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• ### Why do several seemingly identical load combinations occur when combining automatically?

New FAQ 003359 EN

The automatically created load combinations result exclusively from the definition of combination expressions. Thus, it may happen that two load combinations are created according to different combination expressions, but contain the same load cases with the same factors.

However, the load combinations only seem to be the same, because the information saved in the load combination is different. Thus, the load combinations are assigned to the underlying combination expression and can subsequently be selected, for example, when combined in the design.
Consequently, it is necessary to define a unique combination expression for each load combination, so these seemingly identical load combinations are not combined.

• ### Is it possible to create or generate load combinations for the 1st Order Theory and the 2nd Order Theory (including imperfections) in RFEM in parallel?

New FAQ 003347 EN

Yes, it is possible. It works.

If the automatic combinatorics is activated in RFEM or RSTAB, e.g. for the design situation "ULS", the load combinations are set automatically according to the 2nd Order Theory.

Thus, it is possible to get a list of load combinations based on the defined load cases, which are calculated according to the 2nd Order Theory. The consideration of imperfection load cases can also be activated.

If some other load combinations have to be generated according to the 1st order theory (without imperfections) in addition to the existing load combinations calculated according to the 2nd Order Theory incl. imperfection, it is possible to create another combination rule for this. In this additional combination the design situation "ULS" can also be selected by now. However, you can now select the calculation type "1st Order Theory" and deselect the imperfections.

As a result, load combinations according to the 2nd Order Theory incl. imperfection (blue marking in the graphic below) and load combinations according to the 1st Order Theory without imperfection (red selection in the graphic below) are now obtained.

This approach can be used, if structural analysis according to the 2nd Order Theory (incl. imperfection) has to be performed on a part of the structure and on individual structural components, e.g. according to the equivalent member method or model column method.

Optionally, it is also possible to control the numbering of the individual CO groups in the "Combination Rule" tab in advance. Thus, for example, a group can start with CO 100, and the second group with CO 200. As a result of this, the user can improve the clarity or allocation of the COs.

• ### I have generated the earthquake loads manually. How can I combine them according to the superposition rules of the standard?

New FAQ 003346 EN

If you have defined load cases with earthquake loads and can not combine them with the RF-/DYNAM Pro add-on module, you should not apply the automatic combinatorics for this. The following steps describe how to define the manual combinatorics:

• Depending on whether you want to use the SRSS or CQC rule, you may have to activate it in the general data (only necessary in the case of the CQC rule). For the CQC rule, you have to activate additional parameters; this can be set in the load cases.

• Create one result combination per direction. Add all load cases where you have defined earthquake actions in this direction. The type of superposition can then be defined in the calculation parameters.
• Next, the directions are superimposed in further result combinations. For this purpose, the Eurocode 8, for example, specifies the 100/30% rule. To do this, add "and"  to the result combinations of the individual directions and change the factors to 1.0 for the dominant direction and 0.3 for the other directions. It is necessary to create always one result combination for each direction.

• Finally, another result combination is created, which can then be used for the design. In this table, the earthquake loads are superimposed with the permanent and the imposed loads (creation of the unusual combination). Please note that the result combinations for earthquakes must be added with "or".

• ### Is it possible to renumber load cases, load combinations, and result combinations?

New FAQ 003345 EN

To access this function, select Tools - Renumber - Move. This is shown in the attached video.

• ### Why do I get different design results for a load combination (CO) and a result combination (RC) in STEEL EC3 despite the same internal forces?

New FAQ 003313 EN

The difference between a design with RC and CO lies mainly in the moment distribution applied for the calculation of the elastic critical moment Mcr. For a load combination (CO), it is possible to apply explicitly the moment distribution for the existing load position. However, the result combination (RC) can only analyze the enveloping of the moment distributions. Then, the more unfavorable distribution (Max or Min) is applied. As a consequence, unfavorable values result for the critical load factor.

###### Summary:
The internal forces applied for the design can be the same in LC and RC, but the moment distribution in the result combination is applied more unfavorably to determine the critical branch value. Thus, the RC provides a higher utilization for the design with STEEL EC3.

• ### Why is not possible to select alternative or simultaneously acting load cases in the "Combination Expressions" tab?

New FAQ 003259 EN

The option "Individually/Simultaneously Acting Load Cases" is not available for every standard.

In case of selecting e.g. "EN 1990" standard in the general data of the model, this option is available in the "Combination Expressions" tab.

On the other hand, this option is (currently) not available if selecting e.g. "ASCE 7-16".

• ### When solving the serviceability limit state by a nonlinear method, I get the option to export the stiffness within the already cracked structure. Is it possible to recalculate internal forces with these stiffnesses?

New FAQ 003239 EN

Exporting nonlinear stiffness to cracked structures can be enabled in Settings for non-linear calculation of RF-CONCRETE Members or RF-CONCRETE Surfaces. In the Edit Load Cases and Combinations dialog box, check the additional options for the selected combinations. A new tab appears where the stiffness transfer from the additional modules can be switched on.

• ### When designing a column the values of normal forces in the combination of MSU results differ from values in the RF-CONCRETE Columns. What is the cause of it?

New FAQ 003229 EN

The difference between RFEM and RF-CONCRETE Columns is caused by the Result combination set to Max. values. If you switch to Min. or Max and Min. values, the same values are displayed as in the design module.

• ### Where is it possible to define the reference height for the reduction factors of the snow load according to SIA 260?

New FAQ 003218 EN

The reference height can be defined in the factors for the standard SIA 260. They are set in the general data (see Figure 01). The desired reference height is available in the "Combination Factors" tab.

• ### What does the "Different" effect mean when I define the action categories?

FAQ 003193 EN

If load cases are combined in action categories, you can define how the load cases behave within an action category in the Action dialog box.

Simultaneously
All load cases of the action can be combined as required. They can occur in a combination at the same time, but do not necessarily have to.

Alternatively
Of the load cases of the action, only one can be effective (e.g. wind from different directions).

Different
You can define detailed relations between the load cases of an action. If you select this option, an additional column appears in the Load Cases in Action dialog section. There you can assign load cases to a Group so that they are mutually exclusive (as is the case for the action Alternatively). You can select the number of the group from the list.

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