# 6 Compression tables

## 6.1Design resistance of cross-section Nc,Rd

6.2.4
6.2.4 (2)

The design resistance is given by:

(i) For Class 1, 2 or 3 cross-sections:

 Nc,Rd = (ii) For Class 4 cross-sections:

 Nc,Rd = where:

 A is the gross area of the cross-section fy is the yield strength Aeff is the effective area of the cross-section in compression γM0 is the partial factor for resistance of cross-sections (γM0 = 1.0 as given in the National Annexes).

For Class 1, 2 and 3 cross-sections, the value of Nc,Rd is the same as the plastic resistance, Npl,Rd given in the tables for axial force and bending, and is therefore not given in the compression tables.

For Class 4 sections, the value of Nc,Rd can be calculated using the effective areas provided in the software. The values are not shown in the tables.

Sections that are Class 4 under axial compression are marked thus *. The sections concerned are:

Table 5.2
• Square hollow sections, where c / t > 42 ε and c = h – 3 t
• Rectangular hollow sections, where cw / t > 42 ε and cw = h – 3 t
• Circular hollow sections, where d / t > 90 ε2
where:  h is the overall depth of the cross section t is the thickness of the wall ε = (235 / fy)0.5
• Elliptical hollow sections, where (See Reference 5)
where:
 De is defined in Section 4.2.

## 6.2 Design buckling resistance Nb,Rd

6.3.1
6.3.1.1

Design buckling resistances for flexural buckling are given in the tables.

The design flexural buckling resistances Nb,y,Rd and Nb,z,Rd depend on the non-dimensional slenderness ( ), which in turn depends on:

• The buckling lengths (Lcr) given at the head of the table
• The properties of the cross-section.
6.3.1.3

The non-dimensional slenderness has been calculated as follows:

For Class 1, 2 or 3 cross-sections: y = for y-y axis buckling z = for z-z axis buckling

For Class 4 cross-sections: y = for y-y axis buckling z = for z-z axis buckling

where:

 Lcr,y, Lcr,z are the buckling lengths for the y-y and z-z axes respectively iy, iz are the radii of gyration about the y-y and z-z axes respectively

The tabulated buckling resistance is only based on Class 4 cross-section properties when the value of the force is sufficient to make the cross section Class 4 under combined axial force and bending. The value of n (= NEd / Npl,Rd) at which the cross-section becomes Class 4 is shown in the tables for axial force and bending. Otherwise, the buckling resistance is based on Class 3 cross-section properties. Tabulated values based on the Class 4 cross section properties are printed in italic type.

For Class 4 circular hollow sections, EN 1993-1-1 refers the user to EN 1993-1-6. Resistance values for these sections have not been calculated and the symbol \$ is shown instead.

For Class 4 elliptical hollow sections, the design buckling resistance has been taken as the greater of:

1. The design buckling resistance based on an effective area (see Section 4.2) and
2. The design buckling resistance based on the gross area, but reducing the design strength such that the section remains Class 3. The reduced design strength fy,reduced is given by: De is defined in Section 4.2.