Butt Weld Calculator

Full penetration butt weld assessment per EN 1993-1-8 (EC3)

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Load Type

mm
Full penetration — throat = t
mm
Effective weld length
kN
Design value (factored)
Affects penetration factor
EN 1993-1-1 §6.1

Results

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Enter values
Weld cross-section Aw
—
Applied stress σ
—
Design resistance σRd
—
Utilisation η
—
Resistance force FRd
—
Reserve capacity
—
Plate thickness < 4 mm — verify minimum weld requirements per EN 1993-1-8.
Partial penetration: effective throat reduced to 5/8 t. Treat as fillet weld per EC3 §4.7.2.
Utilisation > 80% — consider increasing plate thickness or weld length.
Full penetration butt weld: design resistance equals parent material per EC3 §4.7.1.

Diagram

Method — EC3 Full Penetration Butt Weld

Design resistance

Per ČSN EN 1993-1-8 §4.7.1 — full penetration butt weld is equivalent to parent material:

σRd = fy / γM0

Cross-section area:

Aw = t × l

Section modulus (bending):

Ww = t × l² / 6

Applied stress

  • Tension / Compression:
    σ = F / Aw
  • Bending:
    σ = M / Ww

Utilisation check: η = σ / σRd ≤ 1.0

Full vs partial penetration

  • Full (EXC2/3): throat = t, σRd = fy/γM0
  • Partial (EXC1): effective throat = 5t/8, treated as fillet weld — lower resistance
  • Butt welds in tension always prefer full penetration for reliability

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