AISC 360-22 Steel Design — Specification Overview and Key Provisions

AISC 360-22, the Specification for Structural Steel Buildings, is the primary design standard for structural steel in the United States. Published by the American Institute of Steel Construction (AISC) as part of the 16th Edition Steel Construction Manual, it is adopted by reference in the International Building Code (IBC 2024) and referenced by ASCE/SEI 7-22 for load path requirements. This page provides a practical overview of the specification's structure, key chapters, resistance factors, and design workflow — organized for engineers who need quick answers and direct links to the relevant provisions.

Quick access:

• Specification Scope and Applicability
• Chapter-by-Chapter Overview
• Resistance Factors (LRFD) and Safety Factors (ASD)
• Section Classification — Compact, Noncompact, Slender
• Design Workflow — Step by Step
• Key Changes from AISC 360-16
• Related AISC Standards
• Frequently Asked Questions

Specification Scope and Applicability

AISC 360-22 applies to the design, fabrication, and erection of structural steel buildings and other structures using hot-rolled shapes, hollow structural sections (HSS), built-up members, plates, bars, and connection elements. The specification covers:

• Hot-rolled W-shapes, S-shapes, M-shapes, HP-shapes — the workhorses of US steel construction
• Hollow Structural Sections (HSS) — square, rectangular, and round tubes
• Channels (C and MC), angles (L), tees (WT, ST) — secondary framing and connection elements
• Built-up sections — plate girders, box sections, and welded combinations
• Connection elements — bolts, welds, gusset plates, end plates, angles, and splice plates

What AISC 360 Does NOT Cover

For composite steel-concrete design, AISC 360 Chapter I works in conjunction with ACI 318. For seismic applications, AISC 341 imposes additional ductile detailing requirements beyond AISC 360's base provisions.

LRFD vs. ASD

AISC 360 provides two parallel design philosophies:

LRFD (Load and Resistance Factor Design):

• Factored loads from ASCE 7 load combinations (1.2D + 1.6L, etc.)
• Design strength = phi x Rn (resistance factor applied to nominal strength)
• Required Strength <= Design Strength
• More consistent reliability across load types; preferred by most US engineers

ASD (Allowable Strength Design):

• Service-level loads from ASCE 7 (D + L, etc.)
• Allowable strength = Rn / Omega (safety factor divides nominal strength)
• Required Strength <= Allowable Strength
• Simpler load combinations; used for some serviceability-governed designs

Both methods produce equivalent structural reliability when properly applied. All Steel Calculator tools implement LRFD.

Chapter-by-Chapter Overview

Chapter B — Design Requirements

Chapter B establishes the fundamental design framework:

• B2 — Stability: The Direct Analysis Method (DAM) is the primary method for accounting for second-order effects. It uses reduced stiffness (0.8 tau_b x EI) and applies notional loads (0.002 alpha x Y_i) to capture P-delta and P-delta effects without separate effective length calculations.
• B3 — Member Properties: Classification of sections as compact, noncompact, or slender determines which width-to-height ratio limits apply and what strength reduction is needed.
• Required Strength: Members and connections must be designed for the most critical load combinations from ASCE 7.

Chapter C — Design for Stability

The Direct Analysis Method (Chapter C) replaced the older Effective Length Method as the primary stability approach. Key requirements:

• Use 0.8 tau_b x EI for member stiffness in analysis
• Apply notional lateral loads of 0.002 alpha x Y_i at each story
• tau_b = 1.0 when required axial strength / available axial strength <= 0.5
• tau_b = 4(P_r / P_y)(1 - P_r / P_y) when the ratio exceeds 0.5
• Second-order effects must be included (P-delta analysis)

Chapter D — Design of Members for Tension

Two limit states govern tension members:

1. Yielding on gross section: phi P_n = 0.90 x F_y x A_g (ductile, slow failure)
2. Rupture on effective net section: phi P_n = 0.75 x F_u x A_e (brittle, fast fracture)

where A_e = A_n x U (net area times the shear lag factor from Table D3.1).

The shear lag factor U reduces the effective area when not all cross-section elements are connected. See our Shear Lag Factor reference for all 8 cases.

