Engineers' Corner: Fillet Weld Resistance in CSA S16:19

Engineers’ Corner: Fillet Weld Resistance in CSA S16:19

CSA S16:19, Design of steel structures, has introduced changes to the factored shear resistance of fillet welds.

In both the current edition, S16:19, and the previous one, S16-14, the shear resistance of a concentrically loaded weld segment is given in Clause 13.13.2.2:

where:

If we incorporate the strength enhancement factor and the reduction factor for multi-orientation welds, the expression becomes:

and θ is the angle of the weld segment axis with respect to the line of force. For example, θ = 0^o for a longitudinal weld and 90^o for a transverse weld. As shown in Figure 1, a transverse weld has a strength that is 1.5 times greater than a longitudinal weld:

Figure 1
Strength Enhancement Factor

S16:19 has clarified that the strength enhancement factor does not apply to single-sided welds. Welded connections featuring double-sided and single-sided welds are shown in Figure 2.

Figure 2
Double-Sided and Single-Sided Welds

The reduction factor for multi-orientation fillet welds appearing in Equation 4 (above) has a value of M_w = 1.0 for joints with a single weld orientation. For multi-orientation weld groups, its value was given by the following expression in S16-14:

where θ₁ is the orientation of the weld under consideration, and θ₂ is the orientation of the weld segment in the joint that is nearest to 90^o. This is illustrated for the weld group in Figure 3. For the transverse weld, θ₁ = θ₂ = 60^o, M_w = 1.0; and for the two longitudinal segments, θ₁ = 0^o, θ₂ = 60^o, M_w = 0.895.

Figure 3
Multi-Orientation Weld Group

In CSA S16:19, M_w has been simplified as follows:

Referring again to Figure 3, for the transverse weld and longitudinal welds, M_w = 1.0 and M_w = 0.85, respectively.

Figure 4 shows a comparison between the resistances calculated using S16-14 and S16:19, for a concentrically loaded C-shaped weld group with k = 0.4, incorporating both the strength enhancement factor and the reduction factor for multi-orientation welds, M_w. The resistance given by S16:19 is significantly smaller for this example, especially for a load angle of about θ = 45^o.