#### Further Information

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• ### Is it possible to dynamically analyze an initial deflection of a component with RFEM or RSTAB?

New FAQ 004302 EN-US

Yes, this is possible with the RF-/DYNAM Pro - Forced Vibrations add-on module. This application enables also using time history. It is available for both solution methods (linear Newmark analysis or modal analysis), but the procedures differ slightly.

The procedure is as follows:

1. Define a load case that contains a load that causes the desired initial deflection.
2. Activate the time history method of time diagrams in RF-/DYNAM Pro and define a new time diagram that has a multiplier of 0 over the entire time.

Figure 01 - Time Diagram with Multiplier 0

3. Then, select the defined time diagram in the dynamic load cases (which load case you combine it with is irrelevant because it multiplies the load by 0). You can then import the load case defined in the first step as the initial condition (or only the initial deformation in the modal analysis). Thus, the conditions from this load case are imported at time t = 0 and released immediately afterward.

Figure 02 - Activation of Initial Condition/Deformation in Dynamic Load Cases

Use this procedure to simulate a vibration after an initial deflection. To illustrate this, there is an example file in the download area where this method is displayed on a single-mass oscillator.

• ### Is it possible to consider the static rest position in a time history analysis?

FAQ 004279 EN-US

Yes, you can consider the static rest position in a time history analysis. For this you can use the 'Stationary State' function (not available in the linear modal analysis).

With this function, it is possible to read a condition from a load case or a load combination that exists over the entire time history. These include the deformations, the stiffness modifications, and the states of nonlinearities.

This function is activated in the RF-/DYNAM Pro add-on module, in the 'Calculation Parameters' tab of the Dynamic Load Cases.

The time history diagram is well suited for results evaluation. In the attached example, load case 1 with the dead load was defined as a stationary state. In the time diagram, it can be seen that the deformations oscillate about the value that is reached by the static rest position.

• ### 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?

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.
• ### Which programs and modules are suitable for the calculation and design of steel structures?

FAQ 003551 EN-US

Both RFEM and RSTAB present a suitable solution. Numerous European and international standards, as well as various add-on modules, are available for both programs, which will facilitate the daily work in steel structures.

###### Basic programs RFEM or RSTAB
The basic programs RFEM or RSTAB define structures, materials, and actions. In addition to creating spatial frame structures, for example, halls, RFEM also provides plate, pane, and shell structures, making it a more diverse option. It pays off if it is necessary to carry out design also in other areas, such as solid construction.

###### Available standards
• EN 1993-1-1 (Eurocode 3),
• AISC according to ANSI/AISC 360 (US Standard),
• SIA according to SIA 263:2013 (Swiss Standard),
• IS according to IS 800:2007 (Indian Standard),
• BS according to BS 5950-1:2000 (British Standard) or BS EN 1993-1-1 (British Annex),
• GB according to GB 50017-2003 (Chinese Standard),
• CSA according to CSA S16-09 and CSA S16-14 (Canadian Standard),
• AS according to AS 4100-1998 + Annex 1 - 1999 (Australian Standard),
• NTC-DF according to NTC-RCDF (2004) (Mexican Standard),
• SP according to SP 16.13330.2011 (Russian Standard),
• SANS according to SANS 10162-1:2011 (South African Standard),
• NBR according to ABNT NBR 8800:2008 (Brazilian Standard),
• HK according to the standard for steel structures 2011 (Buildings Department - Hong Kong)
• RF-/STEEL - General Stress Designs
###### Add-on modules for structural steelwork

The functionality of the basic programs is supplemented by add-on modules. With RF-/STEEL EC3, for example, it is possible to perform the design for the structure according to Eurocode 3. The add-on module RF-STEEL Warping Torsion supplements this design according to Eurocode 3 with torsional buckling analysis having up to 7 degrees of freedom, provided it doesn´t refer to a standard case of EC3.

Other more specialized applications such as the plastic design, the stability analysis according to the eigenvalue method or the generation of geometric equivalent imperfections and pre-deformed equivalent models are available. Single modules such as PLATE-BUCKLING provide you with support when designing rigid or stiffened plates. With the SHAPE-THIN add-on module, it is possible to create any thin-walled cross-sections. The cross-section properties are determined and stress analyzes or plastic designs can thereby be performed.

The hinged or rigid connections can be designed by means of the RF-JOINTS add-on modules.

The stand-alone application CRANWAY is available for the design of craneways.

###### Dynamic analysis

If earthquake calculations or vibration analyzes are necessary for the building, the RF-/DYNAM Pro add-on modules provide suitable tools for determining natural frequencies and shapes, analysis of forced vibrations, generation of equivalent loads, or for the nonlinear time history analysis.

In case of having any further questions about the Dlubal software, contact the sales department, please.

• ### 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 can I consider prestressed cables in RF‑/DYNAM Pro?

FAQ 003308 EN-US

The prestress of cables has a governing influence on the behavior of the structure. Therefore, it must also be considered in the dynamic analysis.

In the natural vibration cases of the add-on module, it is possible to consider stiffness modifications on the basis of a load case. This option allows you to rewrite the geometric stiffness matrix for the natural vibration analysis. In order to avoid the falsification of the results or to consider any unwanted effects, it is important to only include the prestress and no further loading in the load case to be imported.

If you want to perform the 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, it is also necessary to consider the prestress. For this, the "Stationary State" feature is available. This option allows you to consider the stiffness modifications resulting from the prestress.

• ### After running a time history analysis, I am not able to see all results on surfaces. Is there a possibility to show them?

New FAQ 003282 EN-US

In the results of the RF‑/DYNAM Pro add-on module, "Basic Internal Forces" and "Basic Stresses" on surfaces are only provided. However, you can use the option to export the results in a result combination to display all results after the time history analysis.

Simply use this option to create a result combination in the add-on module as shown in Figure 01, and show the results in the graphic. All results, such as "Design Internal Forces" or "Stresses," are available then.
• ### 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.

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If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

#### 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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