Wood Diaphragm Supporting Basement Wall
Wood Diaphragm Supporting Basement Wall
(OP)
Hello all. I just searched this forum but didn't find an answer to my question. I'm designing a residential foundation, cut into an hillside, and I'm treating the uphill wall as a basement wall (supported at top and bottom - not a cantilever wall).
The floor diaphragm stresses are a bit high, and will require a blocked diaphragm.
My question is this - have any of you seen a basement wall failure because of an overstressed floor diaphragm or the connection of the diaphragm to the perpendicular walls?
Thanks - I'm looking forward to your response.
The floor diaphragm stresses are a bit high, and will require a blocked diaphragm.
My question is this - have any of you seen a basement wall failure because of an overstressed floor diaphragm or the connection of the diaphragm to the perpendicular walls?
Thanks - I'm looking forward to your response.






RE: Wood Diaphragm Supporting Basement Wall
RE: Wood Diaphragm Supporting Basement Wall
RE: Wood Diaphragm Supporting Basement Wall
With that in mind -jae, how did the Dakota building deform? How bad was it?
Thanks to both of you for responding - its my first post on this site, seems like a great resource.
RE: Wood Diaphragm Supporting Basement Wall
RE: Wood Diaphragm Supporting Basement Wall
The deformation of the building we looked at was pretty severe in that the interior of the building was wide open....cathedral ceiling supported by long glue lam beams, and the building was quite long if I remember right.
The basement was of course under ground on one side and the fill actually came up to within about 4 fee of the eave of the rear upper wall, which had an extended rear concrete block wall to interface with the earth. I seem to recall our conclusion that the original engineer (It was engineered) didn't really follow the load path through (so I second what kkoloj said about following it through).
We ended up temporarily bracing the basement walls and eventually re-excavating and installing some additional structure to better transfer the lateral earth loads away from the diaphragm.
There are lots of wood framed homes that successfully resist earth on one side without any problem. Just do the math and watch not only strength, but the stiffness as well.
RE: Wood Diaphragm Supporting Basement Wall
RE: Wood Diaphragm Supporting Basement Wall
The shear numbers on the side walls are usually quite large and the allowable diaphragm shear values given in the code should probably be ratioed by 0.9/1.6=0.56... If you should some how demonstrate that this works numerically, then as the other posters said, this leaves no strength in the diaphragm for seismic/wind and creep deflections should be considered: flexible diaphragm.
A cantilever retaining wall is typically OK for residential construction. If possible, use the basement slab and downhill stemwall for sliding resistance and then your heel only need work for overturning. Also keep in mind that the contractor is going to want to backfill the wall ASAP so his framers can get to the main structural floor easier; having a retaining structure that does not need the help of the flexible diaphragm is a good idea from a sequence perspective.
RE: Wood Diaphragm Supporting Basement Wall
We design alot of hillside foundations. Soil type and below the footing soil profiles are a big factor in determining what foundation system to use.
Perhaps you can utilize buttresses in the front wall to provide stability without requiring the diaphram and the wall spans horizontally.
RE: Wood Diaphragm Supporting Basement Wall
Thanks everybody for your input. Invaluable!