AISC 360-22 vs. Eurocode 3 (EN 1993-1-1): Structural Steel Guide
Comparing section classification (Compact vs. Class 1–4), column buckling curves, and lateral-torsional buckling between US and European steel codes.
How These Two Standards Actually Compare
Structural steel behaves identically on both sides of the Atlantic, yet AISC 360 and Eurocode 3 differ in two noticeable ways: resistance factors and buckling curves. AISC applies a 0.90 resistance factor (φ = 0.90) and uses a single column buckling curve for all rolled shapes, whereas Eurocode 3 uses a 1.00 material factor (γM0 = 1.00, γM1 = 1.00) and splits sections into 5 separate buckling curves (a0, a, b, c, d) based on flange thickness and residual stress.
Because Eurocode 3 sets γM1 = 1.00 (in the base code and most National Annexes), it has no 10% blanket reduction like AISC's φ = 0.90. Instead, Eurocode builds its conservatism directly into the buckling reduction factors (χ and χLT), which drop off earlier and steeper than AISC's curve—especially for heavy wide-flange columns Buckling about their weak axis.
At a Glance: Side-by-Side Cheat Sheet
Quick reference table of notation, safety factors, and design assumptions.
| Parameter | AISC 360-22 (US) | Eurocode 3 / EN 1993-1-1 | What It Means in Practice |
|---|---|---|---|
| Cross-Section Classification | 3 classes: Compact, Noncompact, Slender (λp, λr) | 4 classes: Class 1 (Plastic), Class 2 (Compact), Class 3 (Elastic), Class 4 (Slender) | AISC 'Compact' covers both EC3 Class 1 and Class 2 (both reach full plastic moment Mp). |
| Yield & Buckling Safety Factors | φb = 0.90 (Flexure), φc = 0.90 (Compression) | γM0 = 1.00 (Cross-section), γM1 = 1.00 (Member buckling) | At zero unbraced length, EC3 gives 10% higher nominal design moment for the exact same Fy. |
| Column Buckling Curves | 1 universal curve (Equations E3-2 & E3-3) | 5 curves (a0, a, b, c, d) with imperfection factors α = 0.13 to 0.76 | In EC3, hot-rolled H-sections use different curves for strong axis (a or b) vs. weak axis (b or c). |
| Standard Steel Grades | ASTM A992 (Fy = 50 ksi / 345 MPa) | S355 (fy = 355 MPa for t ≤ 16 mm; 345 MPa for 16 < t ≤ 40 mm) | ASTM A992 and European S355 are near-exact mechanical equivalents. |
| Modulus of Elasticity (E) | 29,000 ksi (200,000 MPa) | 210,000 MPa (30,450 ksi) | Eurocode assumes a 5% higher elastic modulus E, slightly boosting elastic buckling Fcr. |
Governing Equations Side-by-Side
Direct comparison of the core code formulas and what each term represents.
1. Plastic Flexural Capacity (Compact / Class 1 & 2)
Applies to compact I-shapes when unbraced length Lb ≤ Lp. Zx is the plastic section modulus.
Note axis convention: Eurocode calls the strong axis 'y-y' and weak axis 'z-z', and writes Wpl,y instead of Zx.
2. Flexural Column Buckling Capacity
Single exponential curve transitioning to elastic buckling (0.877 Fe) at Fe = 0.44 Fy.
Reduction factor χ depends on non-dimensional slenderness λ̄ = √(A·fy / Ncr) and the section's imperfection factor α.
Practical Notes When Converting Designs
Real-world rules of thumb and the most common conversion mistake to avoid.
Watch the Axis Naming Convention (x-x vs. y-y)
This trips up every engineer reading international steel tables for the first time: AISC uses x-x for the strong axis and y-y for the weak axis. Eurocode 3 uses x-x along the length of the member, y-y for the strong axis, and z-z for the weak axis. So AISC Ix = Eurocode Iy!
Thickness De-rating in European Steel (S355)
In AISC, ASTM A992 has Fy = 50 ksi (345 MPa) regardless of flange thickness. In Eurocode EN 10025-2, S355 drops from 355 MPa (for t ≤ 16 mm) to 345 MPa (16–40 mm) and 335 MPa (40–63 mm).
Strong-Axis vs. Weak-Axis Symbols (Iy in AISC ≠ Iy in Eurocode)
If you pull a section property from a European HEB or IPE table, remember that 'Iy' is the strong-axis moment of inertia. Plugging Eurocode's 'Iy' into an AISC weak-axis field will overstate weak-axis stiffness by a factor of 10.