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Analyze and design fillet weld and butt weld connections to AS 4100:1998. Resolves combined shear and tension into force per unit length of weld and checks against the design capacity with the appropriate reduction factors.
This calculator uses an earlier code edition (AS4100:1998 (R2016)). It stays available for existing projects. For new designs, check the Calculator Library for the current edition.

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Method & scope

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Calculation method

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.

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How to use it

1

Open the calculator

Open it from Run calc in the About this calculator panel above.
2

Enter your inputs

Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3

Review the results and export

Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.

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Common questions

This calculator checks weld connections to AS 4100:1998 (R2016), Clause 9.7. It evaluates the design force per unit length of weld against the capacity per unit length for fillet welds and butt welds under combined shear and tension loads.
Key inputs are the weld type (fillet or butt weld), throat thickness, effective weld length, weld metal nominal tensile strength f_uw, base metal tensile strength f_ub, total shear force on the connection, and total tension force on the connection. For lap connections, the connection length determines the reduction factor k_r.
The calculator resolves the total shear and tension forces into force per unit length components (tau_w and sigma_w), computes the resultant design force per unit length v*_w = sqrt(tau_w^2 + sigma_w^2), and checks this against the design capacity v_d = phi × v_w. The capacity factor phi and reduction factor k_r for long lap connections are reported alongside the utilization ratio.
Yes. For connections where the weld group carries both shear and axial (tension or compression) forces, the shear force component tau_w = V_w / l_w and tension component sigma_w = N_w / l_w are combined using the square root of the sum of squares. This approach applies to the weld at the point of highest demand along the effective length.
The weld metal tensile strength f_uw is entered directly in MPa, so any electrode classification can be used. For common Australian electrodes, E48XX corresponds to f_uw = 480 MPa. The base metal tensile strength f_ub sets an upper limit on the butt weld capacity.

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Next steps

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