EC 2 and AS3600/ACI punching shear

[bratty]

EC 2 recommends the punching perimeter to be 2d from the column or pile edge as compare to d/2 in AS3600 or ACI.

1. Why the difference? Previously BS 8110 uses 1.5d and EC has further increased to 2d as compare to the AS 3600 remains at d/2 even in 2018 edition
2. In pilecap designs as the piles are closed to each other, this means using AS3600 or ACI will become a issue as compare to EC 2.


Any thoughts?

 

[Guest262653]

Just for reference, Model Code 2010 pushes back the control perimeter to d/2. The next iteration of EC2 will probably see major changes in punching and shear provisions.

 

[Agent666]

For reference NZS3101 also uses d/2.

I am guessing it derives from strut and tie considerations, min strut angle = ~25 degrees, which would result in about 2.25d. You will note figure 6.16 of EC2 that it notes theta > ATAN(0.5), which equates to a theta of ~26.5 degrees. Only a guess mind you!

 

[rapt]

Each code is different in the critical section location and method of calculating shear capacity, but you have to use the complete method from one code. The code writers will hopefully have calibrated their overall method with test data so that their overall method gives safe results.

ACI code uses 45 degrees for flexure shear also, while Eurocode uses a variable value depending on shear loading starting at under 30 degrees and up to 50 or 60 degrees as does Canadian MCFT, but again the overall methods must be used.

 

[bratty]

In this case, AS 3600 and ACI has to check the punching shear for every pile as shear perimeter is very close only d/2. But ignore in EC2 as punching shear of 2d from one pile overlaps with adjacent pile which also has its own 2d?

 

[rapt]

If the piles are that close together, the design is not a flexural member, it is a deep beam and requires strut/tie design. I would not have thought a flexural punching shear check would be required for a non-flexural member.

The loads are transferring from the load above to the piles below by diagonal compression struts.

 

[bratty]

Piles are about 2.5 to 5 pile diameter apart and I have seen designers trying to save material and they designed 400 to 450 thk pile cap thk. The pile spacing is disproportional to the thickness.