Proposed provisions for the design of steel beam-columns in S16-2001

The provisions for the design of steel beam-columns in CSA Standard CAN/S16.1-94 are reviewed and changes are proposed to provide more consistent reliability in the next edition, CAN/CSA-S16-2001. The in-plane strength interaction equations have been checked using plastic-zone finite element analysis based on realistic residual stress patterns and initial imperfections. The same overall format is maintained. P-δ effects have been found to be negligible for members in sway frame. The interaction equation for checking the in-plane strength of sway beam-columns has been modified by taking the factor U1 as 1.0 for members in unbraced frames. For weak-axis bending, a new factor β accounts for the effect of the distributed plasticity on stability. The concept of the notional load for sway buckling, also used in Australia and in Eurocode 3, is now applied for all load combinations and not just as a minimum. The upper limit on U2 of 1.4 is removed. Examples are given illustrating these changes. A re-analysis of the local buckling experiments of other researchers on Class 2 sections, using a widely accepted buckling criterion, shows that no distinction need be made between Class 1 and 2 section beam-columns, i.e., Class 2 sections are treated as Class 1 sections. The changes in total do not increase the complexity of the standard, but reflect better the behaviour of beam-columns. The standard is aligned more closely with the best international practice.Key words: analysis, beam-column, buckling, compact, design, interaction equation, resistance, stability, steel, sway.