overlapping critical perimeter of columns as per EC2 1

[geo321]

Hi,

I am designing a conic silo which has a foundation as per the attached. the dotted blue circles are the columns supporting the silo. The brown circles are the piles under the raft, having a thickness of 1200mm.
The design is conducted as per Eurocode 2.
When checking punching shear, and looking at the critical perimeter which is 2d from the column (drawn in yellow), all the critical perimeter overlap. How do you check punching in this case ?
Personally i think that no punching is to be checked ; only one way shear.
waiting for your comments
Thank you

 

[HTURKAK]

In your case , punching shear shall be checked at the column face and at d to 2 d from the column face.. You should check for probable punching scenarios and one way shear .. I tried to show two probable scenarios ( with red dashed lines )


EC - 1992-1-1 Relevant clauses ;


6.4.2 Load distribution and basic control perimeter

(2) Control perimeters at a distance less than 2d should be considered where the concentrated force is opposed by a high pressure (e.g. soil pressure on a base), or by the effects of a load or reaction within a distance 2d of the periphery of area of application of the force.










I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[geo321]

Thanks for your reply . Shouldn’t the eurocode specify a higher shear capacity when checking at less than 2d ?

 

[HTURKAK]

You are right !!!!!!! The relevant clause of the code ;

6.4.3 Punching shear calculation
......................
vRd,c is the design value of the punching shear resistance of a slab without punching shear reinforcement along the control section considered.
vRd,cs is the design value of the punching shear resistance of a slab with punching shear reinforcement along the control section considered.
vRd,max is the design value of the maximum punching shear resistance along the control section considered.
(2) The following checks should be carried out:

(a) At the column perimeter, or the perimeter of the loaded area, the maximum punching shear stress should not be exceeded:
.........




At the column perimeter, vEd < vRd, max

I hope this respond answers your question..













I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[geo321]

Thanks again Hturkak. But i want to make sure that i dont need any punching shear reinforcement; i verified that along the column perimeter, the stresses are less than vrd,max. The thing is that the Eurocode should give additional capacity for sections located between the column perimeter and 2d. Any thoughts please ?

 

[HTURKAK]

True !!!

The steps for punching check ;

- Check that the maximum punching shear stress is less than the maximum punching shear resistance at column perimeter

vEd < vRd, max

- Check for other critical perimeters. It should be found with iteration , but it is checked at d and 2d.
The concrete punching shear capacity vRd (without shear reinforcement) will be determined from 2d*vrdc/a
( a= distance from the periphery of the control perimeter considered )

- If vEd < vRd no punching reinforcement required.


I will suggest you to look ;

- How to Design Concrete Structures using Eurocode 2 (cement and concrete industry publication )

- EUROCODE 2 COMMENTARY ( Europian concrete platform )

- Reinforced Concrete Design to Eurocodes (By Prab BHATT )








I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[geo321]

"The concrete punching shear capacity vRd (without shear reinforcement) will be determined from 2d*vrdc/a". This is what i am looking for. Can you tell me your reference please? It is somewhere in the EC or in the books you mentioned ? Many thanks again )

 

[HTURKAK]

Sorry but you are asking basic knowledge .. Probably it would be better to ask the services of an experienced design engineer..

Pls look code 6.4.4 Punching shear resistance of slabs and column bases without shear reinforcement

and equation (6.50)..







I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.