Waffle Slab Modelling

[Refaat]

Dear Colleagues

I am just wondering to know if there is any cautions when modelling the rib of waffle slab as single bar or as chain of smaller elements.

Which one of them is more recommended when model a waffle slab as panel with underneath beams?

Thanks in advance

Refaat

[Muhammed.OPERA]

Hi @Refaat

I think if the two of them is the same (of course if there's no difference between the chain of members sections or prop.)

I prefer one bar.

[Refaat]

Hi @ Muhammed.OPERA

" I prefer one bar."

Why do you prefer this approach?

 Mind that as I know the one bar is recommended when the bar is intended to design in provided reinforcement modulus. Knowing that the panel mesh for the second approach (chain of elements) is regular mesh which lead to high quality mesh results whereas the mesh of first approach (one bar) is totally irregular mesh .

That is why I just want to figure out which approach is recommended in order to design the bar in both (required & provided modulus and get perfect results of FE?

Refaat

[Rafacascudo]

Hi Refaat,

If the problem is the mesh , then use the "divide" tool to create nodes along the bar lenght without really dividing the bar in several pieces.
Then the mesh will "find " nodes the way you want /need

[Refaat]

Hi Rafael

I tried as you suggested. It seems doesn't work maybe I missed something. I have attached the dummy model.

Beside that which approach shall I follow to get perfect deflection and design results for frame elements (Beams).

Actually, I would like to design the beams in both modulus (required & provided).

Thanks in advance

Refaat

[Rafacascudo · Accepted solution]

Hi @Refaat

In this case ,marking regular mesh will generate identical (and very good) meshes on all your 3 options for this model. This way I think a single beam would be the better choice

[Refaat]

Hi @Rafacascudo

Perfect , I have to draw attention to that before posting this thread 

Because always we switch it ( Regular mesh option ) off.

Thank you so much .

Refaat

[Muhammed.OPERA]

Hi @Refaat

Sorry for the late respond.

as i can see the best is one bar as i said and i generate simple mesh with small element size , the program begin to generate mesh nodes along the beams with the element size. as Mr @Rafacascudo said.

The thing i'm asking now (as we are talking about waffle slabs), what's the best option for modeling waffle slab:

1- Model the ribs as rec. beams and the slab above.

2- Model the ribs as T- sec. as i design them and make a cladding with the loads above. 

[Refaat · Accepted solution]

Hi @Muhammed.OPERA

The best approach. It is Artur’s approach. On other hand in the static analysis stage the rectangular cross section can be used with increasing the factor stiffness in Y –direction (Iy) then in the design stage change back the cross section to T- shape.

Of course, we all thank Roman to create API macro to generate the stiffness factor. This micro is available in this link.

https://forums.autodesk.com/t5/robot-structural-analysis-forum/api-macro-creation-of-quasi-t-amp-l-r...

I highly recommend you to watch this webinar

https://www.youtube.com/watch?v=Pe8N_gCMA94&list=PLY-ggSrSwbZqow_60fiqJwS69mg1nQMzk&index=4

Refaat