Knowledge Base

In the Knowledge Base, you’ll find technical articles and tips & tricks that may help you with your design using Dlubal Software.

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• Which explicit method is used in the RF-DYNAM Pro - Nonlinear Time History add-on module?

FAQ 002376 EN Add-on Modules RF-DYNAM Pro - Nonlinear Time History

The RF-DYNAM Pro - Nonlinear Time History offers, in addition to the implicit NEWMARK method of mean acceleration, also an explicit method. In the manual of this add-on module, it is mentioned that this is a solver which uses the central difference method.

It should be noted that not the "original" version of the central difference method is used here, but a modified form. The modified form is characterized by the fact that it is simply not a central difference when applying the speed difference. The following two equations show the applied speed and acceleration differences.

Speed: (no central difference)
${\dot{\mathrm x}}_{\mathrm n+\frac12}=\frac{{\mathrm x}_{\mathrm n+1}-{\mathrm x}_\mathrm n}{{\mathrm{Δt}}_{\mathrm n+{\displaystyle\frac12}}}$

Acceleration: (central difference)
${\ddot{\mathrm x}}_\mathrm n=\frac{{\dot{\mathrm x}}_{\mathrm n+{\displaystyle\frac12}}-{\dot{\mathrm x}}_{\mathrm n-\frac12}}{{\mathrm{Δt}}_\mathrm n}$

This approach leads to a faster convergence since it responds "faster" to changes in loading or structure (nonlinearities).
• For wall ends and wall corners, no soil contact stresses are deducted in RF-PUNCH pro, even though the type "Foundation" has been set. It is also nowhere possible to define that the soil contact stresses should be deducted. Why does this happen?

FAQ 002375 EN Add-on Modules RF-PUNCH Pro RFEM 2D RFEM

If you perform a punching shear design for a wall corner or a wall end at a floor slab or foundation plate, this entry is not necessary.

Since the punching load is determined at a wall corner or a wall end from the shear forces in the control perimeter when performing the punching shear design, the ratio of the surface load is missing anyway within the control perimeter (up to the load application). Therefore, this entry is also not necessary in the 1.5 dialog box.

If you, however, perform the punching shear design for a single column at a foundation plate with the punching load from the normal force of this column, you can enter the "Deductible Surface Load" at the end of the dialog box "1.5 Nodes of Punching Shear - Node of Punching Shear - Details" which allows to determine ΔVEd.
• I have modelled a precast slab as "orthotropic surface". Can I use these surfaces also in reinforced concrete design?

FAQ 002374 EN Add-on Modules RF-CONCRETE RF-CONCRETE NL

Yes, you can use "orthotropic surfaces" for the reinforced concrete design in RF-CONCRETE Surfaces.

If you only would like to carry out serviceability limit state designs, you do not have to define additional settings in RF-CONCRETE Surfaces concerning the surface type.

You need the RF-CONCRETE NL add-on module to perform the serviceability limit state designs. Select in the "serviceability limit state" tab (in the dialog box "1.1 General Data") the design method "Nonlinear...". See Figure 01.

You can then change the surface type to "Constant" in the dialog box "1.3 Surfaces" so that the serviceability limit state design is also possible here. See Figure 02.
• How can I enter a one-way continuous slab in RFEM?

FAQ 002373 EN Modeling | Structure RFEM

It is possible to simulate one-way continuous slabs (e.g. precast slabs) by using the "orthotropy" of the surfaces.

You can set the stiffness type "Orthotropic" in the "Edit Surface" dialog box separately for each surface. See Figure 01.

In the "Edit Surface Stiffness - Orthotropic" dialog box, you can define the orthotropy type and select, for example "Effective thicknesses". See Figure 02.

You can then define the effective thickness in the local x and local y-direction of the corresponding surface in the "Effective thickness" tab. Moreover, you also have the possibility in this dialog box to define an effective thickness for the self-weight. See Figure 03.
• Is it possible to perform the structural analysis and design of containers with Dlubal Software?

FAQ 002372 EN General RFEM

With the FEA Software RFEM, it is possible to perform the structural analysis and design of containers (shipping containers, office containers, mobile homes, etc.).

RFEM offers member, surface and solid elements for detailed modeling. All components can be designed in the corresponding add-on modules.

• Why are wind and snow load generator greyed out in my RFEM/RSTAB file?

The prerequisite for using both generators for wind and snow load are that you are working with the 3D model type because when working with a 2D model type, the program does not have the corresponding geomtrical parameters.
The model type has to be set in the "Edit Model - General Data" dialog box. The dialog is opened by right-clicking "Model Data", "General Data" in the Project Navigator - Data. The modeling may have to be adapted.
• What is the difference between RSTAB and RFEM?

FAQ 002370 EN General RFEM RSTAB

RSTAB is a 3D structural frame analysis program where the design of 2D and 3D frameworks is possible. The efficient RSTAB solver allows for linear and nonlinear calculations of internal forces, deformations, and support reactions.

With RFEM, you extend the member design by plates, shells and solids according to the Finite Element Method. These elements can be combined arbitrarily in a structure. RFEM contains almost all functions from RSTAB; that is why also pure frameworks can be designed with it.

The user interface and the handling of RSTAB and RFEM are almost identical, but RFEM offers more functions due to the greater scope of the program. The import of structure and load date from RSTAB to RFEM and vice versa is possible as long as the objects are supported by both programs.

Various add-on modules are available for structural design in RSTAB and RFEM considering both material and standard-specific requirements. Thanks to the modular software concept, it is possible to put together a program package which is adapted to the individual needs. It is possible to upgrade the program at any time.
• How can I change the parameter of a rolled cross-section from the cross-section library?

FAQ 002369 EN General RFEM RSTAB SHAPE-THIN

If a rolled cross-section with the desired dimensions is not available in the cross-section library, it can be created manually. To do so, select the cross-section you wish to change and click the "Parametric Input" button. A dialog box opens where you can enter the desired data (see Figure 1).
• Using the Results navigator, it is possible to show the resultant of all support forces and their components.Is it also possible in RFEM to show the resultant support force of a single surface with foundation?

FAQ 002368 EN Results RFEM

Yes, support forces of single surfaces can be displayed in the table "4.21 Surfaces - Contact Stresses" available in the RFEM table window. This table can be opened by right-clicking one of the tabs of the "4.xx - Results" table (see Figure 1). In addition to the contact stresses, you can also see the corresponding support forces (see Figure 2).
• Where do I find the setting to specify the entered structural component as a "wall" or "floor"?

FAQ 002367 EN General RFEM 2D RFEM RSTAB 2D RSTAB

You find this setting in the "General Data" of the model.
You can distinguish between the model types "3D", "2D - XY", "2D - XZ" and "2D - XY".

If you want to enter a floor as a 2D model, and the axial forces within the slab should not be taken into account, set the model type to "2D - XY". If you want to enter a wall, set "2D - XZ".

Find more information in the RFEM manual, chapter 12.2.1 General - Type of Model.

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