Timber · Beams & joists
Timber beam / joist (AS 1720.1) calculator
Bending and shear capacity with load-duration factor k1 and long-term deflection with j2 for MGP, F-grade and glulam sections.
Standard: AS 1720.1-2010 · k1 duration · j2 creep
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 |
|---|---|---|
| Grade | MGP12 | |
| Breadth b | 45 | mm |
| Depth d | 240 | mm |
| Span | 4.2 | m |
| Dead load (excl. self) | 0.5 | kN/m |
| Live load | 1.35 | kN/m |
| Load duration (governing) | 5 months (k1 0.8) | |
| Capacity factor φ (category per Table 2.1) | 0.85 | |
| Creep factor j2 (seasoned ≈ 2) | 2 | |
| Deflection limit span / | 300 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Section modulus Z | 432 | ×10³ mm³ |
| f'b / E | 28 MPa / 12700 | MPa |
| k1 | 0.80 | |
| Design load w* | 2.70 | kN/m |
| M* / φMd | 5.95 / 8.23 | kNm |
| V* / φVd | 5.66 / 17.14 | kN |
| Long-term deflection (j2·G + 0.7Q) | 12.7 | mm |
| Limit | 14.0 | mm |
- ✓ M* ≤ φMd
- ✓ V* ≤ φVd
- ✓ Deflection ≤ span/300
Method, formulas and assumptions
- φMd = φ·k1·k4·k6·k9·k12·f'b·Z with k4 = k6 = k9 = 1 and k12 = 1 (compression edge restrained)
- φVd = φ·k1·f's·As, As = 2bd/3
- w* = max(1.35G, 1.2G + 1.5Q); k1 should match the shortest duration in the combination (check both)
- δ = 5wL⁴/(384EI) with j2 on permanent load
- Property values are typical characteristic values; confirm against AS 1720.1 / supplier data
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.