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Modeling question in etabs, What does a ribbed shell means?

GJoeRMK

GJoeRMK

Structural
Aug 19, 2024
18
Greeting fellows engineers, I am making a thesis about slab flexibility and so slab rigidity is an important topic to me.
I want to know what exactly does Etabs to shell element when I select the type as "ribbed". The manuals are very blurry in this topic to say at best.

Ribbed -- Specify the overall depth, the slab thickness, the width of the stem top and bottom, the rib spacing perpendicular to the rib direction, and the direction of the ribbing parallel to a specified local axis
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I found an article that claims that a ribbed shell elements mimics the orthotropic stiffness of the element if you select this type

Ribbed and Waffle objects: These objects can be used to model ribbed and waffle slabs. The generated finite elements have an orthotropic stiffness corresponding to the geometric data defined in the cross-section properties. The weight and mass of these objects are calculated excluding any lost formwork, so in these cases, the user must define mass and weight modifiers to account for the action of these non-structural elements. The design and detailing of these slabs also consider the geometric data of the cross-section.​
Click to expand...

If true, It would be counter intuitive consider that there is a material selection where is defined if an element has orthotropic or isotropic behavior.
I known for certain, that weights are exact to a ribbed slab. Also I did some modeling and found no correlation between a ribbed shell an a plain slab using an equivalent thick of the slab.
I shouldn't be guessing what something does in the model, if any has a deep technical inside for what Etabs does, please be free to talk, I truly wish to know your opinion.​
 
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