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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

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.
• ### 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.
• ### What type of procedure is carried out by the RF-/DYNAM Pro add-on module - Equivalent Loads?

FAQ 003510 EN

Like the 'Forced Vibrations' module, the 'Equivalent Loads' add-on module performs the multimodal response spectrum analysis.

Contrary to what the name suggests, the simplified response spectrum method is not carried out here, as it is explained, for example, in EN 1998-1.

The equivalent loads are determined separately for each direction of excitation according to the following formula:

$\begin{Bmatrix}{\mathrm F}_{\mathrm X}\\{\mathrm F}_{\mathrm Y}\\{\mathrm F}_{\mathrm Z}\end{Bmatrix}\;=\;\mathrm\Gamma\;\ast\;\begin{Bmatrix}{\mathrm u}_{\mathrm X}\\{\mathrm u}_{\mathrm Y}\\{\mathrm u}_{\mathrm Z}\end{Bmatrix}\;\ast\;{\mathrm S}_{\mathrm a}(\mathrm T)\;\ast\;\begin{Bmatrix}{\mathrm M}_{\mathrm X}\\{\mathrm M}_{\mathrm Y}\\{\mathrm M}_{\mathrm Z}\end{Bmatrix}\;$

The differences between the two add-on modules are described in this FAQ .

• ### There are two solution methods for the linear time history analysis in the RF-/DYNAM Pro add-on module. What is the difference between both of them?

FAQ 003507 EN

The two solution methods 'Linear Modal Analysis' and 'Linear Implicit Newmark Analysis' are available.

###### Linear Modal Analysis

This solution method uses a decoupled structure that is based on the eigenvalues and mode shapes of the structure. It is essential to assign a defined natural vibration case.

This method should only be used if a sufficient number of eigenvalues of the structure have been calculated in the natural vibration case. This means that care should be taken to achieve an effective modal mass factor of the total structure of approximately 1 in all governing directions. If this is not possible, this method will lead to inaccurate results.

###### Linear Implicit Newmark Analysis

This is a direct time stepping method that does not require a natural vibration case and requires enough small time steps to achieve exact results.

This method is recommended for complex structures, which would require a very large number of mode shapes in order to achieve an effective modal mass factor of around 1.

If a sufficient number of eigenvalues can be guaranteed by means of the linear modal analysis, both solution methods lead to approximately the same results. For more information about both methods see the RF-DYNAM Pro manual.

• ### 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

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

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.
• ### Is it possible to perform a seismic analysis with the masonry material model?

FAQ 003445 EN

The RF-/DYNAM Pro - Equivalent Loads add-on module only contains a linear analysis of structures. If you now apply a nonlinear model for the calculation, RF-/DYNAM Pro — Equivalent Loads will modify it internally and treat it as a linear model. The nonlinearity in your model presents the masonry, which cannot absorb any tensile forces.

The problem is as follows: RF-/DYNAM Pro — Equivalent Loads linearly calculates the equivalent loads and exports the load cases from them. However, the load cases are subsequently calculated nonlinearly on the basis of the material model, which is not entirely correct. In addition, the results are superimposed according to the SRSS or CQC method, which results in tensile and compressive forces being present in the model.

In this case, you could change e.g. the masonry to isotropic linear and work with linear properties of the material model. Additionally, it is possible to introduce line hinges at this place, which could be used to avoid moment restraint, for example.

• ### There are two different modules for the response spectrum analysis in RF-/DYNAM Pro. What are the reasons if the results of both modules differ?

FAQ 003429 EN

The differences between the two modules are explained in this FAQ .

In general, you should also calculate the same results for both add-on modules if the settings are identical. However, this does not apply to existing nonlinearities. This is because no nonlinearities are considered in the RF-/DYNAM Pro add-on module. If the results are output via the Forced Vibrations add-on module, all nonlinearities are ignored. In contrast to this, the equivalent loads are calculated on a linear system, but the exported load cases are then calculated on the real system, that is, with all nonlinearities in RFEM or RSTAB . This may lead to inconsistent results.

If you deactivate the nonlinearities for the exported load cases, they should have identical results.

The way of considering nonlinearities in the response spectrum analysis is described using the tension members in this FAQ.

• ### What does superposition mean according to the CQC rule in the dynamic analysis?

FAQ 003414 EN

The complete quadratic combination (CQC rule) must be applied if adjacent modal shapes whose periods differ by less than 10% are present when analyzing spatial models with mixed torsional / translational mode shapes. If this is not the case, the square root sum rule (SRSS rule) is applied. In all other cases, the CQC rule must be applied. The CQC rule is defined as follows:

${\mathrm E}_{\mathrm{CQC}}=\sqrt{\sum_{\mathrm i=1}^{\mathrm p}\sum_{\mathrm j=1}^{\mathrm p}{\mathrm E}_{\mathrm i}{\mathrm\varepsilon}_{\mathrm{ij}}{\mathrm E}_{\mathrm j}}$

with the correlation factor:

${\mathrm\varepsilon}_{\mathrm{ij}}=\frac{8\sqrt{{\mathrm D}_{\mathrm i}{\mathrm D}_{\mathrm j}}({\mathrm D}_{\mathrm i}+{\mathrm D}_{\mathrm j})\mathrm r^{\displaystyle\frac32}}{\left(1-\mathrm r^2\right)^2+4{\mathrm D}_{\mathrm i}{\mathrm D}_{\mathrm j}\mathrm r(1+\mathrm r^2)+4(\mathrm D_{\mathrm i}^2+\mathrm D_{\mathrm j}^2)\mathrm r^2}$

with:

$\mathrm r=\frac{{\mathrm\omega}_{\mathrm j}}{{\mathrm\omega}_{\mathrm i}}$

The correlation coefficient is simplified if the viscous damping value D is selected to be the same for all mode shapes:

${\mathrm\varepsilon}_{\mathrm{ij}}=\frac{8\mathrm D^2(1+\mathrm r)\mathrm r^{\displaystyle\frac32}}{\left(1-\mathrm r^2\right)^2+4\mathrm D^2\mathrm r(1+\mathrm r^2)}$

In analogy to the SRSS rule, the CQC rule can also be executed as an equivalent linear combination. The formula of the modified CQC rule is as follows:

${\mathrm E}_{\mathrm{CQC}}=\sum_{\mathrm i=1}^{\mathrm p}{\mathrm f}_{\mathrm i}{\mathrm E}_{\mathrm i}$

with:

${\mathrm f}_{\mathrm i}=\frac{{\displaystyle\sum_{\mathrm i=1}^{\mathrm p}}{\mathrm\varepsilon}_{\mathrm{ij}}{\mathrm E}_{\mathrm j}}{\sqrt{{\displaystyle\sum_{\mathrm i=1}^{\mathrm p}}{\displaystyle\sum_{\mathrm j=1}^{\mathrm p}}{\mathrm E}_{\mathrm i}{\mathrm\varepsilon}_{\mathrm{ij}}{\mathrm E}_{\mathrm j}}}$

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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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