Are surfaces calculated as torsionally flexible or torsionally stiff plates in RFEM?
The surfaces in RFEM are calculated as torsionally stiff surfaces.
The only exception are the orthotropic surfaces. For these, you can influence the torsional stiffness (see figure).
In the "Edit Surface Stiffness - Orthotropic" dialog box, you can apply a multiplication factor to the stiffnesses of the orthotropic surface.