Shear reinforcing pile cap
Shear reinforcing pile cap
(OP)
Folks,
I am required to design a pile cap where I am limited in depth and controlled by one way shear at "d" beyond the face of the column. I am using ACI prescribed value for Vc = 3.5 sqrt (fc').
Can anyone provide pointers to how shear reinforcing could be used to make up the difference needed to carry the shear through reinforcing?
I have looked in vain online for suggestions and I am sure someone here has done something similar.
I am required to design a pile cap where I am limited in depth and controlled by one way shear at "d" beyond the face of the column. I am using ACI prescribed value for Vc = 3.5 sqrt (fc').
Can anyone provide pointers to how shear reinforcing could be used to make up the difference needed to carry the shear through reinforcing?
I have looked in vain online for suggestions and I am sure someone here has done something similar.






RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
Also have you considered flat slab punching shear reinforcement if you can get any deep enough?
We need more info to give you better advice.
RE: Shear reinforcing pile cap
It is picking up 2 columns centered on the Pile cap.
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RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
Strength of the pile cap is not you major concern with this flexibility is!
The shallower you make it, the more load goes on the nearer piles and the less load goes on the farther piles. This always happens but it is small enough with the stiff pilecaps that it evens out with the soil. In your case you will make it much more flexible.
You have not said what the piles are bearing on, if it is rock then this is definately an issue, if soil it may be depending on the flexibility of the pile cap relative to the soil. Any deflection more than about 1/4" will have significant effect on pile loads.
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
It is on rock. I have a 7.5 ft thick pile cap which I want to try to reduce to 5.5 - 6'.
RE: Shear reinforcing pile cap
Make sure the stress cone covers the N/S outer piles.
RE: Shear reinforcing pile cap
For example, in pile caps for a tower crane foundation, there are embedments placed in the cap that can decrease your effective depth by 24". You may have a 60" thick cap above your piles but only a 36" thick cap at these inserts.
What I have done is similar to what the previous guy described as "band beams" (I think). Place your typicall bottom and top steel as needed for flexure distributed over the width and length of the cap, but a grid of stirrups in a cage over your piles. So in essence, the 2 top and 2 bottom bars over a pile will be encased by a stirrup and the top/bott bars between piles don't have stirrups. This should solve your punching/beam shear problems.
Stirrups are a pain in grade beams, but sometimes they're unavoidable.
RE: Shear reinforcing pile cap
You should check the deflection of the new pile cap.
RE: Shear reinforcing pile cap
Not clear what you mean by saying "Rigidity is even more important when you are on rock..". Why we need piles in such case - sound rock at footing level?
RE: Shear reinforcing pile cap
With soils there is a lot more give and the uneven loads tend to even out a little more because of the higher failure strains.
RE: Shear reinforcing pile cap
That is very informative. I have a subsequent question regarding distribution of reinforcement.
The ACI code requires T&S reinforcement of 0.0018 Gross Area. What is a good practice regarding distribution of this steel?
I does not seem appropriate to throw in all that reinforcing on the bottom of the cap and have no other reinforcing.
I have looked in ACI for requirements but found none. Would some skin reinforcing and top mat be placed on a deep pile cap (say 5' and deeper)?
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
Reinforcement layout depends on the loads exerted, if there is always a downward force then only bottom reinforcement should be okay.
for a good article on strut and tie go to:
http://www.gostructural.com/pg.asp?id=27
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap
RE: Shear reinforcing pile cap