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# Design a Timber Bolt Connection to AS 1720.1:2010
> Design timber bolted connections to AS 1720.1:2010. Checks bolt patterns under direct shear, in-plane moment, and tension for Australian timber construction.
Easily design and analyze timber bolt connections with the Calcs.com Timber Bolt Calculator to AS 1720.1:2010. The calculator assumes bolt patterns subject to direct shear, in-plane moment, or tension. Detailing requirements including clause 4.4.4 modifications are to be checked separately.
Easily design and analyze timber bolt connections with the Calcs.com Timber Bolt Calculator to AS 1720.1:2010. The calculator assumes bolt patterns subject to direct shear, in-plane moment, or tension. Detailing requirements including clause 4.4.4 modifications are to be checked separately. Joints are assumed as concentric (or effects of eccentricity per clause 4.4.6 are to be checked separately). All bolts and washers must be the same size.
## Method & scope
| Property | Detail |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | AS 1720.1:2010 |
| Regions | Australia & New Zealand |
| What it checks | Characteristic bolt capacity, Design capacity , Type 1 joint (shear), Design capacity , Type 2 joint (tension), Combined shear and tension, Load distribution in bolt groups, Washer requirements, Capacity factors |
#### What it calculates
Design timber bolted connections to AS 1720.1:2010, shear capacity, in-plane moment, and tension checks for bolt patterns in Australian timber construction.
Bolted connections transfer high loads between heavy timber members in post-and-beam frames, glulam portals, and engineered wood structures. Under-designed bolt patterns can lead to timber splitting, fastener shear failure, or group-action overload, all of which are difficult to detect visually after construction. Getting the characteristic capacity, the k17 group factor, and the washer bearing area right from the outset avoids costly rework and keeps the design traceable to AS 1720.1.
#### Calculation method
The Timber Bolt calculator follows the design procedure in AS 1720.1:2010 Section 4.4 to determine the capacity of a bolted timber connection under lateral shear, direct tension, or combined loading.
##### Characteristic bolt capacity
For a single bolt loaded laterally (Type 1 joint), the characteristic capacity Qsk depends on the load angle relative to the grain:
* **Parallel to grain**: Qsk = Qsk1, taken from AS 1720.1 Table 4.9(A) based on bolt diameter and effective timber thickness
* **Perpendicular to grain**: Qsk = Qskp, taken from AS 1720.1 Table 4.10(A)
* **At angle θ to grain**: Qsk = (Qsk1 × Qskp) / (Qsk1 × sin²θ + Qskp × cos²θ)
The system capacity parameters that modify Qsk1 and Qskp for multi-ply arrangements are drawn from Tables 4.9(B-C) and 4.10(B-C).
For bolts loaded in direct tension (Type 2 joint), the maximum tensile capacity per bolt N\_d,tb is taken from Table 4.11 based on bolt diameter and material grade.
##### Design capacity , Type 1 joint (shear)
The design capacity of the bolt group in lateral shear is:
**N\_d,j = φ × k1 × k16 × k17 × n × Qsk**
Where:
* φ = capacity reduction factor from Clause 2.3 (0.6 for most bolted connections)
* k1 = duration of load factor for joints from Clause 2.4.1.1 (0.57 for permanent load, up to 1.14 for wind/earthquake)
* k16 = 1.2 when bolts transfer load through close-fitting holes into steel side plates; 1.0 otherwise
* k17 = group factor from Table 4.12, which reduces capacity for bolt rows with more than 4 bolts parallel to the grain
* n = number of bolts in the group resisting the design action effect in shear
The design action effect must satisfy N\* ≤ N\_d,j.
##### Design capacity , Type 2 joint (tension)
For bolts loaded in direct tension, the group capacity is:
**N\_d,j = φ × k1 × k7 × n × f'\_pj × Aw**
Where:
* k7 = length of bearing factor from Table 2.6
* f'\_pj = characteristic bearing capacity for timber at joint details, from Table C6
* Aw = effective washer bearing area from Table 4.11
This check ensures the washer and timber bearing surface can transfer the tensile load without pull-through.
##### Combined shear and tension
When load acts at an angle to the bolt axis, both Type 1 (shear component normal to bolt axis) and Type 2 (tension component parallel to bolt axis) capacity checks are applied simultaneously per Clause 4.4.3.4. Both utilization ratios must be at or below 1.0.
##### Load distribution in bolt groups
For bolt groups subject to concentric direct loads, the applied force is divided equally across all n bolts. The calculator does not automatically redistribute load for eccentric patterns , eccentricity effects per Clause 4.4.6 must be assessed separately.
##### Washer requirements
Every bolt in a timber-to-timber bolted joint requires a washer at each end per Clause 4.4.5. The minimum washer size is governed by bolt diameter as specified in Table 4.11. The effective bearing area Aw of the washer directly enters the Type 2 tension check.
##### Capacity factors
* φ = 0.6 for bolted connections (Clause 2.3)
* k1 ranges from 0.57 (permanent load) to 1.14 (wind and earthquake, short duration)
* k17 = 1.0 for up to 4 bolts in a row parallel to grain; reduces progressively for larger groups per Table 4.12
## 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
AS 1720.1:2010 (Timber Structures). Bolted connection capacity is determined using characteristic strengths and capacity reduction factors from AS 1720.1 Section 4.4, including clause 4.4.4 modifications where applicable.
Bolt diameter, member thicknesses for each ply, timber species and joint group, number of bolts and pattern layout, washer size, and the applied load (shear, tension, or combined). All bolts and washers in the group must be the same size.
Lateral shear capacity and tension capacity of the bolt group per AS 1720.1 clause 4.4. For patterns subject to in-plane moment, the calculator distributes the load to individual bolts and checks the most critical bolt. Outputs include the governing utilization ratio.
The calculator assumes concentric joints. Effects of eccentricity per AS 1720.1 clause 4.4.6 and the clause 4.4.4 ductility factor modifications must be checked separately when eccentricity is present.
Bolts are used in heavy timber connections and where high shear or withdrawal loads are required. They are common in post and beam, glulam portal frames, and engineered timber connections. For lighter framing connections with smaller load demands, nails or screws are typically more efficient.
## 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).
Check the capacity of nailed timber connections to AS 1720.1:2010.
Design timber screwed connections to AS 1720.1:2010. Checks screw patterns under direct shear, in-plane moment, and tension capacity.
Design timber beams with multiple spans and load cases to AS 1720.1:2010 (Amdt 3). Checks bending, shear, bearing and deflection.
