Footing Punching Shear Reinforcement
Footing Punching Shear Reinforcement
(OP)
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?
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?






RE: Footing Punching Shear Reinforcement
Otherwise, 'collaring on a new column "wrap"' seems feasible, but why would you have to shore up the column to do this? (BTW I don't know what 'bo' is)
RE: Footing Punching Shear Reinforcement
BA
RE: Footing Punching Shear Reinforcement
bo = body odor
You're welcome.
RE: Footing Punching Shear Reinforcement
BA
RE: Footing Punching Shear Reinforcement
BA
RE: Footing Punching Shear Reinforcement
It sounds like he needs bo to be larger to make the punching shear work.
RE: Footing Punching Shear Reinforcement
BA
RE: Footing Punching Shear Reinforcement
Kudos to abusementpark for explaining bo or b0. Collaring onto a steel column may work although I have about 1000 kips to transfer into it.
As for shoring, my intent was to relieve load on the footing to install the repair, although, I can see the collar working without shoring.
RE: Footing Punching Shear Reinforcement
One other idea that I thought of is what I did on an old steel fabrication plant once, where the spread footings were inadequate. We drilled holes through the footing vertically - around the column - and drilled in auger cast piling. The tops of the piling were mushroomed out directly beneath the existing footing to serve as a sort of in-ground capital to engage the existing footing.
For your case, the added piling would increase footing capacity (in terms of the soil) and also perhaps negate the shear issue since you could probably get the piling close enough to the column where shear wouldn't matter.
RE: Footing Punching Shear Reinforcement
Does anyone care to elaborate?
Thanks.
RE: Footing Punching Shear Reinforcement
RE: Footing Punching Shear Reinforcement
RE: Footing Punching Shear Reinforcement
You could use gunite to increase the column size if that would help. If you are adding several stories it would seem that there would be more questions than punching shear in the footing.
RE: Footing Punching Shear Reinforcement
BA
RE: Footing Punching Shear Reinforcement
In the Canadian Code, if the face of the column is less than 5 x d from the edge of the slab, then that face shall not be effective in resisting punching shear.
However, for foundations, more often than not, the pier is less than 5 x d from all edges of the spread footing. Does this automatically rule out punching shear from governing or should I check for punching shear assuming all faces are effective?
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: Footing Punching Shear Reinforcement
RE: Footing Punching Shear Reinforcement
Yes, punching shear is not the only issue, although I have repairs in mind for the underreinforced footing and soil bearing issue.
I suppose I would need shrink reducing agent in my mix, if I were to use a concrete collar. Also, I'm curious if the adhesive anchors would relax to much during loading that would make the collar (steel or concrete) ineffective. Perhaps, the movement is negligible.
Thoughts?
RE: Footing Punching Shear Reinforcement
I would think roughening the contact surface would be a good idea as well as headed studs epoxied into the column.
BA
RE: Footing Punching Shear Reinforcement
Did you test for the concrete strength? 6 ksi is a lot for a foundation.
RE: Footing Punching Shear Reinforcement
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
RE: Footing Punching Shear Reinforcement
(Just curious, if it's irrelevant please feel free not to answer...thanks)
RE: Footing Punching Shear Reinforcement