#### Further Information

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

New FAQ 004279 EN

Yes, you can consider the static rest position in a time history analysis. The "Stationary State" function is available for this (not available in the linear modal analysis).

With this function, you can import a condition from a load case or load combination that exists over the entire time history. These include the deformations, the changes in stiffness, and the states of nonlinearities.

This function is activated in the RF-/DYNAM Pro add-on module, in the "Load 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 steady state. In the time diagram, it can be seen that the deformations oscillate about the value that is reached by the static rest position.

• ### What is the procedure for performing an earthquake analysis in RFEM/RSTAB?

New FAQ 004258 EN

For an earthquake analysis, the RF-/DYNAM Pro - Natural Vibrations and RF-/DYNAM Pro - Equivalent Loads add-on modules are available. Thus, it is possible 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.

In addition, you can evaluate the projectile displacement and the horizontal shear of the building. These and other features are described in detail in the webinar "Seismic Analysis in RFEM ".
• ### Is it possible to hide background layers?

New FAQ 004177 EN

Background layers can be hidden or displayed in the Display Navigator under Guide Objects → Background Layers. The visibility can be defined individually or for all.

• ### Is there a possibility in RFEM to consider friction for the horizontal reactions of  surface support?

New FAQ 004146 EN

For surface supports, this option is only available if a non-linearity in the local z direction has also been defined (failure if contact stress in z is negative/positive). In the dialog box where you can edit the non-linearity, there is the option 'Friction in plane xy'.

This option works as shown in the graphic dialog box: The support in x and y direction is only completely assumed when the contact stress Tau (contact stress Sigma by friction coefficient) is reached. It has to be reduced linearly before this.

In order to use this option, it is necessary to define a support in the horizontal directions. It can be defined as fixed or with an elastic spring. If the spring is defined with 0, no support is considered even when a friction coefficient is entered.

• ### In a nonlinear system, some load cases do not converge. The load combinations, however, can easily be calculated. What is the cause of it?

FAQ 004114 EN

When defining non-linearities, for example, failure of support under tension, it may happen that some load cases cannot be calculated. If these are loads that cannot exist without other stabilizing loads, solving the problem is simple: You can set the load cases to 'Not To Be Calculated'. As a result, only the load combinations are considered in the option 'Calculate All' of the calculation process. This is possible because, for example, some loads can never appear without having a self-weight.

In the attached example, it is clearly evident that the system would buckle in the load case wind, and thus no convergence is found. In contrast to this, it is possible to calculate the load combination in which self-weight and wind are combined without a problem because the self-weight stabilizes the system.
• ### What is the difference between the materials Isotropic Plastic 1D and Isotropic Nonlinear Elastic 1D?

FAQ 003604 EN

The difference between both material models is as follows:

In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state when the load is released.

Whereas in the case of the material model Isotropic Plastic 1D, the plastic deformation is considered.

For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible to define a distribution in both models after the last step.

For the material model Isotropic Nonlinear Elastic 1D, it is possible to enter the stress-strain diagram (different for the positive and negative zone) in an anti-metrical way, whereas for the model Isotropic Plastic 1D, only symmetric input is possible.

• ### 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.

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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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