Concrete Development Length for Hook

[jasonmm]

Hello,

I have a job where I have a one-way-slab (8" deep) that needs to be supported by a 6" wide concrete arch beam. My top slab reinforcement is #4 bars at 12" o.c. Is there a way to obtain the reinforcement development in a 6" wide member or is there a type of connection that would be considered acceptable. ACI says that the absolute minimum development length for a hook is 8 bar diameters or 6". This also made me start thinking about all of the 8" wide concrete walls on condos I see here in Florida. 8" really does not provide enough depth for a reasonable development either. Is there something I am missing here? Any thoughts would be appreciated.

 

[COEngineeer]

JAE is probably the man to answer these questions. If your slab is simply suppoted, there is no reason to get development length? The slab is sitting on the arch beam right?

 

[UcfSE]

With 8" walls and smaller diameter bars, it is possible to develop the hook length. Obviously with a 6" minimum and 6" walls, you're out of luck.

You can increase the width of the arch, change the support condition to one in which the slab bears on the beam instead of frames into the beam, or change your reinforcing so that you do not need to develop the bars.

 

[DaveAtkins]

It sounds to me like this is a pinned end condition--no moment will develop in the slab, and so no development of the top bars is required.

DaveAtkins

 

[haynewp]

For standard hooks it looks like you will have to meet the minimums, but like said it was said above, it may not even apply for your case. As a side, I am not sure about bars that are bent in hooks that extend further.

For example, I know the standard tilt-up concrete wall has dowels that connect the walls to the slab at 1'-0" on center or some such spacing. But some tilt walls I have seen are only 6" thick so you can't get the std hook development length. The dowels (example #4 bars) are bent up into the wall then extend up into the wall further 18 or 24". So I am not sure if ACI allows you to treat the hooked part of the dowel as if it were the same as a straight bar being developed in tension, therefore giving the full development of the hooked dowels.

 

[Gumpmaster]

Try something like the Lenton Terminator (search on Google). It works kind of like a headed anchor bolt that screws onto the end of the rebar.

I'm not sure what the development length for a #4 is, but the development length for a #8 is only 7.25in. I would guess a #4 is significantly less and will possibly work in your situation.

 

[jasonmm]

Thanks for the ideas. I can make the slab bear on the 6" wide beam instead of framing into it. The opposite side will have to frame into a beam but it is 8" wide. I would have increased the beam size but the architect is set on 6". This was my first post and it is good to know that there is a place engineers (who are supposed to know everything) can ask for help.