# Frequently Asked Questions (FAQ)

#### Customer Support 24/7

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.

Receive information including news, useful tips, scheduled events, special offers, and vouchers on a regular basis.

• ### How can I only calculate specific load cases, load combinations, or result combinations by using a command with the COM interface?

In order to only calculate specific load cases, load combinations, or result combinations in the same way as the "To Calculate..." command (see Figure 01), you can use the CalculateBatch method of the ICalculation interface. For the transfer, the method expects a field with the load type of Loading. This Loading includes the number of the load, and the type (for example, a load combination):

Sub batch_test()    '   get interface from the opened model and lock the licence/program    Dim iModel As RFEM5.IModel3    Set iModel = GetObject(, "RFEM5.Model")    iModel.GetApplication.LockLicense    On Error GoTo e        '   get interface for calculation    Dim iCalc As ICalculation2    Set iCalc = iModel.GetCalculation        '   create array with loading types    Dim loadings(3) As Loading    loadings(0).no = 1    loadings(0).Type = LoadCaseType        loadings(1).no = 4    loadings(1).Type = LoadCaseType        loadings(2).no = 4    loadings(2).Type = LoadCombinationType        '   calculate all loadings from the array at once    iCalc.CalculateBatch loadingse:  If Err.Number <> 0 Then MsgBox Err.description, , Err.Source        Set iModelData = Nothing    iModel.GetApplication.UnlockLicense    Set iModel = NothingEnd Sub
• ### How can I check the generated load combinations for different design situations in CRANEWAY?

In the CRANEWAY program, you can select the display of load combinations for the individual design situations in the middle of Window 1.5 Load Combinations.
• ### When importing an RFEM/RSTAB file into Autodesk Revit, I get the error message for the load combination saying that "The given name is not unique Parameter name: name." How can I fix the error?

The description of various load combinations must not be the same, otherwise the error message shown in Figure 01 will be displayed. The relevant load combination can be taken from the error message (Load Combination No. 2 in Figure&nbp;1).

The model shown in Figure 02 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 the import is possible.

• ### Does it make any difference for the calculation of a load combination if I set the calculation for the included load case according to the geometrically linear analysis or the second-order analysis?

No, this makes no difference for the calculation of the load combination. It is decisive which method of analysis is set for this load combination, see Figure 01.

• ### How is it possible to make factorized combinations of a dead load in the context of form‑finding?

The load from the form-finding load case (FF) is fixed to the structural system 1.0‑times. If you want to factorize the dead load related to the combinations, it is possible to additionally create a permanent load case for the dead load with a 0.35‑fold load.
• ### Why there are several load combinations created in the case of the automatic combination that are apparently the same?

The automatically created load combinations are solely generated 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 be selected subsequently for the combined design, for example.
Since it is thus necessary to define a unique combination expression for each load combination, these load combinations that are apparently the same are not combined.

• ### Can I create or generate parallel load combinations for the geometrically linear analysis and the second-order analysis (including imperfections) in RFEM?

Yes, it is possible.

If you activate the option to create combinations automatically in RFEM or RSTAB, load combinations for the "ULS" design situation, for example, are set automatically according to the second-order analysis.

In this way, you can obtain a list of load combinations based on the defined load cases, which are calculated according to the second-order analysis. The consideration of imperfection load cases can also be activated.

To generated the load combinations according to the geometrically linear analysis (without imperfections) in addition to the existing load combinations calculated according to the second-order analysis including imperfection, you can create another combination expression for this. In this additional combination, you can select the "ULS" design situation now. However, you can only select the "geometrically linear analysis" as a method of analysis and deselect the imperfection load cases.

As a result, you obtain the load combinations according to the second-order analysis including imperfection (marked in blue in the figure below) and the load combinations according to the geometrically linear analysis without imperfection (marked in red in the figure below).

This approach can be used to perform the stability analysis according to the second-order analysis (including imperfection) on a part of the structure and according to the equivalent member method or model column method on the individual structural components, for example.

Optionally, it is also possible to control the numbering of the individual CO groups in advance in the "Combination Expressions" tab For example, one group can start with CO 100 and the second group with CO 200. In this way, you can achieve a better overview or allocation of the COs.

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

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

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

• Create a result combination for each direction. Add all load cases where you have defined the earthquake actions in this direction. In Calculation Parameters, you can then define the type of superposition.
• As a next step, the directions are superimposed in further result combinations. In this case, Eurocode 8 provides the 100/30% rule, for example. For 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 always create one result combination for each direction.

• Finally, a further result combination is created, which can then be used for the design. In this combination, the earthquake loads are superimposed with the permanent and the imposed loads (creation of an accidental 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?

003345

Yes, you can access this feature via Tools - Renumber - Move. The attached video shows it.
• ### Why do I get different design results for a load combination (CO) and a result combination (RC) in STEEL EC3 in spite of the same internal forces?

The difference between the design with RC and CO is mainly in the moment distribution applied for the calculation of the ideal elastic critical 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. In this case, the more unfavorable distribution (Max or Min) is applied. As a consequence, unfavorable values result for the critical load factor.
Furthermore, the design according to Section 6.3.3 of EN 1993‑1‑1 requires the moment distribution coefficients set to 1.0 (constant distribution) if the moment distribution cannot be clearly determined, which may also lead to more conservative results.

###### Summary:
The internal forces applied to 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 design ratio for the design with STEEL EC3.

1 - 10 of 39

Did you find your question?
If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

#### 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.

#### Your support is by far the best

“Thank you for the valuable information.

I would like to pay a compliment to your support team. I am always impressed how quickly and professionally the questions are answered. I have used a lot of software with a support contract in the field of structural analysis, but your support is by far the best. ”