Further Information

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.

• Which formula is used in the RF‑/TOWER Loading add-on module to calculate the first natural frequency for the determination of the structure coefficient?

The first natural frequency is required to determine the structure coefficient. It is not determined by using a generalized formula, but the integrated eigenvalue solver RF‑/DYNAM, taking into account the real mass distribution and displaying the results in Column A of Table 2.3.

• How can I create a section via the COM interface?

New

004409

In principle, a section is an element, such as a member, and is also created in the same way. First, the interface to the objects is required. For a member, this would be IModelData, and for sections, it would be ISections. This interface can be found in IModel3:
Sub test_section()'   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        Dim iSecs As RFEM5.ISections    Set iSecs = iModel.GetSections()
All sections created previously are deleted first, and then two new sections are created.
The first section should be a solid section with a visible sectional area (see Figure 01). The data are entered in a similar way as in RFEM. As a type, "SectionOnSectionalArea" is selected, the corner points of the section are set by using "EdgePoint," and a "Vector" defines the direction of the section:

   '   first delete all sections    iSecs.PrepareModification    iSecs.DeleteObjects ("All")    iSecs.FinishModification        '   set section on solid    Dim sec As RFEM5.Section    sec.EdgePointA.X = 2    sec.EdgePointA.Y = 5    sec.EdgePointA.Z = 0    sec.EdgePointB.X = 2    sec.EdgePointB.Y = 8    sec.EdgePointB.Z = 0        sec.no = 1    sec.Name = "solid section"    sec.Plane = GlobalPlaneInPositiveX    sec.ShowValuesInIsolines = False    sec.Type = SectionOnSolidSectionLine    sec.ObjectList = "1"        iSecs.PrepareModification    iSecs.SetSection sec    iSecs.FinishModification

As already known from other elements, the new section is finally transferred in a Prepare-/FinishModification block. As the second section, a surface section is to be created (see Figure 02). For this, it is necessary to use the "SectionViaSurfacePlane" type. In addition to the vector of the section direction, you have to select the display plane of the results for the surface section. In the following example, the xy plane is selected by setting "GlobalPlaneInPositiveX."

'   set section on surface    sec.EdgePointA.X = 2    sec.EdgePointA.Y = 0    sec.EdgePointA.Z = 0    sec.EdgePointB.X = 2    sec.EdgePointB.Y = 3    sec.EdgePointB.Z = 0        sec.no = 2    sec.Name = "surface section"    sec.Plane = GlobalPlaneInPositiveX        sec.ShowValuesInIsolines = True    sec.Type = SectionViaSurfacePlane    sec.ObjectList = "1"        sec.Vector.X = 0    sec.Vector.Y = 0    sec.Vector.Z = 1        iSecs.PrepareModification    iSecs.SetSection sec    iSecs.FinishModification
It is also possible to get the results of a section by using the separate method "GetResultsInSection" of the "IResults2" interface. In the following, the shear forces on the surface section are obtained. The distribution of the internal forces is set to "Continuous within Surfaces" by means of "ContinuousDistributionWithinObjects":

 '   get results    Dim iCalc As ICalculation2    Set iCalc = iModel.GetCalculation        Dim iRes As IResults2    Set iRes = iCalc.GetResultsInFeNodes(LoadCaseType, 1)        Dim secRes() As RFEM5.SectionResult    secRes = iRes.GetResultsInSection(2, AtNo,      ShearForceVy,ContinuousDistributionWithinObjects, False)
Under Downloads, you can find the Excel macro and the test file to comprehend the program.
• Is it also possible to manually enter the load for the punching shear design in RF‑PUNCH Pro?

Yes, it is possible in Window "1.5 Punching Nodes."

For example, this can be used if the determination of the punching load by using the smoothed or unsmoothed distribution of shear forces in the control perimeter is negatively affected by singularities.

• Does RWIND Simulation apply a boundary layer model?

In RWIND Simulation, each model surface in the wind flow is treated as a "smooth" wall. This definition results in a boundary layer in the areas around the flow close to the walls, which has an influence on the velocity profile perpendicular to the wall depending on the air viscosity. This boundary layer is created in RWIND Simulation according to the so-called "wall law." This law describes the velocity profile perpendicular to the wall and can be represented by the dimensionless variables u+ and y+.

