Answer:
If the horizontal force does not act in the shear center so torsion occurs, it is necessary to use the secondary torsional moment M_xs 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 M_xp 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.
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