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Frequently Asked Questions (FAQ)
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AnswerIn the RF-/STEEL add-on module, an equivalent stress design is performed according to von Mises. An elastic stress design (EL-EL) is to be made. In RF-/STEEL EC3, a classification is carried out before the design. If the cross-section is classified as class 1 or class 2, the design is performed against plastic limit internal forces. An EL-PL design is performed. If you do not want to use the plastic load reserves, you can switch the design to EL-EL in the details of the RF-/STEEL EC3 add-on module. The results are then comparable with RF-/STEEL.
AnswerIn this case, it is worth taking a look at the stress points in the cross-section details. If they are not accessible (grayed out), no stress points have been defined in SHAPE-MASSIVE and a design is not possible. In SHAPE-MASSIVE, the option "Stresses in stress points" must be activated in the general data. After recalculating and saving, the cross-section can now be designed in the RF-/STEEL add-on module.
Cross-sections assigned to class 1 or 2 are designed plastically by RF-/STEEL EC3 by default. In order to be able to compare the results with RF-/STEEL, please activate the elastic design of class 1 and 2 cross-sections (Figure 2) in the Details of RF-/STEEL EC3.
Please also check whether the partial safety factors γ for the resistances of the cross-sections are defined identically in both add-on modules (Figure 3 and 4).
AnswerMembrane, bending or other stresses can be switched on using the Details icon in RF-STEEL Surfaces.
AnswerThe RF STEEL Surfaces add-on module is responsible for performing an elastic stress analysis for surfaces. A fire resistance design is not implemented, but can be carried out by manual adjustment of the stiffness in RFEM and by adjustment of the yield strength in the add-on module.
I am trying to compare a design for flexural buckling according to the equivalent member method and internal forces according to the linear static analysis with a stress calculation according to the second-order analysis including imperfections and obtain very large differences. What could be the reason?
AnswerWhile the influence of imperfection increases significantly with increasing axial force and the design increases exponentially, it only increases linearly in the equivalent-member design to the increase of the axial force. Therefore, very strongly and very weakly loaded systems usually deviate more strongly in the ratios of the linear static analysis by means of equivalent member methods compared to second-order analysis by means of stress design.
AnswerIn RF-/STEEL, the stresses are calculated on stress points of the cross-section. The stress points defined for the cross-section can be displayed in the details of the cross-section. For the cross-section displayed in Figure 1, stress points are defined along the section. Thus, stress points (here stress points 1 and 9) are also present at the curves.In SHAPE-THIN, you can only calculate stresses on elements. It is not possible to calculate stresses for point elements with which irregularities in the cross-section geometry such as roundings etc. are displayed. The stress points of the SHAPE-THIN cross-section are displayed in Figure 2. Thus, cross-sections with point elements may show minor variations in stresses due to different stress points.Furthermore, in SHAPE-THIN you can calculate the stresses for the most unfavorable element edge or only for the member centerlines. In RF-STEEL, the stresses are calculated exclusively on the stress points.
This behavior is caused by the detail settings in the RF-/STEEL add-on module. The results of result combinations can be used in many different ways.To use the same maximum internal forces for stress analysis, the settings should be made according to Figure 01.However, this setting is very conservative because not all maximum internal forces can occur at the same time.
The 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 flats
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, it is only necessary to add these new elements in the relevant add‑on module. Figure 01 shows that the "All" check box is not selected and therefore, the new elements have to be added manually.
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