Answer:
In the case of unsymmetric cross-sections (angles, Z-sections), main axes are inclined. The angle α describes the position of the principal axes u and v in relation to the standard axis system: This is the angle between the member axis y and the "strong" cross-section axis u. It is defined as positive if clockwise.
The resulting bending moments of an unsymmetrical cross-section are displayed in relation to the principal axes by default. Therefore, the descriptions Mu and Mv appear in the graphic and in the table. If you want to display the values of the moments related to the member axes y or z, the corresponding setting must be made in the Results navigator (see Image 01). The internal forces My and Mz are then displayed in the graphic and in the table.
The display of the principal axes can be activated in the Display navigator by selecting "Member Axis Systems x,u,v" (see Image 02).
