Underground it is a much harder problem for all those reasons. My
comments were in response to the off hand comment about it being enough
even if it was on top of the ground. Try the calculation with the block
sitting on a hard surface and not dragging, just pivot around the point
closest to the tower by pulling on the 5' pipe at say a 45 degree upward
angle like guy wires would.
On back of the envelope estimate...
The block is 3x5', so the center is 2.5' from the front edge, that is
one arm. The post is 5' from the top of the block, if I didn't miss a
decimal point a 4yd block 3x5 on top would be 7' thick more or less. So
7' plus a 5' pole is 12' high, ignore the 2.5' on the bottom and figure
that arm is just 12'. And make it worse by assuming the guy wires pull
perpendicular to that arm, and gravity pulls down perpendicular to the
2.5' arm... not quite right but what the heck. So the force needed to
overturn the block pulling on the top of the post is 2.5/12 times the
weight of the block, or about 1/5th the weight. At about 150#/ft^3 that
is 16200#, and 1/5 of that is 3240# which just happens to be a hair more
than the static tension on 5 sets of 1/4" ehs guy wire properly
installed. So as far as tipping over the ce was probably right, until
the wind started blowing.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:towertalk-
> email@example.com] On Behalf Of Joe Subich, K4IK
> Sent: Thursday, October 21, 2004 18:57
> To: firstname.lastname@example.org; 'TowerTalk'
> Subject: RE: [TowerTalk] elevated anchor guy points
> > Interesting point. The block that is underground is
> > approximately 3 feet wide and 5 feet long (in direction
> > of guy) if memory serves. Anybody on this list that can
> > figure the lateral force required to tip this block over
> > from a pipe extending five feet vertically from the center?
> What is the soil's bearing capacity and how deep is the top
> of the concrete block? You have several components of force:
> 1) the force required to tip over the block if it was
> setting on the surface of the ground
> 2) the force required to rip the back half of the block
> through the cone of soil on top of it
> 3) the force required to compress the soil below the
> front half for the block (to allow the back half
> to raise)
> 4) the force required to drag the block forward through
> the soil
> The last three require knowledge of the soil characteristics.
> ... Joe, K4IK
> See: http://www.mscomputer.com for "Self Supporting Towers",
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041
> any questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list