Reinforced Concrete Slab to Reinforced concrete wall detail

[MJC6125]

I don't do a whole lot of concrete design besides foundations, so I'd like to get some other opinions on how to detail a structural slab to wall condition. This is in the rocky mountain region, so expansive soils are requiring a structural slab at the first level over void form. How would you detail the connection of this slab to the foundation grade beam? The attached pdf shows a few options that I've thought about. Any opinions on which is best? I have written some comments that I have on each option on the pdf.

For reference, this detail is cut at the party walls of a town home. I didn't want to pour the slab over the top of the wall entirely because I figured the contractor may desire that the wood framed walls be built prior to the first level slab being poured. I also am not planning on doing this full pourover at the exterior walls because it would create a visible cold joint depending on where grade is, and I wanted to use a consistent detail everywhere.

I'm open to other options that I may not have thought about...

 

[jayrod12]

I would make the grade beam 3" wider than you show, 1 1/2" on each side, this could act as a bearing ledge. My experience with adding a corbel as you've shown in detail 3 is the concrete guys hate forming it.

 

[KootK]

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.

 

[KootK]

Some might have thermal/moisture concerns with my proposed detail and that probably warrants some consideration, at least conceptually. I'm also in the rockies and see similar detailing often when we've got town-homes built along a slope.

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.

 

[Archie264]

I deleted an earlier post as I had misunderstood the situation. (I had thought they were elevated slabs.)

 

[bhiggins]

I'm in Texas where expansive soils are everywhere. Every foundation is designed as a stiffened slab and beams and slabs are poured together. Typically the lower foundation will be poured first and there will be a construction joint at the lower slab elevation. The upper slab will then be poured on top of that.

 

[MJC6125]

KootK,

Do they then have to furr out the face of the wall on the right hand side of your image to be able to install the drywall against the concrete? Do they usually not mind having to do that?

bhiggins,

I think drilled piers and structural grade beams is the most common approach to expansive soils here in Colorado. The grade beams and often a structural slab are all designed to span over void form which gives the soil room to expand without putting an upward pressure on the structure. Not exactly sure what's driving the difference in construction practices, but that's what I've seen most commonly.

 

[KootK]

Yup, furring or resilient channel on the concrete with trim at the transition. Everybody cares about cost but this is the detailing that local contractors bring to me so I assume that they’re happy with the trade offs.

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.

 

[bhiggins]

Pier supported stiffened slab over voids are fairly common in Texas. I've only seen horizontal construction joints in these situations. They typically align with the lower slab edge or are roughly 18"-24" from the top of slab turndown depending on the height of basement wall.

I have never seen a vertical CJ in this situation. I imagine blocking out concrete ledges with a couple of 2x6's to be best and easiest here.