Residential Basketball Court Foundation Wall

[Apache1]

Hi everyone. I have a couple of questions on this foundation wall I am designing that separates a basketball court and a higher theater room in a home. See the drawing below for relevant dimensions and design criteria. I have read all the previous threads I could find on this topic but still have some lingering questions I'd like to run past you all.

1 - I have designed this wall in a few different software programs and have come up with the drawing below based on the results from all of these programs. Each program has options to design the wall as "fixed" at the base or "pinned". If I design the wall as pinned then the required footing size approaches 12' wide or more. In my opinion a 12' wide footing is ridiculous and any contractor building this home would laugh in my face. Therefore I design the base as fixed to get a more reasonable footing size at 6' wide. Does this sound like a reasonable approach?

2 - I have a question on whether it matters which way the dowel bars bend once they go down into the footing. A couple of the programs I use provide a visual result showing the completed design. One of these programs shows the bars bending the way I show them in my sketch below. The other program shows the bars bending the opposite direction. Does it matter?

3 - Do you have any other input on my sketch?

 

[HTURKAK]

-Will you post the floor plans to get idea about how the wall fixed in transversal and loads ?

- About Slab in theater room.. is it monolithic with the foundation wall ?







If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[jayrod12]

In my mind, a fixed base wall would end up requiring a larger footing as it would want to resolve the fixed end moment at the bottom. A pinned base wall would only apply shear and axial load to the footing and therefore should require a smaller footing but potentially a bigger wall.

Something in your analysis doesn't add up. Maybe try some quick hand calculations to validate the software before blindly trusting it.

 

[GaryHStr]

Hi there! I have some thoughts on your questions regarding the foundation wall design for your basketball court and theater room.

It's understandable that you want to keep the footing size reasonable, but it's important to ensure that the wall is properly supported and won't settle or crack over time. A fixed base may be more practical in terms of construction, but it could also create more stress on the wall due to differential settlement or thermal expansion/contraction. If you haven't already, I suggest consulting a structural engineer or building code official to confirm the appropriate design and requirements for your specific site and soil conditions. They may be able to suggest alternative options for the foundation that balance cost, durability, and safety.

The direction of dowel bar bending may not be critical as long as they provide enough reinforcement for the wall and footing to resist lateral and vertical loads. However, it's a good practice to follow consistent details and specifications for reinforcement, especially if different programs or contractors may be involved in the project. If you're unsure which direction to use, you could try contacting the software vendors or a local concrete supplier for guidance.

 

[XR250]

Tying the wall back to the upper slab will likely make things a lot cheaper.
edit - I meant the Theatre slab - not the top one.

 

[HouseBoy]

Some thoughts:
6 ft wide at 2 ksf is 12 klf. Not sure if the 4 klf at the top is a summary of the load or in addition to the garage floor, theater and floor truss loading but... 12 klf is a hefty amount. 6 ft wide doesn't seem like too much though if you really have 12 klf.

I THINK Gary is questioning the positioning of your dowels from the footing into the wall. A lot of times they would not look like that but would cross under the wall before they extend up.

As HTU suggests, if you can post the plan drawings, that would give us a better idea if the wall can reasonably be stabilized by the garage floor and surrounding walls. It sure SEEMS like a garage floor would most likely be capable of that and IF SO.... then I would expect that a "simple" (i.e.non moment) base would be fine.

Your vertical reinforcement seems high (more than I would have guessed anyway). If this is the design of a wall without soil pressure on it, then I would really wonder about the wall that does have soil pressure applied to it. Don't know if that exists but it's gotta be happening somewhere (I would think).

 

[phamENG]

You need to push the footing lower. I'm assuming the footing side has to do with sliding? Push it lower and take advantage of the passive pressure beneath the basketball slab.

And yeah - the 12' for a pinned slab makes zero sense.

As for the bar direction, it does matter. Do some searching on here - it's been covered ad nauseam. Search for things like retaining wall rebar development and rebar moment connections.

 

[Apache1]

Thank you everyone for your thoughts. I have attached a couple of images below to clarify a couple of points that were asked about.

UPDATES
- The garage slab will be tied into the wall with dowels as shown in the updated sketch.
- No, the theater room slab will not be monolithic with the foundation wall.
- There is soil behind the wall underneath the theater room as shown in the updated sketch. Sorry, I thought that was obvious from my initial drawing but I see now how it was unclear.

FOLLOW UP
- So the reason I'm getting that 12' footing size with a pinned base is due to the weight of all the soil on top of the heel. Since my net bearing pressure is 2000 psf can I neglect the weight of the soil over the heel since that weight was already there before?
- phamENG, I regret asking if the bar direction "matters" because I know that it matters. What I was really getting at was that I'm unsure if the direction that the rebar turns in the footing depends on whether the wall was designed as pinned or fixed.

 

[DoubleStud]

your wall is only retaining 10 ft of soil. You also have the opportunity to add counterfort(s) right below the theatr slab on grade. If I were to design this, I probably would have longer heel and shorter toe. I would also recommend a ledge (concrete or steel angle) to support the perimeter of the theater slab because it will eventually settle because it will have 10 ft of fill.

Also you need to be careful on when to backfill the theater room slab. Preferably when the floors above are installed, but that may not be possible. So you may want to design it so it doesnt rely too much support on the top of the wall.

 

[KootK]

For base fixity, you want to turn the dowels inward such that they cross. I wouldn't use base fixity however.

I'd be making the following modeling assumptions as a starting point:

1) Top of the wall is braced laterally by the floor diaphragm.

2) Top of the wall is braced laterally by temporary shoring until the contractor says that they want to do it differently.

3) Bottom of the wall is braced laterally be the court SOG.

4) Wall base is pinned and not fixed.

5) Soil bearing is net as you suggested.

My expectation is that this would produce a design with these features:

a) 3' wide strip footing under wall max.

b) No top steel in the strip footing.

c) Probably no theatre side rebar in the wall.

 

[Once20036]

To add to Koot's list, I`d be inclined to tie the wall into the theater slab and design it as a two-span condition.
This would reduce the flexure a bit, but would add the requirement for theatre side rebar in the wall.

 

[KootK]

If one did go the two span route, per Once20036, I'd expect this to be an 8" wall instead of a 16" wall. Maybe 10" if the ledge for the upper precast support drives things.

 

[Apache1]

Thank you everyone, your responses are very much appreciated. I've always been nervous about neglecting the weight of the wall and soil over the heel when I design basement walls so going from a 6' wide footing down to 3' or 4' would be new territory for me.

I would also recommend a ledge (concrete or steel angle) to support the perimeter of the theater slab because it will eventually settle because it will have 10 ft of fill.

I like this recommendation, although I wonder if the slab will still just settle toward the center of the room anyway.

For base fixity, you want to turn the dowels inward such that they cross. I wouldn't use base fixity however.

Yeah so if I go the route of a pinned base then the bars on the basketball court side of the wall will be the tension bars. In this case I would think that the court-side bars should turn toward the toe, but since the moment at the base would technically be zero then it shouldn't matter which way they bend as long as they meet embedment requirements into the footing? Is it fair to say that with a fixed design the bars should cross under the wall, but with a pinned design the bars do not need to cross under the wall?