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Frequently Asked Questions (FAQ)
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AnswerThat is correct. For the verification of the relevant components, these must be defined as rod sets and selected for design. It is also important that in the design case of the wölbkraftanalyse no bars are selected for the dimensioning, which are either already included in the staff sets or claimed to torsion, since the module RF- / STEEL EC3 then want to measure these by means of replacement rod method and this possibly no proof due to the torsion is possible and the warning appears.
Nodal supports and boundary conditions are preset, but not imported. As a rule, you have to adjust them.
In the case of the General Method for the set of members design in RF‑/STEEL EC3, nodal supports phi_x ' and u_y' are predefined at the set of members start and end, which represents a support with torsional restraints for all straight sets of members.
In RF-/STEEL Warping Torsion, nodal supports u_x, u_y, u_z, and phi_x are always predefined at the set of members start and end.
Please check whether you have selected sets of members for the design in General Data: The module extension RF-/STEEL Warping Torsion is only possible to use for the set of members design, not for members.
This warning appears because the torsion is not considered in the equivalent member design of Eurocode.
You can either neglect the torsion at your own discretion and on your own responsibility by setting the limits in the 'Details' dialog box, 'Stability' tab, or perform the stability analysis for open cross-sections according to the second-order analysis (while
To display the mode shape, the calculation must be successfully performed. If this is not possible, there are either invalid boundary conditions or no stability problem was found (convergence not reached). No critical buckling shape can be considered then.
Check the preset support in warping torsion: the supports hold on to the respective set of members at the start and end nodes in the local x‑direction (see figure). Thus, the support 'clings' to the upper support and tension force is calculated and no stability problem is possibly found.
Release the support at the column head in the local x‑direction.
No, they are not. In RFEM/RSTAB or the RF‑/STEEL add‑on module, the warping torsion does not play a role. For members, the warping resistance has no effect here.
RF‑/STEEL calculates torsional stresses close to reality by using MT/WT or MT/(IT/z). With this approach, the warping torsion (primary and secondary torsion or warping bimoment) is not considered.
The warpage is considered in the add‑on modules RF‑/FE‑LTB, RF‑/STEEL Warping Torsion and the cross-section properties program SHAPE‑THIN.
RF-/STEEL Warping Torsion is an extension of the RF‑/STEEL EC3 add‑on module. It performs lateral‑torsional (flexural-torsional) buckling analysis of members according to the second‑order theory with 7 degrees of freedom and application of imperfections with regard to mode shapes. The designs are based on the standard EN 1993‑1‑1:2005 + AC:2009.
Find more information in the webinar 'New Modules RF-/STEEL Warping Torsion and RF-/STEEL Plasticity', that you can download under Links below.
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.
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