Column Footing Punching Shear

[davidfi]

I have a project under construction in which the batch plant closed and they ran out of concrete while pouring a large footing. I have a 18"x24" conc column that sits on what was supposed to be a 12' sq x 2'-6" thick footing. The footing as poured is only 2'-0" thick. I checked the 2'-0" thick footing; bending and one-way shear are fine, but the D/C for punching shear is 1.30.

My thought would be to drill and epoxy dowels at 8" oc each way and pour the remaining 6" of concrete.

How would you handle this?

Thanks!

 

[DaveAtkins]

I agree with your approach. Even if you don't say the footing is now 2'-6" thick, you can say the 6" layer spreads the load out, allowing you to use a larger b_o to check punching shear in the 24" layer.

DaveAtkins

 

[KootK]

I agree that you could do it as proposed with the dowels designed for horizontal shear transfer. If there's space available and the footing works in all respects other than punching shear, it might be more economical to pour a plinth between the column and footing to enlarge the punching shear perimeter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[cliff234]

This is probably too complicated, but how about a big steel baseplate? bolt the plate to the footing with adhesive anchors and grout solid below plate. Weld dowels to the plate. Pour column.

Another idea. Can you make the column bigger?

 

[jayrod12]

it might be more economical to pour a plinth between the column and footing to enlarge the punching shear perimeter.

What do you feel is the difference between just pouring the 6" and specifically a plinth? Some vertical bars and horizontal ties?

 

[dik]

Don't you need horizontal bars to transfer the column load to the new topping?

Dik

 

[KootK]

What do you feel is the difference between just pouring the 6" and specifically a plinth? Some vertical bars and horizontal ties?

I was thinking mainly of the economic difference between 324 drill and epoxy dowels for the over pour and 8-12 for the plinth. Just trying to be contractor friendly. Technically, I see it as just another version of the larger column alternative.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Koot, we're on the same page then. I was thinking some localized drilled bars at the column location to ensure horizontal shear transfer in the immediate area of concern. Outside of the 3-4 foot square of the column, I don't see the need for horizontal shear transfer if the reduced depth footing works in bending and one-way shear.

 

[hokie66]

The way your original post was worded, I thought the column was already in place. But if not, your approach seems fine to me.