## AS 3600 Commentary on Punching Shear

## AS 3600 Commentary on Punching Shear

(OP)

Hi All,

Looking at punching shear, CL 9.2, concrete shear stress fcv may be taken as 0.5*sqrt(f'c) only if a "shear head" is provided - no further guidance or description on this is given. My understanding is that "shear head" in this context are open steel sections cast into the slab itself. I have always ignored this item, as I have never detailed steel sections to combat shear.

However, reading the AS 3600 Commentary on this section, it states that using closed ties, studs, or shear heads allows the use of 0.5*sqrt(f'c).

Depending on your beta-h ratio of the column,fcv can be significantly less than 0.5*sqrt(f'c) (limited to max 0.34).

Is using 0.5 when providing closed ties/other shear reinforcement unconservative? Or have I over designed my punching shear in the past having never seen this statement before/misinterpreting the definition of a shear head?

Any thoughts?

Thank you

Looking at punching shear, CL 9.2, concrete shear stress fcv may be taken as 0.5*sqrt(f'c) only if a "shear head" is provided - no further guidance or description on this is given. My understanding is that "shear head" in this context are open steel sections cast into the slab itself. I have always ignored this item, as I have never detailed steel sections to combat shear.

However, reading the AS 3600 Commentary on this section, it states that using closed ties, studs, or shear heads allows the use of 0.5*sqrt(f'c).

Depending on your beta-h ratio of the column,fcv can be significantly less than 0.5*sqrt(f'c) (limited to max 0.34).

Is using 0.5 when providing closed ties/other shear reinforcement unconservative? Or have I over designed my punching shear in the past having never seen this statement before/misinterpreting the definition of a shear head?

Any thoughts?

Thank you

## RE: AS 3600 Commentary on Punching Shear

Ancon seem to take a limit of 0.34*sqrt(f'c).

## RE: AS 3600 Commentary on Punching Shear

You would have to use the method in ACI318 for shear head design in my opinion as that is where AS3600 says the limit comes from.

## RE: AS 3600 Commentary on Punching Shear

Of course I'd be glad to have over designed for punching, but I'd be happier to understand by how much.

I guess what I'm really wondering is, is the AS 3600 commentary wrong where it states "Where shear reinforcement, in the form of closed fitments, shear studs, shear heads and the like, is provided, the value of fcv is taken as 0.5sqrt(f'c)." ?

## RE: AS 3600 Commentary on Punching Shear

## RE: AS 3600 Commentary on Punching Shear

## RE: AS 3600 Commentary on Punching Shear

The AS3600 shear design method assumes Torsion reinforcement, and shear studs cannot provide this, so the AS3600 formulae cannot be used.

AS3600 does allow the design of shear heads but gives no rules on it. So you would have to revert to another code for this, probably Canadian or ACI318.

## RE: AS 3600 Commentary on Punching Shear

## RE: AS 3600 Commentary on Punching Shear

https://www.ancon.com.au/products/punching-shear-r...

## RE: AS 3600 Commentary on Punching Shear

## RE: AS 3600 Commentary on Punching Shear

If it ain't broke don't fix it. The rectangular stress block approximation is older than that but still sees a lot of use.

## RE: AS 3600 Commentary on Punching Shear

## RE: AS 3600 Commentary on Punching Shear

AS3600 does not give a methodology for increasing shear strength using reinforcement like shear studs. The reinforcement referred to for increasing shear capacity is provided in a torsion strip and is defined as "closed ties". The logic is defined very clearly in the Commentary.

## RE: AS 3600 Commentary on Punching Shear

I guess in this case, we are all in agreement that the commentary is outright wrong with this statement?

AS3600 does not even define what a shear head is, however this clause of the commentary implies that a almost any type of shear reinforcement (closed ties/studs) can be considered a shear head, that can all take advantage of the increase shear stress capacity.

## RE: AS 3600 Commentary on Punching Shear

So Yes, the comment section is incorrect. Bus so is any assumption about AS3600 defining how to design a shear head.

It simply gives a method of defining torsion reinforcement to improve the shear capacity of the connection through increased capacity to transfer moment to the column.

Read the code. 9.2.2 - NOTE!