Punching shear of a steel HSS column through flat slab

[qcjr]

Hello guys,

We are designing a concrete flat slab supported by steel HSS columns with plates. Basically, the contractor (who is also the client) wants to have continuous steel columns (not interrupted at each level).

I have calculated the punching shear through the slab by checking the minimum steel plate dimensions (below the slab) to respect the shear resistance with the corresponding perimeter.

I am just wondering if having a continuous steel column can cause a problem in shear resistance? Think of the slab as having a hole at each column, filled by the steel column itself.

Thank you!

 

[frv]

How are you supporting the slab? Do the columns have brackets?

Your critical perimeter may be only two sides of a rectangle. Also, is that column part of your LFRS? If so, how are you transferring loads to it?

 

[steellion]

If the column was continuous through the slab, then the slab is imparting all of its load into the column through whatever brackets you are using to support the slab. Also, how will you get the top bars to develop at the column? The detailing is critical. It's going to be a tricky detail to get that to work. If the column are discontinuous, then your punching shear area would be taken from the bearing plate width.

 

[slickdeals]

I think the detail will have to assume no moment transfer into the HSS column. The bracket plates will support/transfer the loads from the slab into the HSS. I would provide a bracket plate that is at least a 1/2" thick with studs welded to it. The reinforcing bars will continue around the column in each side. The column will just be assumed as a sleeve penetration.

 

[epr]

Your best bet is to review a publication relative to lift slab construction. The bearing conditions of the lift slab procedure is exactly what you are concerned about.

 

[qcjr]

Well, thanks all for the answers.

The column isn't part of the LFRS: the slab is a diaphragm transferring the lateral loads to shear walls on the perimeter.

The slab is supported with a thick plate with studs (so far). I believe the reinforcement of the column strip will be put on each sides of the column, along with integrity. I was more concerned about punching shear at the moment, although anything related to reinforcement around the column is going to be delicate and critical, as steellion said.

I will check into lift slab procedure. Thanks for the heads up!

Any other thoughts on this detail? As I said, this is the first time I've seen something like that.

 

[demayeng]

The presence of the 'hole' due to the column penetrating the slab shouldn't affect the punching shear strength, as the shear crack will generate from near the edge of the plate diagonally outwards, away from the column.

As long as you put plenty of longitudinal top reinforcement in both directions, it should not be a problem