When designing stability cores and sub-sections in the program SHAPE-THIN, there is the following issue:
The horizontal force does not act in the shear center. Therefore, I need to define a torsional moment to keep the component forces or shear stresses in the cross-section.
Do I have to use the resulting torsional moment as Mtsek or Mtpri?
If the horizontal force does not act in the shear center resulting in torsion, a secondary torsional moment Mxs needs to be used for a correct consideration.
Then, you obtain the shear components due to torsion Vy,k and Vz,k that act on the sub-section k and add to the component shear forces due to bending.
A primary torsional moment Mxp is to be applied, if the torsion from 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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Cross-Section Properties Software
Section properties, stress analysis, and plastic design of open and closed thin-walled cross-sections