In a message dated Tue, 2 Jan 2001 10:48:08 AM Eastern Standard Time, Pete
Smith <n4zr@contesting.com> writes:
<< At 10:02 AM 1/2/01 EST, Tower2sell@aol.com wrote:
..>
>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.
Sure, but a concrete anchor 1/2 cubic yard in volume (13.5 cubic feet)
still weighs over 1000 lb when completely submerged. I'd a helluva lot
rather have that much uplift capacity than the submerged weight of a screw
anchor.
73, Pete N4ZR
Contesting is!
>>
Screw anchors can work in a similar fashion, the controling issue is either
the bearing stress on the plates or the weight on the inverted soil cone,
whichever is less. In other words the anchor may cause the soil to flow
around the plates or the anchor may lift the entire soil mass. The anchor
capacity rating is the structural capacity of the steel rod. the actual
capacity is soil dependent. There is normally an safety factor of two for the
guys and anchors. This means that if the gound becoes submerged (assuming
original design was for dry condition) the weight of the resisting soil is
about half and the foundation (anchor) becomes the weakest link in the
system.
If the rods are rusted then all bets are off.
For these failures, I would love to know if copper ground rods were used and
if the ground was wet. Copper ground rods may cause the anchor rods to
corrode and wet conditions may accerate corrosion.
tower2sell@aol.com
--
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|