Classification (Columns: BS 5950)
General
The classification of the cross section is in accordance with BS 5950-1: 2000.
Steel columns can be classified as:
- Plastic Class = 1
- Compact Class = 2
- Semi-compact Class = 3
- Slender Class = 4
Class 4 sections are not allowed.
Sections with a Class 3 web can be taken as Class 2 sections (Effective Class 2) providing the cross section is equilibrated to that described in Clause 3.5.6 where the section is given an “effective” plastic section modulus, Seff. This approach is not adopted in the current version of Tekla Structural Designer.
All unacceptable classifications are either failed in check mode or rejected in design mode.
Hollow sections
The classification rules for SHS and RHS relate to “hot-finished hollow sections” only (“cold-formed hollow sections” are not included in this release).
Warning: important. The
classification used to determine Mb is based on the maximum axial
compressive load in the relevant segment length. Furthermore, the code clearly
states that this classification should (only) be used to determine the moment
capacity and lateral torsional buckling resistance to clause 4.2 and 4.3 for use
in the interaction equations. Thus, when carrying out the strength checks, the
program determines the classification at the point at which strength is being
checked.