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• ### 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 perform a stability analysis for a tapered member?

Tapered members must not be designed according to the simplified equivalent member method!

For steel structures, the design can be performed by considering the warping torsion or using the General Method. These methods are described in this technical article.

For timber structures, the design can also be performed by considering the warping torsion. The method for timber structures is explained in detail in thiswebinar.

According to the equivalent member method, the design can be performed if the provisions of the explanations for DIN 1052, Section E8.4.2 (3) for variable cross-sections are met. In various sources of technical literature, this method is adopted for Eurocode 5. An example of this can be found in the document on brettschichtholz.de, page 64 ff.

In the RX‑TIMBER program, the design of tapered members is performed according to the equivalent member method. This is briefly explained on a simple example.

Structural System (Figure 01):

• Span length: 8 m
• Beam height right: 80 cm
• Beam height left: 26 cm
• Roof inclination: 3.9°
No stiffening is defined. The lateral-torsional stability becomes governing with 99% (Figure 02) at the x‑location 1.598 m. The cross-section height is 36.8 cm. However, the slenderness ratio is based on the equivalent cross-section height of 60.9 cm (Figure 03).

The equivalent cross-section height results at the x-location 5.2 m about 0.65 × 8 m = 5.2 m.

If the stiffening is in the middle of the span, for example, the equivalent height for the x‑location changes to 45.3 cm.

Since the stiffening is usually applied over the member length, the height must be calculated according to a special algorithm. The supports are always applied as fixed points and the equivalent heights are calculated, based on the x-locations of the designs.

For the example, the following results: x0.65 = 0.32 x 4 m + 1.598 m = 2.878 m
• ### 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.

• ### What are the StandardID and AnnexID of various National Annexes for the processing using the COM interface?

StandardID and AnnexID can be easily displayed at any time by using the following macro:

cominterfaces-en\SDK\Examples\Modules\Excel\RF-STEEL_EC3.xls

You can find this macro in the archive of the product website (see Links).

Here is an overview of the current attachments:

StandardID AnnexID Name

DIN 0 Germany

ÖNORM 1 Austria

CSN 2 Czech Republic

STN 3 Slovakia

PN 4 Poland

SIST 5 Slovenia

DK 6 Denmark

UNI 7 Italy

NEN 8 Netherlands

SFS 9 Finland

SS 10 Sweden

NF 11 France

BS 12 United Kingdom

CEN 13 European Union

BDS 14 Bulgaria

CYS 15 Cyprus

LST 16 Lithuania

SR 17 Romania

SS 18 Singapore

NBN 19 Belgium

NP 20 Portugal

UNE 21 Spain

MAL 22 Malaysia

NS 23 Norway

LU 24 Luxembourg

ELOT 25 Greece

• ### 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.

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#### 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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