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• ### RF-/DYNAM Pro - Equivalent Loads includes the result tables "5.8/5.9/5.10 - Equivalent Loads." Which sum is displayed in the case of the "All mode shapes" option?

The sum indicated in this table does not reflect the correct superposition according to the standard. This is a simple summing up of the equivalent loads. A superposition with the selected superposition rule (SRSS or CQC) is not performed in this table!

Furthermore, there are differences if activating the accidental torsion in the add-on module. This leads to the generation of two load cases for each mode shape. They always contain the torsional moment in the positive and in the negative direction. As a result, the equivalent loads are doubled in this table.
• ### Is it possible to display natural frequencies separately for each direction?

Spatial models with several directions selected in the RF‑/DYNAM Pro - Natural Vibrations add-on module display no separate results of mode shapes for the individual directions. It may happen that one mode shape of the vibrations is dominant in one direction (thus, the mass is only excited in one direction, such as in the X-direction only). However, it may also happen that one mode shape has vibrations in several directions at the same time (that is, the mass is excited in two or more directions, for example in the X- and Y-direction at the same time). Therefore, the mode shapes are not dependent on the global coordinate system, but on the stiffnesses of the structure in the individual directions.

You can check the direction, in which the dominant vibration of a mode shape acts, by displaying the "Effective Modal Mass Factors" table and checking whether the mass was excited in the individual directions. Figure 01 shows on the effective modal masses that the first mode shape acts solely in the Y-direction, the second one in the X-direction, and the third one is the torsional vibration.

It is possible to define several natural vibration cases and to only activate the masses in one direction. Thus, the mode shapes for each direction are obtained separately in each case.

• ### How is the plastic torsion determined in the plastic hinge definition?

The plastic rotation is determined automatically for each hinge, based on the previously determined cross-section and the member length. For this, the following formula is used:

$\varphi_{y,pl}=\frac{W_{y,pl}\cdot f_y\cdot l_b}{6\cdot E\cdot I_y}$

• ### Is it possible to consider the second-order theory in a dynamic analysis in RSTAB?

There is a detailed technical article for considering the second-order theory in a dynamic analysis in RFEM (see the link at the end of the FAQ). This article describes primarily the usage of the RF‑DYNAM Pro - Equivalent Loads add-on module. This add-on module does not allow for any consideration in RSTAB.

In order to correctly display the second-order theory in RSTAB, it is necessary to use the DYNAM Pro - Forced Vibrations add-on module. In this add-on module, the results are fully calculated within the add-on module. If you wanted to export the load cases first, the internal forces could not be calculated with regard to the modified stiffness matrix.
• ### Which formula is used in the RF‑/TOWER Loading add-on module to calculate the first natural frequency for the determination of the structure coefficient?

The first natural frequency is required to determine the structure coefficient. It is not determined by using a generalized formula, but the integrated eigenvalue solver RF‑/DYNAM, taking into account the real mass distribution and displaying the results in Column A of Table 2.3.

• ### Is it possible to control the beam steering of an antenna in RF‑/TOWER Design?

Beam steering is the angular rotation of antennas under the effect of the present loads (wind, overload, earthquake, deformation, and so on). As an indication, for the GSM, the value of the beam steering must not exceed 1°. This limit of beam steering is often accessible in the clauses of the Technical Specifications of the project.
In RF‑/TOWER Design, it is possible to control the beam steering of antennas for the SLS design. To activate this rotation design of antennas, go to DetailsServiceability.

As soon as you select this check box, the antennas are available in Window 1.10.2 Serviceability of Antennas. Here, you can enter the angular rotation limit of each antenna.

After the calculation, the maximum ratio is displayed in Window 2.7 Design by Antenna.

• ### In RF-/DYNAM PRO - Forced Vibrations, why does my time diagram function formula output incorrect values which appear to be off by only a factor?

In the Dlubal programs, all values are stored internally based on SI units. When a user changes the units in the program to metric or imperial, SI units are still used internally and only the value displayed in the interface is modified. Therefore, all values set in the time diagram function also default to SI units unless the user clarifies an alternative unit.

Let's look at a simple example shown in Figure 1 where the parameter x = 1 ft has been set in RFEM.

In RF-DYNAM PRO - Forced Vibrations, the time diagram function is defined as k(t) = 1*x where 1 is the multiplier (1/ft) to convert x to a dimensionless value. You can see in Figure 2, because all values default to SI units, the Multiplier column produces values of 0.305 instead of the correct value of 1.000.

In order to correct the issue, the user only needs to specify the units of the multiplier as (1/ft) in the function equation. This can be done with the formula modification k(t) = 1/1[ft]*x as shown in Figure 3. Notice the Multiplier column now shows the correct values of 1.000.

In summary, when using units in the program other than SI units, coefficients or multipliers in the time diagram function should be accompanied with alternative units defined in brackets.

• ### Is it possible to perform a dynamic analysis of the initial deflection of a structural component in RFEM or RSTAB?

Yes, it is possible by using the RF‑/DYNAM Pro - Forced Vibrations add-on module. This application also allows you to use time history. It is available for both solution methods (linear Newmark analysis or modal analysis), but the procedures are slightly different.

The procedure is as follows:

1. Define a load case containing 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.

3. Then, select the defined time diagram in the dynamic load cases (it is irrelevant which load case you combine it with as 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 afterwards.

Use this procedure to simulate a vibration after the initial deflection. To illustrate this, you can find an example file under Downloads where this method is shown on a single-mass oscillator.

• ### Are the models and presentations from Info Day 2015 freely available, and can you send them to me?

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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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