AS 3600 Concrete Shear at do or Face of wall

[Legoman92]

Hi Gents,

I don't do a lot of concrete design, reinforced concrete footings mainly. I was always taught to check "beam shear" in concrete at do from the support. While reading AS 3600 it says regarding checking shear near a support in the attached image. In regards to checking Shear at do from a support it says "the member is directly supported and diagonal cracking cannot take place at the support or extend into it" what exactly does it mean by "diagonal cracking cannot take place" ? My interpretation is that you take shear at the face of the support if no shear ligs are in the section? You can only take shear at do from the support if there's ligs present? Or is it regarding if the beam or slab is supported on top of the wall/column vs constructed into the side of the side of it?

 

[Just Some Nerd]

Have a look at the AS3600 commentary for a bit of elaboration/diagram. The quick and dirty way to think about it is that if you drew a diagonal cline from the face in the hanger case, there's no support beneath to stop a crack opening / slab falling downwards.

Regarding the sentence in the commentary on large concentrated loads near the support, there was another recent thread you might find helpful, see

https://www.eng-tips.com/viewthread.cfm?qid=502555

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Why yes, I do in fact have no idea what I'm talking about

 

[Legoman92]

Oh I see. So a slab cantilevering over a wall has a support underneath and hence can be taken at do from the support?

 

[Tomfh]

Yes, provided there are no concentrated loads within ‘do’ of the support, and provided any required shear reo is extended to the support.

 

[Legoman92]

Ok thanks guys