Stem Wall/Slab Rebar detailing

[EDub24]

Hi, I posted this in the ACI(concrete) forum but thought I'd put it here as well. I have a project where an elevated concrete slab for a new cmu electrical building is under construction. The slab is elevated a few feet above grade due to the flood level and is supported by a concrete stem wall with strip footings around the perimeter. Both the slab and the stem wall are 12" thick with double layers of reinforcement. Where the slab frames into the stem wall the horizontal rebar in the slab ends in 90-degree standard hooks and the vertical reinforcement in the stem wall also ends in 90-degree standard hooks. This is a detail I've seen typically however someone mentioned that the vertical reinforcement in the stem wall at the outside face should splice the top layer of reinforcement in the slab (negative reinforcement). Because I've never seen this I'm not sure if it's overkill. What do people typically do in this situation?

 

[KootK]

I've seen a fair bit of both conditions. My personal preference is definitely the lap. Based on the information that I've reviewed in the past, the double hook isn't an adequate "closing moment" detail, at least not for full capacity. If you're doing it for crack control and not strength I'd be willing to relax some. In Europe, I think that you're allow to develop around corners. Maybe the number will work out that your two hooks would add up to one of those laps.

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.

 

[EDub24]

I'm unsure of how that would help? I've always considered the joint between the slab/wall (shaded area in my quick sketch I've attached) as a fixed point so that as long as the rebar in the slab/wall is developed at the interface then I'm good. If the force in the top mat is transferred to the spliced bar I don't see how it can 'turn the corner' into the stem wall rebar?

 

[KootK]

I've always considered the joint between the slab/wall (shaded area in my quick sketch I've attached) as a fixed point so that as long as the rebar in the slab/wall is developed at the interface then I'm good.

That is a common and unfortunate misconception. Simply developing all of the bars coming into a joint does not provide a full capacity moment connection.

If the force in the top mat is transferred to the spliced bar I don't see how it can 'turn the corner' into the stem wall rebar?

Turning the corner with the tension force is exactly what needs to happen. You'll find everything available to human kind on this subject here: Link. It's a long, sprawling read but you should be able to zone in on what you need by inspecting the sketches posted.

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.

 

[EDub24]

Thanks! I'll read up on that.

 

[EDub24]

I read that link and I think it makes sense what you say. It's pretty similar to a wall corner detail where there are either corner bars that lap the horizontal rebar at the outside face in both walls or the horizontal rebar on the outside face in one wall bends and laps the horizontal rebar in the connecting wall. The horizontal rebar at the inside face for both situations would end in standard hooks that extend to the opposite face.

 

[KootK]

The horizontal rebar at the inside face for both situations would end in standard hooks that extend to the opposite face.

In your case, I'd be comfortable omitting the hooks on the inside reinforcement in order to aid in constructability. That is, of course, unless you actually expect the joint to see opening moments.

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.