In a message dated 6/29/01 11:58:13 AM Pacific Daylight Time,
w7ni@easystreet.com writes:
> I have heard some of the same things you have heard about rebar cages but I
> can't actually
> say I have ever read this stuff in any Rohn book I have seen.
Actually Rohn doesn't have much to do with rebar and concrete standards.
Every engineered tower comes with boilerplate requirements for rebar and
concrete under something like "Foundation Notes - General".
The general notes invoke grades of rebar, rebar cage construction,
minimum concrete strength, reference to building codes as well as industry
and professional standards.
Rohn uses real general language like "customer's or installer's
responsibility" and "secure the services of a local engineer". They set the
standards for the base on up but not concrete and rebar.
> I may have read the stuff
> about keeping the rebar 3 inches from the edges of the concrete . . .
Part
> of it makes
> some sense since rebar is never galvanized (as far as I know) and Rohn
tower
> legs are
> galvanized, which should make a rather large difference in how fast they
> deteriorate due
> to rusting. There are a lot of rumors and hear-say about what Rohn says
or
> does not say.
> I guess if I wanted to take Rohn's advice on something, I would either
want
> to see it in
> writing in one of their books or hear it, first-hand, from one of their
> engineers on the
> phone. Hear-say and second-hand quotes from Rohn are not really very
> dependable . . . I
> like to quote the page number of the Rohn book for anything I get out of
> that source so
> you could look it up yourself to verify its accuracy. In some cases, Rohn
> simply won't
> put some of their advice in writing so second-hand quoting is the only way
> to pass on the
> info . . . just make sure the secondary source is a reliable one, if you
can.
>
When you install tower lights, Rohn doesn't provide all the necessary
electrical instructions because they're covered somewhere else like the NEC.
Same with everything except the tower structure; that's what you get from
Rohn in a "general" catalog.
I guarantee you that you'll never talk to a Rohn engineer and likewise
you'll get nothing from them in writing like what you're asking. One, they're
too busy and two, it's unnecessary.
> If the rebar really rusts away inside the base, I would worry much more
> about the loss in
> strength by not having the steel in there anymore than I would about any
> void it might leave.
If you read a recent post, the point was made that rebar expands as it
rusts and would crack the concrete and it doesn't leave a void. I'm sure
we've all seen old concrete hanging on to rusty pieces of rebar due to that
very thing. The '3-inches from dirt' rule is a building code, not a Rohn
spec.
Cheers, Steve K7LXC
Tower Tech
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