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

FAQ 003510 EN-US

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?

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.
• ### 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-US

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-US

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??

FAQ 003413 EN-US

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.
• ### 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.

• ### Is there a way to generate a “Response spectrum according to the standard” with user-defined parameters in the module RF-DYNAM Pro?

FAQ 002901 EN-US

Yes, the possibility exists. In many standards we have implemented this possibility. Here you can select the option "Other" as site 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.

• ### 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.
• ### How do I superimpose generated equivalent loads from the seismic analysis?

FAQ 002720 EN-US

When calculating by using the Equivalent Load Method, an equivalent load is determined from the individual mode shapes as the name implies. After a successful determination, you can export these equivalent loads in RFEM. RFEM automatically creates load cases in this way.

These exported load cases are now superimposed in a result combination. One always uses a quadratic superposition for earthquake storm loads. Two types of superposition are possible here. For one thing, the often-used SRSS rule and the CQC rule. All load cases from the earthquake will always be considered as Permanent and superimposed according to the respective regulations. The calculation rules are governed by the common standards.

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