Initially, all cross-sections can be used for the calculation with warping torsion. If you have activated the Torsional Warping (7 DOF) add-on, further options are available in the dialog box for editing the cross-section properties. Chapter Sections of the RFEM manual describes the input dialog box and the most important options. This chapter describes in detail the properties relevant for the calculation with 7 degrees of freedom.
Warping Constant Iω
Once the add-on is activated, you can access the warping constant Iω cross-section value in the editing menu of the cross-section and in the cross-section input table. For a standardized cross-section, this is taken from the values in tables (if available). For all other cross-section types, the warping constant is calculated according to the selected analysis method according to thin-walled or thick-walled theory. You can find more information on this in the manual of the RSECTION program.
Similarly to the values for the shear areas Ay and Az, you can also manually adjust the warping constant Iω in the editing dialog box of the cross-section or in the input table of cross-sections.
Deactivating Warping Stiffness
After activating the add-on, the "Deactivate Warping Stiffness" option is available for all cross-sections. Activate this option for a cross-section to calculate members with this cross-section with only 6 degrees of freedom. The torsional stiffness then results only from the cross-section parameter It, and the warping torsion is not considered. The result output is also reduced accordingly.
Once the add-on is activated, the warping stiffness is activated automatically when creating new cross-sections. If the add-on is activated after creating cross-sections, the warping stiffness of all cross-sections is also activated.
This option is only relevant for members of the "Beam" type; members of another member type are generally only calculated with 6 degrees of freedom, and the warping stiffness is not taken into account.
Warping-Free Cross-Sections
For free-to-warp cross-sections, such as circular hollow sections or angles, the warping constant Iω is zero. The warping stiffness is automatically deactivated for these cross-sections. In the case of quasi-warping-free cross-sections, such as square hollow sections, the effect of the warping stiffness is small compared to the torsional stiffness. In the calculation, however, the warping stiffness is taken into account by default.
Determination of Internal Forces
The determination of internal forces is carried out according to the explanations in the chapter of the RSECTION manual. In the editing dialog box of the cross-sections, you can display the unit stresses according to thin-walled theory (denoted TWA) or thick-walled theory (denoted FEM). This allows you to understand the calculated stresses from all combinations of internal forces.
