AISC 360-16 — Specification for Structural Steel Buildings

The definitive guide to AISC 360 steel design — LRFD & ASD methods, scope, materials, and specification map

AISC 360 is the most influential steel design specification in the world. Published by the American Institute of Steel Construction, it governs the design, fabrication, and erection of structural steel buildings and other structures in the United States and serves as the technical foundation for steel codes in over 28 countries — including Brazil (NBR 8800), India (IS 800:2007), Saudi Arabia (SBC 301), Philippines (NSCP), Indonesia (SNI 1729), and much of Latin America.

This guide is the most comprehensive online reference for AISC 360-16 in any language. Each section below covers the specification with the depth needed for practical design application. Sub-pages provide chapter-by-chapter coverage with fully solved numerical examples using real steel profiles from the CalcSteel catalog.

1. History and Origin

1.1. The First Edition (1923)

The AISC Specification for Structural Steel Buildings was first published in 1923, making it one of the oldest continuously maintained steel design standards in the world. That first edition was a slim document — just a few pages — covering allowable stresses for riveted and bolted connections, basic member design, and column formulas. It used the Allowable Stress Design (ASD) philosophy exclusively: the engineer would compute stresses under working loads and verify they did not exceed a fraction of the yield stress.

1.2. Evolution Timeline

The specification evolved through dozens of editions, reflecting advances in steel metallurgy, welding technology, stability theory, and reliability-based design:

1.3. Who Develops AISC 360?

The specification is developed by the AISC Committee on Specifications, a volunteer body of approximately 50 structural engineers, researchers, and steel industry professionals. The work is organized into Task Committees (TC), each responsible for specific chapters:

• TC 1 — General Provisions (Chapters A, B, L)
• TC 2 — Member Design (Chapters D–H)
• TC 3 — Connections (Chapters J, K)
• TC 4 — Composite Construction (Chapter I)
• TC 5 — Stability (Chapter C, Appendices 1, 6, 7)
• TC 6 — Fabrication and Erection (Chapters M, N)

Changes go through a rigorous ballot process: any substantive change requires a 2/3 approval vote from the full committee, followed by a public review period. This process typically takes 5–7 years per cycle, ensuring that only thoroughly vetted provisions make it into the specification.

1.4. Companion Standards

AISC 360 does not exist in isolation. It is part of a family of standards that together cover the full scope of steel building design:

1.5. Global Influence

AISC 360 is arguably the most globally influential steel design standard. Its direct descendants and adaptations include:

• Brazil (NBR 8800:2008) — Nearly identical member design provisions, same single column curve (SSRC 2P), same interaction equations (H1-1a/b). Brazilian load combinations differ (NBR 8681).
• India (IS 800:2007) — Adopted LRFD philosophy from AISC with modifications; uses multiple column curves (similar to EC3 approach).
• Saudi Arabia (SBC 306) — Directly references AISC 360 with local amendments for extreme temperature conditions.
• Latin America — Colombia (NSR-10 Title F), Chile (NCh427), Mexico (NTC), Ecuador, Peru, and Argentina all base their steel provisions substantially on AISC.
• Philippines (NSCP) — Steel chapter based on AISC 360.

2. Scope and Applicability

2.1. What AISC 360 Covers

AISC 360 applies to the design of the structural steel system or systems, including members and connections, of buildings and other structures. Specifically:

• Commercial and industrial buildings (offices, warehouses, factories)
• Mezzanines, platforms, catwalks, and stairs
• Industrial structures (pipe racks, equipment supports, conveyor structures)
• Multi-story frames (moment frames, braced frames, dual systems)
• Long-span roof structures (trusses, joists, arches, space frames)
• Composite members (steel beams with concrete slabs — Chapter I)
• Storage racks (when designed as structures, not under RMI specification)

2.2. What AISC 360 Does NOT Cover

2.3. Approved Structural Steels

AISC 360 Table A3.1 lists the approved steel materials. The most commonly used in practice are highlighted below. Any steel not in this table requires approval under Section A3.1a ("Other Steel") with documented mechanical properties and weldability.

Steel Properties (Constants)

• $E=\mathrm{29,000}E\; =\; 29\{,\}000$ ksi (200,000 MPa) — Modulus of elasticity
• $G=\mathrm{11,200}G\; =\; 11\{,\}200$ ksi (77,200 MPa) — Shear modulus
• $\nu =0.3\backslash nu\; =\; 0.3$ — Poisson's ratio
• $\alpha =6.5\times {10}^{-6}\backslash alpha\; =\; 6.5\; \backslash times\; 10^\{-6\}$ /°F ($11.7\times {10}^{-6}11.7\; \backslash times\; 10^\{-6\}$ /°C) — Coefficient of thermal expansion
• $\gamma =490\backslash gamma\; =\; 490$ pcf (7,850 kg/m³) — Unit weight

3. Design Philosophy — The Dual Format

AISC 360 is unique among major steel standards in offering two parallel design methods within a single document: LRFD (Load and Resistance Factor Design) and ASD (Allowable Strength Design). Both methods are equally valid, and the specification is calibrated so that they produce essentially the same member sizes for typical load ratios. The engineer chooses one method and applies it consistently throughout the design.

