Further Information

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• Is it possible to display or export certain results over a period of time from the time history calculation in RF-DYNAM Pro - Forced Vibrations?

New FAQ 003622 EN-US

With the time history monitor, you can view all results over a period of time. In this case, it is also possible to select several parts of the structure and then export the results directly to Excel.
• 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-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 self-weight, this option must not be activated. Otherwise, the self-weight of structure is doubled.
• Is there a possibility to display the stresses for a solid model according to the dynamic time history analysis?

FAQ 003518 EN-US

In the results tables of the RF-DYNAM Pro module, the stresses for solids are not displayed. To be able to display the stresses and internal forces, it is necessary to export the results to a load case or to a result combination. Then, you can look at the results in a load case or a result combination as usual.

• In RF-/DYNAM Pro, it is possible to find the Rayleigh damping. How do I determine these coefficients and what is their application?

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 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 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?

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?

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?

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 also possible to use nonlinear material behavior in a 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 is required in RFEM/RSTAB. This module is different in RFEM and RSTAB, depending on the type of nonlinearities to be applied.

RSTAB – Nonlinear Time History Analysis

• 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 if positive or negative internal forces

RFEM – Nonlinear Time History Analysis

In addition to the nonlinearities mentioned above, it is also possible to use 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.

• With the additional module "RF- / DYNAM Pro" there are the parameters modal mass, participation factor and substitute mass. The manual contains the formulas, the meaning and the explanation, as well as usage would be just as helpful.

FAQ 002866 EN-US

Modal mass

Each multi-mass system can usually be represented by a single-mass system. When you do this transformation, you need the modal mass of the system. This mass is needed to generate the frequency of the equivalent single-frequency oscillator.

Beiteilungsfaktor

This factor can also be negative because it is composed of the substitute mass at a node and the associated displacement due to the eigenform. 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 replacement mass factor is only the quotient of the total mass to the substitute mass. As a rule, this makes it possible to check more quickly what proportion of the excited mass of the respective eigenform is. Should it happen that the substitute mass factor is greater than 1, one should check the discretization of the system and, if necessary, refine the division of the nodes or the FE mesh.

For an earth analysis, the substitute mass factor and the substitute mass are usually decisive, since these values are used to calculate the dynamic equivalent loads on the building.

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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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