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Basement wall - fixity

Basement wall - fixity

Basement wall - fixity

(OP)
In case of tall basement walls, it would make sense to use fixity at the bottom of the basement wall instead of assuming a pin-pin connection. Following through with that moment, it would be right to size the foundation of the basement wall to resist that moment.

Is this the right approach? How many of you have designed basement walls for fixity at the footing and carried on to check the wall footing for the moments?

RE: Basement wall - fixity

I have done that in past projects, but not usually.

Just remember to specify when the wall is allowed to be backfilled as related to the presence or absence of any floor diaphragm at the top of the wall. Makes a big difference in steel placement.

Mike McCann
MMC Engineering

RE: Basement wall - fixity

I've also done that on a few occasions. I'm comfortable with it when the wall ties into a serious footing (raft / thick pad footing). When it's just a typical strip footing (600 mm x 400 mm DP etc), I question the stiffness of the soil with regard to providing the necessary rotational restraint.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Basement wall - fixity

(OP)
I think If you transfer the moment due to fixity, automatically the footing will end up becoming big. For example, I have a 5 m tall basement wall carrying some heavy axial loads due to a landscape deck (plus fire tender surcharge) and I am ending up with a 2200 mm (w) x 500 (thick) continuous footing and I am still in partial bearing.

I will tie in the slab to the footing as well to provide additional rotational restraint and provide adequate rebar in the slab as well.

RE: Basement wall - fixity

Yes, with the fixity, the footing will get bigger. However, you can save material and labor if you pour the slab and wall footing monolithically.

Mike McCann
MMC Engineering

RE: Basement wall - fixity

(OP)
M^2, exactly that's what I am doing. I have a slab, which ends up becoming a thickened slab (footing) under the basement wall. I am centering the thickened slab under the basement wall.

Thanks guys!

RE: Basement wall - fixity

As an aside, are there constructibility / sequencing issues associated with pouring the footing as a thickened slab on grade? Does this not force the contractor to pour and finish the slab on grade earlier than they might want to? In my neck of the the woods, SOG are often poured much later than foundations. Obviously, it can be done (I've seen pictures). Are there sequencing issues to consider?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

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