Extensive Coring In Existing Slab

[VBVTEng]

I am working on a project that is new construction –CIP concrete, two-way, flat slab. The design accounted for (6) 4” penetrations and (1) 6” penetration placed fairly close together in a column strip. During construction the contractor placed the sleeves for these penetrations in the wrong location. They now have to core drill the exact same penetrations approximately 10” away from the current location. I am considering creating a FEA in RISA 3D to determine the effects of this on this slab. I planned to maintain the current penetrations in the model as I do not believe that I can gain any strength from filling the existing penetrations. For any required repairs I was thinking carbon fiber. Is there a better approach to this?

 

[gmmolina]

I usually create a RISA model when analyzing two-way slabs for penetrations. I use RISA to determine the maximum shears and moments then compare those values with the slab strength. Very easy to do!

Regarding the mislocated holes, I would model those penetrations also and see if the slabs is OK with all those penetrations. If it is fine, then you can just grout the holes and not worry about it. If it isn't passing with all the penetrations then your repair will have to be detailed differently. We can deal with that then if that's the case.

Good luck.

Gabriel

 

[strucguy]

A sketch would be very helpful. Carbon fiber strips are only good for increasing moment capacity. For shear you can only rely on the slab.

 

[VBVTEng]

Gabriel,
Thanks for your feedback. I appreciate knowing that this is the correct path to move down. I am hoping that all checks out.

Strucguy,
I am attaching a plan with the basic condition. I did not want to overload you with all the dimensions if you were just trying to get a general understanding of what was going on. Please let me know if you would like more detail.

 

[ron9876]

How was this designed. Equivalent frame or FEA?

 

[strucguy]

Don't even bother modeling. You know your original column strip width. calculate the moment capacity after further reduction by 6" due to new penetrations. If it checks out okay you should be fine. When calculating your new moment capacity give consideration to any steel that may be compromised due to drilling. Not sure what your bar spacing is. If it is greater that 6", I would assume atleast one bottom rebar will be compromised.