[TowerTalk] Rebar & Concrete

[k6ll@juno.com]

On Fri, 06 Nov 1998 05:14:04 -0800 "Robert L. Shohet" <kq2m@mags.net>
writes:
>
>Hi guys,
>
>I am getting ready to pour concrete for my Rohn 45 towers bases and 
>guy
>anchors and wondered about the necessity of keeping the rebar away 
>from
>the dirt?  (Towers to be 100' and 130').
>
>
>I can't find Dobie blocks or anything else that will allow me to 
>elevate
>the rebar.

Someone suggested pieces of concrete block. That sounds like a
good idea. There are all sizes and shapes of concrete stuff in
the garden department.


>How crucial is it that the rebar NOT touch the dirt?  I
>understand that the rebar will rust but I find it hard to believe that
>the structural integrity of the rebar and the concrete "load" will be
>compromised so severely if the rebar is dug into the dirt a few 
>inches.

I wouldn't trust an internet answer here. I would just do what the
manufacturer recommends.


>
>Wouldn't this allow for stronger concrete support by maintaining its
>shape since the concrete will not be poured but rather dumped in by a
>backhoe? (necessary in my case since a concrete truck can't access the
>holes).  Also, how much rebar is necessary in the holes?  Is it really
>that important to form a "cage" with rebar and wire?
>(Incidentally, my soil is a crappy clay/rock mixture)
>I bought a lot of 4' and 2' rebar for the purpose of support but am 
>not
>sure on the best way to set it up and don't really know how important 
>it
>will be on top of the heavy duty GAC3455 anchors that I am using which
>have a solid metal plate about 6" x 4" at the bottom of the anchor.

Rebar requirements are detailed on Rohn Drawing C620643, near
the back of the Rohn Catalog. It looks like you are using 
the 4e foundation? Isn't this overkill in the foundation
department if you are only using 1/4" EHS? Anyway, it looks
to me like the rebar is supposed to form a grid with 1'x1'
squares, about 1 inch below the top face and 1 inch inside 
the vertical face nearest the tower.

>
>I would really appreciate your thoughts and comments on this.
>
>Last, how many feet of anchor should be in the concrete and at roughly
>what angle should the anchors be sticking out of the hole?  I can't 
>get
>a good read on this from the Rohn catalog.  Should the anchor be set 
>at
>an angle that will point towards the middle guy, or does this matter?

Since you are using 1/4" EHS, I assume you are following the
design for 90mph/no ice, with a beefier guy anchor foundation? Rohn
dwg C870478 specifies a rod angle of 40.8 degrees for the 100 footer,
and 39.8 degrees for the 130 footer. The horizontal and vertical slopes
to set up these angles are also specified.

Anchor Dwg C620643 shows that the bottom of the rod is positioned
2 inches above the bottom of the hole, the hole being 4' deep.
The rod also passes through the three centerlines of the concrete
block, which tells you how to position it laterally.


Dave Hachadorian, K6LL
Yuma, AZ
K6LL@juno.com





















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