#### Further Information

In addition to our technical support (e.g. via chat), you’ll find resources on our website that may help you with your design using Dlubal Software.

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• ### Is it possible to import the effective lengths from RF-STABILITY or RSBUCKEN in RF- / TIMBER Pro?

New FAQ 004113 EN-US

Yes, that is possible.

First, RF-STABILITY (or RSBUCK in RSTAB 8) can be used to determine the effective lengths for a particular structure and loading.

They can then be imported into RF- / TIMBER Pro in the "Effective Lengths" dialog box.

• ### Why are the equivalent member designs grayed out in the Stability tab when the plastic designs are activated by means of the partial internal force method (RF-/STEEL Plasticity)?

New FAQ 003582 EN-US

Since the equivalent member designs of Eurocode 3 have different interactions than are the case for the designs according to the partial internal forces method and a mixture of these different designs is not desired for reasons of clarity, RFEM deactivates the equivalent member designs when using the RF-/STEEL Plasticity add-on.
• ### In the RF- / STEEL EC3 add-on module, I have selected two braids of equal size for one beam to be designed in the "Parameters" window as the shear panel type. Accordingly, the beam should be supported laterally in the middle. Why is the eigenvector arbitrary?

New FAQ 003562 EN-US

The term "shear panel" indicates that the translational spring, which is created along the beam length by means of the shear panel type including the corresponding parameters, is smoothed, see Figure 1.

This is also the case for the shear panel type "Bracing", so that the mode shape always appears to be arbitrary at this location, see Figure 2.

In order to obtain accurate results, it is recommended to manually define a lateral support by means of a nodal support according to the general method (Figure 3) or to define the effective lengths according to the equivalent member method, including intermediate restraints, if necessary. Finally, a eigenvector with visible lateral restraint in the mid-span is created (Figure 4).

• ### What is the critical load factor and how is it possible to determine it?

New FAQ 003561 EN-US

The critical load factor specifies the factor by which you can increase a load until the system fails. If it is smaller than one, a calculation according to the second-order analysis is usually unstable because the system is already stressed by the critical load. This factor is also taken into account in standardization. For example, Eurocode 3 specifies that a calculation according to the second-order analysis is no longer necessary from a critical load factor of 10.
The critical load factor can be determined by the RSBUCK module or RF-STABILITY.
• ### Which programs and modules are suitable for the calculation and design of steel structures?

New FAQ 003551 EN-US

Both RFEM and RSTAB present a suitable solution. Numerous European and international standards, as well as various add-on modules, are available for both programs, which will facilitate the daily work in steel structures.

###### Basic programs RFEM or RSTAB
The basic programs RFEM or RSTAB define structures, materials, and actions. In addition to creating spatial frame structures, for example, halls, RFEM also provides plate, pane, and shell structures, making it a more diverse option. It pays off if it is necessary to carry out design also in other areas, such as solid construction.

###### Available standards
• EN 1993-1-1 (Eurocode 3),
• AISC according to ANSI/AISC 360 (US Standard),
• SIA according to SIA 263:2013 (Swiss Standard),
• IS according to IS 800:2007 (Indian Standard),
• BS according to BS 5950-1:2000 (British Standard) or BS EN 1993-1-1 (British Annex),
• GB according to GB 50017-2003 (Chinese Standard),
• CSA according to CSA S16-09 and CSA S16-14 (Canadian Standard),
• AS according to AS 4100-1998 + Annex 1 - 1999 (Australian Standard),
• NTC-DF according to NTC-RCDF (2004) (Mexican Standard),
• SP according to SP 16.13330.2011 (Russian Standard),
• SANS according to SANS 10162-1:2011 (South African Standard),
• NBR according to ABNT NBR 8800:2008 (Brazilian Standard),
• HK according to the standard for steel structures 2011 (Buildings Department - Hong Kong)
• RF-/STEEL - General Stress Designs
###### Add-on modules for structural steelwork

The functionality of the basic programs is supplemented by add-on modules. With RF-/STEEL EC3, for example, it is possible to perform the design for the structure according to Eurocode 3. The add-on module RF-STEEL Warping Torsion supplements this design according to Eurocode 3 with torsional buckling analysis having up to 7 degrees of freedom, provided it doesn´t refer to a standard case of EC3.

Other more specialized applications such as the plastic design, the stability analysis according to the eigenvalue method or the generation of geometric equivalent imperfections and pre-deformed equivalent models are available. Single modules such as PLATE-BUCKLING provide you with support when designing rigid or stiffened plates. With the SHAPE-THIN add-on module, it is possible to create any thin-walled cross-sections. The cross-section properties are determined and stress analyzes or plastic designs can thereby be performed.