Chapter E — Design of Members for Compression

Compression members are governed by elastic and inelastic buckling:

• phi P_n = 0.90 x F_cr x A_g
• F_cr depends on the slenderness ratio KL/r
• For KL/r <= 4.71 sqrt(E/F_y): inelastic buckling, F_cr = 0.658^(F_y/F_e) x F_y
• For KL/r > 4.71 sqrt(E/F_y): elastic buckling, F_cr = 0.877 x F_e
• F_e = pi^2 x E / (KL/r)^2 (Euler buckling stress)

The effective length factor K is determined from the Direct Analysis Method (Chapter C) or from alignment charts. See our K-Factor reference and Column Design Guide.

Chapter F — Design of Members for Flexure

Flexural design depends on the limit state of the unbraced length:

For compact sections with adequate bracing, the full plastic moment M_p is available. As the unbraced length increases, lateral-torsional buckling reduces capacity. See our Beam Design Guide and Lateral-Torsional Buckling reference.

Chapter G — Design of Members for Shear

Shear yielding of the web governs for most standard W-shapes:

• phi V_n = 1.0 x 0.6 x F_y x A_w x C_v (LRFD, unstiffened webs)
• A_w = d x t_w (web area)
• C_v = shear buckling coefficient (1.0 for compact webs, reduced for slender webs)

For webs with h/t_w <= 2.24 sqrt(E/F_y), C_v = 1.0 and the full shear yield strength is available. Most standard W-shapes fall in this category.

Chapter H — Design of Members for Combined Forces

Members subjected to combined axial force and bending must satisfy the appropriate interaction equations:

For members with P_r / P_c >= 0.2 (significant axial load):

P_r / (2 P_c) + (M_rx / M_cx) + (M_ry / M_cy) <= 1.0

For members with P_r / P_c < 0.2 (low axial load):

P_r / P_c + (8/9)(M_rx / M_cx + M_ry / M_cy) <= 1.0

Chapter I — Composite Members

Covers composite steel-concrete members: concrete-encased shapes, concrete-filled HSS, and composite deck-slab systems. Works in conjunction with ACI 318.

Chapter J — Design of Connections

The most frequently referenced chapter for connection design:

Connection design is where most GSC queries originate. See:

• AISC Block Shear (J4.3)
• AISC Standard Hole Sizes (J3.3)
• AISC Bolt Spacing Requirements
• AISC Weld Design Basics

Chapter K — HSS Connections

Specialized provisions for connections to hollow structural sections, including branch connections, through-plate connections, and cap-plate connections. HSS connection design is more complex than open-section connections because the load path is three-dimensional.

Chapter L — Fabrication and Erection

Requirements for material handling, cutting, hole making, camber, and fit-up. Not typically a design-governing chapter but important for constructability reviews.

Chapter M — Quality Control and Quality Assurance

Inspection requirements for bolts, welds, and finished connections. Defines when special inspection is required vs. when visual inspection suffices.

Resistance Factors (LRFD) and Safety Factors (ASD)

Trend: phi = 0.90 for ductile limit states (yielding), phi = 0.75 for brittle limit states (rupture, buckling), phi = 1.00 for shear (which is relatively ductile).

Section Classification — Compact, Noncompact, Slender

AISC 360 classifies sections based on width-to-thickness ratios of flanges and webs. The classification determines which limit states apply and what strength is available.

Where lambda = b/t (flange) or h/t_w (web), lambda_p = compact limit, lambda_r = noncompact limit.

Common W-Shape Classification

Most standard W-shapes in AISC steel have compact flanges and webs for F_y = 50 ksi, meaning the full plastic moment M_p is achievable with adequate lateral bracing. Noncompact or slender classifications are relevant for:

• High-strength steel (F_y > 50 ksi)
• Very thin-walled sections
• HSS with certain width-thickness ratios
• Cover-plated sections

See our Compact Section Limits page for complete tables.

