Answer:
If the horizontal force does not act in the shear center so torsion occurs, it is necessary to use the secondary torsional moment Mxs for correct consideration.
Thus, you obtain the shear components due to torsion Vy,k and Vz,k that act on the partial cross-section k and contribute to the component shear forces due to bending.
The primary torsional moment Mxp should be applied if the torsion due to the bracing system does not originate from the horizontal force (with a distance from the shear center), but directly from the acting torsional moment.