The hinged or rigid connections can be designed by means of the RF-JOINTS add-on modules.

The stand-alone application CRANWAY is available for the design of craneways.

###### Dynamic analysis

If earthquake calculations or vibration analyzes are necessary for the building, the RF-/DYNAM Pro add-on modules provide suitable tools for determining natural frequencies and shapes, analysis of forced vibrations, generation of equivalent loads, or for the nonlinear time history analysis.

In case of having any further questions about the Dlubal software, contact the sales department, please.

• ### In RF- / STEEL EC3, I receive the error message saying that a node with supports does not exist in the set of members. What is the reason?

New FAQ 003524 EN-US

One support was defined at a node that is not part of the set of members in the window ‘1.7 Nodal Supports’ of RF-/STEEL EC3. In this case, it is necessary to define support at a node existing in the set of members or delete this nodal support in the window '1.7 Nodal Supports' of RF-/STEEL EC3.

In Figure 1, for example, a set of member supports was defined for the set of members 1 on nodes 2 and 7. When the calculation starts, the message 'Node No. 7 with support does not exist in the set of members No.1. Please correct this in Table 1.7.' appears (Figure 2, Figure 3).

In window ‘1.7 Nodal Supports’ of the RF-/STEEL EC3, it is possible to get displayed only the selected set of members by clicking the 'Show Only Current Object' button and the node numbering can be displayed by clicking the 'Local Coordinate System' button (Figure 4). It is obvious that the node 7 is not contained in the set of members. Instead of at node 7, the support must be defined on a node contained in the member set (for example, node 6).

• ### What is the meaning of the warning message ER061) Minimum amplifier of design loads <1?

FAQ 003491 EN-US

This message indicates that the critical load of the structure or the cross-section has been exceeded.

The causes for this are very diverse. Often, insufficient lateral supports have been defined in the STEEL EC3 add-on module.

It is also possible that the used cross-sections or the structure itself cannot be calculated according to the general method in EC3. This FAQ provides information about such a case.
• ### When designing a set of members by means of the equivalent member method in RF-/STEEL EC3, the calculation fails. The system is unstable delivering the message 'Non-designable — ER055) Zero value of the critical moment on the segment'.What could be the cause?

FAQ 003440 EN-US

Please check if all sets of members selected for the design are sets of members. The equivalent member method is only applicable for straight sets of members with a uniform cross-section involving, for example, no taper. In this case, use the preset General Method.
• ### I am trying to design an open, asymmetrical aluminum cross-section in RF-/ALUMINUM and receive the warning 'Non-designable — 1022) General Cross-section — Stability Check Is Not Available'. What is the reason and what can I do?

FAQ 003435 EN-US

The reason is that there is no stability analysis for unsymmetrical, open cross-sections according to EN 1999-1-1 when the compressive normal forces and the bending moments are effective.
You can neglect the bending moments in Details in the Stability tab by selecting a filter. Then, the flexural buckling design is performed without moments. However, this is under your own responsibility. An alternative is to use a stability check according to the second-order analysis, which would be possible by means of the RF-/FE-LTB add-on module.
• ### According to which formula is the elastic critical buckling load for the torsional buckling Ncr,T calculated in RF-/STEEL EC3?

FAQ 003376 EN-US

The elastic critical buckling load for torsional buckling Ncr,T is calculated as follows:

${\mathrm N}_{\mathrm{cr},\mathrm T}\;=\frac1{{\mathrm i}_{\mathrm M}^2}\;\cdot\;\left(\frac{\mathrm\pi^2\;\cdot\;\mathrm E\;\cdot\;{\mathrm I}_{\mathrm w}}{{\mathrm L}_{\mathrm T}^2}\;+\;\mathrm G\;\cdot\;{\mathrm I}_{\mathrm t}\right)$

${\mathrm i}_{\mathrm M}\;=\;\sqrt{{\mathrm i}_{\mathrm u}^2\;+\;{\mathrm i}_{\mathrm v}^2\;+\;{\mathrm u}_{\mathrm M}^2\;+\;{\mathrm v}_{\mathrm M}^2}$

with

 E Modulus of elasticity G Shear modulus Iw Warping resistance It Torsion moment of inertia iu, iv Pricipial radius of gyration um, vm Shear center coordinates in the principal axis system LT Torsional buckling critical length

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