4 Effective section properties

4.1General

In EN 1993-1-1, effective section properties are required for the design of members with Class 4 cross-sections. In this website, effective section properties are given for sections subject to compression only and bending only.

4.2Effective section properties of members subject to compression

The effective cross section properties of Class 4 cross-sections are based on the effective widths of the compression parts.

The effective cross–sectional area Aeff of Class 4 sections in compression is calculated in accordance with EN 1993-1-1, 6.2.2.5 and EN 1993–1–5, 4.3 and 4.4. 

The effective section properties tables list the sections that can be Class 4 and the identifier ‘W’, ‘F’ or ‘W, F’ indicates whether the section is Class 4 due to the web, the flange or both. In rectangular hollow sections subject to bending about the major axis, the flanges are the short sides and the webs are the long sides.

The effective area of the section is calculated from:

For rectangular hollow sections and square hollow sections:

Aeff = A − 2 tf (1 − ρf ) cf − 2 tw (1 − ρw) cw

For circular hollow sections: 

Effective areas are not tabulated for circular hollow sections in this software. EN 1993-1-1 6.2.2.5(5) refers the reader to EN 1993-1-6.

For elliptical hollow sections:

Effective areas are not tabulated in this software, but may be calculated as follows in accordance with Reference 4.

Aeff =

where:

De  is the equivalent diameter = 

Expressions for the reduction factors ρf, ρw and ρ are given in EN 1993-1-5, 4.4.

The ratio of effective area to gross area (Aeff / A) is also given in the tables to provide a guide as to how much of the section is effective. Note that although EN 1993-1-1 classifies some sections as Class 4, their effective area according to EN 1993-1-5 is equal to the gross area.

4.3Effective section properties of members subject to pure bending

The effective cross section properties of Class 4 cross sections are based on the effective widths of the compression parts. The effective cross-sectional properties for Class 4 sections in bending have been calculated in accordance with EN 1993-1-1, 6.2.2.5 and EN 1993–1–5, 4.3 and 4.4.

Cross-section properties are given for the effective second moment of area Ieff and the effective elastic section modulus Wel,eff. The identifier ‘W’ or ‘F’ indicates whether the web or the flange controls the section Class 4 classification.

Equations for the effective section properties are not shown here because the process for determining these properties requires iteration. Also the equations are dependent on the classification status of each component part.

For cross sections with a Class 3 web and Class 1 or 2 flanges, an effective plastic modulus Wpl,eff can be calculated, following the recommendations given in EN 1993-1-1, 6.2.2.4 (1).  

For the range of sections covered by this software, only a limited number of the hollow sections can be used with an effective plastic modulus Wpl,eff, when subject to bending alone.