Weld Connection

How it calculates

The Weld Connection (AS 4100:2020) calculator checks fillet and butt weld connections against Clause 9.6 of AS 4100:2020. The calculator resolves total applied shear and tension forces into force per unit length of weld and compares the resultant demand against the design capacity.

Force per unit length

Total applied forces are distributed over the effective weld length l_w:

• Shear force per unit length: tau_w = V_w / l_w
• Tension force per unit length: sigma_w = N_w / l_w

The resultant design force per unit length of weld:

v*_w = sqrt(tau_w^2 + sigma_w^2)

This vector combination accounts for the simultaneous action of shear and tension (or compression) at the weld throat.

Weld capacity (Clause 9.6)

The nominal capacity per unit length v_w depends on the weld type:

Fillet weld (SP quality): v_w = 0.6 × f_uw × t_t × k_r

RHS fillet weld: v_w = 0.6 × f_uw × t_t × k_r (with a modified capacity factor)

Butt weld: v_w = f_ub × t_t

where:

• f_uw = nominal tensile strength of the weld metal (MPa)
• f_ub = nominal tensile strength of the base metal (MPa)
• t_t = design throat thickness (mm)
• k_r = reduction factor for lap connection length

Reduction factor for lap connections (k_r)

For lap connections, the reduction factor k_r accounts for non-uniform force distribution along long welds:

• l_w ≤ 1700 mm: k_r = 1.10 - 0.06 × (l_w / 1000)
• 1700 mm < l_w ≤ 8000 mm: linear interpolation
• l_w > 8000 mm: k_r = 0.62

For connections other than lap connections: k_r = 1.0

Capacity factor (phi)

The capacity factor phi depends on the weld type and quality category per AS 4100:2020:

• SP fillet weld: phi = 0.8
• SP butt weld: phi = 0.9
• GP weld category: phi = 0.7

The design capacity: v_d = phi × v_w

Utilization check

Utilization = v*_w / v_d ≤ 1.0

If the utilization ratio exceeds 1.0, the weld is overstressed. Adjustments can be made by increasing the throat thickness, increasing the weld length, or reducing the applied loading.

Scope and limitations

This calculator checks a single weld cross-section under uniform force per unit length. For weld groups carrying bending moment or torsion (such as in eccentric connections), the peak demand at the most stressed point in the group should be determined first and entered as the governing input forces. Minimum weld sizes and end return requirements per AS 4100:2020 Clause 9.7 must be verified separately.