Steel Code Comparison — Engineering Reference

Compare AISC 360, AS 4100, EN 1993, and CSA S16: resistance factors, column curves, LTB methods, and interactive LRFD vs ASD calculator.

Overview

Structural steel design codes worldwide share the same limit state design philosophy but differ in their specific formulations, safety factors, material grading systems, and detailing requirements. Engineers working on international projects, verifying overseas designs, or using software that supports multiple codes need to understand these differences to avoid unconservative errors. The four major codes covered by the Steel Calculator are AISC 360, AS 4100, EN 1993, and CSA S16.

All four codes use partial safety factors applied to either the resistance side (phi factors in AISC/AS/CSA) or the load side (gamma factors in Eurocode). The net safety margins are similar — typically 1.5 to 1.7 against the nominal resistance — but the distribution between load and resistance factors differs.

Design philosophy comparison

Resistance factors (phi / gamma)

The Eurocode uses gamma_M = 1.00 for member resistance (flexure, compression) but gamma_M2 = 1.25 for connection resistance (bolts, welds, net section). This makes Eurocode members appear to have higher capacity, but the higher load factors compensate, producing similar overall safety levels.

Column buckling comparison

The codes use different mathematical models for the column curve:

• AISC: Single curve based on SSRC Curve 2P. Transition at KL/r = 4.71 x sqrt(E/F_y). Simple to apply, conservative for some section types.
• AS 4100: Modified Perry-Robertson with alpha_b section constant (-1.0 to +0.5). Multiple curves depending on section type and fabrication method.
• EN 1993: Five explicit curves (a0, a, b, c, d) with imperfection factors alpha = 0.13 to 0.76. The curve selection depends on section type, axis of buckling, and fabrication (hot-rolled vs. welded).
• CSA S16: Single curve very similar to AISC (both based on SSRC research).

For a W10x49 column with KL/r = 70 (A992/Grade 350/S355), the design capacities are: AISC = 441 kip, AS 4100 = 435 kip, EN 1993 (curve b) = 446 kip, CSA S16 = 438 kip. The variation is less than 3% for this standard case.

Beam flexural capacity comparison

Note the Eurocode uses E = 210 GPa while the other three codes use E = 200 GPa. This 5% difference affects all stiffness-related calculations (deflection, buckling, LTB transition lengths).

Worked example — W14x48 beam, L = 20 ft, uniform load

Comparing the four codes for the same physical beam (equivalent sections used for AS/EN/CSA):

The Eurocode gives slightly higher values due to the higher E and gamma_M1 = 1.00. However, when combined with the higher Eurocode load factors (1.35D vs. 1.2D for AISC), the required member sizes are very similar across all four codes.

Key differences to watch

• Bolt hole deductions — AISC deducts 1/16 in. beyond the nominal hole diameter for net area calculations (effective hole = nominal + 1/16). AS 4100 uses the nominal hole diameter directly. EN 1993 uses d_0 = d_hole (nominal). This difference can affect net section rupture calculations by 5-10%.
• Weld directional strength — AISC allows a 50% increase in fillet weld strength for transversely loaded welds (1.0 + 0.50 x sin^1.5(theta)). AS 4100 does not allow this directional increase. EN 1993 uses a different directional formula. Using the AISC directional enhancement in an AS 4100 design is unconservative.
• Second-order analysis — AISC Chapter C provides the Direct Analysis Method (DAM) with notional loads and stiffness reductions, allowing K = 1.0. AS 4100 and EN 1993 use amplified first-order analysis with effective length factors. The methods give similar results but require different analysis model setups.
• Seismic provisions — AISC 341 provisions do not apply outside the U.S. Each code jurisdiction has its own seismic standard (AS 1170.4, EN 1998, NBC/CSA). The capacity design principles are similar but the detailing requirements, R-factors, and ductility classes differ significantly.

Common mistakes to avoid

• Mixing code provisions — using AISC bolt capacity tables with Eurocode load combinations (or vice versa) invalidates the calibrated safety level. Every element of the design — loads, resistance, detailing — must come from the same code framework.
• Using the wrong E value — AISC uses 29,000 ksi (200 GPa), Eurocode uses 210 GPa. A 5% error in E shifts all buckling calculations, deflection checks, and LTB transition lengths. Always verify which E the code specifies.
• Assuming phi factors are interchangeable — AISC uses phi = 0.75 for bolt shear while AS 4100 uses phi = 0.80. These differences are calibrated to their respective load factor systems and are not interchangeable.
• Ignoring unit systems — AISC is in kip-in-ksi, while the other three codes use kN-mm-MPa. A factor-of-25.4 error in converting inches to millimeters propagates through every calculation. Always convert at the start and verify units at each step.

Run this calculation

• Section Properties Database
• Beam Calculator

Related references

• How to Verify Calculations
• Bolted Connections
• Beam Design Guide
• load combinations guide
• steel beam capacity calculator
• structural engineering unit converter
• Steel Seismic Design

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.