Critical section of shear falling outside the pile cap 1

[MSUK90]

Hi Everyone,
I was recently checking a pile cap and when I tried to check one way shear at distance 'd' from face of column, the section falls outside the pile cap. How can I check shear in pile cap in such situation? Similar way, what if the punching shear perimeter also falls outside the pile cap?

 

[jayrod12]

Then neither of those failure modes will govern. You've essentially got direct load transfer through the pile cap to the piles.

Perhaps posting a sketch with proportions would aid the discussion.

 

[BridgeSmith]

Dislaimer: The following is based on the approach to one-way shear and punching shear in the AASHTO bridge design spec. Other codes may have differing provisions.

Visualize a truncated cone or pyramid section starting at the perimeter of the column or rectangular shaft, respectively, and extending down and out at a 45⁰ angle to the bottom of the pile cap. The faces of the cone or pyramid are your shear failure surface (where the concrete will theoretically break in shear).

If the failure surface for shear is interrupted by an edge of the concrete, the shear capacity will be reduced (because the area of the failure surface is reduced). However, if the top of a pile is inside of the shear failure limit (within the cone or pyramid), the load carried by that pile flows by direct compression through the concrete, to the column. Only loads applied outside the failure surface apply shear force to the failure surface. If you draw the failure surface and the top of a pile is half inside and half outside the plane, half of the pile reaction is applied to the failure surface.

A similar approach should be taken to check shear failure of individual piles. Notice that at a corner of the footing, the pile failure perimeter only has 2 sides.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[EZBuilding]

CRSI has a design guide which does further in depth to these items - it is categorized as deep beam shear and ratios the factor "2" in the concrete shear capacity equation up to "10" depending upon the ratio of depth of element to location of load application.

 

[r13]

If the segment is loaded, then check the shear at pile face. Otherwise, what to worry?

 

[canwesteng]

In this case, you should be checking using strut and tie methods instead of one way/two way shear provisions. You don't simply get to ignore the shear and call it ok.