Structural Engineering
Fillet Weld Strength
Calculate the load capacity of fillet welds under shear, tension and combined loading per EN 1993-1-8 (Eurocode 3).
Units:
Throat thickness a = 0.707 × leg length s. Minimum fillet weld size: typically 3–6 mm for structural steel. Maximum economical leg size: 12 mm (above this, consider full-penetration butt weld). Always specify weld quality class in drawings (EN ISO 5817 class B, C or D).
F_w,Rd = a × l_eff × f_w,Rd where f_w,Rd = f_u / (√3 × β_w × γ_M2)
Input
Weld leg size s iFillet weld leg size in mm. Throat thickness a = 0.707 × s.
mm
Effective weld length iEffective length of the weld in mm. Subtract 2×s from actual length for effective length.
mm
Steel grade iSteel grade determines ultimate tensile strength fu and correlation factor βw.
Loading type iDirection of the applied force relative to the weld axis.
Result
Throat thickness a [mm]
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Design weld strength f_w,Rd [MPa]
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Weld load capacity [kN]
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Capacity per metre weld [kN/m]
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Effective weld area [mm²]
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