For a member with an unsymmetric cross-section, the load plane runs through the centre of gravity of the cross-section and not through the shear centre. Therefore, torsion resistance must occur. Why is there MT = 0 ?

Answer

In RFEM and RSTAB, loads are generally related to the shear centre. Therefore, an intentional torsion due to the section geometry (the centre of gravity unequal to the shear centre) is not considered. The graphic with the system line (=centroidal axis) and the load applied to it can lead to a wrong conclusion.

In order to create the torsion due to a load, which does not act in the shear centre, it is thus necessary to apply an additional torsional moment (a load multiplied by the distance to the shear centre).

As an alternative, you can perform a calculation in the RF‑/STEEL EC3 Warping Torsion add‑on module. It is possible to apply the load in the centre of gravity here.

Keywords

torsion seventh degree of freedom warping torsion shear centre

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