How the steel column calculator works
This free steel column calculator checks a steel column or compression member with any shape from the AISC Shapes Database v16.0: W, M, S and HP shapes, channels, single and double angles, tees, rectangular and round HSS, and pipe. Enter the length, effective length factors and bracing, then the axial loads and end moments for each load case. The calculator finds the available compression strength by AISC 360-22 Chapter E and checks combined axial load and bending with the interaction equations of Chapter H, in LRFD or ASD.
What it checks
- Flexural buckling about both axes (§E3), with Fcr = 0.658Fy/FeFy or 0.877Fe
- Torsional buckling of I-shapes and flexural-torsional buckling of channels, tees and double angles (§E4)
- Slender elements by the effective width method of AISC 360-22 §E7, including the reduced effective area of round HSS
- Double angles with the modified slenderness for the connector spacing (§E6), and single angles loaded through one leg (§E5)
- Combined axial load and biaxial bending by Eq. H1-1a and H1-1b, with the flexural strength from Chapter F and moments amplified by B1 = Cm/(1 − αPr/Pe1)
- Tension from wind uplift, checked for yielding of the gross section
Method
The calculator uses the effective length method: you enter Kx and Ky, and intermediate braces divide the weak-axis and torsional length. The ASCE 7-22 load combinations are built from your service loads, and wind is applied in both directions. For each combination the end moments are amplified for member curvature (P-δ) with Cm = 0.6 − 0.4(M1/M2), and the governing interaction ratio is reported.
The Interaction tab draws the H1-1 interaction diagram in kips and kip-ft for each axis with moment, plus a normalized diagram in which every load combination is plotted with its own Cb and B1, so a point on the line has a ratio of exactly 1.0.
The Strength vs length tab lists the available axial strength for effective lengths from 0 to 40 ft, in the same format as Table 4-1 of the AISC Steel Construction Manual.
Assumptions and limitations
- Sway (P-Δ) effects are not calculated. Enter moments from a second-order analysis or amplified by B2 for sway frames.
- Single angles are checked for axial load only, as §E5 allows for angles connected through one leg. Weak-axis moments are not checked for tees and double angles.
- Tension is checked for gross-section yielding only. Net-section rupture, connections, splices and base plates are not checked.
Frequently asked questions
What K factor should I use for a steel column?
For a column in a braced frame with pinned ends, K = 1.0. In a moment frame, K comes from the alignment charts in the AISC Commentary or the direct analysis method. Use K greater than 1.0 only when the frame can sway and the analysis does not include P-Δ effects.
Why is my W-shape column using the effective area?
Many W-shapes have webs that are slender for uniform compression. AISC 360-22 §E7 reduces the web to an effective width, but only when the element is slender at the critical stress Fcr, so long columns are often fully effective.
When does Eq. H1-1b apply?
When the axial ratio Pr/Pc is below 0.2, AISC uses Eq. H1-1b, which halves the axial term and uses the full moment terms. Above 0.2, Eq. H1-1a adds 8/9 of the moment terms to the axial ratio.
Does the calculator match AISC Manual Table 4-1?
Yes. The Strength vs length tab reproduces the Table 4-1 format, and the hand-calculation tests include AISC Design Example E.1A, a W14X132 with a 30 ft effective length and φcPn = 893 kips.
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For educational and preliminary design purposes only. Always verify results with a licensed PE.