Timber · Columns & studs
Timber pile (structural + geotechnical) calculator
Compression capacity of a tapered round timber pile at ground level (with stability factor k12) and at the toe, and the geotechnical design capacity from shaft and base resistance.
Standard: AS 1720.1 Cl 3.3 compression (k1, k4, k6, k12) · AS 2159 φg
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 |
|---|---|---|
| Head diameter | 350 | mm |
| Toe diameter | 250 | mm |
| Pile length | 12 | m |
| Free length above ground | 1 | m |
| Effective buckling length Le | 3 | m |
| Characteristic f′c (from AS 1720.1 for the grade) | 30 | MPa |
| Capacity factor φ | 0.8 | |
| Load duration k1 | Permanent (k1 0.57) | |
| Moisture k4 | 1 | |
| Temperature k6 | 1 | |
| Other factors (e.g. shaving k21, immaturity k20) | 0.85 | |
| Material constant ρc | 1 | |
| Design axial load N* | 180 | kN |
| Average ultimate shaft friction | 25 | kPa |
| Ultimate base pressure | 2500 | kPa |
| Geotechnical reduction φg (AS 2159) | 0.5 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Diameter at ground | 342 | mm |
| Slenderness S = Le/d | 8.8 | |
| Stability factor k12 | 1.000 | |
| φNc at ground level | 1,066 | kN |
| φNc at toe (no buckling) | 571 | kN |
| Load at toe (base share) | 58 | kN |
| Shaft resistance | 256 | kN |
| Base resistance | 123 | kN |
| Ultimate geotechnical Rug | 378 | kN |
| Design geotechnical φg·Rug | 189 | kN |
| Taper | 8.3 | mm/m |
- ✓ φNc ≥ N* at ground level — 1,066 kN
- ✓ φNc ≥ toe load
- ✓ φg·Rug ≥ N* — 189 kN
- ✓ Toe diameter ≥ 200 mm (driveability)
Method, formulas and assumptions
- φNc = φ·k1·k4·k6·(other)·k12·f′c·A (AS 1720.1 Cl 3.3), A at the critical section
- k12 = 1 for ρcS ≤ 10; 1.5 − 0.05ρcS for 10–20; 200/(ρcS)² above 20, with S = Le/d for a round section (confirm against the current edition)
- Rug = fs·π·d_avg·L_emb + qb·A_toe; design capacity φg·Rug with φg from the AS 2159 risk assessment
- Take f′c, ρc and φ from AS 1720.1 for the species, strength group and member category; the defaults are examples
- Specify preservative treatment (H5/H6) for the part above the permanent water table and check driving stresses
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.