#### Further Information

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• ### How can the real cross-section geometry of bar elements be considered in the RWIND Simulation?

FAQ 004165 EN

In RFEM, the interface application 'Simulate and Generate Wind Loads' makes it possible to exchange member, surface, and solid elements, and in RSTAB to exchange the bar elements.

To avoid generating a too fine mesh along with a corresponding long calculation time, the program simulates all members with a rectangular cross-section as standard. The size of the rectangular cross-section is selected in such a way that the real cross-section geometry is barely included.

By deactivating the option 'Export Optimized Member Topology', you can avoid this additional optimization of the model and allow consideration of the real cross-section geometry within existing cross-section settings.

If the exact representation of the cross-section geometry requires more than 1000000 elements, the interface automatically changes to the simplified rectangular section display of the cross-sections.

• ### SHAPE-THIN calculates a very small shear area. What is the reason for this?

FAQ 003547 EN

The shear area is calculated as follows:

${\mathrm A}_{\mathrm y}\;=\;\frac{{\mathrm I}_{\mathrm z}^2}{\int_{\mathrm A^\ast}\left({\displaystyle\frac{{\mathrm S}_{\mathrm z}}{\mathrm t^\ast}}\right)^2\operatorname d\mathrm A^\ast}$

${\mathrm A}_{\mathrm z}\;=\;\frac{{\mathrm I}_{\mathrm y}^2}{\int_{\mathrm A^\ast}\left({\displaystyle\frac{{\mathrm S}_{\mathrm y}}{\mathrm t^\ast}}\right)^2\operatorname d\mathrm A^\ast}$

Where:

 Iz or Iy: second moment of area in relation to the axis z or y Sz or Sy: first moment of area in relation to the axis z or y t*: effective element thickness for shear transfer A*: surface area based on effective shear thickness t*

The effective element thickness for shear transfer t* has a significant influence on the shear area. Therefore, the defined effective element thickness for shear transfer t* (Figure 1) of the elements should be checked.

• ### I wish to integrate a circular hole plate in an aligned way. Is it possible to generate such an aligned mesh in RFEM?

FAQ 003461 EN

With the FE mesh refinement, it is also possible to create an aligned FE mesh in the program. Thus, the automatic FE mesh generator can be controlled to a certain extent. However, it is not possible to use it for setting of a specified mesh geometry.
• ### How is carried out the automatic creation of c/t-Parts?

FAQ 003430 EN

In the 'c/t-Parts and Effective Cross-Section' tab of the 'Calculation Parameters' dialog box, you can define settings for the automatic creation of c/t-Parts.
It is also possible to specify an angle from which a support should be created between two elements. In case that the angle for connection of elements is smaller, they are considered as an interconnected c/t-Part. Stiffeners (longitudinal ribs, slopes (lips), or bulges, etc.) are not recognized by the program during the automatic generation of the c/t-Parts. The c/t-Parts have to be adjusted manually. The changes can be made in Table '1.7 Cross-Section Parts for Classification' or in the 'Edit c/t-Part' dialog box.
The check box with the reference to Element is 'significant' controls whether a curved element is considered as a c/t-Part. If the length of the arc is larger than the diameter entered here, it cannot be neglected.
A corresponding error message appears before the calculation.
The option Element ist 'straight' refers to curved elements. Arcs are normally excluded from the determination of the effective widths because the standards do not provide clear specifications. A curved element is assumed to be straight if the ratio of connecting line (start/end node) to element length is higher than the specified value.
• ### I need to define different types of lateral intermediate restrains for a single element in RF-/STEEL EC3. Is this possible?

New FAQ 003361 EN

If you need to define different types of lateral intermediate supports, it is necessary to divide the specific member. After that, you can create a set of member and with that done, you can easily define different types of intermediate supports along this set of member, or you can use different nodal supports in the nodes of the set of member.
• ### Where can I see the stresses in RSTAB?

FAQ 003341 EN

RSTAB is a pure framework program and only determines internal forces, deformations, and support reactions.

On the other hand, stresses are variable depending of the cross-section and are calculated on the stress points of a cross-section. This stress determination is performed in the RF-/STEEL add-on module by calculating the existing stresses and comparing them with the limit stresses.
• ### I get an implausible result with the expression "1.#J" in the RF‑/ALUMINUM add-on module.How can I fix it?

FAQ 003317 EN

This kind of result may occur if the limit internal forces of the cross-section cannot be determined. In most cases, the problem lies in a wrongly defined cross-section or in the selection of an unsupported cross-section. Please check if you have selected the cross-section allowed for the aluminum structure in the add-on module. These include the rolled cross-sections and parametric thin-walled cross-sections.

The cross-section HK 120/40/5/5/5/5 shown in Figure 01 is not a valid cross-section as it has been selected from the area of solid cross-sections (concrete components).
In this case, it is necessary to change the cross-section to TO 120/40/5/5/5/5.

In the case of the design in RF‑/ALUMINUM, please note that you have to select the material which also involves thicknesses used for the cross-sections. A material that is only allowed up to t=3 mm cannot be used for a cross-section with t=5 mm.
• ### When determining the effective cross-section properties according to EN 1993‑1‑1, EN 1993‑1‑5, or EN 1999̩1‑1, SHAPE‑THIN displays a warning message saying that the effective widths are only determined for straight elements. What does it mean?

FAQ 003232 EN

The cross-section class is defined according to EN 1993‑1‑1 and EN 1999‑1‑1 by the maximum width/width ratio c/t or b/t of the cross-section parts subjected to compression. EN 1993‑1‑1 or EN 1999‑1‑1 only cover various straight c/t or b/t parts. Therefore, the classification and determination of effective widths is not possible for the curved c/t or b/t sections.
• ### Why RF‑/STEEL does not display the same maximum internal forces when calculating a result combination, as it is in the results of the result combination itself?

FAQ 003134 EN

This behavior is caused by the detail settings in the RF‑/STEEL add-on module. The results of result combinations can be used in many different ways.

To use the same maximum internal forces for stress analysis, the settings should be made according to Figure 01.

However, this setting is very conservative because not all maximum internal forces can occur at the same time.
• ### Why does my calculation in the RF‑/ALUMINUM add‑on module take so long?

FAQ 003057 EN

By default, the computation kernel of the cross-section program SHAPE‑THIN is used in the RF‑/ALUMINUM add‑on module to determine the stresses of the effective cross-section in an iterative procedure. This method is precise as all corners and edges of the cross-section are covered, but can be very time-consuming in the case of compound cross-sections.

As an alternative, it is possible to determine the effective cross-section by using the simplified analytical method (see Figure 01), which is significantly faster. In the case of using this approach, the corners, roundings, and others, are neglected and then compensated by a factor. No iterative calculation is performed. Therefore, the effective cross-section values might be higher than with the SHAPE‑THIN calculation.

In such a case, it is recommended to carry out the calculation using the analytical method and then to only design the governing structural component with the governing load combination by using the SHAPE‑THIN solution.

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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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