3.1. LRFD — Load and Resistance Factor Design

LRFD separates the uncertainty into two parts: load factors (applied to loads) and resistance factors (applied to the nominal strength). The general requirement is:

where $\varphi \backslash phi$ is the resistance factor (always ≤ 1.0), $R_{n}R\_n$ is the nominal strength, ${\gamma }_i\backslash gamma\_i$ are the load factors from ASCE 7, and $Q_{i}Q\_i$ are the nominal load effects. The product $\varphi R_n\backslash phi\; \backslash ,\; R\_n$ is called the design strength.

3.2. ASD — Allowable Strength Design

ASD uses a single safety factor applied to the nominal strength. Loads are used at their unfactored (service) values:

where $\mathrm{\Omega }\backslash Omega$ is the safety factor (always ≥ 1.0). The quotient $R_n\mathrm{/}\mathrm{\Omega }R\_n\; /\; \backslash Omega$ is the allowable strength.

3.3. Resistance Factors and Safety Factors

The $\varphi \backslash phi$ and $\mathrm{\Omega }\backslash Omega$ values are related by $\mathrm{\Omega }=1.5\mathrm{/}\varphi \backslash Omega\; =\; 1.5\; /\; \backslash phi$. This relationship ensures that LRFD and ASD produce comparable results when the live-to-dead load ratio is approximately 3:1 (the calibration point).

3.4. ASCE 7 Load Combinations

AISC 360 does not define load combinations — it references ASCE 7 (Minimum Design Loads). The basic combinations are:

LRFD Combinations (ASCE 7 Section 2.3.1)

ASD Combinations (ASCE 7 Section 2.4.1)

D = dead, L = live, Lr = roof live, S = snow, R = rain, W = wind, E = earthquake.

3.5. Numerical Example — LRFD vs ASD Comparison

Problem: A simply supported W12×26 (A992) beam spans 24 ft (7.32 m), carrying a uniform dead load $w_D=0.50w\_D\; =\; 0.50$ kip/ft and live load $w_L=0.80w\_L\; =\; 0.80$ kip/ft. The beam is continuously braced (L_b = 0). Find the maximum bending moment and check if the beam is adequate.

W12×26 properties: $Z_x=37.2Z\_x\; =\; 37.2$ in³, $S_x=33.4S\_x\; =\; 33.4$ in³, $F_y=50F\_y\; =\; 50$ ksi. Compact section (all W shapes in A992 are compact for flexure).

3.6. Reliability Calibration

AISC 360 was calibrated using first-order reliability methods (FORM) to achieve target reliability indices:

• $\beta =2.6\backslash beta\; =\; 2.6$ for members (tension, compression, flexure, shear) — corresponds to a probability of failure of approximately 1 in 200 over 50 years
• $\beta =4.0\backslash beta\; =\; 4.0$ for connections (bolts, welds) — connections must be more reliable than members to ensure ductile failure modes (member yields before connection fractures)
• $\beta =3.0\backslash beta\; =\; 3.0$ for composite members — intermediate reliability reflecting the combination of steel and concrete variability

The higher reliability index for connections ($\beta =4.0\backslash beta\; =\; 4.0$ vs 2.6) is why connection-related $\varphi \backslash phi$ factors are lower (0.75 vs 0.90). This is a deliberate design philosophy: if overloaded, the member should fail before the connection.

3.7. Why LRFD Dominates US Practice Today

While ASD remains legal and valid, approximately 80–85% of US structural steel design is now done using LRFD, according to AISC surveys. The reasons:

• LRFD is typically 5–15% more economical in steel weight
• University education has focused on LRFD since the mid-1990s
• Seismic design (AISC 341) uses only LRFD load combinations
• Most design software (including CalcSteel) defaults to LRFD
• The ASD load combinations in ASCE 7 have become complex (combinations 4, 6a, 6b with 0.75 factors), reducing the "simplicity" advantage that old-style ASD had

4. Organization of the Specification

AISC 360-16 is organized into Chapters A through N plus Appendices 1 through 8. The following map helps you find which chapter applies to which design check:

Appendices

4.1. Which Chapter Do I Need? — Decision Flowchart

For a typical member design, the workflow through the specification is:

5. International Comparison

Engineers who work across borders — or who use literature from different regions — benefit from understanding how AISC 360 compares with other major steel standards:

Explore Each Design Check

Each chapter below provides complete coverage of an AISC 360-16 design check — formulas, classification rules, fully solved examples with real W, HSS, and L profiles, and comparisons with Eurocode 3 and NBR 8800.