Canadian Weld Capacity — Fillet Weld Design per CSA S16-19 Clause 13.13

Complete reference for weld capacity per CSA S16-19 Clause 13.13. Covers fillet weld shear resistance per millimeter, electrode matching for CSA G40.21 steels, weld size selection (minimum and maximum), directional strength enhancement, and a step-by-step worked example.

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CSA S16 Weld Design Philosophy

Per CSA S16-19 Clause 13.13.1, the factored shear resistance of a fillet weld per unit length is:

Vr_weld = 0.67 × phi_w × Xu × A_throat

Where:

• phi_w = 0.67 (resistance factor for welds)
• Xu = electrode tensile strength (MPa)
• A_throat = effective throat area per unit length = 0.707 × D for a 90° fillet (D = leg size in mm)

Per unit length: Vr = 0.67 × phi_w × Xu × 0.707 × D

This simplifies to: Vr (kN/mm) = 0.67 × 0.67 × Xu × 0.707 × D / 1000 = 0.317 × Xu × D / 1000

Fillet Weld Capacity Table — E48XX Electrodes (Xu = 480 MPa)

Fillet Weld Capacity — E49XX Electrodes (Xu = 490 MPa)

Fillet Weld Capacity — E55XX Electrodes (Xu = 550 MPa)

Electrode Selection for CSA G40.21 Steels

Per CSA W59-18 Table 5.2:

E48XX is the default electrode for 350W — the most common combination in Canadian structural steel fabrication.

Directional Strength Enhancement

Per CSA S16 Clause 13.13.2, fillet welds loaded transversely to their axis have higher strength than longitudinally loaded welds. The enhancement factor:

Enhancement = 1.0 + 0.5 × sin^1.5(theta)

Where theta = angle between weld axis and load direction:

Design implication: For a welded bracket with fillet welds on all sides, the side welds (longitudinal) have Vr = 1.0 × base capacity, while the end weld (transverse) has Vr = 1.5 × base capacity. The total connection capacity is the sum of all weld segments with their respective enhancement factors.

Minimum and Maximum Weld Sizes

Per CSA W59-18 Clause 5.8:

Minimum Fillet Weld Size (Base Metal Thickness — Thicker Part)

Maximum Fillet Weld Size

Along edges of connected parts:

• For t ≤ 6 mm: D_max = t (full edge thickness)
• For t > 6 mm: D_max = t - 2 mm (to allow for edge condition)

Worked Example — Welded Bracket

Given: Bracket supporting 150 kN factored load (static). Bracket plate = 16 mm 350W. Connection to column flange using fillet welds on two sides and one end. Weld length: two sides at 200 mm each, one end at 150 mm. E48XX electrodes.

Step 1 — Weld Size: Thicker part = column flange (assume 25 mm). Min weld = 8 mm (per CSA W59). Maximum on 16 mm plate: D_max = 16 - 2 = 14 mm. Try 10 mm fillet weld.

Step 2 — Weld Capacity: E48XX, Vr per mm for 10 mm = 1.525 kN/mm (from table above). Directional enhancement:

• Side welds (2 × 200 mm longitudinal): theta = 0°, factor = 1.0
• End weld (150 mm transverse): theta = 90°, factor = 1.5

Side welds: 2 × 200 × 1.525 × 1.0 = 610 kN End weld: 150 × 1.525 × 1.5 = 343 kN Total Vr = 610 + 343 = 953 kN

Step 3 — Check: Vf = 150 kN ≤ Vr = 953 kN. Ratio = 0.16. Weld is overdesigned.

Optimisation: Reduce weld to 6 mm. Min weld for 16 mm = 5 mm → 6 mm is acceptable. Vr per mm for 6 mm = 0.915 kN/mm. Side welds: 2 × 200 × 0.915 = 366 kN End weld: 150 × 0.915 × 1.5 = 206 kN Total = 572 kN ≥ 150 kN. Ratio = 0.26. OK.

Result: Use 6 mm fillet weld, E48XX, on all three sides.

Frequently Asked Questions

What is the shear capacity of an 8 mm fillet weld per 100 mm length with E48XX electrodes? Vr = 0.67 × phi_w × Xu × 0.707 × D × L = 0.67 × 0.67 × 480 × 0.707 × 8 × 100 / 1000 = 122.0 kN per 100 mm. Using the simplified formula: Vr (kN/mm) = 0.317 × Xu × D / 1000 = 0.317 × 480 × 8 / 1000 = 1.22 kN/mm = 122 kN/100 mm.

What electrode should be used for welding CSA G40.21 350W steel? E48XX electrodes (SMAW) or E49S-6 (GMAW) with Xu = 480-490 MPa. This provides matching or slightly overmatching strength relative to the 450 MPa Fu of 350W steel. E48XX is the most common electrode in Canadian structural fabrication for 350W.

How does directional strength enhancement work for fillet welds? Per CSA S16 Clause 13.13.2, a transverse fillet weld (loaded at 90° to its axis) has 1.5× the strength of a longitudinal fillet weld (loaded along its axis). The enhancement follows: 1.0 + 0.5 × sin^1.5(theta). This is significant for bracket connections where end welds receive the direct load reaction.

What is the minimum fillet weld size for 12 mm 350W plate? 5 mm minimum leg size per CSA W59-18 Clause 5.8. The minimum weld size depends on the thicker part being joined. For both parts at 12 mm: the applicable minimum is 5 mm. An 8 mm fillet weld is typical for 12 mm plate in structural connections (providing adequate capacity without excessive heat input).

Related Pages

• CSA Weld Electrodes — Matching Guide
• CSA Weld Sizes — Minimum Fillet Weld Table
• CSA W59 Welding Procedure Specifications
• Canadian Weld Symbols — AWS Standard
• CSA S16 Connection Design
• Welded Connection Calculator
• All Canadian References

This page is for educational reference. Weld capacity per CSA S16-19 Clause 13.13. Verify electrode selection per CSA W59. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

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