Basement foundation wall with lateral restraint from garage slab reinforcing 2

[TroyD]

I am assisting a custom home designer on a project with a basement sport court. One foundation wall of the sport court is adjacent to the garage (slab on grade). At this location, I am considering the foundation is restrained from lateral earth pressure at the top via dowels tied to the reinforcing in the garage floor slab. Please refer to the attached detail. I have evaluated the foundation wall using RetainPro, and have used this detail on several similar projects. I'm just revisiting my detailing for constructability. It gets a bit complicated with the 6" curb around the garage perimeter, etc. The concrete mason will need to allow for the bent dowels to penetrate thru the formwork for the wall pour. Just curious if others have used a different method to accomplish this? Any input is appreciated.

-Troy

 

[KootK]

This is something that I've struggled with myself. The concern that have with your detail is shown below. In shear, tt seems to me that you're only mobilizing about 3" of your 8" section straight out of the gate. Maybe that's enough, may it's not. Mechanically, I prefer the detail where the slab dowels are taken across to the far side of the wall and the curb is added as a third pour. I acknowledge that contractors often prefer your detail however.

 

[Celt83]

Where does the lateral force go once its in the garage slab? If you are using it as restraint you need to detail the full load path, you will likely discover that friction between the slab and grade is not adequate for the reaction. I would even assume all of the soil within the active soil wedge is not effective in providing friction resistance.

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[KootK]

Some ideas that preserve your formwork concept.

 

[KootK]

For me, this is one of those situations that is more salient turned on its side. You're effectively "hanging" the wall.

 

[HTURKAK]

MR Celt83 (Structural) has a valid point..and a big PS for him.. A simple calculation assuming friction angle 30 degr, soil wt 20 kN /m3 will produce around 7.0 kN/m necessary reaction for garage slab so, the friction force developing btw garage slab and soil will not be enough. The garage slab should extent up to the other walls of basement which are vertical in plan to the subject wall to complete the load path.

What is the situation for other walls?
If the basement is full basement, you should need a perimeter walkway frame around the bldg designed for lateral loads.

I would prefer RC slab monolitic with the basement walls at GF ... since the garage floor or perimeter walkway could be destroyed for renovation works etc..

 

[TroyD]

KootK, Celt, & HTURKAK, thanks for the good input.

Koot: I am familiar with the "form saver" inserts, and I've also seen masons use rebar dowels and bend them like you describe. My initial thought is that the reinforced garage slab, if detailed correctly, should be capable of easily resisting the soil pressures...something that we rely on the floor joist system to typically do. I'll do some calcs to confirm. The hooked dowel comment makes good sense to engage the full wall thickness.

Another thought: I have evaluated these foundation conditions for sport courts and open stairwells a few different ways, the most interesting method is the rectangular tank analysis... For these height:width ratios, I've found that the perpendicular foundation walls, if adequately reinforced, make a significant contribution to the overall stability of this wall.

HTURKAK, the other wall conditions around the perimeter of the sport court cause the most grief. Beyond the garage, the wall is unsupported at the top, so it needs to be evaluated as a cantilever retaining wall. It requires a wider footing, more reinforcing, and absolutely need to spec well-drained granular backfill to keep the lateral earth pressure manageable. Again, the rectangular tank analysis yields better results.

 

[Ron247]

Are you providing temporary lateral bracing for the 8' wall as you backfill and compact the backfill? If not, what keeps the wall in alignment during backfilling?