Circular Concrete Column "Overlay"

[GreatDane2022]

I would love some ideas from the group...

I have four 12-inch diameter structural concrete columns that I designed and planned to be architectural for a large interior residential space. Unfortunately, since it was my first self-performed concrete pour, it did not come out very architectural. To add insult to injury, the scale for the room is way too small (engineer not architect). I considered wrapping the columns in masonry but really like the concrete industrial look. We are about to pour suspended slab above and as part of that pour I was thinking of placing 24-inch diameter sonotube around the existing 12-inch columns and "wrapping" the columns in a layer of concrete but this time doing a better job vibrating and change mix design to smaller aggregate. It's a small price to pay when I will already have concrete coming and the boom truck.

Anything thoughts, ideas, suggestions?

Thanks!

 

[BridgeSmith]

My only advice is provide reinforcing near the surface of the wrap. Reinforced concrete columns with about 8" of concrete 'cover' is a recipe for massive cracks.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[GreatDane2022]

Thanks for advice Rod. Since my coverage on each side would only be 6 inches, you’ve given me something else to think about.

Are you thinking cracking would be coming from the vertical pressure on the column cover (donut) or the lateral movement of the underlying column exerting forces on such a thin cover? If it’s the former, I could leave the top few inches of cover down so there were no pressure on it from the suspended slab and then hide the gap with trim or the like.

 

[KootK]

1) If you attempt to pour the column wrap along with the suspended slab, you may get plastic settlement shrinkage.

2) If the column rests on a suspended slab, ensure that your setup doesn't cause a punching shear issue down there.

It would be helpful to see sketches of what you have in mind for the connections of the wrap to the slabs above and below it. Also, will you add shear dowels into the sides of the existing columns?

 

[BridgeSmith]

Are you thinking cracking would be coming from the vertical pressure on the column cover (donut) or the lateral movement of the underlying column exerting forces on such a thin cover?

I was thinking that with your reinforcement in the 12" column so far from the new face of the concrete, without additional reinforcement near the outer surface of the 24" column, any flexure, or even drying shrinkage, could open some fairly wide cracks in the surface of the column.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[GreatDane2022]

Hi KootK!

I think you and Rod answer all of my questions and I truly appreciate it.

Attaching picture for your viewing pleasure…be kind.

Columns are currently resting on very large footers situated in rock. I left a column blocked out when I poured slab around the columns and was planning on filling that blockout when I poured the suspended slab above(and possibly my column cover).

I have not put much thought yet into connections or dowels. I wanted to make sure I wasn’t going down a crazy path with the overlay.

 

[GreatDane2022]

I am not sure that I explained that thoroughly, the footer is just below that slab on ground that is in the picture. They only suspended slab is going on top of the columns.