[TowerTalk] Newbee concrete rebar questions

[Scott Reed]

  I don't do towers on a regular basis, nor concrete, but from what I 
have done, I have never seen a foundation specified with no vertical 
rebar members.  Stand the vertical members on the ground and as Perry 
says tie them to the horizontal memebers.  The place you get the rebar 
should have "tie wire" as well.  For the most part you wrap it 
diagonally around the joint and twist it so it holds the horizontal 
members where you want them.

On 9/16/2010 3:53 PM, Perry - K4PWO wrote:
> 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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-- 
Scott Reed
Owner
NewWays Networking, LLC
Wireless Networking
Network Design, Installation and Administration
Mikrotik Advanced Certified
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(765) 855-1060