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Steel Beam Check

For a compact, fully braced section the plastic moment is simply M_n = F_y·Z. That is the easy half. In practice deflection governs more beams than strength does — a beam can pass on stress and still bounce unacceptably, so the span check below matters as much as the moment.

Method

Design moment (kN·m)

Yield strength Fy (MPa)

Section plastic modulus Zx (10³ mm³)

Span (mm)

Predicted deflection (mm)

Deflection limit L /

Required Z

—

Moment capacity

—

Utilisation

—

Strength check

—

Deflection limit

—

Serviceability check

—

Compact, fully braced sections only — no lateral-torsional buckling, no local slenderness, no shear or web crippling check. L/360 is the usual limit for floors under live load, L/240 for roofs; brittle finishes need tighter.

PRELIMINARY SIZING ONLY — not a code-compliant design check. These are first-pass equations; they omit member stability, local buckling, shear and combined-stress interaction, connections, second-order effects and jurisdiction-specific factors. Codes vary by country and edition. Structural design must be performed and sealed by a qualified engineer.