Minimum shear reinforcement in pile caps?
Minimum shear reinforcement in pile caps?
(OP)
Do ACI's minimum shear reinforcement apply to pile caps? I know it says that the minimum reinforcement requirements don't apply to "footings." Do pile caps fall under this category?






RE: Minimum shear reinforcement in pile caps?
RE: Minimum shear reinforcement in pile caps?
When the strut fans out more than 45 deg is when I start introducing shear reinforcement.
RE: Minimum shear reinforcement in pile caps?
>>Pile caps are normally designed by strut and tie methods
That's true, but the strut-and-tie is to replace flexure check.
You still have to check single pile punch shear, one way shear, two way shear.
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RE: Minimum shear reinforcement in pile caps?
No, the strut and tie method is a truss analogy approach, where a truss model consisting of compression and tension elements is used rather than a flexural model. Don't combine provisions for the two methods.
RE: Minimum shear reinforcement in pile caps?
RE: Minimum shear reinforcement in pile caps?
11.4.6.1 - exemption for footings and "solid slabs" (ie don't put any voids in you pile cap).
11.7 Deep Beam provisions (almost always apply regarding pile caps.)
11.7.6 use A.3.3 instead of providing shear reinf.
App A
A.2.5 - max angle between strut and tie = 25 deg. for a 4'-0" depth to bottom reinf, this gets us approximately 8'-0" from column to pile plan distance.
A.3.2.2 - b- allowance for no cross reinforcement
A.3.3 - Requires cross reinforcement if A.3.2.2 a was used (ie don't use a use b)
Back to the original question, yes the minimum shear requirements apply if you don't meet the exemptions (very useful to add for expensive excavations to minimize the pile cap depth). However, for standard pile cap designs, I'd recommend designing to the current CRSI manual so you don't go and reinvent the wheel.
RE: Minimum shear reinforcement in pile caps?
Does the strut have to emanate from the column? Or can you break up the strut-and-tie model like a truss with multiple panel points to the meet the 45 degree requirement?
Where does the 45 degree requirement come from?
RE: Minimum shear reinforcement in pile caps?
Are their designs based on the strut-and-tie method? Because it does not appear that they apply the minimum shear requirement to their designs.
RE: Minimum shear reinforcement in pile caps?
I read a good quote in a paper for strut-tie pile cap design.
"Unlike traditional design procedures, strut-and-tie models do not separate flexural and shear design; however it may be said that the "shear design" of deep members using strut and tie models involves limiting the concrete stresses to ensure that the tensile tie reinforcement yields prior to concrete shear failure".
The paper is called "Design of Deep Pile Caps by Strut-and-Tie models" and I found it by google search.
RE: Minimum shear reinforcement in pile caps?
It appears that they do not believe that the minimum shear provisions apply to pile caps.
RE: Minimum shear reinforcement in pile caps?
RE: Minimum shear reinforcement in pile caps?
Could you please share your resources/materials for S&T design of pile caps. I have come across a few for standard 4 PC's but nothing for multiple piles.
RE: Minimum shear reinforcement in pile caps?
RE: Minimum shear reinforcement in pile caps?
I did look, but there doesn't appear to be much in the way of published resources for design of pile caps with a lot of piles. Since it is essentially a truss analysis, it would be similar to the design of a spaceframe. Follow the forces. Sorry not to be of more help. In most cases, my approach has to use bigger piles rather than a larger number of piles.
RE: Minimum shear reinforcement in pile caps?
I can't say I have a real alternative, though.
RE: Minimum shear reinforcement in pile caps?
They would then increase depth as required to avoid shear reinforcement.
RE: Minimum shear reinforcement in pile caps?
Which provision of 15.5 are you referring to that says that "diagonal tension" can be neglected?
RE: Minimum shear reinforcement in pile caps?
RE: Minimum shear reinforcement in pile caps?
I think you are reading into 15.5.4.2 something that it doesn't say. It just means that if a pile is wholly inside a given section through a footing, then it doesn't contribute to shear on that section. That is quite obvious, but the reason for including the statement, along with 15.5.4.1 and 15.5.4.3, is to define how much shear is to be included when piles straddle a given section.
RE: Minimum shear reinforcement in pile caps?
For very thick pile caps, I use "shear reinforcement" but thats really the strut and tie requirement as well as an ACI publication.
I would also put flexural steel top and bottom if you have seismic loads.
RE: Minimum shear reinforcement in pile caps?
I don't think that ACI requires strut and tie for loads within d for a pilecap.