Column bearing pad/footing separate from slab?

[BoHboH]

Hey guys just wanted some different opinions and thoughts about a detail I use. The scenario is this: a house with HSS columns in the wall that need larger bearing pads. The finished floor is a slab on grade. Typically you want to keep the bearing pads separate from the slab due to movement/settlement but this becomes tricky. Its also tricky to install these columns plumb and in the correct location before the slab is poured. Its also hard to separate them because most customers want a smooth finish slab with no separation joints as a finished floor. What experience or details do you guys have with this? Do you just tie the slab and bearing pad together? Has anyone done what I have shown below? Thank you in advance!

 

[XR250]

I usually just integrate it into a thickened slab. You can also place the footing and let the slab bear directly on it.
I try to oversize it to help mitigate diff. settlement.

 

[Jdub Engineer]

What you show is pretty typical. I wrap the post and base plate in Isolation Joint material so that the little infill concrete stays isolated from the column and foundation. We've got expansive soils so it's important to make sure the slab stays isolated from the column to allow the slab to move without picking up the building.
JW

 

[JoshPlumSE]

What you show is pretty typical. I wrap the post and base plate in Isolation Joint material so that the little infill concrete stays isolated from the column and foundation. We've got expansive soils so it's important to make sure the slab stays isolated from the column to allow the slab to move without picking up the building.

That's what I saw in an office building project that I was given a presentation on. The key was (as Jdub said) that this was related to expansive soils and the desire to have the main structure isolated from the floor slab. Not sure if the isolation joint material would be needed if the soils were not so expansive.

 

[BoHboH]

@XR250: this house has pretty expansive soils or I would have, I should have mentioned that. Thank you!

@Jdub Engineer: thats a great idea thank you!

@JoshPlumSE: yeah good call thank you!

 

[XR250]

We've got expansive soils so it's important to make sure the slab stays isolated from the column to allow the slab to move without picking up the building.
JW

So how do you deal with the diff. movement between partition walls on the slab and whatever the column is holding up?

 

[BoHboH]

@XR250: Yeah I know good point, the columns have significantly more load so I would expect some movement but don't want that movement to crack the slab. If there is a load bearing wall on the slab I put a thickened strip with over-ex under to mitigate movement but I see your point. I could just over-ex under the whole slab and integrate the bearing pad, but customers usually don't love the cost of all the structural fill/compacting.

 

[XR250]

I could just over-ex under the whole slab and integrate the bearing pad, but customers usually don't love the cost of all the structural fill/compacting.

They wish they would have spent the money once they start having problems. Then it could also be your problem in a lawsuit unless you had some really good CYA on your drawings.

 

[Jdub Engineer]

With expansive soils, we usually don't set any bearing walls on the slab on grade. we isolate all the loads to a few interior steel columns that heavily load the soil. the slab is more likely to heave, because it is lightly loaded. The footing pads are much less likely to heave because of the dead load counterpressure.

Supporting the non-bearing partitions, That's a whole nother game we play. "floating partitions". either at the top or the bottom.
for residential basements, it's normal to do it at the bottom and hang the wall from the floor above.
for commercial projects with a main level slab on grade, we normally put the gap at the top of wall similar to how you would do a Light gauge steel wall with a deflection track. but, it's all kinds of messy trying to get it really done right.
JW

 

[JoshPlumSE]

So how do you deal with the diff. movement between partition walls on the slab and whatever the column is holding up?

I should point out that the project I'm talking about, the block out for the column was "diamond" shaped and oriented 45 degrees off the principal directions of the column and slab. And, that any "walls" were merely partition walls and not carrying any loading from the floors above.