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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

RE: AS 3600 Commentary on Punching Shear

I'd be happy I over-designed punching shear situations.

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

RE: AS 3600 Commentary on Punching Shear

AS3600 does not define a method of calculation of a Shear Head. It is not simply some ties added.

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

(OP)
Thanks for your reponses.

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

It has to be designed as a Shear Head. Not just ties added using the normal shear formulae. AS3600 doers not define a calculation method for Shear Heads.

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