## How to calculate punching shear stress?

## How to calculate punching shear stress?

(OP)

Hi,

I've found this document from CSI SAFE software, set out the procedure to calculate

punching shear stress that involves unbalanced moments.

https://files.engineering.com/getfile.aspx?folder=...

but it has limitations that the shape of the critical punching sections has to be parallel to X or Y axis.

What is the procedure that you would follow to calculate the maximum punching shear stress for a circular shape or a shape that has an edge not parallel to X or y-axis?

Thank you in advance.

NTCOnline.

I've found this document from CSI SAFE software, set out the procedure to calculate

punching shear stress that involves unbalanced moments.

https://files.engineering.com/getfile.aspx?folder=...

but it has limitations that the shape of the critical punching sections has to be parallel to X or Y axis.

What is the procedure that you would follow to calculate the maximum punching shear stress for a circular shape or a shape that has an edge not parallel to X or y-axis?

Thank you in advance.

NTCOnline.

## RE: How to calculate punching shear stress?

For example

600 diameter column and 200 thick slab,

Circular punching shear area = pi*(0.6+0.2)*0.2 = 0.502m^2

Equivalent square column (0.502 m^2/0.2)/4)-0.2= .427m therefore I would run the calcs based on a 400 square column to be conservative.

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

Also fib 12 guide also has quite a bit of stuff relating to review of various standards and in particular some stuff on circular columns and how they are treated by various standards around the world.

Otherwise do what Rapt noted as this is the "code approach" for any irregular section/punching shear perimeter, I can't imagine its that hard and is somewhat analogous to finding the polar moment of inertia for weld groups (I think...famous last words perhaps...). Report back if you go this way to compare with other assumptions.

## RE: How to calculate punching shear stress?

## RE: How to calculate punching shear stress?

But i would assume you can use it directly for any irregular section taking the critical width equal to the widest(?) part of the critical section. For a circle or a square the ratio of b1/b2 is obviously the same anyway if taking the widest location stands true, so the ratio of moment being transferred by flexure or by eccentricity of shear is the same whether you take a circle or equivalent square.

## RE: How to calculate punching shear stress?

I agree that we should be able to calculate the Polar Moment of Inertia of the shear plane for any shape. However, the textbook calculations usually assume the axis of torsion is perpendicular to the section. So I am quite unsure for the case where the axis of rotation is not perpendicular to the section, which is quite often the case in punching shear (one shear plane might not be perpendicular or parallel to the bending axes)

Maybe I should project the shear plane to the plane that perpendicular to the rotational axis, and go ahead and calculate the torsional constant J of the projected plane? Does this sound reasonable?

NTC

## RE: How to calculate punching shear stress?