#### 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.

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• ### What is the procedure for performing an earthquake analysis in RFEM/RSTAB?

New FAQ 004258 EN

For an earthquake analysis, the RF-/DYNAM Pro - Natural Vibrations and RF-/DYNAM Pro - Equivalent Loads add-on modules are available. Thus, it is possible to perform the multimodal response spectrum analysis. After the analysis in the add-on modules, the calculated seismic loads are exported to load cases, which can be evaluated as usual.

In addition, you can evaluate the projectile displacement and the horizontal shear of the building. These and other features are described in detail in the webinar "Seismic Analysis in RFEM ".
• ### I have used the RF-/DYNAM Pro add-on module to generate the governing result combinations of seismic loads. What is the next way to perform a design of the individual components?

FAQ 003598 EN

With the Equivalent Loads and Forced Vibrations add-on modules, you can create result combinations that contain the governing combinations of seismic loads. To perform a design with them, they have to be combined further on the basis of the extraordinary combination. This combination is defined, for example, in EN 1990 Art. 6.4.3.4:

${\mathrm E}_{\mathrm d}\;=\;\underset{}{\sum_{}^{}\;{\mathrm G}_{\mathrm k,\mathrm j}\;+\;\mathrm P\;+\;{\mathrm A}_{\mathrm{Ed}}\;+\;}\overset{}{\underset{}{\sum{\mathrm\psi}_{2,\mathrm i}\;{\mathrm Q}_{\mathrm k,\mathrm i}}}$

This accidental combination has to be defined manually in RFEM. Make sure that (for a direction combination with the 100/30% rule), both created result combinations from RF-/DYNAM Pro have to be added with the "Or" condition. A combination like this is displayed in Figure 02.

This accidental combination can then be used for further design. It is possible to evaluate the governing internal forces as well as to import and calculate this combination in the design modules.
• ### In RF-/DYNAM Pro, the option "From Self-Weight of Structure" is available in the mass case. Does this option always have to be activated to consider the self-weight of the structure?

FAQ 003573 EN

No, this option does not necessarily have to be activated to consider the self-weight. If the masses are imported from a load case that already contains the self-weight, this option must not be activated. Otherwise, the self-weight of structure is doubled.
• ### When calculating eigenvectors with RF-/DYNAM Pro, I receive effective modal mass factors, which are all approximately 0. What can be the reason for this?

FAQ 003365 EN

The cause of small effective modal mass factors can be very diverse. Often, this can be observed for larger structures. The reason for this problem consists in most cases in the fact that only local eigenvectors occur. The following describes how you can handle this point:

• If they really refer to local eigenvectors, or not, should be analyzed in the results graphic. If single members or surfaces have a very low angular frequency, they occur first.
• If you want to include these local eigenvectors in the calculation, you should increase the number of eigenvectors to be calculated.
• If local eigenvectors occur on surfaces, the masses of the affected surfaces can be neglected. This feature is described in this article .
• In case of local eigenmodes on members, it is recommended to deactivate the FE mesh splitting on members.
If all of these notes have been observed, only the global eigenmodes of the structure should be activated, which also activate a high mass.

• ### How should be considered the prestressed cables in RF-/DYNAM Pro?

FAQ 003308 EN

The prestressing of cables has a governing influence on the behavior of a structure. Therefore, it must also be considered in the dynamics.

In the natural vibration cases of an add-on module, it is possible to consider stiffness modifications on the basis of a load case. With this option, the geometric stiffness matrix is rewritten for the natural vibration analysis. In order to avoid falsifying the results or to consider any unwanted effects, it is important that the load case to be imported contains only the prestress and no further loading.

If you want to perform a time history analysis, make sure that the implicit Newmark analysis and the explicit analysis do not use the natural vibration cases, but that the calculation parameters are defined directly in the dynamic load case. Therefore, the prestress must also be taken into account. The "Stationary State" function is available for this. With this option, the stiffness modifications resulting from the prestress are taken into account.

• ### How can I display nodal masses?

FAQ 003303 EN

For members (RSTAB) or members, surfaces, and solids (RFEM), you can display the material weight W. Simply select the entire structure or a part thereof and right-click to open the shortcut menu. Here you will find the entry "Center of Gravity and Info ...".

However, the nodal masses are not apparent from this.

To generate nodal masses, you can use the RF-/DYNAM Pro Natural Vibrations add-on module. In this case, you it is possible to create a natural vibration case where the mass acts e.g. only in the Z direction. After having calculated the natural mode case, the "nodal masses" are available in the results tables of RF-/DYNAM Pro.

In RF-/DYNAM Pro, you can optionally convert the nodal loads into masses by applying the force components of the respective load case to the natural case calculation.

• ### In RF‑/DYNAM Pro, I get the error message No. 10040: "It was impossible to calculate all eigenvalues with required accuracy. [...]." How can I fix this error?

FAQ 003162 EN

In a dynamic analysis, you can only calculate as many mode shapes as the structural system has degrees of freedom. The degrees of freedom mean the number of mass points multiplied by the number of the directions in which the masses act.

Example

A cantilever that is not split by the FE mesh has a mass point at the end. The action direction of the masses in RF‑/DYNAM Pro is limited to the X and Y direction. Thus, the system has 2 degrees of freedom, thus 2 mode shapes can only be calculated.

Please note: In this case, the selection of the method for solving eigenvalue problem is very important. In contrast to the "Root of the characteristic polynomial" method, the Lanczos method cannot calculate all eigenvalues of the system, but only n -1, which means only 1 eigenvalue in this example.

• ### Which modules are responsive via the COM interface RS‑COM or RF‑COM?

FAQ 003034 EN

With the COM interface, you can access most operating elements as well as results of the following programs or add-on modules:

• RF-/STEEL
• RF-/STEEL EC3
• RF-/ALUMINUM
• RF-/CONCRETE
• RF-STABILITY
• RF-/TIMBER Pro
• RF-/DYNAM Pro
• ### In RF-/DYNAM Pro, I get the error message: "The assigned mass case does not exist," although I have defined a mass case. What is the reason?

FAQ 003028 EN

Before you start the calculation in the add-on module, it is recommended to check all tabs. This message appears if you did not open the calculation parameters of the natural mode case at least once. In spite of having defined a mass case, it has not yet been assigned to the natural vibration case.

• ### I create a picture for the time in DYNAM PRO, and paste it via the clipboard in the printout report, this picture appears very blurred. What can I do about it?

FAQ 002913 EN

In this case, you have the option to print the image in the timeline diagram directly into the printout report. Here you proceed as described in the picture.

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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.

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