AISC 360-16

The AISC 360-16 engine implements the Specification for Structural Steel Buildings (ANSI/AISC 360-16) published by the American Institute of Steel Construction. Both LRFD (Load and Resistance Factor Design) and ASD (Allowable Stress Design) methods are supported.

Open AISC 360-16 Calculator

Standard Reference

Supported Section Types

• I-Shapes (W, S, M, HP - rolled and built-up/welded)
• Channels (C, MC)
• Tees (WT, ST, MT - beam and column tees)
• Rectangular Hollow Sections (HSS rectangular and square)
• Circular Hollow Sections (Pipe, HSS round)
• Angles (equal and unequal leg)

Checks Performed

Section Classification (Table B4.1)

Elements are classified as compact, noncompact, or slenderbased on width-to-thickness ratios. The engine evaluates flanges, webs, and stems independently for both compression and flexure, applying the correct limiting ratios from Table B4.1 including the kc-dependent limits for built-up sections.

Tension (Chapter D)

• D2-1: Tension yielding on gross section
• D2-2: Tension rupture on net section (A_e = 0.85A_g assumed - conservative default without connection details)

Compression (Chapter E)

• E3: Flexural buckling about strong and weak axes with user-defined effective length factors (K_y, K_z)
• E4: Torsional and flexural-torsional buckling for I-shapes, tees, and channels
• E5: Single-angle compression with modified slenderness (standalone calculator only; FEA uses standard E3 per principal axis since the analysis captures real moments)
• E7: Effective area reduction for members with slender elements (P_n = F_cr × A_e)
• Advisory: Slenderness ratio check (KL/r ≤ 200 for compression, ≤ 300 for tension)

Flexure (Chapter F)

• F2: Compact doubly-symmetric I-shapes and channels - yielding and LTB
• F3: I-shapes and channels with compact webs and noncompact/slender flanges - FLB
• F4/F5: Plate girder provisions (noncompact and slender webs)
• F6: I-shapes and channels - minor-axis yielding (M_n = min(M_p, 1.6M_y)) and FLB. Tees use F12 and angles use F10-1 for minor-axis yielding (see below).
• F7: Rectangular HSS - FLB, WLB, and LTB. FLB and WLB are evaluated for both major- and minor-axis bending; for sections with D/B > 2 the long-side plates often classify as slender for minor-axis bending and trigger the F7-5 effective section modulus reduction even when the major-axis classification is compact.
• F8: Circular HSS - local buckling
• F9: Tees - yielding, LTB (F9-2/F9-6 stem-tension or F9-4/F9-13 stem-compression), FLB, and stem local buckling. The F9 branch (stem in tension vs compression) is selected per station from the local moment sign rather than member-wide, because the stem-compression LTB mode physically cannot initiate at a station where the flange is in compression. This matches industry practice and recovers capacity that the older conservative "stem-compression anywhere" interpretation over-penalized.
• F10: Single angles - yielding at M_n = min(M_p, 1.5M_y) per F10-1 (applies to both major and minor principal axes), LTB (F10-2/F10-3 using F10-5 Mcr with shortest leg, conservative vs F10-4), and leg local buckling. Uses principal-axis properties throughout.
• F12: Tee minor-axis yielding (Mn = F_y·S, elastic only). Tees lack the plane of symmetry about this axis, so F6's plastic moment and 1.6M_y cap do not apply.

Shear (Chapter G)

• G2.1: I-shapes and channels (strong axis), with φ_v = 1.0 for qualifying rolled shapes
• G3: Tee stems and single angle legs (k_v = 1.2)
• G4: Rectangular HSS
• G5: Circular HSS
• G6: Minor-axis shear through flanges. I-shapes/channels use A_w = 2·b_f·t_f; tees use A_w = b_f·t_f (single flange). Sideways tees route physical V_y through the flange path, not the stem.

Combined Actions (Chapter H)

• H1-1a/b: Combined axial force with biaxial bending interaction check for doubly and singly symmetric members. Uses the appropriate equation based on the P_r/P_c ratio. The engine evaluates the interaction at every member station (with additional interpolated points) and reports the governing ratio — summing peak |M_z| + peak |M_y| from non-coincident stations would conservatively inflate the result. Also applies to pure biaxial bending with no axial force (equation H1-1b). For axisymmetric circular HSS (M_cz = M_cy), the engine combines biaxial moments as the resultant √(M_z² + M_y²) acting on a single M_n, matching the physical circular interaction surface rather than the bounding square of the linear additive form; this matches common commercial steel design software and recovers roughly 30% of the capacity that AISC's linear additive expression over-penalizes for round tubes.
• H2-1: Stress-based interaction check for unsymmetric members (single angles). Evaluates f_ra/F_ca + f_rb,u/F_cb,u + f_rb,v/F_cb,v at critical fiber points of the cross-section, station-by-station along the member, with the worst combination governing.
• H3.2 (V+T): For closed hollow sections with torsion, (V_u/φV_n)² + (T_u/φT_n)² is evaluated per station so non-coincident peak shear and peak torsion don't inflate the combined ratio.

Calculator Inputs

The standalone AISC calculator accepts the following inputs. All values are in imperial units.

Design Method

Toggle between LRFD (Load and Resistance Factor Design) and ASD (Allowable Stress Design). This controls which resistance/safety factors are applied to the capacity calculations.

Section Geometry

Select a shape group, then enter dimensions or pick from the built-in section library (AISC shapes database).

Material Properties

Member Lengths & Bracing

A Continuously Restrained checkbox sets L_b = 0, bypassing the LTB check.

Design Actions

Resistance Factors

Limitations & Notes

• Slender elements (E7): Uses the AISC 360-16 effective area method (P_n = F_cr × A_e). Effective widths per E7-3 with Table E7.1 imperfection factors. Single-iteration approach (f = F_cr from E3/E4).
• Angle LTB (F10): Uses the shorter leg for M_e. Conservative for unequal-leg angles (β_w = 0 assumed).
• Plate girders (F4/F5): Assumes doubly symmetric I-shapes. Tension flange yielding (F4-15/F5-4) is not checked — it does not govern for doubly symmetric sections but would be needed for singly symmetric built-up I-shapes with unequal flanges.
• CHS wall thickness: US library sections have the 0.93 design wall thickness factor already baked into section properties per AISC Manual convention. Custom or non-US sections may need manual adjustment.
• C_b factor: Auto-computed from the quarter-point moment distribution (F1-1) for I-shapes, channels, angles, and rectangular HSS. Tees use C_b = 1.0 (conservative — the F1-1 formula overestimates tee LTB capacity). Can be overridden via element design settings in the FEA tool or the standalone calculator.
• Net section: A_e = 0.85A_g is assumed for tension rupture (both standalone calculator and FEA tool). This is conservative without detailed connection information.
• Torsion (H3): Not an input in the standalone calculator. In the FEA tool, torsion is checked for closed hollow sections (HSS rectangular and round) only. Warping torsion for open sections (I-beams, channels, angles, tees) is not performed.

Verification

The engine is benchmarked against 78 independent test cases from the AISC Design Examples v15.0 with an average difference of 0.11%. Checks cover classification, tension, compression, flexure (including LTB and FLB), shear, C_b factor computation, and biaxial interaction.