Concrete columns strength vs footing strength 2

[serhatk]

Hi All,

I was wondering if any of you are aware of a provision that limits the concrete strength for footings supporting columns (and walls) of concrete strength 10 ksi. Can I specify 3 ksi concrete footings?

Thanks.

 

[dik]

Check confined bearing strength... and, why 10Ksi for walls... must be a huge load... need a whole bunch of dowels...

Dik

 

[serhatk]

Thanks dik, forgot the mention the walls I was referring to shear walls of a tall building. What do you mean by confined bearing strength?

 

[KootK]

If the walls are going to rock up on their compression blocks, then footing concrete strength will need to be sufficient for:

1) Bearing checks of the wall compression block bearing on the footing.
2) Punching shear checks of the wall compression block trying to punch through the footing.

If you can make those things work with your f'c discrepancy, then you should be okay. That's a pretty big discrepancy though.

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.

 

[serhatk]

Thank you very much for the answers, specifically I was wondering if there was something similar to the column vs slab concrete strength relationship as discussed in ACI 318 section 10.12 which requires puddling of column concrete within the slab concrete.

 

[KootK]

If punching shear works, I could see an argument for applying the 3/4 strength provision that you mentioned.

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.

 

[hokie66]

A footing is a slab, so the same rules apply. But the rules would not allow a 10/3 ratio. Puddling is impractical enough for slabs of large area, and is never employed for footings. You probably need to increase the strength of your footings to at least 4000 psi, maybe more, depending on the application of the code provisions.