Footing Punching Shear Reinforcement

[Galambos]

I have an EXISTING 24"sq concrete column bearing on a 10ft sq footing, 30" thick, f'c=6ksi.

i am adding several stories above this footing on top of the existing 4 story structure, but i am limited by the punching shear capacity of the footing.

i wondered if anyone has any ideas to reinforce the footing for punching shear. i think that thicknening the footing with a composite topping wont work because the bearing stresses will still be founded below the new topping.

im trying to avoid shoring up the column and collaring on a new column "wrap" to increase bo.

any ideas?

 

[BAretired]

You could drill sloping holes into the footing all around the column into the truncated pyramid describing the punching shear failure surface under the column. You could then epoxy reinforcing bars in the holes with the top projecting up and away from the column.

A concrete collar, say 4'-0 x 4'-0 in plan would then totally enclose the sloping bars. The vertical component would assist in carrying the column load. The horizontal component would tend to improve the bond between collar and column.

Such bars would need to be totally developed below the punching shear failure surface.


BA

 

[engrbon]

Are you also going to increase the rebar area of the foundation due to additional loads?

(Just curious, if it's irrelevant please feel free not to answer...thanks)

 

[par060]

using ACI...if you say your "d"=27"....then bo is 312"....that would result in over 2200 kips....I think you might have issues with the 10x10 footing unless your on somethin really really stiff