Chuck:
I'm no expert either but have had a course or two on concrete and foundation
design. Sorry, I can't say you are full of c**p. Like you, I find several
troubling things about this thread. Most of it is where folks go to get
info.
I've been flamed on this news group before for saying this, but the design
of a steel reinforced concrete structure is not trivial. It can be done by
the mortal man however. The place to go to get the design requirements is
the code -- the American Concrete Institute's "Building Code Requirements
for Structural Concrete", commonly called the "ACI". It takes quite a bit of
work to understand this document. Although I've always hated the "Prime
Directive" mentality, it is best to stick to the tower manufacturer's specs
unless you willing to do this work or hire someone who has.
The advice from the industrial concrete contractor is particularly bad
advice. The industrial concrete contractor is the man that implements the
specifications laid out by the engineer. He is not a designer. He is correct
in saying that epoxy coated rebar is used when corrosion is a problem but
one can't just make the substitution into an existing design without the
analysis! Epoxy coated bar requires a much longer development length (by a
factor of 1.5!) than deformed steel rebar. The development length is the
amount of bar that needs to be imbedded in concrete to prevent pull-out.
This can be quite significant, particularly at the dowels that connect the
slab to the column. As you pointed out, the tension at this point will be
tremendous. Pull-out would not be a good thing here.
John
KC4ZXX
.
----- Original Message -----
From: "Chuck Lewis" <clewis@knology.net>
To: "Phil - KB9CRY" <kb9cry@attbi.com>; "TowerTalk"
<towertalk@contesting.com>
Sent: Tuesday, December 03, 2002 11:53 PM
Subject: Re: [Towertalk] Pouring base of tower
> Wait a minute!!!
> This application is NOT like a footing! I hope someone with some
credentials
> will chime in here and keep us from doing some dumb stuff! Footings do not
> have to withstand overturning moments, and your freestanding tower base
> does. The tower base does more than simply support the weight of the
tower,
> and the tower is not held vertical simply because of the weight of the
base.
> When the wind tries to tip the tower, the small 'pier' is pulled up and
away
> from the large 'pier' on the windward side. The large 'pier' is hooked
under
> several feet of (hopefully) undisturbed soil, and the two chunks of
concrete
> are being pulled apart. Now there might indeed be an epoxy or similar
> compound or a rebar configuration which will give the two pours the
tensile
> strength of a single pour, but you need to ask the question relative to a
> tower base, NOT a foundation/footing, and the answer needs to come from
the
> right source. Your concrete contractor no doubt knows a great deal about
> foundations and footings, but I'll bet he knows diddley-squat about TOWER
> BASES. Neither do I, for that matter, but let's not make the mistake of
> thinking that if it looks just like a foundation/footing it can be treated
> as a foundation/footing. These are two distinct applications despite the
> fact that they LOOK identical. Tower bases have a unique set of
requirements
> which include a combination of compressive, tensile and shear loads, but a
> foundation/footing is mostly compressive. Didn't the manufacturer specify
a
> SINGLE pour? Why?
>
> Please check with someone who knows about TOWER BASES!
>
> Chuck, N4NM
> (hoping someone who knows about TOWER BASES will tell me I'm full of cr*p)
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