Australian Weld Capacity — AS 4100 Clause 9.7 Guide
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Comprehensive guide for weld capacity design per AS 4100:2020 Clause 9.7. Covers fillet weld design, SP/GP categories, throat shear, parent metal checks, and weld volume estimation for Australian structural steel connections.
Fillet Weld Capacity — Clause 9.7.3.10
Design capacity per unit length: φvw = φ × 0.6 × fuw × tt × kr
Where:
- φ = 0.80 (AS 4100 Table 3.4 for welds)
- fuw = weld metal tensile strength (490 MPa for E48XX)
- tt = throat thickness = 0.707 × leg size (for equal-leg fillet)
- kr = reduction factor for angle of loading (kr=1.0 for GP, varied for SP)
Simplified GP weld capacity: φvw = 1.0 kN per mm of throat per 100 MPa fuw
Fillet Weld Capacity Table (GP Category, E48XX)
| Weld Size (mm) | Throat (mm) | Capacity per mm run (kN/mm) | Capacity per metre (kN/m) |
|---|---|---|---|
| 4 | 2.83 | 0.67 | 670 |
| 5 | 3.54 | 0.83 | 830 |
| 6 | 4.24 | 1.00 | 1,000 |
| 8 | 5.66 | 1.33 | 1,330 |
| 10 | 7.07 | 1.66 | 1,660 |
| 12 | 8.49 | 2.00 | 2,000 |
| 16 | 11.31 | 2.66 | 2,660 |
Capacity = 0.80 × 0.60 × 490 × tt × 1.0 / 1000 (kN/mm). E48XX electrode, GP category.
Parent Metal Check — Clause 9.7.3.10
φvwp = φ × 0.6 × fyp × tp × kr
Where tp = parent metal thickness (connected part)
Match requirement:
| Parent Metal Grade | Minimum Electrode | Fuw (MPa) | Match Condition |
|---|---|---|---|
| Grade 300 | E48XX | 490 | Undermatched (OK) |
| Grade 350 | E48XX | 490 | Undermatched (OK) |
| Grade 400 | E55XX | 550 | Matched |
| Grade 450 | E55XX | 550 | Slightly undermatched |
Worked Example
Problem: 8 mm GP fillet weld, E48XX. Design connection for tension force N*=600 kN across 300 mm weld length (2 sides).
Solution:
- Weld capacity per mm run = 1.33 kN/mm (from table)
- Two sides: Total capacity = 2 × 300 × 1.33 = 798 kN > 600 OK
- Check parent metal (10 mm Grade 300 plate): φvwp = 0.80 × 0.60 × 300 × 10 × 1.0 = 1.44 kN/mm across weld width Shear transfer width ≠ exact match to weld, conservatively > 1.33 kN/mm OK
- Weld volume: 8 mm fillet, 300 mm × 2 = 600 mm run → weld metal ≈ 600×8×8/2 = 19,200 mm³
Design Resources
- [[Australian Steel Grades|/reference/australian-steel-grades/]] | [[Australian Steel Properties|/reference/australian-steel-properties/]] | [[Australian Beam Sizes|/reference/au-beam-sizes/]] | [[Australian Bolt Capacity|/reference/australian-bolt-capacity/]] | [[AS 4100 Beam Design|/reference/as4100-beam-design-example/]] | [[All Australian References|/reference/]]
FAQ
What is the design capacity of an 8 mm fillet weld per AS 4100? For GP category, E48XX electrode: φvw = 1.33 kN per mm of weld length. This is the most commonly used weld size in Australian structural steel.
What is the difference between SP and GP weld categories? GP (general purpose) uses kr=1.0 — conservative. SP (structural purpose) uses kr accounting for load angle — more economical (up to 20% higher for transverse welds).
Can an undermatched weld electrode be used? Yes. E48XX (fuw=490 MPa) is slightly undermatched for Grade 400 (fyp=400 MPa). Per AS 4100 Clause 9.7.3.10, this is acceptable as long as the parent metal check is satisfied.
Educational Use Only — This reference is for educational and preliminary design purposes only. All structural designs must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) in accordance with AS 4100:2020 and all applicable Australian Standards. Results are not for construction.