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Basement Wall Top Restraint

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Loui1

Structural
Apr 25, 2006
102
Designing a typical basement wall with granular backfill. In design of the wall, I am assuming restraints at the elevated floor level and the basement floor slab. Therefore the wall simple spans.

My question is, if you have wood floor framing, what detail would typically be used to provide the top of wall restraint? In all the buildings I've observed, I havent seen any special connection of the floor joists to the top of the wall. I'm calculating a 900 lb/joist required restraint force, and toenails do not provide anywhere near this amount. I could use a simpson product that provides 750 lb/joist, but thats about it.

Any pointers would be appreciated.
 
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If you have a 9 ft deep basement, approximately 6" will be bottom slab and 18" will project above grade, so your loaded length is about 7 feet. say lateral load is 33 #/ft.
the pressure will be .5 x 33 x 7^2or about 800 #/ft. Because it is a triangular distribution, approx 2/3's will go to the slab and 1/3 to the framing (actually a little less as the framing is above grade) so the load is about 250 per ft. See an AIA Graphics standard for floor connection details (Most libraries have ones that are a few years old - these details rarely change.) The important thing is the plywood floor acts as a diapragm tying the joists togeter. The foundation should not be backfilled untill the floor is complete.
 
Loui1, it sounds from your post like you are bearing your joists on top of the wall. Could you attach a ledger to the side, and face-mount your joists to the ledger? I would think this would give you more resistance. I could be misunderstanding the question.
 
rholder98 Yes, the joists are bearing on top of the wall. What is the typical attachment to provide the required joist to t/wall connection? I do not want to use a field bolted ledger board.


DRC1 I'm not sure where you're getting your numbers. Im assuming EFP, with a triangular pressure distribution of 0 to 495psf (per geotech report) over 9'. W/3 = 745 lb/ft into the wood joists and 2W/3 = 1485 lb/ft into the floor slab.

Simpson HGA10KT's get enough capacity, I may just go with those.
 
Generally the basement wall from top of wall to bottom of slab is 8'-6" to 9' depending on slab thickness and footing so an 8 foot wall panel can be used. the wall will generally extend above grade at least 18" to keep water from the sill. Thus your distance from top of slab to top of ground is about 7 feet. At 495, the geotech is using at rest pressure over the full 9 feet. I would just check how much of your wall is buried. If it is only 7 ft, the load goes from 745 to 450. If it is 9 ft from the top of ground to top of slab, then the load in the wood is 745 #/ft.
 
Interesting Comments.
In NC the minimum wall height usually is about 8'-9.5" which is coursing. The ground is usually 8" (the required minimum) giving approximately 8' unbalanced fill and if you read table1610.1 note c, you will see that soil pressure is 60 psf. That gives you a lot larger force at the top of the wall than you state above. There is a friction value between the sill plate and the wall and the anchor bolts need to cary the remainer. Usually we frame the entire house and not just the floor before the walls are backfilled.

 
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