Then a truck and hydraulic system
is needed to install them, more $$. All of this beyond even advanced
ham skills and technology.
Permitting authorities would allow them to the same extent they allow
other designs. The Rohn drawings make assumptions about soils, for
instance. That's part of what the engineer at the plan check does -
they know the soils in different parts of the municipality so they go
"oh, 1234 Crescent Lane, that's old river bottom and mostly sand - your
design assumes clay, so that's not going to fly"
Yes, the difficulty of putting them in is the usual barrier for hams -
digging a big hole and filling it with concrete (or, for that matter,
forming up a big concrete block, above ground) is pretty easy and is a
"cheap in materials and tools, expensive in labor" approach that's
attractive if labor hours are free.
Once you're going to "power tools", though, it's worth considering -
they're an off the shelf item, there's lots of companies that plant them
for you. I don't know if it's cheaper to hire the auger guy than to buy
a few yards of concrete and an hour of backhoe time. It's probably very
situationally dependent.
We loved them because you could plant them into an asphalt parking lot,
then, when you were done, you could cut them off slightly below grade,
and pave over the relatively small hole. Or, you could unauger them, if
needed.
At JPL, we use 5000 pound cubes of concrete for guy anchors on temporary
structures or in places where "digging" isn't allowed.
A rental mini-excavator, some rebar ordered bent to spec, and a few
yards of concrete can be DIY. My (Rohn65) anchors are 2x4x6', full
rebar cages, buried 4' all DIY with some laborer help. One advantage is
the shank before backfull is available to be tar coated and 0.020" gas
pipe tape wrapped so there is no chance of corrosion failures. (see TT
posts of anchor shank failures).
My smaller prior R25 built to Rohn spec tower anchors and base were all
hand dug, rebar bent on site and Sakrete mixed in wheelbarrows with
friends and 807's..
Grant KZ1W
On 4/14/2020 04:02, Tyler Stewart via TowerTalk wrote:
It’s like anything else, if engineered and installed properly there is
nothing wrong with earth anchors. Lots are in use at big stations for
decades successfully. Improper concrete based anchors are just as bad.
Ty K3MM
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On Tuesday, April 14, 2020, Rob Atkinson <ranchorobbo@gmail.com> 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. 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).
73
Rob
K5UJ
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