two way slab punching shear collar 1

[structineer]

I am reinforcing a two way slab for punching shear. I have reviewed several documents, mostly studies, for reinforcement options. The option that seems to be the most effective is a steel collar. I've attached a picture of one option that was used in a study. In this study, they roughened the sides of the concrete column and then "pinched" the column with the collar. They are relying only on the friction between the steel and roughened concrete to transfer the load to the column. I'm not a huge fan of this. I would prefer to have a positive connection, although adding through bolts requires several bolts to transfer the amount of load that I am dealing with. It looks like I will be using a combination of through bolts and friction. PCI 4th edition gives a coefficient of friction between steel and concrete of 0.4. Has anyone ever done anything like this? Would it make sense to use a high strength adhesive between the steel and the concrete? Is there a better way of reinforcing the slab? I've seen studies with frp stirrups and laminates, but the results were not all that impressive. The collar makes sense to me in that it increases the perimeter to take shear. Of course, my concern is the transfer to the column.

 

[dcarr82775]

We have done similar steel collars, but we always put in the thru bolts. Just assuming friction makes me uncomfortable

 

[hokie66]

Agree with dcarr. Relying on friction is for heroes, and I am no hero.

 

[bookowski]

Have you seen the Hilti system for post installed shear reinforcing? Hilti HZA-P - basically post installed diagonal shear reinfocing. I've never used it but it may be an option for you. Otherwise I agree with others, I've only done through bolts.

 

[structineer]

Thank you all for your responses. In regards to the through bolts, what length of the through bolt do you use when checking bearing on the concrete? It's not next to an edge, so concrete breakout shouldn't be a concern. I would think direct bearing would with higher concentrations of stresses located at the outer face of concrete where the shear force is transferred to the concrete.