The formulas used in this calculator are based on the Guide to Stability Design Criteria for Metal Structures by the Structural Stability Research Council. Anyone designing metal columns should consult this guide or other well estabilshed publications.
The column is classified as either long or short/intermediate, and two different formulas are used in these two regions.
The critical slenderness ratio SRc separates long columns from short/intermediate columns. Basically, SRc corresponds to the case when the stress due to the axial load reaches the proportional limit and the critical load at the same time.
If Leff / r < SRc, the column is considered short/intermediate. Inelastic buckling is likely to be the cause of failure, where the stress exceeds the proportional limit before reaching the critical load. The ASIC safety factor and resulting allowable stress are given by,
If Leff / r > SRc, the column is considered long. Elastic buckling in accordance with Euler's formula is expected. The ASIC safety factor and resulting allowable stress are given by,
If the safety factor specified by the user is larger than the ASIC safety factor in the above formulas, the user's value will be used in calculating the allowable stress.