[TowerTalk] Newbee concrete rebar questions

[Perry - K4PWO]

Even though not "specified", you can add vertical rebar to form a true
"cage".  Then you just support the rebar off the bottom of the hole.  You
would probably want at least one diagonal on each side to prevent "racking"
of the cage if you "tie" it together.  A "X" would work even better.
I had a basic welded "skeleton" of a "cube" built out of rebar and then tied
in the additional horizontal rebars at the bottom and top.

73 de Perry - K4PWO

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Dick Dievendorff
Sent: Thursday, September 16, 2010 2:28 PM
To: towertalk at contesting.com
Subject: [TowerTalk] Newbee concrete rebar questions

I have never personally installed rebar.

 

My tower and guy anchor foundation drawings specify a "mat" of #5 (5/8")
rebar , 5 rods each way, top & bottom, just below the top surface and just
above the bottom surface of the concrete block.

 

I know to suspend the bottom mat at least 3" above the bottom of the hole
with little concrete blocks so that the bottom rebar mat ends up 3" above
the bottom of the concrete so that it is adequately covered.

 

I also need to suspend a top 5 x 5 mat about 1-1/2" to 2" below the top
surface of the concrete block.  If it were going to be later protected from
the elements,  I'd be able to suspend it with wires from the wooden form and
cut the wires flush with the foundation after the concrete sets. But since
this tower foundation is going to be exposed to the elements, I'm worried
that even if I cut the wire off flush, the wires themselves will become a
conduit for corrosion to get to the embedded rebar.

 

What techniques are used to support the top "mat" so that it ends up about
1-1/2" below the top finish surface?

 

I found "high support chairs" in some literature, but the top mat is about
28 inches from the bottom of the hole, and the "chairs" don't seem  to be
that high. 

 

Maybe I can find some vertical plastic rods to tie the top mat to the bottom
mat and the plastic rods could stick out the bottom. 

 

I'm sure this is a well-understood fairly basic technique by those who do
this. But I need to be educated.

 

73 de Dick, K6KR

 

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