Foundation wall
Foundation wall
(OP)
I have a project that has a 20 foot tall cast in place concrete foundation wall That will be back filled full height with sand. The wall is 14" thick, I am using 30 pcf for my active pressure on the wall. I want to design the wall as pin-pin. the top will be pinned by the main floor diaphragm. How do I achieve a pinned condition at the base? I have a 4000 lb/ft horizontal reaction at the top of footing that I dont know how resolve. Can I use the basment slab as 4"thick x 12" wide column to support the reaction? The slab is 8" above the top of footing so I am ignoring passive pressure. This seems like a very simple issue I think I am just looking at it the wrong way. Please help






RE: Foundation wall
What sometimes happens in larger structures is that the footings settle a bit, causing a downward movement of the edge of the slab at the wall, thus, an upward bow in the slab occurs (very slight) that then creates Pδ forces and upward buckling.
Usually slabs aren't all that thick and have very little resistance to this upward buckling. Of course the dead weight of the slab itself counters this buckling to an extent.
You should consider thickening the slab, thickening the footing, etc. to account for this lateral thrust.
RE: Foundation wall
RE: Foundation wall
Other issues you might consider:
1) the sequence of construction may be such that the backfill is placed before the basement slab. You'll need to be clear in your communication about what's required.
2) I only use at-rest pressure for a restrained wall. In my thinking, the active pressure implies a deformation that relieves the pressure and this deformation is generally not acceptable in a basement wall.
3) Since you're assuming loading due to sand, make sure the sand occupies the entire zone which will influence the lateral pressure.
RE: Foundation wall
Add a few dowels and just 'drop' that wall right in...
RE: Foundation wall
RE: Foundation wall
1. Yes, you can design the wall as pinned both on top and bottom. The support mechanism is the same for both - reinforcing according to your analysis to allow relative deformation (rotation) at the joints. You may need to add water stop at the bottom slab-wall joint, because the concrete will crack as intended (Preferabily the slab shall be casted after the wall).
2. Yes, the base slab acting like a beam-column. You need to account for both the compression and subgrade reaction.
3. I will ignore earth pressure below the level of base slab, and, as structuralEIT pointed out correctly, using "at-rest" earth pressure, not active pressure since no movement will occur on the upper support, which is the single requirement for soil to be in the active state.