If a fillet weld size is 8 mm, what is the minimum effective length?

If a fillet weld size is 8 mm, what is the minimum effective length?

• A. 8 mm
• B. 16 mm
• C. 38 mm
• D. 48 mm

Answer: (C)

The idea behind effective length is that only the portion of a fillet weld away from the ends fully develops its strength; ends and toes have stress concentrations and don’t carry load as effectively. To ensure a safe, practical length, codes use a minimum effective length that’s larger than the weld size. In many CSA W59 practice guidelines, the minimum effective length is taken as four times the weld size plus a small end allowance: Lmin = 4t + 6 mm. With a fillet weld size of 8 mm, that becomes Lmin = 4×8 + 6 = 38 mm. This is the length needed to reliably develop the weld’s strength and avoid end effects. Shorter lengths (like 8 mm or 16 mm) would be under the required minimum and could compromise performance, while a longer value (such as 48 mm) exceeds the standard minimum. Hence 38 mm is the correct minimum.

The idea behind effective length is that only the portion of a fillet weld away from the ends fully develops its strength; ends and toes have stress concentrations and don’t carry load as effectively. To ensure a safe, practical length, codes use a minimum effective length that’s larger than the weld size.

In many CSA W59 practice guidelines, the minimum effective length is taken as four times the weld size plus a small end allowance: Lmin = 4t + 6 mm. With a fillet weld size of 8 mm, that becomes Lmin = 4×8 + 6 = 38 mm. This is the length needed to reliably develop the weld’s strength and avoid end effects.

Shorter lengths (like 8 mm or 16 mm) would be under the required minimum and could compromise performance, while a longer value (such as 48 mm) exceeds the standard minimum. Hence 38 mm is the correct minimum.