Punching Shear Steel Collar Design

[VaStruct]

We’ve been working on a remedial repair project of a flat plate three story building that has punching shear issues and have been working on designing some steel collars to extend the critical perimeter around the column.

We determined the required perimeter in order to provide an adequate shear capacity for the slab based on 4*(f’c)^(1/2)*bo*d so that we can determine the required steel plate sizes but where we have been running into the most difficulty is in the design of the anchorage of the steel collar to the column.

We found several articles that referenced designing the steel collar to column connection to take the full shear load resulting from the punching shear check. For some of the columns, this results in factored loads on the order of 240 kips. This makes connections of the steel to the concrete columns very challenging.

Does anyone have any thoughts on this approach?

 

[ChaChaMan]

Just thinking out loud
-if the concrete column is exposed;

Add a full height reinforced concrete collar to the column and weld the rebars to the steel capital collar to ensure development and transfer of stresses.

 

[ron9876]

Or gunite.

 

[hokie66]

VaStruct,
The connections must take the full load, as the articles you read recommended. Yes, fixing punching shear problems is very challenging. If space is available, making the columns bigger is often the most practical and economical solution.

 

[BAretired]

Maybe you could use something similar to the Ellis shore which has been used with timber posts to support concrete formwork for many years.

http://www.youtube.com/watch?v=sQ2yeHlPTgw

BA

 

[hokie66]

???scratching head...BA, how does that relate to increasing punching shear perimeter?

 

[csd72]

hokie66,

I think he is one step ahead of us and looking at the problem of how to ensure the load is taken by the new brace.

Anyway, I have seen these types of things in seismic retrofit so I suggest you google that to see if you can find any references.

 

[BAretired]

hokie,

The new collar would provide the increased perimeter. The Ellis attachment would connect the collar to the column. Just a passing thought...it may not be practical.

BA