concrete reentrant corner reinforcement

[CloudCastle]

Since my earliest days I was aware that "The Code" fobade the wrapping of rebar around a concrete reentrant corner.

I was actually challenged by some plans inspector saying that I wasn't allowed to use my detail for reinforcement. I had to use his. His detail showed wrapping of rebar around in a manner I was told was incorrect.

I was unable to find the code reference to rebut him.

Does anyone know what the code reference is? I'm pretty sure it is not in the UBC. I was told it was in ACI, but I can't find the specific reference.

 

[jike]

I know of no code requirement but it is engineering common sense to extend the bars past the corner in each direction! If a bar is needed, it needs to be developed by extending past the corner.

If it is simply bent around the re-entrant corner, what is going to happen when it tries to take stress? The bar will try to straighten out and the corner will pop off.

 

[JAE]

jike - exactly!

 

[DaveAtkins]

But keep in mind--I see many structural engineers making this mistake--that the available development length for a hook is determined by its length BEFORE wrapping around the corner. You cannot develop a hook bar after it has wrapped around the corner. So if you have, for example, a 12" thick wall, the corner bar will only have 10" of available hook development length (assuming 2" concrete cover). You could wrap the bar around the corner and run it for 10 miles, but your available development length would still only be 10".

DaveAtkins

 

[archeng59]

I don't understand what type of re-entrant corner you are questioning. so perhaps I'm about to ramble about the wrong thing here, but I'm curious to know what you are dealing with. Corner bars in a wall or continuous footing typically do not have significant flexural forces applied to them since the horizontal bars are for crack control. If the wall is thick enough to have two layers of steel, I always detail the corner bars so they extend beyond the inside corner to the far mat of steel. similarly corner bars for horizontal reinforcing in continuous footings and grade beams. If there is a single layer of steel, the bars are centered in the wall. If there are significant flexural forces in the horizontal "corner bars", I add a pilaster at the corner. In slabs, typically the edge bars can be extended beyond the corner as far as necessary in each direction. Or add bars at a 45 degree angle to the corner. for elevated structural framing, the top and bottom steel in the edge beams typically extend beyond the corner.

thoughts? rebuttals? am I on the same page?

 

[miecz]

Cloudcastle-

The specific Code Reference is then, ACI 12.5.1, the requirement for development of standard hooks.

 

[CEGG]

It has always been my understanding that there is no Code requirement for reentrant corner bars - but placing them there will prevent the likelyhood of cracking at these corners, so its good common sense practice. Even if the bar does not reach its full development length, it will provide some cracking resistance.

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