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Deep Beam Shear in Pile Caps

Deep Beam Shear in Pile Caps

(OP)
Afternoon,

I've recently been involved in a few pile cap shear strength discussions and was wondering if anyone here had any additional insight on the topic.

Basically, I have a pile cap that qualifies as a "deep beam" per ACI 318-08 section 15.5.3 (specifically, it qualifies as the case mentioned in 15.5.4.3). Because my shear plane is overlapping my pile cross-section, the code is allowing me to take a reduced shear force (based on linear interpolation). Given these design parameters, my pile cap works as designed.

Now, there is some commentary, specifically R15.5.4, which states that some additional shear checks should be considered, which directs me to the CRSI Handbook. When you get to the CRSI Hnadbook, you see that there are many "Special Investigations" as denoted on page 13-24. One of these special investigations (#5) is 1-way shear at the face of the column. When I check my current pile design against the shear equations provided on page 13-26 (when w/d < 1), my pile cap design fails in shear (mostly because we're required to use the entire pile reaction for these calculations).

My ultimate question: Do I need to follow the CRSI handbook "special investigations" on deep beam shear in pile caps, or will simply satisfying ACI 15.5.4.3 be suitable. Ultimately, I need to verify a design done by another engineer, which did not take the CRSI special investigations into account.

Thanks in advance for your help

RE: Deep Beam Shear in Pile Caps

CRSI is in the process of publishing a new Design Guide on Pile Caps, which was prepared by Dr. Timothy Mays at the Citadel, in cooperation with CRSI, Deep Foundations Institute, and the steel pile and drilled shaft industries. In the process of developing this guide, if I am remembering correctly, ACI's concerns about shear were investigated and found to be sufficiently addressed by the current methods. There have been some minor changes to address certain conditions, but the "old" CRSI methods and cap designs were found to be conservative. The new guide also includes cap designs for larger H-pile sections. The new guide is not in on our store yet and I do not have a copy, but I will see if I can get a better answer later today.

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