30" tall perimeter shallow foundation stem wall

[radiocontrolhead]

I am preparing a detail to have a 1 story wood framed structure over a 30" tall foundation stem wall. The slab on grade on the interior will be 30" below the top of the stem wall.

I have a slight concern for rotation of the stem wall due to the unbraced nature at the top of stem wall but because of how light the structure is, don't think there will much of an issue.


What is your take on this? I have details i can employ to brace the top of wall but would end up costing a fortune for the size of this project and i'm trying to avoid it if i can. I was going to use the slab on grade to help brace it and thicken the footing as necessary to increase the moment arm couple between the S.o.g. dowels and the passive pressure against the foundation.

 

[KootK]

Is this not an exterior wall delivering wind load to the top of the foundation? I think you've got a baby retaining wall on your hands and should design it as such. Maybe cheat a bit on the rigorous rebar detailing in acknowledgement of the small scale of the thing.

I like your SOG/passive pressure couple too if there is not a geotechnical requirement to let the SOG float relative to the foundation. I'd do it using active pressure instead of passive in order to reduce the amount of movement required to engage the soil.

 

[radiocontrolhead]

Thanks Koot for the quick feedback.

 

[KootK]

Another idea: with the right detailing, you might be able to use an SOG thickening as kind of a toe for a faux retaining wall.

 

[radiocontrolhead]

So footing and s.o.g are poured monolithically?

 

[KootK]

Or rebar connected. Most contractors in my area do SOG as a later operation to keep it undamaged.

 

[r13]

A sketch of section cut will help explain a lot.

 

[radiocontrolhead]

There isn't a lot of force albeit wind load imposed laterally at the top of the foundation wall. I guess I'm more concerned of the overall stability of it from a long term stand point.
I can get the numbers to check out quite easily through analysis, but theres just something about this "hinge" that is getting me.

Alternatively i can embed a steel post from teh top of footing to the underside of framing and use that as my vertical "mullions" if you will. This is the option i am trying avoid due to cost.

 

[r13]

If only wind is the concern, do a quick check on stability (overturning) of the invert T footing about the toe on the building side, and bearing. You should ignore the SOG and interior soil pressure for rotation. I would carryout the analysis on an interior column with 5' strip width. If works, just design the footing as usual. If not, bring the post down and embed in the stem wall is a good idea

 

[XR250]

I sometimes do these as retaining walls and use the slab as the toe (as KootK mentioned). Waterproofing can be dicey as well as insulation around the slab perimeter. Best to construct a separate, adequately sized footing for the retaining wall and let the slab float.