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• ### How do I display the load combination description according to an action category, such as "D, L, W" instead of "LC1, LC2, LC3"?

In the Program Options menu, under Program tab, you can check the "Combination description according to action category" to display "D, L, W" instead of "LC1, LC2, LC3."
• ### How can I consider loads from the self-weight as "favorable" and "unfavorable" for the combinations?

For this, there is an option in the "Combination Expressions" tab when activating the automatic combinations, which allows you to activate the favorably acting permanent loads.
• ### For a specific combination rule, I would like to consider a load case with a combination coefficient that deviates from the standard. How can I proceed?

First, you should consider whether it is not easier for the different combination rule to define the load combinations manually in addition to the automatically generated combinations: If there are only a few load combinations, they can be created quickly. However, if the effort is too great due to many load cases, you can proceed as follows:

###### Example

For the combination rule "earthquake" according to EN 1990, the snow (≤ 1000 m) should be considered with 0.5 instead of ψ2 = 0.0. For the "Permanent/Temporary" design situation, however, soll2 should be considered as 0.0 according to the standard.

In order to consider different values for the two combination rules, it is necessary to copy the snow load case and to change the action category of the copied load case to "Other" (see Figure 01).

By default, the combination factor ψ2 is stored with 0.5 for this action category (see Figure 02).

If you need a different value, you can select a different, suitable action combination for the copied load case. If there is no action category that meets the desired value, you can create a user-defined standard. You can find the description of how to do it under the link below this FAQ.

In order to avoid the superposition of Load Case 3 and Load Case 4 shown in Figure 01, the respective load case must be excluded in the combination expressions. To do this, use the "Reduce number of load cases ..." function (see Figure 03).

Then, you can assign the load cases to be combined with the respective combination expressions (see Figure 04 and Figure 05).

• ### 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 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.
• ### Where can I define a wind velocity diagram according to a specific wind standard for the numerical wind tunnel analysis in RWIND Simulation?

In RWIND Simulation, the wind velocity is organized by means of the height of the wind tunnel inlet in a table, depending on the height coordinates and wind speeds. You can enter the data in this table manually in RWIND, or by using specific function generators.

If you do not create the model directly in RWIND Simulation, but transfer it from RFEM or RSTAB to RWIND Simulation, you can also define the wind velocity diagram in the interface window according to one of the available wind standards:
• EN 1991-1-4
• ASCE/SEI 7-16
• NBC 2015
The wind velocity diagram then results from the respective standard parameters (zone, terrain category, and so on).

• ### What is the formula used to calculate the ASCE 7 wind velocity profile?

The wind velocity profile in RWIND Simulation according to the ASCE 7-16 standard [1] is calculated based on Eq. 26.10-1. The coefficients and basic wind speed in this equation below are incorporated in the wind pressure equation.

Velocity wind pressure (imperial): qz = 0.00256 Kz Kzt Kd Ke V2

We must reference this equation to calculate the inlet velocity relative to elevation for the RWIND Simulation CFD wind tunnel. To consider only velocity rather than pressure from this equation, the basic wind speed is multiplied by the square-root of each coefficient. Notice the velocity variable in Eq. 26.10-1 is squared which requires the square root of the coefficients to be considered.

$Inlet\;velocity\;=\;V\sqrt{K_e\;\cdot\;K_{d\;}\cdot\;K_z\;\cdot\;K_{zt}}$

Because the ASCE 7-16 standard does not address wind CFD analysis and magnitude of the required inlet velocity, it is difficult to draw comparisons. Therefore, this is the closest estimate for calculating the RWIND Simulation inlet wind velocity per the code.

• ### Is it possible to perform automatic live load reduction in RFEM or RSTAB per the ASCE, IBC, or NBCC?

Live load reduction is not considered automatically in RFEM. RFEM and RSTAB are general FEA and framework programs. The program does not understand what is a floor element vs wall element. Only a general plate element is defined. It is not possible for the program to determine the area of a floor for live load reduction.

A user must manually consider the reduction by modifying the live load magnitude directly in the load application.

• ### Is it possible to use the RF‑/STEEL AISC add-on module itself to specify the internal forces, for example, from another calculation or program?

Unfortunately, this is not possible. The design module can only be used together with the internal forces from RFEM or RSTAB.
• ### Is the Gust-effect (G or Gf) from the ASCE 7-16 Sect. 26.11 considered in RWIND Simulation?

Yes, the Gust-factor G or Gf, can be adjusted in RWIND Simulation. This value can be changed within the "Wind load" tab under "Wind velocity."

In the ASCE 7-16, the conservative value for the Gust-factor, G, is 0.85 for rigid buildings. The engineer can calculate an alternative and more accurate value. The Gust-effect, Gf, for flexible buildings accounts for size and gust size similar to rigid buildings but also considers dynamic amplification including wind speed, natural frequency, and damping ratio.

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Wind Simulation & Wind Load Generation

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The generated wind loads acting on these objects can be imported to RFEM or RSTAB.

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