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Frequently Asked Questions (FAQ)
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AnswerThe stress calculations are performed on the stress points of the cross-section.
Cross-sections of cross-section types
- Flat steel
- Square Steel
- Hexagonal steel
- Octagonal steel
- Wide flat steel
If a member with one of these cross-sections is subjected to the design by shear force or torsion, the solid cross-sections should be selected.
AnswerYou have to create a custom cross section (see picture). Afterwards the stress points with all necessary values have to be indicated. After successful entry, stresses in the additional module STAHL be calculated.
AnswerThe DUENQ cross-section consists of several non-contiguous partial cross-sections, so that in DUENQ it is calculated according to the theory of stiffening systems. DUENQ also gives a hint before the calculation. The dimensioning of such cross sections is not possible in add-on modules such as RF / STEEL EC3, RF / ALUMINUM etc.In most cases, however, the cross-sectional parts should be connected to each other. The FAQ describes how this connection can be modeled.
One or more stress points of the cross-section have a thickness that is not covered by the material properties. Therefore, the add-on modules cannot go back to the yield strength for the design and display the warning.
Please select another material that covers the thickness range, or change the thickness range of the existing material.
AnswerFor general cross-sections, also including SHAPE-THIN cross-sections, the elastic design can only be performed in RF-/STEEL EC3: Plastic interactions are only applicable to a few cross-section shapes.
I have modified cross-section properties or reduced stiffnesses of a members in RFEM/RSTAB. After a new calculation, the deformation of the structural system has adjusted itself to the new cross-section properties. However, this change is not taken into account when performing design in add-on modules.
In principle, the modified cross-section properties are not transferred into add-on modules, such as RF‑/STEEL or RF‑/STEEL EC3. They are only used for the calculation of internal forces.
In the add-on modules, stresses are calculated using the real cross-section dimensions, which cannot be modified. This would be difficult to implement as many designs require the element width or height and due to the modification, it is not known which parameter has been reduced exactly. This is important for the c/t-designs in RF‑/STEEL EC3, for example.
There are several ways to apply reduced allowable stresses. In the STEEL Members and RF-STEEL Members modules, you can activate the Manually option in table column 1.2 in the "1.2 Materials" window (see Figure 01) and then modify the limit stresses in the following table.
Alternatively, you can create a user-defined material in the material library for which you specify the material properties (yield strength and strength) individually (see Figure 02).
If a different cross-section is used in the add-on module than in RFEM / RSTAB, it is displayed in blue. It should also signalize that the internal forces are determined with the cross-section defined in RSTAB / RFEM (in Figure 01: IPE 300), but the design is carried out in the add-on module with the cross-section assigned there (see Figure 01: IPE 80). The cross-sections have different cross-sections if the cross-section in the add-on module has been modified manually or optimized by the program.
You can either read the cross-section from the RFEM / RSTAB again (select "Edit → Import Cross-Section from RFEM / RSTAB") or transfer the cross-section of the add-on module to the main program (menu "Edit → Sending Cross-Section to RFEM / RSTAB", see Figure 02). And. The cross-sections are then identical again and are displayed in black.
AnswerThe cause lies less in the defined cross section, but rather in the material characteristics. The yield strengths and limiting stresses are stored there as a function of the component thickness. An unacceptability results when the thickness of a cross-sectional part is greater than the existing thickness range.
To fix this, you have the following options:
1) You can create another thickness range with the appropriate voltages in the mask 1.2 "Materials" module-internal
2) Alternatively, you can select a different material with suitable thickness ranges in the library of RSTAB / RFEM
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.
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