AISC 360-16

This page covers design checks to the AISC Specification for Structural Steel Buildings (ANSI/AISC 360-16) for I-sections, channels, tees, angles and HSS, in the standalone calculator and the FEA design tab. Both LRFD (Load and Resistance Factor Design) and ASD (Allowable Strength Design) are supported.

Open AISC 360-16 Calculator

Standard Reference

Supported Section Types

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

Checks Performed

Each check in the design-check table reports the clause it applies. The checks are grouped as follows:

• Section classification (Table B4.1): Compression and flexural element classes are reported separately where they affect member checks.
• Tension (D2/D3): Gross yielding and effective-net-section rupture are checked; detailed bolt-hole paths are not inferred. Channels require an entered shear-lag factor U; without it, rupture and dependent tension interactions are INCOMPLETE. Confirm assumed shear-lag factors against the actual connection; defaults are not universally conservative. A valid tensile strength is required for rupture and dependent tension interactions.
• Compression (E3/E4/E5/E7): FEA member angles use E3 with recovered eccentric moments and H2 interaction; standalone angle calculators retain E5 eccentricity treatment. Both paths additionally check E4 when the longest full leg b/t exceeds 0.71√(E/Fy), using E7 effective area where required. For I-sections that need an E4 check, missing or invalid torsional or warping properties leave compression resistance unresolved, and the dependent compression-bending checks are not reported.
• Flexure (F2-F12): Flexural paths follow section family and axis. Channel major-axis bending requires compact webs and flanges; noncompact or slender channels have no major-axis resistance or dependent H1 interaction. Unequal-I major bending uses conservative F5 only where the compression flange is braced (continuous top-flange restraint under sagging moment, or both flanges braced), including both flange yielding limits, flange local buckling and web reduction. Other unequal-I major-axis flexure is not checked; the remaining checks are still reported.
• Shear (G2-G6): Web, flange, HSS, tee-stem, and single-angle shear rows report the applicable local shear path.
• Combined actions and torsion (App. 8 A-8-3 / H1/H2/H3): Compression-bending interactions include Appendix 8 B1 amplification for local member effects. P-Delta analysis retains frame sway and checks local member effects separately; section checks retain the full analysis moments. Where a P-Delta member has no first-order moment diagram (for example an internally subdivided member), B1 is applied to the P-Delta moments, which is conservative. Standalone moments are treated as first-order and receive B1. Invalid amplification prevents completion of the affected interaction. Frame sway amplification B2 and the complete Chapter C / Appendix 7 frame assessment remain separate. Closed-HSS torsion is checked when applied torsion is available.

Calculator Inputs

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

Design Method

Select LRFD or ASD. The method sets the resistance or safety factors applied to the capacities.

Section Geometry

Select a shape group, then enter dimensions or pick from the built-in US section library. Manually entered I-shape, channel, tee and angle sections are calculated without root fillets.

Fabrication: for I-shapes, Hot Rolled or Welded / Built-up. Built-up affects flange classification, removes the G2.1(a) shear factor of 1.00 and triggers the E4 check. For HSS, ERW uses 0.93 t_nom and SAW uses t_nom. Optionally, I-shapes accept a different bottom flange (bf,bot and tf,bot).

Material Properties

Member Lengths & Bracing

In the FEA Design tab these lengths are entered as factors on the member length: K_z, K_y, K_t and KLT.

Continuous Restraint means the top flange is continuously restrained, for example by a concrete slab or welded metal deck. Negative (sagging) major-axis moment compresses the top flange, so lateral-torsional buckling does not govern (L_b = 0). Positive (hogging) moment compresses the unbraced bottom flange, so no credit is taken for the top-flange restraint: hogging is checked as an unbraced member over L_b = KLT × L, with the same C_b and cantilever rules, and is reported separately. H1 uses the sagging or hogging strength according to the sign of the moment along the member. Enter KLT = 0 if the bottom flange is also braced. For single angles the setting treats the whole member as restrained for both moment signs.

In the FEA Design tab the Cantilever control has three settings: Auto (default) follows the model and shows what it detected, for example "Auto (detected: cantilever, held at Node A)"; Span and Cantilever override the detection. A cantilever uses C_b = 1.0 for Chapter F lateral-torsional buckling.

