CONCRETE REINFORCING DEVELOPMENT - HOOKS

[fne]

ACI 318 has a length required in a hook ("L") to develop the bar. If the full length of the hook is not available, does increasing the length of the other leg help? I am assuming that if the other leg was long enough to develop the bar I am ok, but what if conditions are somewhere in between?

 

[KootK]

This has come up a few times recently. My thoughts:

1) ACI gives you no explicit means of assessing this situation.

2) Some codes, such as Britain's do give you a means of assessing it.

3) For some bar sizes, standard ACI hook radii may result in crushing of the concrete inside the bend and unacceptable slip in the anchorage.

4) There is a strut and tie technique called the curved bar node method that, in my opinion would allow you to do this and remain in compliance with ACI. it's a fair bit of work.

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.

 

[BUGGAR]

Headed bars?

 

[TehMightyEngineer]

Smaller bars in greater numbers?

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[JedClampett]

We have this issue on occasion, mostly when the slab is too shallow to put in normal hooks (i.e. a 16 inch slab with #8 hooks). There's very little guidance in textbooks or codes. So what I've suggeste is to shorten the hook, and use that bar size in the calculation (for instance, if you had a 14 inch hook on a #8, see if a #7 would work).

 

[DaveAtkins]

JedClampett,

fne is talking about hook development length, not the length of the hook extension.

DaveAtkins

 

[fne]

Thanks for the input. Question arose on a cantilevered retaining wall. If the footing were 12" thick and allowing for 3" cover at the bottom you would be left with less than 9". Not enough even to develop a #3 bar. Perhaps a larger radius bend to minimize the crushing mentioned and then provide the full development length on the end of the hook?

 

[KootK]

This is probably the thread for you: Link. Or, at least, one of them.

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.

 

[MrHershey]

Might want to double check that hook embedment length. Barring lightweight concrete or epoxy-coated bars, I'd think you'd be able to easily develop a grade 60 #3 bar in to a 12" footing with 3" of end cover, even with the minimum 2500 psi concrete you're allowed to use by ACI 318. Should actually have a couple inches to spare.

 

[DaveAtkins]

By my calculation, if you use the 0.7 factor, you can fully develop a #5 hook in a 12" footing, assuming 3" bottom cover.

DaveAtkins