Frequently Asked Questions (FAQ)

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• When trying to perform a calculation, I get the message "The path to RWIND Simulation working directory cannot contain any non-ASCII characters." What can I do?

New

FAQ 004338 EN-US

Answer

The working directory is a local path where the data of the currently opened structure is temporarily handled and saved. It consists of the first letters of the file. Only ASCII characters may be used.

The non-ASCII characters are, for example, "ä," "ö," and "ß."

To avoid this problem, replace the special characters in the file name by the ASCII characters, such as "ae" and "ss" instead of "ä" and "ß." When you open the file again, the message will no longer appear.
• How can I only calculate specific load cases, load combinations, or result combinations by using a command with the COM interface?

FAQ 004337 EN-US

Answer

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
• Does the RF‑LAMINATE program consider the shear correction factor for cross-laminated timber plates?

Answer

The shear correction factor is considered in the RF‑LAMINATE add-on module by using the following equation.

$k_{z}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{\left(\int_{-h/2}^{h/2}E_x(z)z^2\operatorname dz\right)^2}\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz$

with $\int_{-h/2}^{h/2}E_x(z)z^2\operatorname dz=EI_{,net}$

The calculation of shear stiffness can be found in the English version of the RF-LAMINATE manual, page 15 ff.

For a plate with the thickness of 10 cm in Figure 01, the calculation of the shear correction factor is shown. The equations used here are only valid for simplified symmetrical plate structures!

 Layer z_min z_max E_x(z)(N/mm²) G_xz(z)(N/mm²) 1 -50 -30 11,000 690 2 -30 -10 300 50 3 -10 10 11,000 690 4 10 30 300 50 5 30 50 11,000 690

$\sum_iG_{xz,i}A_i=3\times0.02\times690+2\times0.02\times50=43.4N$

$EI_{,net}=\sum_{i=1}^nE_{i;x}\frac{\mbox{$z$}_{i,max}^3-\mbox{$z$}_{i,min}^3}3$

$=11,000\left(\frac{-30^3}3+\frac{50^3}3\right)+300\left(\frac{-10^3}3+\frac{30^3}3\right)$

$+11,000\left(\frac{10^3}3+\frac{10^3}3\right)+300\left(\frac{30^3}3-\frac{10^3}3\right)+11,000\left(\frac{50^3}3-\frac{30^3}3\right)$

$=731.2\times10^6 Nmm$

$\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz=\sum_{i=1}^n\frac1{G_{i;xz}}\left(χ_i^2(z_{i,max}-z_{i,min})\;χ_iE_{i,x}\frac{z_{i,max}^3-z_{i,min}^3}3+E_{i,x}^2\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)$

$χ_i=E_{i;x}\frac{z_{i,max}^2}2+\sum_{k=i+1}^nE_{k;x}\frac{z_{k,max}^2-z_{k,min}^2}2$

 χ1 13.75 106 χ2 8.935 106 χ3 9.47 106 χ4 8.935 106 χ5 13.75 106

$\sum_{i=1}^n\frac1{G_{i;yz}}\left(χ_i^2(z_{i,max}-z_{i,min})-χ_iE_{i,y}\frac{z_{i,max}^3-z_{i,min}^3}3+{E^2}_{i,y}\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)=$

 8.4642 1011 3.147 1013 2.5 1012 3.147 1013 8.4642 1011

Total 6.7133 x 1013

$k_z=\frac{43.4}{{(731.2e^6)}^2}6.713284\;e^{13}=5.449\;e^{-3}$

$D_{44}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{k_z}=\frac{43.4}{5.449\;e^{-3}}=7,964.7 N/mm$

This corresponds to the resulting value in RF‑LAMINATE (Figure 02).
• How is the coupling stiffness determined in RF‑GLASS?

FAQ 004232 EN-US

Answer

In RF‑GLASS, there are two different types of calculations. On the one hand, there is the "2D" calculation. In this case, a glass structure is displayed as a surface element. When considering the shear coupling, the program determines an equivalent cross-section by using the laminate theory On the other hand, there is the "3D" calculation. In this case, the composition is modeled as a solid element in the calculation, and thus the effectiveness of stiffnesses between the foil and glass is determined exactly when considering the coupling.

Further information about the calculation methods can be found in the RF‑GLASS manual, Chapter 2.

