Basement wall with wood flooring

[mike20793]

I've got a retaining wall in a basement on a house and I'm trying to use the floor to restrain the top of the wall so I don't have to design it as cantilevered. I'm having a problem coming up with a detail that I feel good about. I need like 1100 lb/ft (strength level) restraint at the top of the wall, so the typical joist bearing on treated ledger on the top of the wall with J/L bolts into the wall isn't going to cut it. I'm left with framing 16" deep I joists into the side of the wall. Has anyone done this before? I'm worried about the ledger connection since the joists are 16" deep. Any suggestions? Thanks.

 

[KootK]

The attached document is quite helpful for this topic.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

I've also done the side mount ledger detail without issue. Other alternatives, depending on the furring situation, could be a ledger below the joists or the use of the furring walls as a load bearing wall.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

I usually do the side mount ledger detail. Never had any real complaints from the contractors.

 

[Signious]

An alternative I have used to a side mount ledger would be to do a 'traditional' top mount joist with tension strapping running from the top of the joist, inside the rim board, over the top of the concrete foundation wall, and down onto the inside face of the wall.

I can't open the attachment Kootk posted for some reason - but I suspect it is the AHITC Lateral Bracing guidelines. See Fig. 4c.

I use a 48" stainless steel strap w/ corrosion resistant concrete screws to the wall.

 

[KootK]

but I suspect it is the AHITC Lateral Bracing guidelines. See Fig. 4c.

Jeez... I need to be less predictable.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

... Or extend the wall top plate to the inside edge of the concrete wall and hang the joists off the plate.

Mike McCann, PE, SE (WA)

 

[Signious]

I need to be less predictable.

the name of the attachment is also, 'Guidlines_for_Bracing_of_Residential_Foundation_Walls.pdf'

 

[manstrom]

1100 lb/ft sounds huge. Usually basement walls get more like 300 to 500.

If it's that big, you may need to resolve the lateral forces on the other end of the floor. Joists at 16" o.c. would have a compression force of 1500#!

Maybe a cantilevered wall (or counterfort wall) is required.

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

 

[XR250]

I was just going to post that. You also have to worry about overall stability of the house if the fill is not resisted on the opposite side of the structure. Ask me how many houses I have seen racked due to this issue

 

[mike20793]

Thanks guys. Yea, this house is a doozy and its a freebie job, so I'm just checking a few things for the architect. It's a little odd because the basement has a higher floor to floor than the rest of the house (retaining 14 ft), hence the large reaction even with a propped cantilever analysis. I think the cantilever wall is the way to go. There's just too much that (most likely) wouldn't get installed or built correctly to rely on the floor taking that load. The last thing I need is some subcontractor to backfill the thing when the floor isn't constructed all the way. Based on the rest of the house (>15,000 sq ft), this guy won't feel the increase in concrete in his pocket to do a cantilever wall.

 

[msquared48]

So the total thrust from the lateral pressure prism is 3300#/ft., with 1100#/ft at the top?

(50×8×8/2)/3 = 533#/ft. Seems high.

Mike McCann, PE, SE (WA)

 

[Signious]

quick & dirty napkin calc based on 8ft backfill on an ~8ft wall for sanity check only.

-115PSF * .33 (assumed Ka) * 1/2 * 8ft^2 (wall height = 1214psf @ 1/3rd wall height from top of ftg
-equv tabular load brings us: (8ft*1214plf*5.5ft*x2.5ft)/(8ft^2) = 2090#
-2090#/2 = 1045# taken by top and bottom w/o factoring loads.

I can see how he is getting near 1100#/ft

 

[XR250]

You may also want to try interior or exterior concrete buttresses if the floor plan allows. A 14 ft. cant. wall is super expensive
The last house I looked at with 14 ft. of backfill had slid about 3" off the opposing foundation wall.

 

[msquared48]

50 psf/ft is normal for restrained walls, unfactored.

Mike McCann, PE, SE (WA)

 

[Signious]

Haven't heard that approximation before msquared, good to know - thanks. I have always used the integral formula based on Rankines formulas:



P(acting at 1/3rd height of wall, in #/linear ft) = 1/2*(Active or passive coefficient)*(Unit weight of soil)*(BF. height)^2