Fw: [TowerTalk] Rebar

[Tom Hellem]

Hi TT'ers:
I was taught the same thing in trade school about concrete- it will handle 
a tremendous amount of load in compression but its tensile strength is 
minor. I can see how you may not need much steel in a properly guyed tower, 
as all the lateral wind forces are converted to straight downward pressure 
by the guy system (i.e. compression), but a self supporting tower is 
another matter. Seems to me if the base developed any vertical cracks, the 
tower may be allowed to move sideways. If this is not a structural 
question, then what is? That is what the steel is doing- providing the 
required tensile strength in the concrete. I remain unconvinced.

73
Tom K0SN
-----Original Message-----
From:	Michael J. Castellano [SMTP:km1r@snet.net]
Sent:	Friday, January 21, 2000 5:57 PM
To:	Tom Hellem
Subject:	Re: Fw: [TowerTalk] Rebar

Tom Hellem wrote:
>
> -----Original Message-----
> From: K7LXC@aol.com <K7LXC@aol.com>
> To: towertalk@contesting.com <towertalk@contesting.com>
> Date: Friday, January 21, 2000 8:16 AM
> Subject: [TowerTalk] Rebar
>
> >
> >Howdy, TowerTalkians --
> >
> >      Working with my PE on a Trylon Titan self-supporting tower
> drawing/calc
> >package, I found out something interesting. Since the vast majority of 
the
> >tower base concrete is below grade, the purpose of the rebar isn't
> >structural. That is, it doesn't have to help hold any exposed concrete
> >together. It turns out that the primary purpose for rebar in the tower 
base
> >is to control concrete shrinkage. That was news to me.
> >
> >Cheers,   Steve   K7LXC
>
> I have a hard time believing that the steel in a concrete tower base is 
not
> structural. Why do engineers specify lots of steel in foundation walls,
> bridge piers, etc? They are also below grade. Controlling shrinkage in
> concrete is done by controlling the amount of water in the mix-the higher
> the slump, the more shrinkage you will get.
>
> 73. K0SN
>
> --
> FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com
> Search:                   http://www.contesting.com/km9p/search.htm


my two cents!

i agree with both of you guys... in a way...  we were taught in
'concrete school that concrete fails in tension, while it is fine under
compression... thus rebar to "keep it together.

The only thing i can think of (in a self supporting tower) footing is
that the tower applies both downward and upward force when it is in the
wind ie, tension and compression on the pad.

maybe the re-bar is to compensate for this.

Like Steve...been in the tower business for a long time... now you guys
got ME thinking!!!!!!!

73, and be careful out there on the steel...

Mike KM1R

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm