Free Tool · EN 1993-1-1 §5.5 Table 5.2

Cross-Section Classification

Determine cross-section class (1–4) per EN 1993-1-1 §5.5 Table 5.2. Web and flange classified separately — governing class gates the resistance formula (Wpl for Class 1/2, Wel for Class 3, effective section for Class 4).

★ Start here — this gates every resistance formula downstream
Section Parameters
Only for combined loading. α = 0.5 = pure bending, α = 1.0 = pure compression
Only for combined loading. ψ = 1 = uniform compression, ψ = -1 = pure bending
b=150mm h=300mm tf=10.7 tw=7.1 Flange Cl1 (c/t=6.68) Web Cl1 (c/t=39.24)
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Classification Result
Section Class 1
Decision tree — Table 5.2

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Next step
→ Moment capacity → Mc,Rd (EN 1993-1-1 §6.2.5) → Column buckling → Nb,Rd (EN 1993-1-1 §6.3) → Bolt capacity (EN 1993-1-8) → Weld sizing (EN 1993-1-8 §4.5.3)
Frequently asked questions
What is cross-section classification and why does it matter?

Cross-section classification (EN 1993-1-1 §5.5) determines whether local buckling limits a section's resistance before yielding. Class 1/2 sections can develop their full plastic capacity (Wpl). Class 3 sections are limited to elastic yielding (Wel). Class 4 sections locally buckle before yield — effective properties from EN 1993-1-5 are needed. Using the wrong class overestimates resistance.

How is ε = √(235/fy) used in Table 5.2?

ε is a normalisation factor that makes the c/t limits grade-independent. A stronger steel (higher fy) has lower ε, which means tighter c/t limits — the section must be more stocky to achieve the same class. For S235, ε = 1.0. For S355, ε = 0.814. For S460, ε = 0.714.

What is the difference between web and flange classification?

The web is an "internal compression part" — both edges are restrained by the flanges, so it has higher c/t limits (72ε/83ε/124ε for bending). The flange is an "outstand compression part" — only one edge is restrained (at the web), so limits are tighter (9ε/10ε/14ε). The governing class is max(web_class, flange_class).

When does loading condition affect the web class?

Under pure bending, roughly half the web is in compression (neutral axis at mid-height) — limits are 72ε/83ε/124ε. Under pure compression, the entire web is under uniform stress — limits tighten to 33ε/38ε/42ε. For combined N+M, use α (fraction of web in compression) and ψ (stress ratio) from the combined N+M stress distribution — the tool applies the relevant Table 5.2 formula.

Does manufacturing (rolled vs. welded) affect the limits?

For hot-rolled sections, EN 1993-1-1 Table 5.2 Sheet 2 applies (outstand flange limits 9ε/10ε/14ε). For welded plate girder flanges, the same limits apply per the table, but weld geometry and residual stresses mean welded sections tend to be more imperfection-sensitive. Some national annexes (notably UK NA) impose tighter Class 3 limits for welded flanges. This tool uses the base EN limits for both.

What happens for Class 4 sections?

Class 4 sections locally buckle before yield. Resistance must be computed using effective section properties per EN 1993-1-5, which reduces the area and moduli to account for the buckled portions. This tool flags Class 4 but does not compute effective properties — Pro handles that for full drawing-set checks.