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# Design a Weld Connection to AS 4100:2020
> Analyze and design weld connections to AS 4100:2020, Cl 9.6. Checks fillet weld and butt weld capacity under combined shear and tension force per unit length.
Analyze and design fillet weld and butt weld connections to AS 4100:2020. Resolves combined shear and tension into force per unit length of weld and checks against the design capacity with weld quality and reduction factors per Cl 9.6.
The Calcs.com Weld Connection Calculator to AS 4100:2020 enables the easy analysis and design of weld connections to AS 4100:2020, Cl 9.6.
## Method & scope
| Property | Detail |
| ---------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | AS 4100:2020 |
| Regions | Australia & New Zealand |
| What it checks | Force per unit length, Weld capacity (Clause 9.6), Reduction factor for lap connections (k\_r), Capacity factor (phi), Utilization check, Scope and limitations |
#### Calculation method
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.
## How to use it
Open it from **Run calc** in the About this calculator panel above.
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](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
## Common questions
This calculator checks weld connections to AS 4100:2020, Clause 9.6. 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 loading per the current Australian standard.
Key inputs are the weld type (fillet weld, butt weld, or RHS fillet), throat thickness, effective weld length, weld metal nominal tensile strength f\_uw, base metal tensile strength f\_ub, weld quality category (SP or GP), total shear force on the connection, and total tension force on the connection.
The calculator computes the design force per unit length v*\_w = sqrt(tau\_w^2 + sigma\_w^2) and compares it against the weld design capacity v\_d = phi × v\_w. Outputs include the shear component tau\_w, tension component sigma\_w, resultant demand v*\_w, nominal capacity v\_w, reduction factor k\_r for lap connections, capacity factor phi, and the governing utilization ratio.
Yes. When the weld carries simultaneous shear and tension or compression (as is typical in beam-column connections, bracket plates, and gusset plates), the shear and tension force per unit length are resolved using the square root of the sum of squares formula. This gives the resultant weld demand at the critical cross-section.
The weld metal tensile strength f\_uw is entered directly in MPa, so any AS/NZS 2980-classified electrode can be used. Common values: E48XX = 480 MPa, E55XX = 550 MPa. The weld quality category (SP or GP) affects the capacity factor phi per AS 4100:2020.
## Next steps
Complete list of Calcs.com design calculators available for Australian and New Zealand projects (AS 3600, AS 4100, AS 1720, AS/NZS 1170, and related standards).
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