# Frequently Asked Questions (FAQ)

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• ### How can I display the stresses of a surface via RF‑COM?

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The stresses of a surface can be displayed via the COM interface. First, you need the interface for the model (IModel) and then the interface for the calculation (ICalculation2). Using this interface, you can get the interface for the results (IResults2):

Sub stresses_surfaces_example()Dim iApp As RFEM5.ApplicationDim iModel As RFEM5.modelSet iModel = GetObject(, "RFEM5.Model")On Error GoTo EIf Not iModel Is Nothing Then    '   get interface from model    Set iApp = iModel.GetApplication    iApp.LockLicense        '   get interface from calculation    Dim iCalc As RFEM5.ICalculation2    Set iCalc = iModel.GetCalculation        '   get interface from results from loadcase 1    Dim iRes As RFEM5.IResults2    Set iRes = iCalc.GetResultsInFeNodes(LoadCaseType, 1)        '   get equivalent stresses    Dim str_equ() As RFEM5.SurfaceEquivalentStresses    str_equ = iRes.GetSurfaceEquivalentStresses(1, AtNo, VonMisesHypothesis)    End IfE:If Err.Number <> 0 Then    MsgBox Err.Number & " " & Err.descriptionEnd IfIf Not iApp Is Nothing Then    iApp.UnlockLicenseEnd If

The GetSurfaceEquivalentStresses function requires the specification of the calculation hypothesis. In this case, the results of the von Mises stress are displayed. Please note that the COM interface uses SI units so the stress is transferred in N/m².

• ### Why do I get the message 28) in RF‑CONCRETE Members, saying that I have to make a "calculation without second order effect" with the internal forces according to the gemetrically linear analysis?

RF-CONCRETE Columns determines the equivalent moment M0e from the moment M02 at the column head and M01 at the column base according to EN 1992‑1‑1, 5.8.8.2 (2), and performs the design according to the model column method with this equivalent moment M0e.

Now, it may happen, for example, that a computationally larger required reinforcement area would result from the cross-section design with the moment M01 at the column head.

To ensure this, message 28) is displayed, according to which the user should perform a standard design with the internal forces according to the linear static analysis. To do this, simply open the RF‑CONCRETE Members add-on module and perform pure design of the internal forces according to the linear static analysis for the member designed in RF‑CONCRETE Columns.

• ### How can I set as quickly as possible that the load combinations generated by the program will be calculated according to the geometrically linear analysis, for example?

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In the "Edit Load Cases and Combinations" dialog box, you can specify in the bottom right of the "Combination Expressions" tab which method of analysis should be used as the basis for the generated load combinations. By default, the linear calculation according to the geometrically linear analysis is preset for load cases and the nonlinear calculation according to the second-order analysis for load combinations.

Thus, you can quickly determine whether the load case or the load combination is calculated according to the geometrically linear, second-order, or large deformation analysis. The postcritical analysis option allows you to carry out the stability analysis according to the large deformation analysis with regard to the post-critical failure of the entire structure.

In case the model includes cable members, the calculation according to the large deformation analysis is preset in all cases.
• ### "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?

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 can I set the calculation parameters by using the COM interface?

The following code shows how to get different calculation parameters via the COM interface. It also shows how to specify the 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
Under Downloads, you can find the EXCEL macro.
• ### How can I obtain internal forces, calculated in CRANEWAY, for a special x-location?

In CRANEWAY, the internal forces are usually displayed for the max and min locations only. If you want to obtain all internal forces on all x-locations, you have to run a detailed calculation and to disable the "Show only governing results" option. The short video shows how to do it.
• ### What is the difference between the materials Isotropic Plastic 1D and Isotropic Nonlinear Elastic 1D?

The difference between both material models is as follows:

In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state after the load relief.

In the case of the Isotropic Plastic 1D material model, the plastic deformation is considered.

For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible in both models to define the distribution after the last step.

The Isotropic Nonlinear Elastic 1D material model allows for the anti-symmetric input of the stress-strain diagram (different for the positive and negative zone), whereas the isotropic Plastic 1D model only allows for symmetric input.

• ### Which calculation methods are used in RSTAB and RSBUCK?

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RSTAB is a FEM program that uses trigonometric trial functions for members. For this reason, it is not necessary to divide the members to obtain sufficiently accurate results and the calculation speed is higher accordingly.

RSBUCK determines the eigenvalues of the stiffness matrix and can thus linearly calculate the critical load and buckling mode of the structure.

• ### Which programs and add-on modules are suitable for the structural analysis and design of steel structures?

Both RFEM and RSTAB provide a suitable solution. For both programs, there are numerous European and international standards as well as various add-on modules that facilitate your daily work in steel construction.

###### Main Programs RFEM or RSTAB
The main programs RFEM or RSTAB are used to define structures, materials, and actions. In addition to the option to create spatial frame and truss structures, such as halls, RFEM also allows for plate, wall, and shell structures, and thus provides a more versatile option. It pays off if it is necessary to also carry out design in other areas, such as solid construction.

###### Available Standards
• EN 1993-1-1 (Eurocode 3),
• AISC according to ANSI/AISC 360 (US standard),
• SIA according to SIA 263:2013 (Swiss standard),
• IS according to IS 800:2007 (Indian standard),
• BS according to BS 5950-1:2000 (British standard) or BS EN 1993-1-1 (British Annex),
• GB according to GB 50017-2003 (Chinese standard),
• CSA according to CSA S16-09 and CSA S16-14 (Canadian standard),
• AS according to AS 4100-1998 + Annex 1 - 1999 (Australian standard),
• NTC-DF according to NTC-RCDF (2004) (Mexican standard),
• SP according to SP 16.13330.2011 (Russian standard),
• SANS according to SANS 10162-1:2011 (South African standard),
• NBR according to ABNT NBR 8800:2008 (Brazilian standard),
• HK according to the standard Code of Practice for the Structural Use of Steel 2011 (Buildings Department - Hong Kong)
• RF-/STEEL - General stress analysis of steel surfaces and members
###### Add-on Modules for Steel Structures

The add-on modules complement the functionality of the main programs. For example, RF‑/STEEL EC3, allows you to perform design of steel structures according to Eurocode 3. The RF‑STEEL Warping Torsion add-on module supplements the design according to Eurocode 3 with torsional buckling analysis with up to 7 degrees of freedom, provided it does not refer to a standard case of EC3.

Further specialized application areas, such as plastic design, a stability analysis according to the eigenvalue method, or the generation of geometric equivalent imperfections and pre-deformed equivalent models are available. Stand-alone modules, such as PLATE-BUCKLING, support your design of rigid or stiffened plates. The SHAPE-THIN program allows you to create any thin-walled cross-sections. Thus, the cross-section properties are determined and stress analyses or plastic designs can be performed.

You can design hinged or rigid connections by using the RF‑/JOINTS add-on modules.

The stand-alone program CRANWAY is available for the design of craneways.

###### Dynamic Analysis

If it is necessary to perform seismic analysis or vibration designs of a building, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.

If you have any question about the Dlubal Software programs, please do not hesitate to contact our sales department.

• ### When calculating a connection using the FRAME‑JOINT Pro add-on module, a message appears saying that the value is out of the valid range (existing value: 108, minimum value 100, maximum value 100). What does this message mean?

The easiest way is to change to the design notes after the calculation or after the note appears in the design notes (see Figure 02). In that case, this shows that the width of the end plate is not correct. From the input window 1.4.2, it is possible to quickly recognize in the graphic that the value is not within the valid range.

This can be corrected very quickly by adjusting the horizontal bolt spacings (see Figure 03).

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#### 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.

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