Timber · Connections
Bolted timber joint at any angle to the grain calculator
Timber joint with a group of bolts loaded at an angle to the grain. The characteristic capacities parallel and perpendicular to the grain (from AS 1720.1 Tables 4.10–4.11 or the supplier) combine by Hankinson's formula, then the joint factors apply: load duration k1, steel side plates k16, group effect k17. Minimum spacings depend on the loading direction.
Standard: AS 1720.1-2010 Cl 4.4 bolts: Nd = φk1k16k17·n·Qsk · Hankinson formula for load at an angle to the grain · Table 4.13 spacings
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Bolt diameter | 16 | mm |
| Characteristic capacity per bolt ∥ grain Qskl | 9.5 | kN |
| Characteristic capacity per bolt ⟂ grain Qskp | 4.5 | kN |
| Rows | 2 | |
| Bolts per row | 3 | |
| Load angle to the grain | 30 | ° |
| k1 | 0.8 | |
| Steel side plates k16 (1.0 timber, 1.2 steel) | 1.2 | |
| Group factor k17 | 0.9 | |
| φ | 0.75 | |
| Design load N* | 25 | kN |
| Member in | Tension (end 8D) |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Hankinson capacity per bolt Qθ | 7.43 | kN |
| Number of bolts | 6 | |
| Joint design capacity Nd | 28.9 | kN |
| Minimum end distance | 128 | mm |
| Spacing along / across the grain | 80 / 64 | mm |
| Edge distance | 32 | mm |
- ✓ N* ≤ Nd — 86 %
- ✓ Group factor reflects ≤ 4 bolts in a row (else k17 lower)
Method, formulas and assumptions
- Hankinson: Qθ = Qskl·Qskp/(Qskl·sin²θ + Qskp·cos²θ).
- Nd = φ·k1·k16·k17·n·Qθ; k17 reduces with the number of bolts in a row and the ratio of member to plate areas (AS 1720.1 Table 4.15).
- Spacings (Table 4.13): along the grain 5D, end 8D (tension) or 5D (compression), edge 2D for parallel loading; perpendicular loading needs 4D on the loaded edge.
- Take Qsk for the joint group (JD1–JD6), bolt diameter and effective timber thickness from AS 1720.1 Tables 4.10–4.11.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.