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• ### I get the error message "Entry in the 'Beam spacing' box is not within the allowable range." What can I do?

You have probably defined a shear panel and a rotational restraint for your design case in the RF‑/STEEL EC3 add-on module, but have not yet defined all specifications for the rotational restraint.

In Window 1.13, scroll down under Settings. For the rotational restraint, the "spacing of beams" is still defined as s = 0 m. Adjust the value accordingly.

• ### I cannot find any reason why no plastic design is performed for a class 1 cross-section. Normally, you have to select the check box for the elastic design.

In principle, the program always tries to perform a plastic design for cross-section classes 1 and 2. However, if torsion is additionally contained, the design can only be performed elastically. This is due to the interaction conditions according to EN 1993-1-1 clause 6.2.9, which do not include any torsional component.

For this reason, the "Cross-Section Design and Torsion" setting is available in the details of the add-on module. By adjusting the limit shear stress for the cross-section designs, you can also neglect the torsion under your own responsibility.

• ### How can I change the details and the National Annex in the STEEL EC3 add-on module by using the COM interface?

The following code displays all elements of the STEEL EC3 add-on module that can be modified via the COM interface:

//  get interface to active modeliModel = iApp.GetActiveModel();//  get interface to STEEL EC3 moduleIModule module = iModel.GetModule("STEEL_EC3") as Dlubal.STEEL_EC3.IModule;//  get interface to module caseICase iStEC3case = module.moGetCase(1, Dlubal.STEEL_EC3.ITEM_AT.AT_NO);//  get ultimate limit state options (Details > Ultimate Limit State)ULS_OPTIONS optsULS = iStEC3case.moGetULSOptions();//  get options for stability design (Details > Stability)STABILITY_OPTIONS optsStab = iStEC3case.moGetStabilityOptions();//  get options for serviceability design (Details > Serviceabiltiy)SERVICEABILITY_DEFORMATION_TYPE optsServDef = iStEC3case.moGetServiceabilityOptions();//  get fire resistance options (Details > Fire Resistance)FIRE_RESISTANCE_OPTIONS optsFire = iStEC3case.moGetFireResistanceOptions();//  get other options (Details > General)OTHER_OPTIONS optsOther = iStEC3case.moGetOtherOptions();//  get national annex (e.g. DIN, CEN, ...)NATIONAL_ANNEX natAn = iStEC3case.moGetNationalAnnex();//  get interface for national annex detailsINationalAnnex iNatAn =  iStEC3case.moGetNationalAnnexOptions();//  get base data for national annexNATIONAL_ANNEX_OPTIONS_BASE natAnBase = iNatAn.moGetBaseOptions();//  get data for general method from national annexNATIONAL_ANNEX_OPTIONS_GM natAnGM = iNatAn.moGetGMOptions();//  get data for lateral-torsional buckling from national annexNATIONAL_ANNEX_OPTIONS_LTB natAnLTB = iNatAn.moGetLTBOptions();//  get data for stainless steel from national annexNATIONAL_ANNEX_OPTIONS_STEEL natAnSTEEL = iNatAn.moGetSteelOptions();

The corresponding elements in the parameter dialog box of the add-on module are shown in Figure 02.

• ### I would like to perform a stability analysis of the upper flange in a long truss. What is the best way to proceed?

According to DIN EN 1993‑1‑1:2010‑12 [1], Annex BB.1.1, the buckling length may be used in the individual bracing under certain conditions. This means that in this case, the individual members, not a set of members, can be applied with the effective length factors specified in the standard.

Since this approach only considers the local failure, it is necessary to analyze the global failure of the entire structure. For this design, the set of members must have the corresponding imperfection. Under certain conditions, the design can be performed on single members, depending on the model (for example, a tower), or the set of members must be analyzed for a failure from the plane (the truss), as in the attached example.

• ### How can I design any SHAPE‑THIN cross-section in detail in RFEM or RSTAB?

Any SHAPE‑THIN cross-section can be designed as follows:

• Stability and stress analysis with the RF‑/STEEL EC3 add-on module and the RF‑/STEEL Warping Torsion module extension, see Figure 01

• Generating surfaces from the cross-section (possible in RFEM only, see Figure 02), and a new definition of support and stress analysis of the newly created surfaces with RF‑STEEL Surfaces, if necessary, see Figure 03; under certain circumstances, a stability analysis with RF‑STABILITY for the surface model is reasonable, see Figure 04.

• ### Is it possible to deactivate the stability analysis by member within a case in the RF‑/STEEL EC3 add-on module?

Yes, this setting can be made in Window "1.5 - Effective Lengths." Deactivate "Buckling Possible" or "Lateral-Torsional and Torsional-Flexural Buckling Possible", see the figure.

• ### I design a set of members using RF‑/STEEL EC3. In accordance with the manual calculation, the design is fulfilled, but it cannot be performed successfully in the add-on module. Why?

Please check the definition of the support of any intermediate nodes in Window "1.4 Intermediate Lateral Supports" or Window "1.7 Nodal Supports" in the add-on module, see Figure 01.

Since the module has its own solver, the support conditions are not automatically imported from RFEM/RSTAB, but must be defined manually.

• ### Which cross-sections can I design with the "RF‑/STEEL Cold-Formed Sections" add-on module?

The "RF‑/STEEL Cold-Formed Sections" add-on module allows you to design cold-formed L‑sections, Z‑sections, C‑sections, channels, top‑hat sections, and CL‑sections from the cross-section library.

Furthermore, it is also possible to design general cold-formed (not perforated) SHAPE‑THIN 9 cross-sections.

• ### What is the difference between the RF‑/STEEL and RF‑/STEEL EC3 add-on modules?

Even if the description of the add-on modules is very similar, the calculations performed are different.

###### RF-/STEEL

This add-on module performs a general stress analysis by calculating the existing stresses and comparing them with the limit stresses. The designs are performed elastically. The designs do not depend on a standard.

###### RF-STEEL EC3

This add-on module, on the other hand, performs all typical designs of ultimate limit state, stability, deformation, and fire resistance for steel members according to Eurocode 3 (numerous National Annexes are available). There is a range of module extensions available within this add-on module. These include: warping torsion analysis, plasticity analysis, designs for cold-formed sections.

###### Comparison of Both Add-on Modules

The results of RF‑/STEEL can be compared with the results of the cross-section design of RF‑/STEEL EC3.

Why the results can differ is explained in FAQ 003489.

• ### When entering data in the RF‑/STEEL EC3 add-on module, I get the error message "Incorrect location of the intermediate lateral restraint". Why?

The input of intermediate lateral restraints is used to enter lateral supports on a member without having to insert a node in the model at this location. Furthermore, the design of sets of members using the equivalent member method requires them to define the existing support conditions at the intermediate nodes of the set of members.

The entered intermediate lateral restraints are then considered as additional boundary conditions in the eigenvalue solver. However, some boundary conditions are already included in the input tables of the nodal supports or the effective lengths.

To avoid conflicts or duplicate entries for the same location, the error message "Invalid location of the intermediate lateral restraints" appears. The following locations are not allowed as they are already defined in the other entries:

Design of Members:
- Start and end of a member

Design of Sets of Members:
- Start and end of all members if they are entered using nodal supports
- Start and end of a set of members for the design using the equivalent member method

However, it is very easy to find the error, because the first line with the wrong entry is automatically selected after confirming the error message.

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

#### Wind Simulation & Wind Load Generation

With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.

The generated wind loads acting on these objects can be imported to RFEM or RSTAB.

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