Answer:
If you enter models in two-dimensional space, only cross-section rotation angles of 0° and 180° are allowed. The direction of the local axis system in the member (xyz) is clearly defined, and for 2D models, only the member internal forces My and Vz are calculated.
The major axis of the cross-section (y-axis) is always aligned in the direction of the global Y-axis; the minor axis (z-axis) is not considered at all (assumed to be completely immovable).
If cross-section rotations were allowed, double bending could occur, since the loads can only be defined in the XZ plane in 2D space. However, the resulting Vy, T, and Mz components would then not be taken into account. For this reason, only cross-section rotations are allowed where the local z-axis of the cross-section points into the XZ-plane.
Finally, we recommend entering a 3D model where any cross-section rotations are allowed.
