Different principal shell stresses in Karamba

Hi everybody,

I’m working on a shell bridge made out of concrete. The goal is to optimize the thickness of the shell. For this I need my principal stresses of the shell. There are four loadcases so at first I used the shell view four times to see what the principal stresses are. This caused lots of time to make so therefore I tried to use the ShellVecResults. However these sigma1 and sigma 2 values differ from the ones out of the shell view component.

Is there somebody who can explain this difference?

I attached a picture to show the difference.

Hi @mlthesis2019,
the ShellVecResults-component returns the results at the element centroids.
For producing the rendering of the principal stresses one needs values at the vertices however. In Karamba3D these get calculated as a weighted average over the elements which connect to a given node. The weighting factor is the opening angle of an element divided by the sum of all opening angles at that node.
This is probably the reason for the deviation. With increasing mesh refinement the difference should shrink unless there are points with steep stress gradients.