Interior columns bearing on finished exposed slab

[AaronMcD]

Designing a house. There are 8 concealed steel columns and 2 exposed wood columns at the interior slab. Many of the steel columns act as wood shear wall end chords as well as roof support (we have snow load at this location). Originally I have been designing this with continuous footings spanning across the short direction to support seismic uplift an gravity bearing. Anchors, leveling nuts on the footing, slab poured around the steel columns or around a steel pedestal for the exposed wood columns. Alternative I said they can do diamond blockouts.

The contractor seems to REALLY think it'll save a lot of money to do monolithic slab/footings, and put the columns on that. I guess so they can finish concrete before erecting steel.

Does anyone here have experience with not using leveling nuts, and bearing the base plate directly on the finished concrete?

We would need to route out the bottom of the wood to conceal nuts, and use 2 anchors and bracing at the steel columns which are concealed in a 2x6 wall.

 

[jerseyshore]

I'm sure we've all done it, but they take on the risk of seeing cracks develop around the base of the columns. Will there be flooring on top or will the concrete slab be exposed?

And who wants to look at the bottom of a column and trip on anchor bolts walking around their house?

 

[Eng16080]

Sure, I've done that before. A very thin layer of grout might be a good idea to get a smooth contact surface.

But why not use the same detail you always use? Why does it matter that the baseplate is on top of the slab? Doesn't the baseplate need to be concealed anyway? Otherwise, it seems it would be a tripping hazard (as jerseyshore mentioned).

Without fully understanding what you're trying to accomplish, perhaps it makes sense to provide a recess in the slab for the baseplate to sit in, and then fill in later with grout.

(Gotta get back to chugging lite beers and eating hotdogs now.)

 

[AaronMcD]

The slab will be exposed as mentioned in the title. The anchor bolts have to be concealed. I suppose we could use leveling nuts and grout at the concealed steel columns. I was thinking it might be difficult to fit it within 5.5" stud width.

Looking more into this, I am learning there are other methods than nuts (shims, leveling plate).

I am thinking I can specify a minimum layer of grout at the concealed columns and let the contractor decide how he wants to get the columns plumb.

The wood posts are double LVL bolted to a knife plate and bearing on exposed inset steel base plate. I can't see how to get grout under this plate since the concrete slab is exposed. The load is about 20 kips.

 

[Eng16080]

If your main concern with the steel columns is leveling/plumbing them, if you provide some extra holes in the base plate, then weld nuts above those holes, you can level the plate from above by inserting a bolt into the nut and turning until it bears on the concrete and pushes the column up. I haven't done this, but it should technically work.

Also, be careful with only having 2 bolts for a column. That might not meet OSHA.

Not sure about the LVL detail.

 

[Tomfh]

In Australia the standard method is shims followed by grouting. It works fine. If the slab is sufficiently flat and level you can put the post straight on the slab, no grout.

 

[jerseyshore]

Is this already poured? Typically when we have exposed concrete or trying to fit a steel column in a 2x wall we have them cast in the base plates/ anchors first. Then it's easy to drop the column right on since it's already level.