# Frequently Asked Questions (FAQ)

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• ### The definition of a result beam does not seem to be correct. There is no integration area and no results are displayed. What can be the reason for this?

If you use the "Within cuboid - general" integration option, the reason may be incorrectly defined parameters for the application area. The application lengths must be entered as an amount. This is especially important in the negative direction: If you enter the application length as a negative value, this value is subtracted from the positive direction.

Example: You want to define an integration area of 1 m for the result beam. For the "Within cuboid - quadratic" option, simply enter an application length of 1 m. In the case of the "Within cuboid - general" option, you have to enter a length of 0.5 m as the amount in both the positive and the negative direction. These lengths are added together and you get a total application area of 1 m.
• ### I would like to check the internal forces on a member. Can I display the axis system, and what do the internal forces refer to?

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You can activate the display of the local axis system of members either by right-clicking a member in the member shortcut menu or in Project Navigator - Display.

Member internal forces are displayed with regard to the member axes or the principal axes (FAQ 003291).

You can also find the definition of member internal forces in the online manual.

• ### I would like to calculate the results, such as ordinates, static moments, stresses, at a specific location of a cross-section. What should I do?

If you want to display the results at a specific location of the cross-section, it is necessary to divide the element at this location.

To divide the element, right-click it and select the "Divide Element" option in the shortcut menu (Figure 01).

For example, if you want to determine the stress at a distance s = 32.5 mm from the start of Element 1, you have to divide Element 1 at this point. This is also shown in the video.

• ### How can I change the display of deformation for members from colored cross-sections to lines?

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This change can be done in the Display navigator under "Results" → "Deformation" → "Members" → "Lines," see Figure 01.

• ### How can I display the stresses in the stress points in RF‑STEEL Members?

The "Extended Display" button allows for a targeted evaluation of the results for each stress point. It opens the "Cross-Section Properties and Stress Distribution" dialog box (Figure 01).

In the "Position" section, the current member number and location x on the member are preset. You can also select other members or x‑locations in the list.

The "Stress Points" section lists all stress points of the cross-section. The "Coordinates" columns show the centroidal distances y and z, and the "Static moments" columns show the surface moments of the first degree Sy and Sz. The "Thickness t" column shows the thickness of the cross-section part that is required for the determination of shear stresses. In the case of closed cross-sections, the cell area A* is specified, which is required for the determination of the stress due to torsional moment.

The "Stresses" section shows all stresses at the current stress point (selected in the section above). In this dialog box, it is also possible to select a stress type by a mouse click to display the stress diagrams in the graphic.

• ### How can I assign certain surfaces to a result beam in order to integrate internal forces?

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In the detail settings of the respective result beam, you can specify which objects (members, surfaces, or solids) are to be considered by this result beam.

For example, if there is an unexpected result displayed for the result beam, you should check in this dialog box whether the integration area has been set correctly for the objects.

• ### The results of my model are available and displayed graphically, but without result values. How can I display the result values?

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There are two ways to display result values:

• Click the "Show Result Values" button in the toolbar (see Figure 01).

• Activate the result values in the Display navigator under "Results" (see Figure 02).

• ### How do I get the actual member length of cables, for example, after the calculation in RF‑FORM‑FINDING?

This information is available in the Results navigator for members (see Figure 01). The member lengths are displayed with regard to the stressed structural system and the unstressed system. The "stressed length" is obtained from the form-finding under consideration of prestresses.

The recalculation to the "stressed length" can be done manually using Hooke's law:

${\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\mathrm{Δl}\\\\\mathrm\sigma\;=\;\mathrm E\;\cdot\;\mathrm\varepsilon\\\frac{\mathrm F}{\mathrm A}\;=\;\mathrm E\;\cdot\;\frac{\mathrm{Δl}}{\mathrm l}\\\mathrm{Δl}\;=\;\frac{\mathrm F\;\cdot\;\mathrm l}{\mathrm E\;\cdot\;\mathrm A}\\\\{\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\frac{\mathrm F\;\cdot\;{\mathrm l}_{\mathrm{stressed}}}{\mathrm E\;\cdot\;\mathrm A}\;=\;{\mathrm l}_{\mathrm{stressed}}\;\cdot\;\left(1-\;\frac{\mathrm F\;}{\mathrm E\;\cdot\;\mathrm A}\right)$

• ### Is it possible to use the table to evaluate which member has the greatest internal forces in relation to other members?

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Yes, it is possible.
The result tables show in color whether there are the positive or negative internal forces and what is the relation to the extreme values. The negative values are symbolized by red bars, the positive ones by blue bars. Thus, the table also allows for a visual evaluation of results.

The result tables of the design modules use color scales to represent the respective design ratios. In this way, the governing locations are apparent immediately.

• ### I get the message in RF‑/PLATE‑BUCKLING, saying that the distance between stiffeners exceeds the minimum requirement. What should I do?

The message shown in Figure 01 is displayed if you select the "Minimum distance between stiffeners: 30 ε t" check box in Details and the clear distance between the stiffeners is smaller than this minimum distance amin. The minimum distance is calculated as follows:

amin = 30 ⋅ ε ⋅ t

where

ε = √(235 / f[N/mm²])
fy is the yield strength,

t is the thickness of the buckling panel.

In this case, the distance of the stiffeners must be increased in Window "1.2 Stiffeners." For the buckling panel shown in Figure 01, the clear distance between the stiffeners is:
Δz = z2 - z1 - (t1 + t2) / 2 = 890 - 600 - (10 + 10) / 2 = 280 mm

This distance is smaller than the minimum distance:
amin = 30 ⋅ ε ⋅ t = 30 ⋅ √(235 / 355) ⋅ 12 = 292.9 mm

Therefore, the position of Stiffener 2 should be entered at least
z2 = z1 + (t1 + t2) / 2 + amin = 600 + (10 + 10) / 2 + 292.9 ≈ 903 mm

This distance is also displayed as information in Window "1.2 Stiffeners" when placing the mouse pointer over Stiffener 2 (Figure 02).

If the calculation should also be performed for a stiffener distance smaller than the minimum distance, the "Minimum distance between stiffeners: 30 ε t" check box must be deactivated (Figure 03).

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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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