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2024-01-31

Sections

All cross-sections available in the model are listed again in the Input Data of the design add-on.

Allowable Cross-Sections

The font color of the cross-section gives you the information about the utilization and validity of a cross-section in the selected design add-on:

  • Blue = a cross-section not used in the entire model
  • Red = a cross-section not suitable for the design in the active add-on
  • gray = objects with this cross-section are not selected for design in the active add-on
  • black = objects with this cross-section are selected for design in the active add-on

In the steel design, only cross-sections with materials of the Steel type are allowed (see also Chapter Materials). Furthermore, there are restrictions regarding the cross-section type. Regardless of the selection in the "To Design" check box, objects with invalid materials are not considered in the design (an automatic classification in "Not Valid / Deactivated").

Info

Design is only possible for built-up cross-sections with interaction. In this case, it is also possible to determine plastic resistance values and compare them with a valid set of internal forces. Built-up cross-sections without interaction must be split into two separate members for the design.

Removing Cross-Sections from Design

For all valid cross-sections, you can deactivate all objects with this cross-section by clearing the "To Design" check box. Thus, these objects are assigned to the "Not Valid / Deactivated" column and removed from the design (see Objects to Design).

Section Type

The section type of a cross-section provides the information about the possible design. Some cross-section types are not allowed for the design in the add-on or can only be used with restrictions. The following cross-section types are allowed in the steel design:

  • Standardized - Steel
  • Parametric - Thin-Walled
  • Parametric - Bars
  • Built-up - Steel
  • General by RSECTION

Cross-Section Classification (for EN 1993 only)

This column is only available if you select the design standard EN 1993. By default, the automatic cross-section classification is activated, provided that there is a subpanel available for the cross-section type. The c/t ratios of the existing subpanels are checked and the classification is carried out automatically in cross-section classes 1-4.

Info

For a Class 4 cross-section, the effective section properties are determined in order to consider the effect of local buckling.

If no subpanels for local buckling are defined for a cross-section in accordance with the selected design standard, the cross-section is automatically classified as Class 3 and then designed elastically. A check of the c/t ratios and designs for local buckling are then not possible.

Select the "Class 1/2" option to obtain the design with the plastic section resistances without further checking the c/t parts. Select "Class 3" for an elastic design where no additional check for local buckling is to be performed. The "Class 4 possible" option allows for checking whether the effective section properties have to be taken into account. Depending on the result, the cross-section is classified in Class 3 or Class 4 and designed accordingly.

Design of Cold-Formed Sections (for EN 1993 and AISC only)

Cold-formed sections usually require special design checks of local buckling and cross-section stability. If a cross-section has the "cold-formed" manufacturing type and has been selected as the EN 1993 design standard, the checks for objects with this cross-section are automatically performed according to EN 1993‑1‑3 (except for cold-formed hollow sections). When selecting the AISC 360 standard, the cold-formed sections are designed according to AISI S100. For other design standards, no special design of cold-formed sections is currently implemented.

Adjusting Cross-Sections

Section properties can be adjusted in the editing dialog box of the cross-section. Double-click a row or click the Open Editing Dialog Box button to go directly to the editing dialog box of the cross-section.

The "Options" column includes the icons for various existing settings or modified values, so you can quickly get an overview and, for example, identify the cross-sections calculated according to the thin-walled theory.

To create and design any cross-section, you can use the RSECTION program.

Important

Factors entered in a Member Stiffness Modification or Structure Modification are not taken into account for the design in the Steel Design add-on.

Notes on Stress Determination

If stress-based design checks are performed for a cross-section, the required stresses are determined according to the analysis method selected in the cross-section. Select the "Thin-walled model" option for a cross-section to determine all cross-section properties and stresses used for the design according to the thin-walled analysis. If this option is not activated, the determination of the cross-section properties and stresses is based on the FE solution.

To verify the stress values used in the design, you can use the unit stresses of the corresponding analysis method as a basis. They are displayed in the editing dialog of the cross-section.

Further information on stress determination and the analysis methods used can be found in the corresponding chapters of the online manual for the RSECTION program.

Notes on Design of RSECTION Cross-Sections

The options for designing cross-sections from RSECTION depend on the selected cross-section modeling. If a cross-section has elements, subpanels are generated automatically that allow for the calculation of the effective cross-section properties. If no elements but only parts are defined in the cross-section, no subpanels can be created and an automatic cross-section classification is not possible.

Info

In order for a cross-section from RSECTION to be designed taking into account effective section values, it must be saved in RSECTION with an active license for the Effective Sections add-on.

Using Another Cross-Section for Design

If you want to use a different cross-section for the design than for the RFEM calculations, you can select the cross-section to be used for each cross-section. This does not affect the internal forces, which are also used for the design of the other cross-section.

If a different cross-section is entered in this column, further options are available in the shortcut menu (Export Section to RFEM, Export All Sections to RFEM, Import Section from RFEM, Import All Sections from RFEM).

Simplified Cross-Section Optimization

For standardized cross-sections, it is possible to optimize the cross-sections from their respective series of the cross-section library. In this case, the program searches for the smallest possible cross-section from the corresponding row, for which all design checks provide a smaller design criterion than the limit value defined in the Global Settings.

For this simplified cross-section optimization of the standardized cross-sections, the same boundary conditions apply as for using another cross-section for the design. With the given internal forces, the design checks are carried out for all cross-section variants to be optimized and then the optimal variant is displayed.

Info

For the simplified cross-section optimization in the add-on, the effects of the cross-section changes on the stiffnesses and internal forces in the RFEM model are not taken into account initially.

Therefore, the final design requires transferring the optimized cross-sections to RFEM and performing the calculation again. Comprehensive structural optimization is only possible with the Optimization & Cost / CO₂ Emission Estimation add-on.

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