How to use the column combined stress calculator
When an axial load sits off the centroid of the section, the member carries compression and bending together. The eccentric moment is M = P × e, and the elastic combined stress is the axial stress P/A plus the bending stress M/S, which raises the stress on one face and lowers it on the other. Once the bending stress exceeds the axial stress the far face goes into tension, a useful warning that base plate anchors or the connection above may need a tension check.
The real adequacy check is the AISC 360 Section H1-1 interaction equation rather than a stress sum. When Pr/Pc is 0.2 or more, Pr/Pc + (8/9)(Mr/Mc) must not exceed 1.0; below 0.2 the form becomes Pr/(2Pc) + Mr/Mc ≤ 1.0. Pc and Mc are available strengths that already include flexural buckling and lateral-torsional buckling, which makes this check both more realistic and usually more demanding than comparing stress with yield strength.
A value above 1.0 means a larger section, a shorter unbraced length, or added bracing. This is a first-order screening calculation: moment amplification, biaxial bending, local plate buckling, and connection detailing are not included. Enter Pc and Mc from a design aid or analysis that follows the code procedure, and have a licensed structural engineer confirm the final member size.
Frequently Asked Questions
Adding P/A and M/S ignores buckling. A slender column fails well below yield, so AISC checks the ratio of required strength to available strength, where the available values already account for flexural and lateral-torsional buckling.
This tool is first-order only. The extra moment caused by the column deflecting under load must be added through the B1 and B2 amplification factors of AISC 360 Appendix 8 or by direct analysis, and the gap grows with slenderness.