One way shear in a pile cap 1

[wakeboats]

What force should you use to check the one way shear in a pile cap? The sum of the actual pile reactions outside the critical section, (max pile reaction)*(# piles outside the critcal section), or something else? FYI there is biaxial moment on the pile cap.

Thanks

 

[johnbridge231]

If biaxial moments are developed, you should perform your design considering their interaction with the normal axial forces.
This software might be helpful for that case.
As for the shear check, you can assume the pile cap as a continuous beam and plot its shear force diagram considering the calculated reactions of each pile. Then you should check every section along its length.

Regards

 

[wakeboats]

Let me clarify. I probably should have called it a pile footing rather than a pile cap. It is a 16' x 21' footing with piles in a rectangular pattern embedded into it. The reason why I said the footing has biaxial moment was so that you would know that there was a linear variation in the pile reactions in both directions. My question is what value do you use for "Vu"? Do you use the actual pile reactions that are outside the critical section in the direction you are checking one way shear, or do you use the (max pile reaction outside the critical section)*(# of piles outside the critical section) or do have some other way to calculate the shear?

 

[BAretired]

If there is a linear variation in pile reactions in both directions (not sure why there should be), I would take the sum of the loads outside the critical section and correct for the torsional shear stress caused by the lack of symmetry.

BA

 

[UcfSE]

Use the pile reactions outside the critical section, cut in two orthogonal directions and cut diagonally across the pile cap whatever critical ways you can think of. Personally, I use the pile capacities instead of reactions.

 

[amec2004]

Attached PDF file contains the full pilecap design examples, from 2-pile pilecap to 9-pile pilecap, in Canadian CSA A23.3-04 code. The ACI 318 code version should be fairly similar.

After going through all the examples in attached PDF file, you will know what force should you use to check the one way shear in a pile cap.

anchor bolt design per ACI 318-11 crane beam design

http://www.civilbay.com

 

[wakeboats]

Thanks amec, this is exactly the kind of thing I was looking for. From the examples it looks like you use a critical section that is located at distance of "d/2" when checking the individual pile one-way shears, but use a distance of "d" when checking the column one-way shear. Why are you using the different distances? I would have thought you would just use "d" for both the pile and column one-way shear check.

Thanks

 

[amec2004]

>>From the examples it looks like you use a critical section that is located at distance of "d/2" when checking the individual pile one-way shears, but use a distance of "d" when checking the column one-way shear. Why are you using the different distances? I would have thought you would just use "d" for both the pile and column one-way shear check.

From the first impression it seems we shall use d for one-way shear check, for both [red]corner[/red] pile and column case.
I highlighted [red]corner[/red] pile in red and the answer is the in the [red]corner[/red] word.

--> Column one way shear check refers to CSA A23.3-04 13.3.6.1 which uses d
--> Corner pile one way shear check refers to CSA A23.3-04 13.3.6.2 which uses d /2

I check through ACI 318-11 and find there is on specific one-way shear definition similar to CSA A23.3-04.

ACI 318-11 quotes corner column in clause 11.11.1.1, which used d/2. The one-way shear check in ACI 318-11 is same as beam shear check, which shall refers to clause 11.2.1.1, in this beam shear case, d shall be used.

From above comparison, the use of d/2 for corner pile one-way shear check and use of d for column one-way shear check in my spreadsheet is correct !

Please refer top attached PDF file for more details.

anchor bolt design per ACI 318-11 crane beam design

http://www.civilbay.com

 

[wakeboats]

amec, I have the 318-08 code and I can't find any special provision for corner columns with reguard to one-way shear. But I'll assume that your reading between the lines of the ACI code due to your previous experiences with the CSA code.

Getting back to one of my intail questions. In your examples the column has no moment on it, so all of your piles have the same reaction. If your column had biaxial moment on, so that each of the piles had a different reaction. Would you still use the actual pile reations even though that would put a much higher level of shear on one side of your critical section? Or would you conservativly take your max pile reaction and multiply by the number of piles outside the critcal section and use this for "Vu" in the one-way shear check?