Critical load is an ideal reference.
Euler theory gives the elastic critical load for an ideal prismatic member. It is useful for understanding why a long, flexible column can lose stability before its gross axial stress looks high.
Effective length carries the end-restraint assumption.
The effective length is KL. The factor K represents an idealised support condition, so it should be selected for the actual bracing and connection model rather than treated as a universal constant.
Always check the weaker axis.
Radius of gyration r = √(I/A) and slenderness KL/r keep the axis visible. A column may have a much larger strong-axis stiffness while buckling about its weaker axis.
Do not use Pcr as a code resistance.
- Imperfections, eccentricity, residual stress, yielding, local buckling, connection flexibility, and second-order actions change real capacity.
- Apply the applicable code, load combinations, buckling curves, resistance factors, and material limits.
- Keep the section-property axis and effective-length model consistent with the analysis and drawings.