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• ### In RF- / DYNAM Pro, the option "Based on the building own weight" 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-US

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 dead load, this option must not be activated. Otherwise, the structure's own weight is doubled.
• ### In RF-/DYNAM Pro, it is possible to find the Rayleigh damping. How do I determine these coefficients and what is their application?

New FAQ 003505 EN-US

For some solution methods, the Rayleigh coefficients are absolutely necessary. Since only the Lehr's damping values are given in the literature, they have to be converted.

The following formula is used for converting Lehr's damping values into Rayleigh coefficients:

${\mathrm D}_{\mathrm r}\:=\:\frac12\;\left(\frac{\mathrm\alpha}{{\mathrm\omega}_{\mathrm r}}\;+\;\mathrm\beta\;{\mathrm\omega}_{\mathrm r}\right)$

Where α and β are the Rayleigh coefficients. It is necessary to set up a system of equations always containing the natural angular frequencies of the two most dominant mode shapes. In the case of these two mode shapes, the structure will then be damped with the specified damping value. All other mode shapes of the structure will have different damping values. These result from the curve displayed in Figure 01. The curve shows an example of the two natural angular frequencies of 10 and 20 rad/s and Lehr's damping of 0.015.

It is also possible to use the 'Calculate from Lehr's Damping ...' button to activate corresponding conversion tool.
• ### How can I display the results of the RF-/DYNAM Pro add-on module in the printout report?

New FAQ 003486 EN-US

The results of the RF-/DYNAM Pro add-on modules Forced Vibrations , Nonlinear Time History and Equivalent Loads are not listed directly in the printout report. This is generally due to the fact that a lot of data and results are required for dynamic calculations.

In each of the mentioned modules, it is possible to create a result combination with the envelope results. In this generated result combination, you can find the same results as in the main programs and display them in the printout report as usual.

Additionally, you can print pictures in the printout report as usual. There is also an option to display the time history graphically in the printout report.
• ### How should be considered the prestressed cables in RF-/DYNAM Pro?

New FAQ 003308 EN-US

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.

• ### After running a time history analysis, I'm not able to see all results on surfaces. Is there a possibility to show them?

New FAQ 003282 EN-US

In the results of the module RF-/DYNAM Pro only "Basic Internal Forces" and "Basic Stresses" on surfaces are provided. But with the option to export the results in a result combination, you have the possibility to display all results after a time history analysis.

Simply use the option to create a result combination in the add-on module as shown in Figure 1 and show the results of this in the graphic. All results, such as "Design Internal Forces" or "Stresses" are available.

• ### Is it possible to also use nonlinear material behavior in the time history analysis?

FAQ 003013 EN-US

To be able to consider nonlinearities in dynamics, the RF-/DYNAM Pro - Nonlinear Time History add-on module for RFEM/RSTAB is required. This module is different in RSTAB and RFEM, depending on the type of nonlinearities to be applied.

###### RSTAB - Nonlinear Time History

• Nonlinear member types such as tension and compression members, as well as cables
• Member nonlinearities such as failure, tearing, and yielding under tension or compression
• Support nonlinearities such as failure, friction, diagram, and partial activity
• Hinge nonlinearities such as friction, partial activity, diagram, and fixed for positive or negative internal forces

###### RFEM - Nonlinear Time History

In addition to the nonlinearities mentioned above, it is also possible to work with nonlinear material behavior.

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

FAQ 002913 EN-US

In this case, you have the option to print the image in the time course diagram directly into the printout report. Proceed as described in the picture.

• ### Which time step should I select for the calculation of the time history analysis in the RF- / DYNAM Pro add-on module?

FAQ 002655 EN-US

There are two options to choose from: an automatic time step selection and a manual one. Especially for a structure with nonlinearities, it is always recommended to manually select the time step and perform a time step convergence study that compares the computation time and accuracy.

The time step to choose depends on many factors, including the excitation frequency, the frequency and size of the structure, and the degree of non-linearity. So no general statement about the size of the time step can be made.

For detailed information on this and many other topics, see the <a href="https://www.dlubal.com/-media/3BEF143083FA4DC3A9463B0E4166CCF0.ashx" target="_blank"> manual </a> of the additional module RF- / DYNAM Pro.

• ### I am interested in one of the modules for dynamic analysis. Can I buy each module separately or only in a package?

FAQ 000206 EN-US

You always need RF-/DYNAM Pro - Natural Vibrations. The additional modules can be purchased depending on your needs. The following additional modules are available: RF-/DYNAM Pro - Forced Vibrations and RF-/DYNAM Pro - Equivalent Loads.