Layers of hollow panel overlap

Dear Karamba3d staff,
I am trying to simulate a three-point bending test on a rectangular shaped hollow panel with support conditions and applied load as shown in Figure 1. When I perform the structural analysis, the two shell layers orthogonal to the applied forces behave as independent layers, and they penetrate each other (overlap), as shown by the deformed configuration in the Figure 2 attached. How can I model them to behave as a single element?
Thank you in advance.
Figure 2
Figure 1

Hi, to make the two layers work together you need to introduce shear stiff connectors. This can be done e.g. via springs (see 3.3.3: Spring Cross Sections - Karamba3D 2.2.0).