# Frequently Asked Questions (FAQ)

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

#### Answer

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 module as it is and to specify the internal forces, for example, from another calculation or program?

New

FAQ 004305 EN-US

#### Answer

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

#### Answer

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.

The Gust-factor G or Gf, is considered to be 1.0 in RWIND Simulation. The structure is rigidly simulated in the numerical wind tunnel. The loads which are transferred back into RFEM are applied to the elastic structure with true stiffness considered.

To account for any value other than 1.0 for this factor, the wind load case factor can be adjusted in RFEM under the applicable load combination.
• ### Will other standards be added to the wind profile generation options in RWIND Simulation?

New

FAQ 004299 EN-US

#### Answer

Additional standards and codes to generate the wind profile automatically in RWIND Simulation will be added in the future. We are always considering feedback from our current customers on which standards will be beneficial.

• ### Does software RWIND Simulation account for the internal pressure coefficient (GCpi) from the ASCE 7-16?

#### Answer

The internal pressure coefficients do not need to be considered with in the RWIND Simulation program.

RWIND Simulation always outputs the net pressure on the surfaces in RFEM. When it comes to a simulation with a building that has open windows in RWIND Simulation, there is an internal pressure acting on the inside of the building. The program uses this information to determine the resulting pressure based on the external and internal surfaces. This can be seen in Figure 1.

A comparison cannot be made between this coefficient in the standard and a CFD calculation because there is no direct correlation.

• ### Does the software RWIND Simulation consider the wind directionality factor (Kd) from the ASCE 7-16?

#### Answer

The wind directionality factor (Kd) from the ASCE 7-16 Sect. 26.6 is not automatically considered in the ASCE 7-16 wind load profile or RWIND Simulation calculation. The wind directionality factor (Kd) can be considered in RWIND Simulation by modifying the load case factor for the load cases generated by RWIND Simulation in RFEM. These equivalent load case factors can be edited and customized under the "Load Combinations" tab with in the "Edit Load Case and Combinations" dialog box.

This factor for various structure types can be determined from table 26.6-1 from the ASCE 7-16 [1].

• ### 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?

#### Answer

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 2.

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.
• ### How would you best model hold down elements within panels?

#### Answer

In a short overview, creating hold down elements involves modeling rigid links and adding in nodal supports with non-linearity settings that allows the supports to take only tension forces. A line support is added at the bottom of the wall that only takes compression forces. The individual nodal supports connected with rigid members only take tension forces.

A more detailed look on how these elements can be model can be seen in the video below.
• ### Why is it not possible to select the individually or simultaneously acting load cases in the "Combination Expressions" tab?

#### Answer

The "Individually/simultaneously acting load cases" option is not available for all standards.

For example, if you select the standard "EN 1990" in General Data of the model, this option is available in the "Combination Expressions" tab.

On the other hand, if you select "ASCE 7‑16", for example, this option is (currently) not available.

• ### In the RF-/DYNAM Pro - Equivalent Loads module, it is possible to consider random torsional effects. What is the calculation method behind the calculation? Which values have to be entered for the eccentricities e X and e Y ?

#### Answer

The random torsion is governed by EN 1998-1, clause 4.3.2. The eccentricities must be determined manually; in EN 1998-1, they are specified with 5% of the building length. In other international seismic standards, the principle of random torsion is regulated in a similar way, but the determination of the eccentricities may differ.

For each equivalent load (at each FE node/internal node), a torsional moment is determined according to the following formula:

$\mathrm M\;=\;\left|{\mathrm F}_{\mathrm x}\;\ast\;{\mathrm e}_{\mathrm y}\right|\;+\;\left|{\mathrm F}_{\mathrm y}\;\ast\;{\mathrm e}_{\mathrm x}\right|$

Then, the exported load cases are output in duplicate - with the torsional moment M rotating about the vertical axis once in the positive and once in the negative direction of rotation.

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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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