Steel column

A W-shape, rectangular or square HSS, round HSS or pipe member in axial compression or tension with bending about both axes and shear, to AISC 360-22 Chapters D, E, F, G and H, with ASCE 7-22 load combinations and the approximate second-order analysis of Appendix 8.

Inputs of the steel column #

• Member: the shape (AISC Shapes Database v16.0: W, HSS, pipe) and the steel. W-shapes take A992, A572 Gr. 50, A913 Gr. 65 or A36; HSS take A500 Gr. C (Fy = 50 ksi), A500 Gr. B (46 ksi) or A1085 (50 ksi); pipe takes A53 Gr. B (35 ksi). A steel that does not suit the section is reported as not feasible.
• Lengths and bracing: the member length L and, for each buckling axis, the unbraced length and the effective length factor (Kx Lx, Ky Ly, and Kz Lz for torsional buckling of W-shapes). K is the engineer's input (Commentary Table C-A-7.1 or Appendix 7); with the direct analysis method K = 1.0 (Section C3). Lb is the unbraced length of the compression flange for lateral-torsional buckling.
• Loads: either service loads by load type (D, L, Lr, S, R, W, E), combined by ASCE 7-22 2.3.1 / 2.4.1 (W and E in both directions), or required strengths entered per case (factored for LRFD). Each row has the axial force P (compression positive, tension negative), the moments at the top and the bottom as moment-diagram ordinates (the same sign at both ends is single curvature), the mid-height moment of loads applied along the member (wL²/8, added to the end-moment line), and optionally the shears Vx and Vy (blank: taken from the moments as

  |Mtop − Mbot|/L + 4|Mmid|/L).

• Second-order effects: either the moments come from a second-order analysis, or the approximate method of Appendix 8 is applied: B1 = Cm/(1 − αPr/Pe1) ≥ 1 on the no-translation moments, with Cm from the end moments (Eq. A-8-4) or 1.0 when there is transverse loading, Pe1 = π²EI*/L² (K1 = 1.0) with EI* = 0.8τbEI for the direct analysis method or EI for the effective length method. B2 is entered from the story analysis and multiplies the axial force and moments of the W and E load types (taken as the lateral-translation effects Plt and Mlt).
• Flexure: Cb by Eq. F1-1 from the moment diagram along the member (when Lb is the member length; for a shorter Lb, Cb = 1.0 unless entered), or entered. The H1.2 increase of Cb by √(1 + αPr/Pey) under axial tension can be switched off.
• Tension end connection: no holes and all elements connected (Ae = Ag), or the net area An (B4.3b) and the shear lag factor U (Table D3.1) entered.

Auto-design (editor toolbar) varies the shape of the given family (W, rectangular HSS, round HSS or pipe), lightest first, optional depth limit; steel grade when unlocked. Objectives: lightest (steel weight); smallest depth, then lightest. Kept unless you select them: steel. Every other input is kept; see Auto-design.

Checks performed #

The flexure and interaction checks report the combination that governs each; the diagrams show the first-order moments along the member, bottom to top.

Drawings #

The drawing sheet (PDF / DXF, Drawing sheet button) shows the column elevation with the axial loads by type (or the governing required strength) on the top, the member length, the ends as braced points and a callout with the effective-length factors and unbraced lengths used in the design, the first-order moment diagrams about each axis for the governing combination drawn along the column from the base to the top, and the section (W-shape, rectangular HSS or round HSS / pipe) with its dimensions. End fixity, brace locations between the ends, the base plate and splices are not part of the calculation and are not drawn; the sheet notes say so.

Limitations #

• W, rectangular / square HSS, round HSS and pipe only. Channels, angles, tees and built-up sections are not covered. A W-shape whose web is not compact for flexure (F4 / F5) is reported as not feasible.
• H1.3 (separate in-plane and out-of-plane checks) and H2 are not offered; H1.1 is used, which is always permitted. Torsion (H3) is not checked.
• The approximate second-order method takes Mr = B1 Mnt + B2 Mlt with the member's largest first-order moments (conservative). B2 is not computed (it is a story quantity, entered). In the direct entry mode all moments are treated as Mnt.
• The moment diagram between the ends is the end-moment line plus a parabola for the transverse load (Cb and the largest moment are taken from it); other load patterns can be entered as required strengths with Cb.
• Concentrated forces (J10), bearing, splices and connections are not checked.
• A500 Gr. B round HSS are taken with Fy = 46 ksi (ASTM A500-21); the Manual Table 2-4 text on disk was not legible for this row, so this value is still to be confirmed against the printed table.

Verification examples #

AISC Design Examples v16.0, LRFD and ASD (all within 1 %):

AISC Steel Construction Manual, 16th Ed., column tables (φcPn / Pn/Ωc in kips, pinned, Lc on both axes):

E.1C reads Fn from Manual Table 4-14 and H.3 / H.4 take Cb = 1.14 from Manual Table 3-1 (ILX computes 1.136 by Eq. F1-1). For F.8 the Manual table value is compared: ILX computes Se with the compression flange reduced and the neutral axis shifted, as F7.2(c) states; Example F.8B removes the ineffective width from both flanges, which is conservative (45.4 kip-ft). Flexure and shear examples written for beams are run as a member with the same moment or shear entered and no axial force.