Yeow!
Gene -- you're thinking about doing the same thing that I was, namely,
putting a self-supporting tower next to my house. This is still my plan.
However, I have a PE doing a foundation design for a 30 foot Rohn 55G
self-supporter. I wanted the tower to clear the 18 inch deep soffet by
12 inches. The PE wants to move it away from the house another 16 inches
at least. A few things have come up in this attempt:
1) You are probably in the "backfill" area of your home. The soil in that
area could be *anything* and in *any packing condition* out to about
3-4 feet away from the TOP of the cinder block house wall and tapering
down to the house footing.
2) The overturning force of the tower translates into SIDEWAYS force on
the wall. A tower that will stand up in soil COULD push a foundation
wall down if not properly designed and sited.
3) The "zone of interaction" of the tower base according to EIA standards
starts at the tower foundation BOTTOM and goes up at an angle of 30 degrees
from vertical AWAY from the centerline of the tower. This is the zone that
a foundation with a FOOTING will interact heavily with the surrounding
soil. If your wall is in that zone, force could be a problem.
4) WITH YOUR PE, think about the idea of having the DIAGONAL of the square
cross section of the tower footing at right angles to the house wall (think
of it from top view). This will disperse the forces on the wall from the
tower foundation over a larger area of the house wall.
This stuff is really tricky, Gene. Be careful and get good professional
engineering advice. You could collapse your house AND loose your tower!
(I haven't even mentioned the frost considerations in MN!)
Best 73's
--Paul
wa0rse@amsat.org
P.S. I am NOT a P.E. -- these are only my LAY opinions!! Get PE help!
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