To do this, use the "Orthotropic" stiffness of a surface in RFEM. In the K33 text box, you can specify factor D33 for torsional stiffness around axes x' and y' in the stiffness matrix.
Determination of Internal Forces for Plates: Torsional Stiffness
In a plate with full torsional stiffness, a significant part of the loads is transferred by torsional moments. If it is impossible to set the positive effect of this additional stiffness in the calculation (for example, due to a butt joint of a precast plate in the stiffness area), you have to reduce the torsional stiffness.
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