# Member buckling resistance, Clause 4.8.3.3.3 (Columns: BS 5950)

This check is used for Class 1, 2 and 3 Plastic, Compact and Semi-compact hollow sections (Class 4 Slender sections and Effective Class 2 sections are not included in this release).

Four formulae are provided in clause 4.8.3.3.3 (c) to cover the combined effects of major and minor axis moment and axial force. These are used irrespective of whether all three forces / moments exist. Clause 4.9 deals with biaxial moment in the absence of axial force, clause 4.8.3.3.3 (c) can also be used in such cases by setting the axial force to zero.

The second and third formulae are
mutually exclusive – that is the second is used for CHS, SHS and for RHS when the
limits contained in Table 15 are **not** exceeded. On the other hand the third
formula is used for those RHS that exceed the limits given in Table 15. Thus only
three formulae are checked; the first, second and fourth or the first, third and
fourth. Either the second or third (as appropriate) is calculated twice – once for
Face C and once for Face A.

Only one value of F is used, the worst anywhere in the length being checked. If the axial load is tensile, then F is taken as zero.

See also the **Important Note** at
the end of Member buckling
resistance, Clause 4.8.3.3.2.