Fillet weld capacities (AS 4100)

Design capacity per millimetre of length of equal-leg fillet welds to AS 4100:2020, for SP and GP weld categories and the weld metal strengths of Table 9.6.3.10(A). Welding to AS/NZS 1554.1 (Cl. 9.6.1.1).

Leg t_w (mm)	Throat t_t (mm)	E43XX / W40X SP f_uw = 430 MPa, φ = 0.8	E43XX / W40X GP f_uw = 430 MPa, φ = 0.6	E49XX / W50X SP f_uw = 490 MPa, φ = 0.8	E49XX / W50X GP f_uw = 490 MPa, φ = 0.6	E55XX / W55X SP f_uw = 550 MPa, φ = 0.8	E55XX / W55X GP f_uw = 550 MPa, φ = 0.6
3	2.12	0.438	0.328	0.499	0.374	0.560	0.420
4	2.83	0.584	0.438	0.665	0.499	0.747	0.560
5	3.54	0.730	0.547	0.832	0.624	0.933	0.700
6	4.24	0.876	0.657	0.998	0.748	1.120	0.840
8	5.66	1.168	0.876	1.330	0.998	1.493	1.120
10	7.07	1.459	1.095	1.663	1.247	1.867	1.400
12	8.49	1.751	1.314	1.996	1.497	2.240	1.680
16	11.31	2.335	1.751	2.661	1.996	2.987	2.240

Values are φv_w in kN per mm of weld length, with k_r = 1.0. Example: two 200 mm runs of 6 mm E49XX SP fillet weld carry 2 × 200 × 0.998 = 399 kN. E49XX (W50X for submerged arc) is the usual match for Grade 300 and 350 steel; the 2020 edition gives it f_uw = 490 MPa, where the 1998 edition used 480 MPa for E48XX.

Formulas (AS 4100:2020)

Fillet weld (Cl. 9.6.3.10): φv_w = φ0.6f_uwt_tk_r, with f_uw from Table 9.6.3.10(A) and φ = 0.8 for SP and 0.6 for GP welds (Table 3.4). Longitudinal fillet welds on RHS thinner than 3 mm use φ = 0.7 (SP only). For an equal-leg fillet the design throat thickness t_t = t_w/√2.
Design force: v*_w is the vector sum of the design forces per unit length on the effective area of the weld. Weld groups are covered by Cl. 9.7.
Long welds in lap connections: k_r = 1.0 for l_w ≤ 1.7 m, 1.10 − 0.06l_w for 1.7 < l_w ≤ 8 m and 0.62 beyond (Table 9.6.3.10(B)); other connections use k_r = 1.0.
Weld metal strength (Table 9.6.3.10(A)): 430 MPa for E43XX/W40X consumables, 490 MPa for E49XX/W50X and 550 MPa for E55XX/W55X, with equivalent flux cored, gas metal arc and gas tungsten arc classifications. Higher strengths (up to 830 MPa) apply to quenched and tempered steels welded to AS/NZS 1554.4.
Butt welds: complete penetration butt welds use φ = 0.9 for SP and 0.6 for GP (Cl. 9.6.2.7, Table 3.4); incomplete penetration butt welds use the fillet weld factors.
Categories: SP (structural purpose) and GP (general purpose) welds are defined in AS/NZS 1554.1; GP welds use the lower capacity factor.

Design aid only, not a substitute for a qualified engineer or for AS 4100 itself. See the disclaimer and data sources.