#### Further Information

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For seismic design, the add-on modules RF-/DYNAM Pro - Natural Vibrations and RF-/DYNAM Pro - Equivalent Loads are available. They allow you 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.

Furthermore, you can evaluate the story drift and the horizontal shear of the building. These and other features are described in detail in the webinar "Response Spectrum Analysis in RFEM."
• ### When designing seismic equivalent loads with a Response Spectra Analysis (RSA) in RFEM, how can I apply the modal response parameters Ie/R according to Sect. 12.9.1.2 in the ASCE 7-16 to my results?

The modal response parameters can be set  in the RF-DYNAM PRO - Equivalent Forces add-on module under the Response Spectra tab. In the Code Parameters table > Type of Spectrum > Modal Response Parameters, the default is set to "No Modification." This setting can be seen in Figure 2.

Changing this to "Force Related" in the drop-down window will divide the response spectra by Ie/R based on Sect. 12.9.1.2 [1]. Additionally, in the Code Parameters table > Coefficients, the Seismic Importance Factor (Ie) and the Response Modification Factor (R) can further be set.
• ### 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?

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?

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 .

• ### How can I display the results of the RF-/DYNAM Pro add-on module in the printout report?

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.
• ### 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?

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?

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:

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

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

In the Settings, you can define how results from different mode shapes of the structure are combined. The modal combination is the first step of the dynamic combinations. The modal responses can be combined with the Square Root of the Sum of Squares (SRSS) or the Complete Quadratic Combination (CQC). Both of these quadratic combinations can be applied in the standard form or modified as an equivalent linear combination. The standard form of the SRSS rule combines maximum results and the algebraic signs are lost; the combination expression is as follows:

${\mathrm E}_{\mathrm{SRSS}}\;=\;\sqrt{\mathrm E2\;1\;+\;\mathrm E2\;2\;+\;\dots\;+\;\mathrm E\;2}$

In the RFEM add-on module RF-DYNAM Pro, a modified form of the SRSS rule is available to determine the corresponding results, such as the corresponding internal forces. In relation to the standard form of the SRSS rule, the corresponding internal forces are usually much smaller. Furthermore, the corresponding signs are correct in relation to the governing internal force. The SRSS rule is used as an equivalent linear combination:

${\mathrm E}_{\mathrm{SRSS}}\;=\overset{\mathrm p}{\underset{\mathrm i=1}{\sum{\mathrm f}_{\mathrm i}}}{\mathrm E}_{\mathrm i}$

with:

$f_i=\frac{E_i}{\sqrt{{\displaystyle\sum_{i=1}^p}E_j^2}}$

If this formula is applied, the results are consistent.
• ### 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?

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.
• ### Is there a possibility in the module RF-DYNAM Pro to generate a "response spectrum according to standard" with user-defined parameters?

Yes the possibility exists. In many standards we have implemented this possibility. Here you can select the option "Other" as subsoil class and thus adapt some parameters according to your wishes.

The following annexes to EN 1998-1 have this option: CEN, NBN, CSN, DIN, UNI, NP, STN, CYS, BS, NS and NF.

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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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