• "During the calculation of material non-linearity, the material with a decreasing branch of the diagram can be calculated with one load increment only." Why do I get this error?

Answer

Only the default setting of 1 load increment can be set when a complex nonlinear material model is defined. The reason for this is because the program cannot determine the correct material stiffness for each incremental loading amount. The exact maximum load needs to be applied to the structure in order to determine the state of the material's stress/strain diagram.

Figure 01 - Material Model - Nonlinear material defined

This setting can be found and changed under "Calculation Parameters" as well as under the "Calculation Parameters" in the load cases and combinations dialog box.

• How to set the calculation parameters using the COM interface?

FAQ 004184 EN-US

Answer

The following code shows how to get different calculation parameters via the COM interface. It also demonstrates how to specify a setting for deactivating shear stiffness:

    '   get model interface    Set iApp = iModel.GetApplication()    iApp.LockLicense        '   get calculation interface    Dim iCalc As RFEM5.ICalculation2    Set iCalc = iModel.GetCalculation        '   get surface bending theory    Dim calc_bend As RFEM5.BendingTheoryType    calc_bend = iCalc.GetBendingTheory        '   get settings for nonlinearities    Dim calc_nl As RFEM5.CalculationNonlinearities    calc_nl = iCalc.GetNonlinearities        '   get precision and tolerance settings    Dim calc_prec As RFEM5.PrecisionAndTolerance    calc_prec = iCalc.GetPrecisionAndTolerance        '   get calculation settings    Dim calc_sets As RFEM5.CalculationSettings    calc_sets = iCalc.GetSettings    'get calculate options    Dim calc_opts As RFEM5.CalculationOptions    calc_opts = iCalc.GetOptions        '   set ShearStiffness to false    calc_opts.ShearStiffness = False    iCalc.SetOptions calc_opts
In the annex, there is an EXCEL macro to download.
• Is it possible to perform stability analyses on reinforced concrete structures by means of RF‑STABILITY?

Answer

Since concrete has a nonlinear material behavior that can only be simulated with the CONCRETE NL module, it is not possible to analyze it by using the RF‑STABILITY add-on module.

The use of another material model such as isotropic linear elastic or isotropic plastic would not represent the crack formation correctly, and the results are therefore not usable.

The stability analysis on columns can be performed with RF‑CONCRETE Columns or RF‑CONCRETE NL. You can find a small example under Downloads.

This example includes the design of a column by the RF‑CONCRETE Columns add-on module. Make sure that the calculation of the internal forces in RFEM is performed according to the geometrically linear analysis and that no imperfections are required because the method used in the add-on module takes them into account.

The example also includes the design with RF‑CONCRETE NL. Here, it is also necessary to calculate according to the second-order analysis and it requires the imperfections in the form of inclinations. For better comparability, the layout of the longitudinal reinforcement was aligned with the result from RF‑CONCRETE Columns, as shown in Figure 01 and Figure 02. Since the reinforcement is optimized by the module after a new calculation, the desired reinforcement was saved as a template (see the red arrow).

• How does the asynchronous calculation via the COM interface work?

FAQ 003605 EN-US

Answer

The asynchronous calculation is used if a self-created program should only open or continue RFEM or RSTAB. When the calculation is complete, the event is transferred via a delegate. You can find a C# example in a Visual Studio project in the download area below.
• During the calculation, I receive an error message in RFEM with the Error No. 1639 or in RSTAB with the Error No. 1640 'Member No. XY | Member end hinges No. YZ are freely rotating about the x-axis. Please check this in Table 1.17 (or 1.7 in RSTAB) or in a related table'. How to solve this problem?

FAQ 003596 EN-US

Answer

In fact, this error message appears only if a member end hinge that allows a rotation about the local x-axis has been assigned to a member at both ends. Thus, the member can rotate freely about its own axis and is therefore unstable.

Assign a new release to one of the member ends where the degree of freedom φx is not hinged.
• For the deformation analysis by means of RF-CONCRETE Deflect, I have activated the consideration of creep and shrinkage. Where can I see the creep coefficient and shrinkage strain applied for the calculation?

FAQ 003581 EN-US

Answer

In Table 1.3 Surfaces, you can specify the parameters in the corresponding tab for the automatic determination of the creep coefficient and shrinkage strain. It is also possible to enter user-defined values there, if necessary.

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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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