As a retired Chicago licensed contractor, I can speak with some practical
knowledge.
DO NOT allow rebar to contact the earth. Moisture will rust the bar in
incredible time.
Rust can expand and produce unbelievable amounts of pressure which will
fracture the concrete.
I don't even like the idea of placing the rebar cage on concrete blocks as
there will be a seam for moisture to wick up.
I've had no trouble with either placing the cage into the hole, pouring
sufficient amount of concrete to cover the bottom and then wiggling the cage
up.
or
If a real heavy cage, support it from 2x4's laying across the hole with tie
wire, pour half the hole and cut the tie wire so it doesn't protrude to
within 3" of the concrete surface.
IF you have J bolts protruding above the concrete surface, use only the
highest grade of galvanized.
You may want to do an experiment. Take the normal grade foundation bolts and
leave the exposed to the weather for a month.
Then take a look and decide if you want to trust you tower to them.
----- Original Message -----
From: "Bob Gates" <regates@kingwoodcable.com>
To: "Tower Talk" <towertalk@contesting.com>
Sent: Sunday, August 10, 2003 3:11 PM
Subject: [TowerTalk] Rebar cage for tower footing
> I've noted the UST footing design for most/all their towers, and they
specify a
> rebar cage with the vertical pieces set approximately 3" above the bottom
of the
> footing. This is obviously a clumsy undertaking in the real world,
because it
> would entail pouring 3" of concrete in the hole, let it set up, insert the
cage
> and continue the pour. After 30 years in the construction business, I've
seen a
> few footings poured, and many were designed by engineers who never had to
> actually install their designs, such as spread footings which are
extremely
> labor intensive, and for no reason. To make a long question short, any
civil
> engineers out there who see a problem with the rebar cage sitting on the
dirt
> floor of the hole and pouring around it?
>
> Regards,
> Bob KG7KW
> _______________________________________________
>
> 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.
>
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