Question regarding tension development of hooked bars.

cliff234 · Apr 18, 2018

When computing the development length of 90-degree hooked bars in tension, ACI 318-14 permits a 0.70 reduction factor on the development length when there is at least 2.5” of cover measured normal to the plane of the hook (i.e, side cover) and when there is at least 2” of cover “…on the bar extension beyond hook”.

The wording has been like this for at least 20 years. What is “…2” of cover on the bar extension beyond hook”? Is it 2” cover past the tip of the hook (as shown in option B on attached sketch) or is it 2” cover from the hooked leg to the edge of concrete (option A), or is it something else? The wording is confusing to me.

KootK · Apr 18, 2018

I believe that it's "A" but I agree, it is a bit confusing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

cliff234 · Apr 18, 2018

Thanks KootK. That makes sense.

JAE · Apr 18, 2018

I’d second KootK’s choice of A.

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cliff234 · Apr 19, 2018

JAE, I agree. I have been confused about this for 20 years - but it was something that was not as critical as say, lap splice lengths. The ACI 318 committee could have clarified this with a simple illustration showing the dimensions in question - perhaps using one of the figures that are already in the commentary.

MrHershey · Apr 19, 2018

The answer is A.

Screenshot from PCA Notes (for 318-05, not that it matters):

JAE · Apr 19, 2018

I think ACI would rest their case on the fact that they say the 2" cover is on the bar extension beyond the hook....and not the hook extension end.

There is the bar (with the extension) and there is the hook - they would say their semantics is correct and clear enough.
That's my expectation on how they would respond.

But you are accurate to say that those of us out here in the hinterland need to work through the language a bit to "get it".

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dik · Apr 19, 2018

JAE said:
I think ACI would rest their case on the fact that they say the 2" cover is on the bar extension beyond the hook....and not the hook extension end.

I've never given it much thought... but I've used the bar extension and used regular concrete cover for the hook extension.

I've always thought that the minimum cover was to prevent a splitting bond failure of the hook.

Dik

KootK · Apr 19, 2018

Semantics indeed. So if there is such a thing as the extension beyond the hook, does that mean that the "hook" is just the curved part of the bar? I'd always taken it to be everything after the point of tangency on the primary bar length.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

dik · Apr 19, 2018

I've used the back of the hook.

Dik

SoFloJoe · Apr 19, 2018

Looks like this is busted! Yes the definition of the phrase "extension beyond hook" would suggest A.

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Question regarding tension development of hooked bars.

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