Australian Residential Slab - Waffle

[HozC1]

AS2870 says that for waffle on piers, not shear fitments are required for internal rib when piers are located on the intersection of every third internal rib.

With every third rib, the span is 3.6m. So for 85mm slab, the shear in internal rib can be around 25kN without having extra point or line loads. I wonder how a 110mm x 385mm rib without having shear fitments can take this much shear? (only about 9kN shear capacity according to my calculation)

 

[Enhineyero]

Not sure if you are aware that details of AS2870 are based on data and research. The starting point of the most standard designs (i.e. raft slab, strip footing) came from industry experience and documented research. Waffle slabs on the other came from extensive R&D by several Adelaide guys. Dimensions for waffle slab are based on test data and are likey pushing the limits of design.

Personally, I try to steer clear of it due to the above reason.

To answer your question, you may have to look-up their test data/research (I don't have a copy of this) and make your own judgement. If you strip away safety factors of AS 3600, increase capacity due to load distribution/redundancy, and increase capacity of shear friction/aggregate interlock/dowel action to unconservative levels you might come close to their test data.

 

[HozC1]

Thanks Enhineyero. Do you know what the title of that research is?
AS3600 reduces shear capacity of beams without ligs to 0.5Vu only so if I ignore this 0.5 reduction factor I can increase the capacity to around 20kN. But I am not sure if it is allowed. AS2870 says it is deem-to-comply for single storey while in my case I have some small line loads applied to waffle as well. So I have reduced to spacing to 2x3 rib to reduce the shear but still I don't know how to verify its capacity.

 

[Enhineyero]

Not sure if it is already available to the public as most of it is patented. Try searching Koukourou and Partners.