Weld Connection (old AS 4100:1998)

How it calculates

The Weld Connection (AS 4100:1998) calculator checks fillet and butt weld connections against Clause 9.7 of AS 4100:1998. Given the total shear and tension forces on the connection and the weld geometry, it resolves the demand into force per unit length and compares it to the design capacity.

Force per unit length

The total applied shear force V_w and tension (or compression) force N_w 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)

Weld capacity (Clause 9.7)

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

Fillet weld: v_w = 0.6 × f_uw × t_t × k_r

where:

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

Butt weld: v_w = f_ub × t_t

where f_ub = nominal tensile strength of the base metal.

Reduction factor for lap connections (k_r)

For lap connections, the force distribution along the weld becomes less uniform as the connection length increases. AS 4100 applies a reduction factor:

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

For non-lap connections, k_r = 1.0.

Design capacity

The design capacity per unit length of weld is:

v_d = phi × v_w

The capacity factor phi for weld connections to AS 4100:1998 is:

• phi = 0.8 for fillet welds (SP category)
• phi = 0.9 for butt welds (SP category)

Utilization check

Utilization = v*_w / v_d ≤ 1.0

When the utilization ratio exceeds 1.0, the weld is overstressed. The throat thickness, weld length, or applied loading must be adjusted.

Design notes

This calculator checks the weld at a single cross-section under uniform loading. For weld groups with moment or torsion, the peak demand location should be identified separately and the maximum force per unit length at that location used as the input. Detailing requirements (minimum throat thickness, end returns, etc.) must be verified by the engineer per AS 4100:1998 Clause 9.8.