Gridshell : local coordinates issue


I am form-finding an elastic timber gridshell with rectangular sections,

When trying to introduce bending hinges, I realized that local coordinate systems of elements are not updated during the process (Z vectors are kept verticals) and that my hinges behave badly.

Can anybody help me ? Many thanks in advance !

Karamba Gridshell - orientation, joints, (98.9 KB)

Hi Sebastien,
the beam orientations are already defined automatically in the same way that you tried to defined them - flat beams - Z direction is usually the global Z axis, for vertical members, the x direction of the beam is already at the global Z direction. Therefore you do not see any change in the orientations. Turn the local axes in the ModelView component to visualise the axes of the beams.

Dear Matthew,

In fact I was not able to display local axis neatly with ModelView, so I both disassembled the model and used “orientate” components to retrieve them

Anyway, as you can see after large deformation I end up with local Z colinear to global Z ; I was expecting rotations of local planes and sections during the process !

Also when releasing Rx at some beam ends, I rather get a Ry release behaviour !

Do I rather use AnalysiseNonlin solver (I could not managed to make it work here) ?

Many thanks in advance for your help

Dear @sperrault,
at the moment (Karamba3D 1.3.2.) the ‘Analyze Large Deformation’-component only updates the position of the endpoints of an element but not the rotations of the local element coordinate system (see details here).
In case of beams this means that the local X-axis points in the correct direction whereas the local Y- and Z-axis do not. The latter two get calculated in each load-increment based on the usual conventions applied in Karamba3D (see here) or a user-defined beam-orientation.
You could try the geometric non-linear analysis (see here) however it is still work in progress.
– Clemens

HI Clemens,
Thanks for the explanation; I guess I misunderstood this part of your manual : “The local coordinate system of each element gets updated along with its positions”

Would you please provide some guidance on my attempt apply NLA here ?