Punching shear repair by bonded brackets

[hokie66]

An existing slab has inadequate punching shear capacity at several columns. A proposed approach is to provide steel brackets/shear heads/corbels, epoxy bonded to the column and slab. Does anyone know of this being done? Any opinions appreciated.

 

[JAE]

I'd be wary of epoxy bonding to transfer direct load from a bracket to a column. Can you bolt plate/brackets to the column sides to transfer load into the columns?

Or possibly extend plates or channels down the sides of the columns to allow more room to bolt into the column. If channels on the column faces were to extend all the way down to the next floor, you could then simply direct-transfer the loads down the columns with no significant bolting.

 

[theonlynamenottaken]

Be careful trying to distribute loads in this fashion. I would certainly assume that any "bracket" type assembly is design for 100% of the shear at the column. In other words, I would not design the brackets for Bracket Design Force = Total Applied Shear - Slab Punching Capacity. The difference in stiffnesses for the slab in punching shear and the brackets will cause sequential failure, not "composite" action. (bolt bending, oversized hole slip, bolt bearing yielding, steel member bending - as opposed to - cured concrete compression strut stiffness) So make the brackets your "safety net".

Also, if the slab does fail in punching shear imagine the shape of detached slab in figuring your bracket contact area to the bottom face of slab... you will most likely find that you need to get your bracket bearing pretty far out from the column face.

 

[hokie66]

Thanks for your responses, and I am also wary of relying on epoxy bond between steel and concrete to develop these forces. And I agree with theonlynamenottaken that bolted connections would not act compatibly with the concrete. That is the reason the epoxy bonding idea is under consideration. Any other opinions will be welcomed.