Two Way Shear

[joelperez]

Hi guys, I've been reading about how to calculate the Vu to check the Two Way Shear (Punching Shear)
in foundations. By definition the punching shear is "The shear force, Vu2, consists of all the net upward pressure, qu , on the hatched area shown, that is, on the area outside the part tending to punch out. In the expressions to follow,b0 is the perimeter around the punching area, equal to 4(a + d)", this pressure neglects the effects of the flexural moments at the base,why is that, because the pressure would be different if the moment are taken into account.

 

[atrizzy]

There is a method to account for the moments in punching shear calculation, and you should certainly do so.
Sounds like the method you're reading assumes no moment on the footing.

 

[joelperez]

Can you provide me a document with this method?

 

[HTURKAK]

IMO ,the definition is clear..for thickness design, the designer is expected to use the most stringent upward pressure looking to the applicable combinations.

If you want to check the stresses you may use ACI 318 Commentary R 8.4.4.2.3 .

 

[Agent666]

The ACI421 series of standards give a pretty good account of all things punching shear related. Though ACI318 also covers the assessment of moment in addition to axial load on the critical perimeter. I don't think it covers in great detail the corner and edge cases, but ACI421 covers these cases in more detail and provides plenty of example calculations.

https://engineervsheep.com

 

[dik]

FYI


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

and...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[joelperez]

Hi,dik and Agent666 these procedures that you mention are applicable for a flat slab supported by columns and a foundation that its going to be against the soil?

 

[Agent666]

They mainly address the slab supported by columns, but the only difference is another load from the soil. Just work out the resultant axial load and moment from the column and soil pressure resultants.

https://engineervsheep.com

 

[dik]

Yup... but, check the program to be comfortable with it...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

1) Yes to using the same moment transfer provisions for bending at raft joints as we do for elevated slab joints.

2) It has been my experience that designers will often ignore the base moments coming into the raft/footing joints from gravity columns. Some possible reasons for that:

1) Laziness,

3) Don't like the results.

3) For multi story buildings, axial load at the foundations tends to dominate strongly relative to base moments.

4) Often the raft slab will be designed assuming the column bases to be pinned.