Discontinuous SOG at interior wood-stud bearing wall 1

[Ben29]

The geotech report for my 3-story apartment building project reads, "We recommend that all grade slabs be designed to be discontinuous at walls and pier footings so that differential settlement will not induce shear stresses in the floor slab. Does this mean that I should have a construction joint near every interior wood bearing wall, like detail B below? Typically I would provide a footing like detail A below.

 

[phamENG]

Probably means footing, stem wall (CMU or concrete, depending on local preference), bearing wall. Slab dies into the side of the stem wall with now positive attachment.

 

[Ben29]

So something like this detail below? Ignore that 10" dimension string below the footing. I forgot to delete that.

 

[phamENG]

more or less, yes. Watch the distance from bottom of slab to top of footing - if it's too small then you won't be protecting the slab at all.

 

[Ben29]

Pharm: So then, this detail below? Or just lower the footing? I don't know how much to lower the footing in order to protect the slab. I assume a 3" differential between bottom of slab and top of footing is not adequate per your last post.

 

[manstrom]

IMO, geotech reports always say this, but they don't understand what it would would mean to float a slab on grade in the middle of a structure. I dont think I have ever done it.

If the slab moves, then you ruin the floor finish. Also, I doubt your concrete sub will pour it that way.


When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[Ben29]

manstrom: That is what I was thinking too.

 

[KootK]

My experience matches manstom's for light frame bearing walls. SOG's are not usually significant life safety things so it's often a game of serviceability issue risk management. Similar to how SOG are usually dowelled in at door thresholds etc. Yes, cracking the slab is a serviceability issue. Not being able operate doors is just a larger one in most cases.

 

[Ben29]

So I think the consensus is to go with "detail A" as shown in my first post. And notify the architect and owner that cracking may occur in the basement slab, therefore use appropriate floor finishes so cracks are not translated through the floor finishes.

 

[KootK]

Well, as much as one can consider a 2:1 sample a "consensus"...

I'm torn on the discussion with the owner:

1) One the one hand, more communication is almost universally a good thing.

2) On the other hand, I think that your risks here are small and, when that is the case, I often just absorb the risk my self rather than burden other parties with it who aren't likely to do much about it. I'm sure that you're client will be using the same floor finishes regardless of your detailing. I like the slab level rebar that you have in your detail. If there's a tendency for cracking I could see that helping quite a bit. Most versions of this that I've seen do not have the rebar at the top and instead have saw cut joints at the sides of the footing that are ugly and probably often omitted. I like your version better.

This would be a #2 for me.

You know how clients tend to dislike "nickel and diming" on cost extras? I feel that we often do something similar with risk. Risk nickel and diming sort of. Particularly in a situation like this where it will be difficult for anyone to really quantify the risks. Somebody on the project will need to look at this and say "meh, I think it will be okay". For this particular risk, I feel that the right party is probably you.