Karamba3D Tension & Compression Shell faces

Hi everybody,

I am working with Karamba3D. I identified a shell using Kangaroo for the form finding that should work only on compression. I am analysing the shell with shells in Karamba. And I would like to identify which
faces are under compression and which one is under tension. Basically, I would like to be able to select the faces base on the compression/tension forces. How can I do it? Attached is the file.

Compression Tension Test.gh (137.3 KB)

Thank you
Gianfranco

You can check the utilization/stress values. Positive values are for tension, negative for compression.

edit: ok sorry I answered too quickly… the question might be a little bit more tricky than I first thought

Here I culled points with first principal stress values for the upper and lower layer of the shell (principal stresses are ordered by magnitude) that are lower than 0, i.e. negative.
This is, however, not necessarily the same as checking the utilization values, as utilization is defined as a ratio of equivalent stresses to yield strength (as far as I understood Karamba3D correctly). The equivalent stresses are depended on the failure theory (van Mises for ductile materials like steel, Rankine for brittle materials like concrete, and many others…)

…also, it would be interesting to see how you derived this shell shape, as it influences the structural behavior a lot.

Also keep in mind, that for “real” compression only shell, many factors have to be met - one of them being a moment and shear free support. The current way you supported the shell induces shear forces near the supports.

Hope this is helpful!
Cheers, Rudi