Size a fillet weld group for a bracket or lap joint — effective throat, direct and torsional shear combined vectorially at the worst corner, the required leg size, and a plan view of the weld group with the governing stress drawn to scale.
This is the trial size — the tool reports the leg you actually need.
Distance from load line to weld-group centroid. Zero = concentric (direct shear only).
Allowable shear = 0.30 × Fexx (AWS D1.1 elastic).
The 0.30 factor already embeds safety; use >1 for fatigue or critical joints.
For min/max leg-size checks per AWS Table.
Plan view. Blue = direct shear (uniform over the group). Brass = torsional shear (perpendicular to the radius from the centroid, largest at the far corner). Red = their vector sum, the resultant that governs.
Throat & area. An equal-leg fillet carries load on its effective throat, t = 0.707 × leg. The group throat area is A = t × (total weld length). Stress is always taken on the throat, never the leg.
Elastic vector method. Direct shear is uniform: τ_d = P/A. Eccentricity e applies a torque T = P·e that adds torsional shear τ_t = T·r/J, where J is the polar moment of the weld group treated as unit-throat lines (J = I_x + I_y) and r is the distance from the centroid to the point checked. The two are combined vectorially — τ_r = √[(τ_dx+τ_tx)² + (τ_dy+τ_ty)²] — at the corner farthest from the centroid, where the resultant is largest.
Capacity. Allowable throat shear is 0.30 × F_EXX per AWS D1.1 (elastic/ASD). The required leg scales linearly with the resultant stress, since stress ∝ 1/throat ∝ 1/leg.
Leg-size limits. AWS sets a minimum fillet size by the thicker part joined and a maximum (≈ base thickness − 2 mm for material ≥ 6 mm) so the weld can't overload a thin edge. Both are checked.
Elastic method — conservative versus the AISC instantaneous-centre approach. Base-metal shear, plate bending, weld returns, fatigue, and inspection class are separate checks. The directional strength increase (up to 1.5× for transverse loading) is not applied here.