# Frequently Asked Questions (FAQ)

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• ### I would like to model a threaded rod as a 3D solid in RFEM. My question would now be how I get the thread, is a kind of spiral or similar possible?

New FAQ 004322 EN-US

A thread cannot be created by means of a function in the program. Here, you have to create this geometrically via nodes and lines. In the program, there is the option to create the turns by means of trajectory surfaces. However, you can use the copy and rotate function to quickly reach the destination.
• ### Is it possible to connect a rib member to two surfaces with different thicknesses? And where can I check the cross-section values of this composite cross-section? In RFEM, I can only see the eccentric rectangular cross-section and its cross-section values.

New FAQ 004318 EN-US

You can connect a rib member to a line on two surfaces with different thicknesses.

To determine the stiffness or the determination of internal forces, the eccentricity for the rectangular cross-section is determined in RFEM with the mean value of the two connected surfaces.

For the design in RF-CONCRETE Members, the add-on module determines its own cross-section, which is displayed in the "1.4 Ribs" input dialog box of the add-on module.

By clicking the "i" button (see Figure 02), you can open an info dialog box for the generated rib cross-section, in which all cross-section values, the position of the shear center and centroid, etc., which are applied for the design in the module, can be viewed.

If the "Effective Width" is adjusted in the "1.4 Ribs" dialog box (e.g. to 0.50 m), this has an influence on the cross-section applied in RF-CONCRETE Members and its cross-section values.

However, this has no influence on the stiffness or the determination of internal forces in the 3D model in RFEM.

• ### When trying to calculate the design in RF-STEEL Surfaces, I receive Warning No. 1162 - Surface No. XX is of the type "Orthotropic" and cannot be designed. What does this Warning mean?

New FAQ 004308 EN-US

Orthotropic surfaces are non-linear and cannot be designed within the RF-STEEL Surfaces add-on module. It is still possible to get the full stress analysis in RFEM which can be compared to the limiting stresses manually. Otherwise, the surface will need to be set to "standard" for it to be designable within the add-on module.

• ### After running the design in RF-STEEL AISC, I receive error message 1002 - Invalid cross-section of type "Channel" according to F2. What does this error mean?

New FAQ 004307 EN-US

Section F2 out of the AISC 360-16 [1] states that doubly symmetric I-Shapes and Channels that are bent about their major axis must be compact sections in order to be designed. An example of this can be seen below.

Non-compact sections cannot be designed according to F2. Figure 2 shows a non-designable section.

• ### Is the Gust-effect (G or Gf) from the ASCE 7-16 Sect. 26.11 considered in RWIND Simulation?

New FAQ 004301 EN-US

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

New FAQ 004284 EN-US

Yes, the data is freely available. Use the following download option to load the presentations and finished models of the consultants.
• ### Does the program RF-LAMINATE consider the shear correction factor for cross-laminated timber slabs?

New FAQ 004281 EN-US

The shear correction factor is taken into account in the RF-LAMINATE program using the following equation.

$k_{z}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{\left(\int_{-h/2}^{h/2}E_x(z)z^2\operatorname dz\right)^2}\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz$

with $\ int _ {- h/2} ^ {h/2} E_x (z) z ^ 2 \ operatorname dz = EI _ {, net}$

The calculation of the shear stiffness itself can be found on page 15 of the English version to the manual of RF-LAMINATE as follows:

For the 10 cm thick plate in Figure 1, the calculation of the shear correction factor is shown. The equations used here are only valid for the simplified symmetrical plate structures!

 Layer z_min z_max E_x (z) (N/mm²) G_xz (z) (N/mm²) 1 -50 -30 11000 690 2 -30 -10 300 50 3 -10 10 11000 690 4 10 30 300 50 5 30 50 11000 690

$\sum_iG_{xz,i}A_i=3\times0,02\times690+2\times0,02\times50=43,4N$

$EI_{,net}=\sum_{i=1}^nE_{i;x}\frac{\mbox{$z$}_{i,max}^3-\mbox{$z$}_{i,min}^3}3$

$=11000\left(\frac{-30^3}3+\frac{50^3}3\right)+300\left(\frac{-10^3}3+\frac{30^3}3\right)$

$+11000\left(\frac{10^3}3+\frac{10^3}3\right)+300\left(\frac{30^3}3-\frac{10^3}3\right)+11000\left(\frac{50^3}3-\frac{30^3}3\right)$

$=731,2\times10^6Nmm$

$\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz=\sum_{i=1}^n\frac1{G_{i;xz}}\left(χ_i^2(z_{i;max}-z_{i,min})\;χ_iE_{i,x}\frac{z_{i,max}^3-z_{i,min}^3}3+E_{i,x}^2\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)$

$χ_i=E_{i;x}\frac{z_{i;max}^2}2+\sum_{k=i+1}^nE_{k;x}\frac{z_{k,max}^2-z_{k,min}^2}2$

 χ1 13.75 106 χ2 8.935 106 χ3 9.47 106 χ4 8.935 106 χ5 13.75 106

$\sum_{i=1}^n\frac1{G_{i;yz}}\left(χ_i^2(z_{i,max}-z_{i,min})-χ_iE_{i,y}\frac{z_{i,max}^3-z_{i,min}^3}3+{E^2}_{i,y}\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)=$

 8.4642 1011 3.147 1013 2.5 1012 3.147 1013 8.4642 1011

Total 6.7133 x 1013

$k_z=\frac{43,4}{{(731,2e^6)}^2}6,713284\;e^{13}=5,449\;e^{-3}$

$D_{44}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{k_z}=\frac{43,4}{5,449\;e^{-3}}=7964,7N/mm$

This corresponds to the value output in RF-LAMINATE (Figure 2).
• ### Why do the equivalent stresses of RFEM and RF-STEEL differ from each other, although the same CO is considered?

New FAQ 004277 EN-US

It is possible to display or calculate the stresses in RFEM as well as in the add-on module by means of the following smoothing options:

• Constant on elements
• Not continuous
• Continuous within surfaces
• Continuous total
• Continuously by groups or Continuous by groups

To compare the results, the same display type and calculation type must be selected in RFEM and RF-STEEL Surfaces.

In RFEM, it is possible to do this in the Project Navigator Show → Results → Surfaces → Distribution of Internal Forces/Stresses (Figure 02). In RF-STEEL Surfaces, this can be displayed or changed in the Details → 'Options' tab (Figure 03).

• ### Despite having defined average regions, they are not taken into account for the design in RF-LAMINATE Surfaces. Which setting did I miss here?

New FAQ 004275 EN-US

To consider average regions when designing in RF-LAMINATE, they must always be activated in the detail settings of the add-on module. See Figure 01 with the detailed settings in RF-LAMINATE for this.
• ### What happens if I activate the "Soil failure" function in RF-SOILIN?

New FAQ 004261 EN-US

The zero coefficient of structural soil strength can be used for better convergence of deeper excavations or small loading. Damaged soil have no structural soil strength. Therefore, it better picture damaged subsoil in the upper layers with this function. The possible entry for the depth of the soil failure is from 0.0 m to 1.0 m.

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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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