RF-/STEEL EC3 - Online Manual Version 5/8

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RF-/STEEL EC3 - Online Manual Version 5/8

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2.3 Cross-Sections

This window lists the cross-sections used for the design. In addition, you can specify optimization parameters.

Figure 2.17 Window 1.3 Cross-Sections
Cross-Section Description

The cross-sections defined in RFEM or RSTAB are preset together with the assigned material numbers.

To modify a cross-section, click the entry in column B. Thus, you set the field active. Then, open the cross-section table of the current input field by clicking the [Cross-Section Library] button or at the end of the box. You can also use the function key [F7] (see Figure 2.18).

In this dialog box, you can choose a different cross-section or even a different cross-section table. If you want to select a completely different cross-section category, click the [Back to Cross-Section Library] button. Then, the general cross-section library opens.

Chapter 4.13 of the RFEM manual, or Chapter 4.3 of the RSTAB manual, describes how to select cross-sections from the library.

You can also enter a new cross-section description directly into the input field in column B. If the entry is already listed in the database, RF-/STEEL EC3 will import the cross-section properties. A modified cross-section is highlighted in blue.

Figure 2.18 IS cross-section types of cross-section library

If cross-sections set in RF-/STEEL EC3 are different from the ones used in RFEM or RSTAB, both cross-sections are displayed in the graphic to the right. The designs will be performed with the internal forces from RFEM or RSTAB for the cross-section selected in RF-/STEEL EC3.

Cross-Section Type

This column shows the cross-section type that is used for the classification. The cross-sections listed in [1] Table 5.2 can be designed plastically or elastically depending on the class. Cross-sections not included in this table are classified as General and can only be designed elastically, which means class 3 or 4.


RF-/STEEL EC3 performs the classification Automatically. If this is not desired, you can define the cross-section class manually in the drop-down list. For example, an I-section embedded in concrete cannot buckle locally. By classifying it manually into class 3 it is possible to perform the design without taking into account the effective widths.

Max. Design Ratio

This column is displayed only after the calculation. It is intended to be a decision support for the optimization: Looking at the design ratios and colored relation scales, you can clearly see which cross-sections are hardly utilized and thus oversized, or extremely stressed and thus undersized.


Each cross-section of the library can pass through an optimization process: For the internal forces from RFEM or RSTAB, the program searches the cross-section that comes as close as possible to a user-defined maximum ratio that can be defined in the General tab of the Details dialog box (see Figure 3.11).

To optimize a cross section, open the drop-down list in column E or F, and select the relevant entry: From current row or, if available, From favorites 'Description'. Recommendations for optimizing cross-sections can be found in Chapter 7.2.


This column shows remarks in the form of footnotes. They are explained below the cross-section list.

If the warning Incorrect type of cross-section! appears before calculating, a cross-section is set which is not listed in the database. This may be a user-defined cross-section or a SHAPE-THIN cross-section that has not yet been calculated. To select an appropriate cross-section for the design, click the [Library] button (see description below Figure 2.17).

Member with tapered cross-section

For tapered members with different cross-sections at the member start and end, both cross-section numbers are shown in two rows, in accordance with the definition in RFEM or RSTAB.

RF-/STEEL EC3 also designs tapered members, provided that the cross-section at the member's start has the same number of stress points as the cross-section at the end. Normal stresses, for example, are determined from the moments of inertia and the centroidal distances of the stress points. If the cross-sections at the start and end of a tapered member have different numbers of stress points, the intermediate values cannot be interpolated. The calculation is neither possible in RFEM or RSTAB nor in RF-/STEEL EC3.

The cross-section's stress points including numbering can be checked graphically: Select the cross-section in Window 1.3, and then click the button. The dialog box shown in Figure 2.19 appears.

Info About Cross-Section

Below the cross-section graphic, you find the [Info] button. Click it to open the Info About Cross-Section dialog box where you can see the cross-section properties, stress points and c/t-parts.

Figure 2.19 Dialog box Info About Cross-Section

The buttons below the cross-section graphic have the following functions:

Table 2.3 Buttons of cross-section graphic
Button Function

Displays or hides stress points

Displays or hides c/t-parts

Displays or hides numbers of stress points or c/t-parts

Shows details of stress points or c/t-parts (see Figure 2.20)

Displays or hides dimensions of cross-section

Displays or hides principal axes of cross-section

Resets full view of cross-section

Use the [Details] buttons to call up specific information about stress points (centroid distances, statical moments of area, warping ordinates, etc.) and c/t-parts.

Figure 2.20 Dialog box Stress Points of HE B 260
Buckling curves of cross-section

If the situation requires it, you can change the buckling curves in the Cross-Section Properties table (lower part of Window 1.3 Cross-Sections).

Figure 2.21 Changing buckling curve BCy
[1] Eurocode 3: Design of steel structures - Part 1‑1: General rules and rules for buildings; EN 1993‑1‑1:2010‑12