# Frequently Asked Questions (FAQ)

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• ### What is the approach for seismic design in RFEM/RSTAB?

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 1.

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.

• ### What method is applied in the RF‑/DYNAM Pro - Equivalent Loads add-on module?

Just as in the "Forced Vibrations" add-on module, the "Equivalent Loads" add-on module performs the multimodal response spectrum analysis.

Although the name may suggest otherwise, the simplified response spectrum method is not carried out here, as explained in EN 1998‑1, for example.

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 both 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 dynamic calculations require a lot of data and results.

In each of the mentioned add-on 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.

Furthermore, 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 add-on modules for a response spectrum analysis in RF‑/DYNAM Pro. What can be the reasons for the different results of both add-on modules?

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

In the case of the same settings, there should also be the same results calculated in both add-on modules. However, this does not apply to the existing nonlinearities. The reason is that there are no nonlinearities considered in the RF‑/DYNAM Pro add-on module. If displaying the results in the Forced Vibrations add-on module, all nonlinearities are thus ignored. In contrast, the equivalent loads are calculated on a linear structural system, but the exported load cases are then calculated on a real structure in RFEM and RSTAB, that is, with all nonlinearities. This may lead to inconsistent results.

If you deactivate the nonlinearities for the exported load cases, you should obtain the same results.

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

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

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.

• ### When starting the program, I get Warning No. 50 "Program authorization failed." What is the reason?

If you are using a single-user license (as a student, for example), make sure that you do not try to get access to this license via remote access. Moreover, a single-user license cannot be used on virtual machines. Both cases cannot be covered by a single-user license.

If you see this message when trying to access a network dongle, it may be due to the server's response time. Copy the hasp_48521.ini file into the folder
C:\Users\#USER#\AppData\Local\SafeNet Sentinel\Sentinel LDK\
(replace #USER# with your user name).

Then, open the hasp_48521.ini file. Enter the IP address of the dongle server as well as the access times (see Figure 02).

If you access the dongle server via VPN connection, please make sure that the IP address of the dongle server is stored in Admin Control Center (see FAQ 002070).

• ### Can I display the equivalent loads generated by the RF‑/DYNAM Pro - Equivalent Loads add-on module?

The RF-/DYNAM Pro - Equivalent Loads add-on module allows you to perform a multimodal response spectrum analysis. Equivalent loads are created and exported in load cases to the main program RFEM or RSTAB. The load cases are created separately for each selected mode shape and excitation direction. You can display the loads as usual.

The equivalent loads are generated at each finite element node (or each inner node). If the number of generated loads is too large, the graphical display is deactivated. You can change this setting in the details of the RF‑/DYNAM Pro add-on module.

• ### How is it possible to consider tension members in RF‑/DYNAM Pro?

Dynamic analyzes are always performed on linear systems. To avoid nonlinearities, such as Considering tension members in a dynamic analysis requires a complex approach. This procedure is described for the add-on modules Natural Vibrations and Equivalent Loads in this technical article.

However, it should be considered whether this time-consuming consideration is necessary for your system or whether linearization is sufficient.

In the Nonlinear Time History add-on module, tension members are considered as usual. An example is described in this technical article.

• ### RF‑/DYNAM Pro - Forced Vibrations and RF‑/DYNAM Pro - Equivalent Loads perform the multi-modal response spectrum analysis. What are the differences?

RF-/DYNAM Pro - Equivalent Loads performs a multi-modal response spectrum analysis with the export of equivalent loads.

1) The static equivalent loads are calculated and exported to load cases. This happens separately for each mode shape and each direction of excitation.

2) The total earthquake forces can be determined easily for each mode shape.

3) The accidental torsional actions can be considered automatically.

4) The load cases are calculated in the main program RFEM/RSTAB. Possible nonlinearities are taken into account; the calculation parameters of the load cases can be adjusted (for example, the calculation according to the second-order analysis, deactivation of nonlinearities).

5) The stiffness modifications from the natural vibration cases (NVCs) are not transferred to the load cases automatically.

6) The result combinations are generated individually for each excitation direction (combined modal responses with SRSS or CQC) and for the combination of results from different excitation directions (SRSS, 100%/30% (40%)).

7) The sign-dependent results are available on the basis of the dominant mode shape, which results in unique RCs.

8) The results can be reproduced step by step.

In RF‑/DYNAM Pro - Forced Vibrations, a multi-modal and multi-point response spectrum analysis is performed.

1) A building can be subjected to the excitations by different response spectra at different supports and in different directions.

2) The calculation and superposition are carried out within the RF‑/DYNAM Pro add‑on module. The calculation is linear, nonlinearities are not taken into account. The stiffness modifications from the ESFs are applied.

3) The result combinations of the superimposed results are only exported.

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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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