Free Tool · EN 1993-1-8 §4.5.3
Fillet Weld Sizing Calculator
Calculate required throat thickness a, design resistance Fw,Rd and combined utilisation per EN 1993-1-8 §4.5.3. Directional and simplified methods. S235–S460. Live results — no sign-up needed.
areq throat
Fw,Rd resistance
σ⊥ · τ⊥ · τ∥
§4.5.3 directional
§4.5.3.3 simplified
S235 · S275 · S355 · S420 · S460
NL / DE / BE
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Results
areq (rounded up)
3 mm
areq,raw (calculated)
0 mm
amin §4.5.2
3 mm
amax = 0.7 × tmin
5.6 mm
fvw,d (simplified resistance)
261.73 N/mm²
Fw,Rd at acheck (simplified)
785.2 N/mm
βw Table 4.1
0.9
γM2
1.25
η directional
0.001
η simplified
0.001
η σ⊥ cap §4.5.3.2
0.000
PASS — a = 3 mm ≤ 5.6 mm max, η = 0.1%
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Worked Example
IPE 360 Web-to-Endplate — VEd = 200 kN
Beam web-to-endplate weld. IPE 360 (tw = 8 mm), S355 steel, V_Ed = 200 kN, shear only. L_w = 298 mm (web height), double-sided (sides = 2). Directional method.
Weld length per side Lw = 360 – 2×12.7 = 298 mm (d1).
Force per unit length: V / (2 × Lw) = 200 000 / (2 × 298) = 335.6 N/mm.
Steel S355: βw = 0.90, fu = 510 N/mm², γM2 = 1.25.
Directional method:
Pure shear ⟹ σ⊥ = 0, τ∥ = 335.6 / a.
Combined check: √(3 × τ∥²) = √3 × 335.6 / a ≤ 510 / (0.90 × 1.25) = 453.3 N/mm²
⟹ areq = √3 × 335.6 / 453.3 = 1.28 mm.
Minimum governs: a = 3 mm. Utilisation η = √3 × 335.6 / (3 × 453.3) = 42.8% ✓
Note: this tool uses V_Ed as the per-unit-length force (N/mm) when L_w = 0. For the example above, enter V_Ed = 335.6 N/mm, L_w = 0. The "Try worked example" button above loads the equivalent total force input (V_Ed = 671, L_w = 298, sides = 2) which divides internally to the same per-mm value.
FAQ
Common Questions
What is the difference between the directional and simplified methods?
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The directional method (§4.5.3.2) resolves stresses on the weld throat into components σ⊥, τ⊥ (perpendicular) and τ∥ (parallel) and checks them against two criteria: a von-Mises-style combined check and a direct σ⊥ cap. It is more accurate and typically gives a smaller required throat. The simplified method (§4.5.3.3) uses a single resultant force and a reduced shear resistance f_vw,d = f_u / (√3 · β_w · γM2). For pure shear (web welds) both methods give similar answers; for weld groups with dominant normal force the directional method can save 10–20% in throat size.
Why is the minimum weld throat 3 mm?
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EN 1993-1-8 §4.5.2(2) sets a_min = 3 mm to ensure adequate fusion and avoid a weld too small to carry handling loads. In practice, smaller welds are also hard to quality-control reliably. For base plates and stiffeners where plates are thicker than 20 mm, the minimum is sometimes increased by the fabricator or national annex.
What does β_w (beta-w) mean and why does it vary by steel grade?
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β_w is the correlation factor from EN 1993-1-8 Table 4.1. It accounts for the mismatch in ductility between the weld metal (which the code treats as class S355 filler) and the parent material. For S235, the parent metal is weaker and more ductile (β_w = 0.80), so the weld can exploit a larger fraction of filler strength. For S420/S460 (β_w = 1.00), the weld metal and parent are closely matched and no bonus is given.
How do I size a weld for a beam flange carrying moment?
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Convert the moment to a flange force: F_flange = M_Ed / (h – t_f). Distribute over the weld length (typically full flange width minus web, both sides). Enter N_Ed = F_flange / (2 × l_w) as normal force per mm into this tool. For a standard IPE/HEA end-plate joint, the FrameAI Pro pipeline does this automatically from the extracted connection data.
What is the maximum weld throat per EN 1993-1-8?
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EN 1993-1-8 §4.5.2(2): a_max = 0.7 × t_min where t_min is the thickness of the thinner connected part. Exceeding this limit means the heat-affected zone extends beyond the plate thickness, degrading properties. Some national annexes allow a_max up to 0.85 × t_min when weld procedure qualification data is available — always check the project specification.
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