Steel Column (LRFD, AISC 360-22)

How it calculates

The Steel Column (LRFD, AISC 360-22) calculator designs hot-rolled steel columns and posts using the latest edition of the AISC Specification. It runs a first-order structural analysis to determine demands, then applies AISC 360-22 capacity equations for all relevant limit states.

Structural analysis

The calculator performs FEA on the column as a beam-column, resolving axial forces, moments, and deflections under applied loads. End conditions (pinned, fixed, roller) are specified at each support. Concentrated axial and distributed lateral loads can be applied at any height. A first-order moment amplification factor accounts for P-delta effects, consistent with the assumption that the member is part of a braced frame.

Axial compression capacity

Nominal compressive strength follows AISC 360-22 Chapter E:

utilization = Pu / (phi_c * Pn) ≤ 1.0

where phi_c = 0.90. Fcr is determined from the slenderness-based equations using the governing KL/r ratio. For doubly-symmetric shapes flexural buckling about the weak axis controls. For singly-symmetric and unsymmetric shapes, flexural-torsional buckling is additionally evaluated. Slender element reduction (Q factors) is applied per Section E7 where local buckling reduces the member's available strength.

Flexural capacity

Moment demands from eccentricity or lateral loads are checked per AISC 360-22 Chapter F:

utilization = |Mu| / (phi_b * Mn) ≤ 1.0

where phi_b = 0.90. Compact, non-compact, and slender section classifications per Table B4.1b govern the applicable strength equations. Lateral-torsional buckling is evaluated based on the unbraced length relative to Lp and Lr.

Combined axial compression and bending

The AISC H1-1 interaction check covers simultaneous axial and biaxial bending demands:

• For Pu / phi_c Pn ≥ 0.2: (Pu / phi_c Pn) + (8/9) * (Mux / phi_b Mnx + Muy / phi_b Mny) ≤ 1.0
• For Pu / phi_c Pn < 0.2: (Pu / 2 phi_c Pn) + (Mux / phi_b Mnx + Muy / phi_b Mny) ≤ 1.0

This covers columns carrying gravity plus wind or seismic moments simultaneously.

Axial deformation

Axial shortening under factored loads is calculated and reported alongside strength checks for serviceability review.

Outputs

Results are displayed as colour-coded utilization ratios for each limit state with full code clause references. The governing check, critical load combination, and section properties are summarised for straightforward QA.