Calculate effective cross-section properties for Class 4 sections

Did you know that you could use Consteel to calculate effective cross-section properties for Class 4 sections?

The classification of cross-sections is used to understand how local buckling affects the strength and rotation capacity of structural members. As stated in Eurocode 3 (EN 1993-3-3, Section 5.5), this classification helps determine whether a cross-section can reach its full resistance or if its behavior is limited by local instability.

Class 4 cross-sections are those in which local buckling occurs before the material reaches the yield stress in one or more parts. Because of this, their resistance must be calculated using effective section properties that take into account the reduction caused by local buckling.

Typical Class 4 sections are characterized by slender elements with high width-to-thickness ratios. These commonly include thin webs or flanges, hollow sections (RHS/CHS) with slender walls, thin-walled cold-formed profiles such as C- or L-sections, and welded I-sections with slender webs. In this example, we consider a welded I-section with the following geometric parameters:

In Consteel, we can then see the section classification from the Global Checks tab. After selecting the investigated section either in the model or from the table and clicking on the Calculate Section option, and then choosing the Plate Classes in the Properties tab.

The effective section properties can then be viewed using the second option in the Properties tab.

In addition, stresses can be visualized by clicking on the Stresses icon. They can be represented either as a colored figure or as a 3D diagram.

For Class 4 sections, the Standard Resistance tab in the section module provides a complete assessment for the selected loading case.

The section module performs all necessary calculations according to the Eurocode (EN 1993-1-1 and relevant parts of EN 1993-1-5), including general elastic resistance, pure case resistance, conservative interaction checks, and web buckling analysis.

All resistances are calculated using the effective section properties to account for local buckling, and the module identifies the dominant case to ensure all relevant checks are covered.

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