Stair Opening in Exist. Slab

[Heldbaum]

Hi folks,
has any of you ever done a stair opening roughly 9'x7' in exist. RC building just next to the column? It's a 20-story residential building, two ways 8" flat slab - column structure. The client wants to create a duplex. It's at 10th floor. The opening would have to be located a few inches from the column so it's the worst location. I am quite familiar with ACI requirements when it comes to opening's location but there is nothing about openings strengthening to make it work. I cannot run any steel beams from column to column underneath the slab..I was thinking about steel flat bars connected to the columns and closing the edge of the opening from 3 sides with reinf. welded to the side plate. Does anyone have any experience with something like that? Any good reference? I see two obvious issues:
1. Punching shear
2. Temporary slab shoring - it's a residential building so LL 40 psf, and the concrete slab is min. 8" so DL is more than twice bigger.

I already spoke about that with my more experienced colleagues but I would like to get some insight from you guys. Thanks!

 

[Heldbaum]

BA,

as far as I know that was the condition in order the project to happen. Architect was told that this opening can be done without any beam underneath.. otherwise there would be no project.
I know that if the opening was outside the column strip, there will be no issue..but it is not. I ran some quick calcs and it looks like Mx and My increase approx. 8 times when the slab is modeled with the opening.
Yes they need a beam there..
Thank you very much for all your input here, I appreciate it very much!

 

[BAretired]

Okay. It is not a project I would encourage in any case as it seems a bit daft, but I can't see much harm in a channel located under the floor and flush with the party wall.

BA

 

[dik]

HSS beam is prettier than a C section, albeit, less costly.

Dik

 

[dcarr82775]

ACI made changes to punching shear a little after the time of construction if memory serves me correctly. They corrected some unconservative equations.

I know beams are not allowed, but what about right around the column itself to make a shear cap? Cast a concrete shear cap, or add short section of vertical HSS bolted to the concrete column to increase critical shear perimeter.

Flexure is another story.