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Frequently Asked Questions (FAQ)
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Description of different load combinations must not be identical otherwise the error message shown in Figure 1 will be displayed. The relevant load combination can be taken from the error message (in Figure 1 Load Combination No. 2).
The model shown in Figure 2 contains the load combination LC1 and LC2. Both load combinations have the same description 'ULS'. It is necessary to change one of the two descriptions so that an import is possible.
AnswerThe 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.
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.
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".
To access this function, select Tools - Renumber - Move. This is shown in the attached video.
AnswerThe difference between designing by means of RC and CO consists mainly in the moment distribution applied for the calculation of the ideal lateral-torsional buckling moment Mcr. For a load combination (CO), it is possible to clearly apply the moment distribution for the present load position. For a result combination of the '+' type or an RC that does not correspond to the 'permanent/or' type, however, you can only analyze the enveloping moment distribution. Then, the more unfavorable distribution (Max or Min) is applied. As a consequence, unfavorable values result for the critical load factor.Furthermore, it should be noted when designing according to clause 6.3.3 of EN 1993-1-1 that the moment distribution coefficients are set to 1.0 (constant distribution), provided that the moment distribution cannot be determined unambiguously, which may also lead to more conservative results.
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 factor. Thus, the RC provides a higher utilization for the design with STEEL EC3.
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'.
AnswerYou can activate the export of nonlinear stiffness of a cracked structure in Settings for Nonlinear Calculation of the RF‑CONCRETE Members or RF‑CONCRETE Surfaces add-on modules. In the Edit Load Cases and Combinations dialog box, select "Extra options" for the selected combinations. A new tab appears where you can activate the transfer of stiffnesses from the add-on modules.
AnswerThe difference between RFEM and RF-CONCRETE Columns is caused by setting the result combinations to Max Values. If you switch to Min or Max and Min Values, the same values are displayed as in the design module.
AnswerThe reference height can be defined in the factors for the standard SIA 260. These can be found in General Data (see Figure 01). The desired reference height is available in the "Combination Coefficients" tab.
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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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