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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.
AnswerIn most cases, these new elements only have to be added in the relevant add-on module. In Figure 1, you can see that the tick for "all" is not set and therefore new elements have to be added manually.
AnswerFor the design of steel surfaces please use the module of the same name RF-STEEL Surfaces. If you also want to consider local denting, then the additional modules RF-STABIL (to determine the bulge and branching loads) and RF-IMP (to determine the imperfection figure, based on the bulge pattern) are also recommended.
AnswerThe dimensioning of cold - formed, thin - walled components and sheets is possible as a finite element calculation with the following programs. Basic program RFEM + RF-Stable (determination of the branching figure) + RF-IMP (generation of the pre-deformed FE mesh for the proof of stability) + RF-STAHL surfaces (calculation of the second-order theory determined stresses on the pre-formed model).
AnswerSince the surface has been decomposed into components when creating a penetration, the components are now sized. The original surface is not taken into account in the design.
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.
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).
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