Design Workflow — Step by Step

A typical AISC 360 steel design follows this workflow:

Step 1: Establish Loads and Load Combinations

Determine dead, live, wind, snow, seismic, and other loads per ASCE/SEI 7-22. Apply LRFD load combinations (ASCE 7 Section 2.3.1). Use our Load Combination Calculator for automatic combination generation.

Step 2: Analyze the Structure

Perform a second-order elastic analysis using the Direct Analysis Method (Chapter C). Include P-delta effects, notional loads, and reduced stiffness. Software like ETABS, RISA, or SAP2000 handles this automatically.

Step 3: Design Members for Each Limit State

For each member, check all applicable limit states:

1. Tension: yielding + rupture (Chapter D)
2. Compression: buckling at K-factor (Chapter E)
3. Flexure: yielding, LTB, flange/web local buckling (Chapter F)
4. Shear: web yielding and buckling (Chapter G)
5. Combined forces: interaction equations (Chapter H)

Use our calculators for automated checks:

• Beam Capacity Calculator
• Column Design Calculator
• Section Properties Lookup

Step 4: Design Connections

Design bolted and welded connections per Chapter J:

1. Determine demand (force and moment at connection)
2. Select bolt size, grade, and pattern
3. Check bolt shear, tension, bearing, and tearout
4. Check plate yielding, rupture, and block shear
5. Design welds (fillet, groove, or combination)

Use our Bolted Connections Calculator and Welded Connections Calculator for automated checks.

Step 5: Check Serviceability

Verify deflection limits per AISC Design Guide 3 and IBC Table 1604.3. Check vibration if applicable for floor systems.

Step 6: Verify Stability

Ensure the structure has adequate lateral stability through bracing, moment frames, or a combination. Check that all members have sufficient lateral bracing for their unbraced lengths.

Key Changes from AISC 360-16

AISC 360-22 introduced several significant changes:

Related AISC Standards

AISC 360 does not operate in isolation. A complete design typically requires:

• ASCE/SEI 7-22 — Minimum design loads and load combinations
• AISC 341-22 — Seismic Provisions for Structural Steel Buildings
• AISC 358-22 — Prequalified Connections for Special and Intermediate Moment Frames
• AISC Code of Standard Practice (AISC 303-22) — Trade practices for fabrication and erection
• RCSC Specification — High-strength bolt installation and inspection
• AISC Design Guides — 40+ guides covering specific topics (base plates, bracing, crane runways, etc.)

Calculator

Check any steel member or connection against AISC 360-22 with our free tools:

• Beam Capacity Calculator — Flexural and shear checks for W-shapes
• Bolted Connections Calculator — Bolt shear, bearing, tearout, and tension
• Welded Connections Calculator — Fillet and groove weld capacity
• Section Properties Lookup — Complete AISC section database

FAQ

Q: What is the current edition of AISC 360? A: AISC 360-22 (16th Edition), published in 2022. It is referenced by IBC 2024 and ASCE 7-22. The prior edition was AISC 360-16 (15th Edition).

Q: Do I use LRFD or ASD? A: LRFD is the more common approach in US practice and is required for certain load combinations involving wind and seismic. ASD is permitted for all structures but produces slightly different member sizes. Both methods are acceptable under AISC 360 and IBC.

Q: What is the difference between AISC 360 and AISC 341? A: AISC 360 covers general steel design (all structures). AISC 341 adds seismic-specific requirements for structures in seismically active regions — ductile detailing, special moment frames, buckling-restrained braces, and other seismic force-resisting systems. When seismic loads govern, both standards apply simultaneously.

Q: Where do I find the phi factors? A: Resistance factors (phi) are listed in the table above and in each chapter of AISC 360. They are also shown in every Steel Calculator output for transparency.

Q: How do I handle combined axial and bending? A: Use the interaction equations in Chapter H. For significant axial load (P_r/P_c >= 0.2), use the combined formula. For low axial load (P_r/P_c < 0.2), use the simplified formula. Our beam and column calculators automatically check combined loading.

Related: AISC Table D3.1 — Shear Lag Factors | AISC Block Shear — Section J4.3 | AISC Standard Hole Sizes | AISC Bolt Spacing | AISC Weld Design | AISC Deflection Limits | AISC Steel Construction Manual