Two Way Slab- Block-out

[LoneStarEngineer]

I have a steel structure building with first floor two way structural slab. The columns plinths are fairly large (40" diameter) and we need to leave block-outs for steel columns.The blockouts would be about 28" in diameter so we have about 6" of slab bearing around the plinth. The critical section for shear is at d/2 from the face of the plinth and the opening is inside the critical perimeter. I will have any interrupted bars due to this opening on the sides so the rebar is adequate for moment.
How would this blockout affect the structural integrity of the slab? I am trying to get some more opinions and thoughts.
Appreciate your responses.

Thanks.

 

[BAretired]

I will have any interrupted bars...

Do you mean "I will NOT have any interrupted bars..."?

BA

 

[LoneStarEngineer]

My bad, should have been more clear. What I meant was any interrupted bars due to the block-out will be added to the sides of the block-out so there is continuity of moment transfer. So basically the As (area of steel) will be the same as if there were no block-out.

 

[Lily_Linton]

you are correct. It is also stated in in ACI 318-14 Section 8 that opening are permitted provided that the location of the block outs will be as per their requirement. It also stated there that the total quantity of reinforcement in the panel shall be at least equal to that interrupted opening and shall be added on each side

 

[LoneStarEngineer]

Thanks. But since this opening is inside the critical perimeter, should b₀ in the punching shear equation be reduced??

 

[BAretired]

I don't think b₀ should be reduced, but I feel it's important to have interrupted bars carried as far as possible beyond the edge of plinth. Because of the circular hole, there is a good chance that some bars could be short, so I suggest adding hooked dowels top and bottom of the same size and spacing as the interrupted bars.

BA