In a message dated Tue, 2 Jan 2001 7:45:34 AM Eastern Standard Time,
n4kg@juno.com writes:
<< N4KG responses inserted below.
On Mon, 01 Jan 2001 Pete Smith <n4zr@contesting.com> writes:
> At 06:09 PM 1/1/01 -0500, Jerry Keller wrote:
> >Which is better,,,,,concrete guy anchors.... or....screw anchors?
>
> Screw anchors are a lot more dependent on specific soil
> characteristics than concrete anchors. As an example,
> the concrete anchors on my tower weight about ~1800 lb each,
> and get the remainder of their anchoring power from the weight
> of soil above them. Screw anchors weigh what -- maybe 50
> lb each?
I suspect that much (most?) of the "holding power"
of the earth is not from the weight but from the
'cohesion' of the earth. Loose dirt could weigh
as much as undisturbed (compacted) earth but
would have little or NO 'cohesion'. K5RC once
lost a tower when an anchor (cased in concrete)
pulled through 'soupy' earth after sustained rains.
For small anchors, the surface area and depth is
more significant than the weight. (I agree that
Pete's 1800 lb anchors are pretty substantial)
de N4KG
>
> Of course, none of this is protection against a failure if the
> anchor rod corrodes to the breaking point.
AMEN ! - N4KG
>
> 73, Pete N4ZR
Some people have forgot their science today. If you have a concrete anchor
underwater, it has less uplift capacity. To figure the submerged capacity you
subtract 62.4 lb/cubic foot from the volume/density of the concrete and soil
mass. This is about half the capacity of a normal dry installation. This
means an anchor designed for dry conditions may pull out when submerged.
Tower2sell@aol.com
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