[TowerTalk] How much concrete to set a pole?
w8ji at contesting.com
Mon Nov 7 18:06:45 EST 2005
> To fill the holes (2 x 2 x 5 feet) most concrete
calculations dictate 30 80
> lb bags of concrete. (2400 lb of concrete)
That's a bunch of concrete to hold a very weak pipe. I can't
imagine you needing that much.
> To fill the holes to the 4 foot level (2 x 2 x 4 feet)
> calculations dictate 24 80 lb bags of concrete. (1920 lb
> A suggestion has been made to use only 15 bags of concrete
(1200 lb) to
> secure the base of the pipes.
Don't know where advice like that would come from. Most of
the bending moment would be where the pipe leaves the solid
ancoring. I can't imagine why you would move the only
reliable thing supporting the pipes down lower!
> Question 1: Given the size and type of pipe being used,
what would be the
> ideal dimensions of the hole (and thus the amount of
My guess would be two foot diameter or more extending up to
nearly the top of the pipe. In other words, I think you have
the wrong material for the pipes. I think you have far too
much pipe out of the ground, the pipe is too weak, and
especially that the pipe is too small in diameter.
> The tower will not be heavily loaded. It is hope that a 3
> yagi and a single dual band VHF/UHF base station antenna
will be installed
> at the top. A pipe for a pulley to support the center of a
135 foot wire
> antenna will also be installed at the top of the tower.
I've seen many installations with TV receive antennas fail
with larger and shorter pipes to support guys. I'd look at
the breaking strength rating Rohn specifies for guy lines on
a tower like yours. I'd then calculate the bending moment
and look at the yield of the pipe when the guys are at the
angle they say. Every good long lasting installation I've
seen used large steel I-beam for posts. IMO a 2.5 inch pipe
16 feet out of the ground will be like a noodle, and back
guying it won't make the noodle much better.
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