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# Design a Steel Bolt Connection to AS 4100:2020
> Design and analyze steel bolt connections to AS 4100:2020. Supports arbitrary bolt layouts with shear, tension, bearing, and friction serviceability checks.
Design and analyze bolt groups under shear, tension, and combined loading to AS 4100:2020. The elastic method distributes applied forces across an arbitrary bolt layout and checks all ULS and serviceability limit states for the critical bolt.
Easily design and analyze steel bolt connections with the Calcs.com Steel Bolt Calculator to AS 4100:2020. The calculator supports the design and analysis of an arbitrary number of steel bolts located at x and y locations, and supports the use of a wide variety of bolt categories and sizes. Detailing requirements must be checked by users.
## Method & scope
| Property | Detail |
| ---------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | AS4100:2020 |
| Regions | Australia & New Zealand |
| What it checks | Load distribution, Bolt shear capacity (Clause 9.3.2), Bolt tensile capacity (Clause 9.3.3), Combined shear and tension (Clause 9.3.4), Ply bearing capacity (Clause 9.3.2), Serviceability friction checks (8.8/TF bolts), Capacity factors |
#### Calculation method
The Steel Bolt (AS 4100:2020) calculator applies the elastic method to distribute applied loads across the bolt group and then verifies each limit state in AS 4100:2020 Clause 9 for the critical bolt.
##### Load distribution
Applied design actions (shear V\*, tension N\*, in-plane moment M\_z, and out-of-plane moment M\_x) are resolved at the centroid of the bolt group. The centroid is computed assuming uniform bolt area.
For in-plane loads, the elastic method resolves direct shear and torsional shear components using the polar moment of inertia I\_z of the bolt group. The critical bolt is identified as the one carrying the highest resultant from the vector sum of all components.
##### Bolt shear capacity (Clause 9.3.2)
Nominal shear capacity V\_f per shear plane depends on the location of the shear plane relative to the threads:
* Through the threaded portion: V\_f = 0.62 × f\_uf × A\_s
* Through the unthreaded shank: V\_f = 0.62 × f\_uf × A\_o
Total shear capacity sums across all shear planes. Design capacity: V\_d,f = phi\_b × V\_f.
**Utilization** = V\*\_f / V\_d,f ≤ 1.0
##### Bolt tensile capacity (Clause 9.3.3)
Nominal tensile capacity is based on the bolt tensile stress area:
N\_tf = A\_s × f\_uf
Design capacity: N\_d,tf = phi\_b × N\_tf.
**Utilization** = N\*\_tf / N\_d,tf ≤ 1.0
##### Combined shear and tension (Clause 9.3.4)
For bolts loaded simultaneously in shear and tension, the interaction is governed by the circular interaction formula:
**Interaction ratio** = (V*\_f / V\_d,f)^2 + (N*\_tf / N\_d,tf)^2 ≤ 1.0
##### Ply bearing capacity (Clause 9.3.2)
Bearing failure of the connected ply is checked through two mechanisms:
* **Ply tearing** (edge failure): V\_b,t = a\_e × t\_p × f\_up
* **Ply bearing** (interior): V\_b,b = 3.2 × d\_f × t\_p × f\_up
Design bearing capacity V\_d,b = phi\_p × min(V\_b,t, V\_b,b).
**Utilization** = V\*\_b / V\_d,b ≤ 1.0
##### Serviceability friction checks (8.8/TF bolts)
For 8.8/TF friction bolts, the serviceability shear capacity is derived from the clamping force and slip factor:
V\_d,sf = phi\_b,f × V\_sf
For combined serviceability shear and tension, the linear interaction formula applies:
**Utilization** = V*\_sf / V\_d,sf + N*\_sf / N\_d,sf ≤ 1.0
##### Capacity factors
* phi\_b = 0.8 (bolt connections)
* phi\_p = 0.9 (ply in bearing)
* phi\_b,f = 0.7 (friction bolt serviceability)
## 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 steel bolt connections to AS 4100:2020, Clause 9. It covers bolt shear and tensile capacity, ply bearing capacity, the combined shear-and-tension interaction check, and serviceability friction checks for high-strength bolts in the friction category.
Key inputs are the bolt category and size, number of shear planes (threaded and unthreaded), ply thickness, ply tensile strength, edge distance on the controlling ply, and the applied design actions, shear, tension, in-plane moment, and out-of-plane moment on the bolt group. Friction bolt checks also require the slip factor and serviceability load factor.
Outputs include the design shear capacity per bolt V\_d,f, tensile capacity N\_d,tf, ply bearing capacity V\_d,b, and the combined shear-and-tension interaction ratio. For friction bolt configurations, the serviceability shear capacity V\_d,sf and combined serviceability interaction ratio are also reported.
Yes. The calculator checks the circular interaction formula per AS 4100:2020 for bolts under simultaneous shear and tension: (V/V\_d,f)^2 + (N/N\_d,tf)^2 ≤ 1.0. The interaction ratio is the governing utilization for combined loading.
The calculator supports the bolt categories defined in AS 4100:2020, including 4.6/S, 8.8/S, 8.8/TB, and 8.8/TF categories, across standard metric bolt diameters. Bolt positions are entered as a table of X and Y coordinates, so any bolt group geometry is supported without restriction on the number of bolts.
## 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).
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.
Design steel beams to AS 4100:2020 with multiple supports and loads. Floor- and roof-beam presets cut repetitive entry.
Guide to the Steel Lintel calculator for steel angle lintels to AS 4100:2020.
