#### 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.

• ### 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?

New 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 unusual combination. This combination is, for example, in the EN 1990 clause 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 unusual 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. Such a combination can be seen in Figure 02.

This unusual 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?

New 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 not possible to calculate the eigenvalues for the entered precision [...]". How can I fix this error?

New FAQ 003162 EN

In a dynamic analysis, you can only calculate the eigen modes as many degrees of freedom as the system has. With degrees of freedom, the number of mass points multiplied by the number of directions into which the masses act is meant.

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, so only 2 eigen-modes can be calculated.

Caution: In this case, the choice of the solution method is very important. In contrast to the "Root of Characteristic Polynomial" method, the Lanczos method can not calculate all eigenvalues of the system, but only n -1, which means in this example only 1 eigenvalue.

• ### Which modules can be addressed 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 the 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 for this?

FAQ 003028 EN

Before you can start the calculation in the add-on module, you should check each tab. This message appears if you have not opened the calculation parameters of the natural mode case at least once. Although a bulk case has been defined, it has not yet been assigned to the natural mode 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.
• ### For the "RF-/DYNAM Pro" add-on module, there are the parameters Modal mass, Participation factor, and Equivalent mass. Although the manual contains the formulas, the meaning and the explanation, it is also helpful to use them.

FAQ 002866 EN

Modal mass

Each multi-mass system can usually be represented by a single-mass system. When performing this transformation, the modal mass of the system is necessary. This mass is required to generate the frequency of the equivalent oscillators with a single degree of freedom.

Participation factor

This factor can also be negative because it consists of the equivalent mass on a node and the corresponding displacement due to the mode shape. If the deflection is in the negative direction, the participation factor becomes negative. The replacement mass factor is then still positive, since the participation factor is squared. (see formula)

Equivalent mass

The equivalent mass of a system is a part of the total mass which is excited due to the vibration of the multi-mass oscillator. The equivalent mass of a system can be between zero and the total mass. The equivalent mass factor is only the quotient from the total mass to the equivalent mass. Thus, it is usually possible to check more quickly what the ratio of the excited mode mass of the respective mode shape is. Should it happen that the equivalent mass factor is greater than 1, you should check the discretization of the system and, if necessary, refine the division of the nodes or the FE mesh.

For an earthquake analysis, the equivalent mass factor and the equivalent mass are generally decisive because these values of the dynamic equivalent loads are calculated for the building.

1 - 10 of 19