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RE: Hooks on bottom reinforcing steel in pile caps

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ACI does give some indirect indication that 90 degree hooks may have
limitations by setting a minimum cover.   While ACI does a pretty good job
it must be remembered that the code is a concensus of a committee and as a
result is not perfect.   

As far as telling somebody to do something that is not specifically
required by the code, that is part of being an engineer.   Prior to the
introduction of modern codes this was a regular fact of life.  In addition
I have yet to find an engineer, who was not arbitrary in at least some of
the things they did.

In my opinion the best solution is to use T-headed bars in place of hooks. 
Steel plates are welded to the end of the bar and act to develop the bar. 
Look at the strut and tie provisions in the latest ACI to understand this
concept.  This approach shortens the development length, is not concerned
about the hook straightening, and reduces conjestion.

Mark Gilligan


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What confuses me is the implication that you and
several others made (and that intuitively sounds
correct) that a 180 degree hook has better holding
capacity than a 90 degree hook. The thing that I'm
having a problem with is that ACI 318 says NOTHING
about 180 degree hooked bars providing better
structural performance as compared to bars with 90
degree hooks.

If ACI 318 says that both hook types have identical
pullout capacity, how can I tell someone, "No, you
can't use bars with 90 degree hooks. You have to use
bars with 180 degree hooks. Even thought the code says
that they are both identical, I get a warm and fuzzy
feeling with the 180 degree hooks - so that's what you
have to use."

Can anyone list a single report, research study, or
structural failure that would highlight the difference
in structural integrity between bars with 180 degree
hooks and bars with 90 degree hooks?

Thanks everyone for your responses to my question!
This is an issue that I've been wondering about for
several years - but which I've never been able to find
a definitive answer to.

Cliff Schwinger

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