Dimensionless variable u+:
$\mathrm u^+=\frac{\mathrm U}{{\mathrm u}_{\mathrm\tau}}$
where
U is the velocity on the wall,
uτ is the frictional velocity.

Dimensionless variable y+:
$\mathrm y^+=\frac{{\mathrm u}_{\mathrm\tau}\cdot\mathrm y}{\mathrm\nu}$
where
y is the wall distance,
uτ is the frictional velocity,
ν is the kinematic viscosity of the air.

Using the friction velocity uτ:
${\mathrm u}_{\mathrm\tau}=\sqrt{\frac{{\mathrm\tau}_{\mathrm w}}{\mathrm\rho}}$
where
τw is the shear stress,
ρ is the air density.

By describing the boundary layer model in the viscous partial layer directly next to the wall
$\mathrm u^+=\mathrm y^+$

and in the subsequent logarithmic layer
$\mathrm u^+=\frac1{\mathrm\kappa}\cdot\ln\;\mathrm y^++\mathrm C$

you obtain the following velocity distribution,

where
κ is the Kármán constant (κ = 0.41 for the simulation of a smooth wall),
C is the constant (C = 5 for the simulation of a smooth wall).

To ensure that the solution process is relatively fast and robust, the program specifies the corresponding boundary layer model directly in the first cell next to the model surface. The remaining part of the boundary layer results from the solution of the globally applied Navier-Stokes equations.

A user-defined wind load distribution is not provided in the Eurocode. In order to implement a user-defined wind load distribution in the RF‑/TOWER Loading add-on module, this can only be done after conversion to DIN, for example, DIN 4131:1993‑11, see Figure 01, Window "1.3 Wind Load - Part 1."

Then, you can select the user-defined distribution in Window 1.4 "Wind Load - Part 2," and define it in the adjacent table, see Figure 02.

• I have defined a nonlinear line support with failure. Implausible results are displayed during the result evaluation. What can I do?

Similarly to surfaces, there are various smoothing options for displaying the results of support reactions. For a nonlinear support, you should always select the actual distribution to display the results.
• I cannot graphically display a variable polygon load on a surface correctly. It is not clear which load is actually applied. Is there any display option for this?

There is an option for this in the Results navigator of RFEM 5.

After the calculation of a load case or a CO, you can switch to the Results navigator and select the "Load Distribution" result type.

Thus, you can display the load applied in the respective element. This can also be used very well for a graphical documentation of the load and printed as a graphic in the report.

• When rotating the view, it seems that the coordinates X and Y are reversed. Is there a display problem?

The described effect is not a display error, but only a question of perspective and a good example of an optical illusion. It depends on whether you perceive the representation of the axis system as an inner or outer corner.

Example: Rubik's Cube in Isometric View

The yellow side of the cube is the top surface. In the preset isometric view, you can see the inner corner of the coordinate system diagonally from above. If you simply turn the view upside down, so that Z points upwards, X to the right, and Y to the left, you can look at the bottom side of the cube, that is from above on the lower outer corner of the coordinate system.

If you rotate the view by 45 ° about the horizontal axis, you may get the impression that you look at the inner corner of the coordinate system. However, this is the outer corner.

• Where in RF‑CONCRETE Members can I display the location of the neutral axis or the neutral axis depth of concrete for a cross-section?

After the calculation, you can switch to the result window "2.4 Required Reinforcement by x‑Location" in the RF‑CONCRETE Members (RFEM) or CONCRETE (RSTAB) add-on module.

Here, you can select a certain result row for a particular design and x-location (upper table in Window 2.4). Then, you can evaluate the intermediate results in the lower table in Window 2.4. This covers the "Neutral Axis Depth x", for example. The location of the neutral axis for the selected design location is displayed in the graphic on the right of Window 2.4 .

Furthermore, you can display the distribution of the neutral axis depth along the member length graphically in the model or in "Result Diagrams on Member."

• Where can I activate the reduction of shear forces or moments on a support in RF‑CONCRETE Members?

You can find the setting in Window 1.5 Support.

Here, you can enter the support width and type, and specify whether to carry out the moment redistribution, or the reduction of moments or shear forces.

Depending on the standard selected in Window 1.1, there are different options available. The option applies to RF‑CONCRETE Members (RFEM 5) and CONCRETE (RSTAB 8).

1 - 10 of 229

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. ”