I've just completed the transit work for a Rohn 55 rotating tower. I want
to start pouring concrete for the base and anchors very soon. I have a
couple of unique situations inherent to my property and wonder if anyone
could offer me some advice. i.e. has anyone "Been there, done that."?
I'd like to use a regular 55G straight section as the base. The bottom of
the legs would extend below the level of the concrete and into some gravel
for drainage. However, the area where I MUST locate the tower is relatively
low with a high water table. Bedrock is probably at about seven to eight
feet beneath the surface so there is stable support down there.
I am concerned that water may enter the legs from beneath, seek its own
level in the legs, freeze inside the legs in the winter, and do structural
damage to the concrete base or legs themselves.
The alternative to the would be to utilized the Rohn base plate for concrete
(BPC-55G), a flat plate with stubs to mount the first section on and a
central pier pin. This makes the above situation a non-issue, but I loose
the solid support an embedded section would afford. Temporary guying would
be more critical during erection, AND, I wonder about the stresses tower
rotation or wind torque would impose on the stubs of the BPC-55G with the
rotating tower scenario.
What does everyone think about this? Which way would you go? Is the
BPC-55G a bad choice for use with a rotating tower?
This also relates to the terrain where I have to put up the tower. I plan a
tower height of approximately 180 feet. My guy points will be 220 feet from
the tower's center. This will give me additional room to swing the beams
under the guy lines, but are there any precautions I need to take when
guying this far from the tower base? I cannot move the guy points in closer
because of the terrain.
Should the tensioning be adjusted differently since forces on the tower will
be different than if guyed at the conventional 80% of tower height distance?
I'd appreciate comments on the above. You can e-mail me directly.
Ralph - K0IR
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