Design Actions

Resistance Factors

Limitations & Notes

• Analysis and amplification basis: Compression-bending checks include Appendix 8 B₁ amplification (Eq. A-8-3) for local member effects in both linear and P-Delta FEA. In P-Delta FEA the analysis moments keep the frame sway effects and B₁ covers the local member effects; section checks retain the full analysis moments. Where a P-Delta result does not include first-order member moments, B₁ is applied to the full analysis moments, which is conservative. If B₁ cannot be evaluated (αP_r reaches P_e1), the affected interaction check is not reported. Enter first-order moments in the standalone calculator; moments that already include local second-order effects would be amplified twice. Frame sway amplification B₂ and the complete Chapter C / Appendix 7 frame assessment remain separate.
• Custom-section axes: Check that the major and minor axes, moments of inertia, and elastic and plastic section moduli match the section preview; incorrect axes change the bending, buckling and LTB resistances.
• Channel major-axis bending: Chapter F2 requires compact webs and flanges. Noncompact or slender channels have no major-axis bending resistance or dependent H1 interaction; check those limit states separately. Axial, shear and minor-axis checks are still reported.
• Slender elements (E7): Slender-element compression uses the effective-area method, Pn = Fcr Ae, with F_cr from E3 or E4.
• Combined axial force and biaxial bending (H1): H1.2 tension uses the governing Chapter D design strength, including net-section rupture. H1-1 adds the orthogonal moment ratios, including for round HSS; the resultant moment of round HSS is used only in the Chapter F8 flexural check.
• Angle LTB (F10): Principal-axis single-angle LTB uses F10-4, with the monosymmetry factor zero for equal angles and calculated from the geometry for unequal angles. Equal-angle geometric-axis bending uses F10-5 where applicable.
• Angle H2 stress points: The H2-1 interaction is evaluated at six points: the heel, the outer and inner tip of each leg, and the re-entrant corner. For single angles near capacity, confirm the principal-axis section properties and moment-axis assumptions against the AISC Manual tables.
• Angle compression (E4/E5): The coupled E4 check applies when b/t exceeds 0.71 sqrt(E/Fy), where b is the full width of the longest leg; equal angles use E4-3 and unequal angles E4-4. It is made in addition to E3 (FEA design tab, with the eccentric end moments from the analysis) or E5 (standalone calculator, leg ratio below 1.7), and the lower capacity is used in the H2 interaction.
• Plate girders (F4/F5): Doubly symmetric plate girders use F4 or F5. With Continuous Restraint, unequal-I sections use conservative F5 with tension-flange yielding (F5-10) where the compression flange is braced: under sagging moment, or under either moment sign with KLT = 0. Other unequal-I major-axis flexure, including hogging with only the top flange restrained, is not covered.
• Slender-web rectangular HSS (F7): Rectangular HSS with a slender web are not covered when that bending axis is loaded; pure axial checks remain available.
• Connection/detail inputs not inferred: D3 HSS shear-lag Cases 5/6, D5 pin-connected members, D6 eyebars, and F13 bolt-hole proportioning require connection geometry and are checked separately.
• HSS wall thickness (B4.2): ERW / cold-formed HSS use t = 0.93 t_nom; SAW / hot-formed HSS use the full t_nom. US library sections already store the AISC Manual design thickness and properties, so 0.93 is not applied again. For custom and non-US ERW sections the reduced t is used for slenderness, local buckling, shear and torsion; A, I, S and Z are used as entered.
• C_b factor: In the FEA design tab a blank C_b is calculated from the member moment diagram. Where KLT is not 1.0 the member diagram does not represent the segment between braces, so a blank C_b is 1.0; in the standalone calculator a single moment entry is a uniform moment, so a blank C_b is also 1.0. Enter the segment value to take credit for moment gradient. An override changes the factor only; it does not substitute a separately calculated buckling resistance.
• Required torsional buckling properties: For I-sections that need a Chapter E4 check, missing or invalid torsional or warping properties leave compression resistance unresolved and dependent compression-bending interactions are not reported. Passing the flexural-buckling checks alone does not complete the member assessment.
• Net section: Tension rupture follows D2/D3 using A_n and U where entered. Blank A_n defaults to A_g; holes, staggered paths, connection length and shear-lag geometry are not inferred. Confirm U for the actual connection: assumed family values are not universally conservative. HSS using the default U = 0.75 are flagged with a limitation.
• Concentrated forces and reactions: J10 checks are not performed, and FEA reactions, point loads and connection forces are not used to derive them. Check flange local bending, web local yielding, web crippling, web sidesway buckling, bearing stiffeners and doubler plates separately at supports, point loads and connections.
• Design stiffness: Resistance and stability checks use E = 29,000 ksi and G = 11,200 ksi as defined in the Specification. Material stiffness entered for structural analysis does not change these design values.
• Bracing design: Effective lengths, unbraced lengths and restraint conditions are taken as entered. Brace strength and stiffness, diaphragm stiffness, and whether lateral bracing is attached to the correct flange for each member and load case are not verified.
• Torsion: H3.1/H3.2 closed-HSS torsion is checked in the FEA design tab where torsion demand is available; torsion is not an input in the standalone calculator. E4 torsional buckling of compression members is still checked for supported section families. Applied open-section torsion requires separate warping verification.
• Scope exclusions: Ponding, fatigue, fire design, corrosion allowance, composite member design, seismic detailing/proportioning, and serviceability limits are outside this AISC member-strength check unless handled by a separate workflow.

Verification

The public verification pages contain 55 published comparisons from AISC Design Examples v15.0, with an average numerical difference of 0.19%. Classification outcomes do not contribute to the numerical mean.