Waffle slab design

[Gus14]

I Know that two way ribbed slab works by distributing slab loads to hidden interior beams ( bands ) that carry the load to columns this is easy to design manually for irregular columns layout. However, I don't understand how a waffle slab ( without interior hidden beams ) works. I know the Direct design method, but I don't understand how loads work their to columns. So what is the load path to columns ? and how to design it for irregular columns layout manually and check long term deflection ?

 

[KootK]

I find it most expedient to visualize a two way waffle slab as pretty much the same thing as a two way flat plate slab with with respect to how loads move around the floor deck. Just imagine a flat plate slab with bits of concrete chipped out between bottom bars to save weight. The Concrete Reinforcing Steel Institute has published some excellent guides on waffle slab design that you might look into.

 

[Gus14]

I am not comfortable with flat slabs either, what annoys me the most is not being able to check deflection manually, and that the ACI thickness ratios don't take the load into consideration and are strict to regular columns layout, which architects don't give a toss about.

 

[KootK]

In that case, I'd say that your first step would be to get comfortable with flat slabs.

I agree, there are not great methods for hand calculating the deflection accurately and that is frustrating.

 

[dik]

You design them as a standard plate, but with concrete removed... they are one of the most attractive concrete framing items, IMHO. I really like them... not common though.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Gus14]

The thing about flat slabs with irregular columns layout is that there are multiple possible load paths before failure that need to be checked ( I was hoping for something easier). But for deflection I will use a software and I will be conservative.

 

[dik]

Well aware of that... as far as deflections go... after 50 years, I still don't have a lot of confidence in long term deflections... same with creep. Your column location has to match the layout of the 'dome' forms to some extent. They are attractive... and I like them without ceilings... to expose them.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik