Non-linear analysis and cable elements


I’m quite new with Kiwi. Currently using it on a simple study case : steel trussed beam with lower external tie rods.

These tie rods are basically cables.

Linear analysis using only beam elements is pretty consistent, as the rod cross section has very small bending stiffness, behavior is close to cable. Resulting efforts N in the beams are consistent with some FEM (linear and non-linear) structural calculations.

But when trying to use ‘real’ cable elements in Kiwi, so running non-linear analysis (I suppose it’s a must with cable elements), axial forces results N are far from what I should get.

NB : a very low pre-stress was introduced for convergence purpose only

Maybe I missed some fine parametrization of the non-linear analysis ?
Otherwise I don’t get it.

I attach the gh file. (39.2 KB)



you have to use a load value that is in the range of the loadbearing capability of your structure (or adapt the cross section etc.). The nonlinear analysis is not converging. That’s the reason for the odd results. If you have to scale down the deformation in order to get a reasonable deformation, typically the deformation is to large for the real structure.
If you have moderately large deformations, the forces differ between linear and non-linear.
You can also use linear analysis with cables if they have only tension or as trusses under compression when using lines and refinement P=U=1

Hi Anna,

thanks for the quick answer.

The max. vertical displacement must be 6mm (for a 15m span), which is totally fair regarding loadbearing capacity.
It seems there is a 10^3 factor even in the linear analysis.

Are there defaults units embedded in the different section, material, load components ?
The Profile component unit input is supposed to be consistent with Rhino space or else ?

Also, is there a way to access shell window of solver (after solving) to check for convergence ?

Best regards,

You choose the units on your own. You can read more here:

Everything has to be consistent in your input.

The profile component input U enables the choice of the unit.

There is a file called out.log next to your grasshopper file. This contains the log of the latest analysis in this folder.