Timber · Beams & joists
Glulam / LVL beam (AS 1720.1) calculator
Simply supported glulam or LVL beam carrying a floor or roof strip. Design capacities φk1k12·f′b·Z and φk1·f′s·As for the two load durations (1.35G with k1 = 0.57, 1.2G + 1.5Q with the chosen k1), lateral stability from the restraint spacing (k12 via S1 and ρb), long-term deflection with creep factor j2, and the floor natural frequency.
Standard: AS 1720.1-2010 Cl 3.2 bending (k1, k12 stability), Cl 3.2.5 shear, Cl 2.4.1 creep j2 · AS/NZS 1328 glulam grades
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 | GL17 | |
| Breadth b | 135 | mm |
| Depth d | 540 | mm |
| Span | 7.2 | m |
| Tributary width | 3 | m |
| Dead load (excl. self-weight) | 1 | kPa |
| Live load | 2 | kPa |
| k1 for G + Q (5 months floor = 0.8) | 0.8 | |
| Spacing of lateral restraints to the compression edge | 1.2 | m |
| Capacity factor φ | 0.85 | |
| Creep factor j2 (seasoned) | 2 | |
| Deflection limit L / | 300 |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Properties f′b / f′s / E | 42 / 3.7 / 16700 | MPa |
| Self-weight | 0.400 | kN/m |
| S1 / ρb / k12 | 7.45 / 0.885 / 1.000 | |
| 1.35G: M* / φMd (k1 0.57) | 29.7 / 133.5 | kNm |
| 1.2G + 1.5Q: M* / φMd (k1 0.8) | 84.8 / 187.4 | kNm |
| 1.2G + 1.5Q: V* / φVd | 47.1 / 122.3 | kN |
| Deflection: dead (short) / live | 4.0 / 7.1 | mm |
| Long-term j2(G + 0.4Q) + 0.6Q | 18.0 (L/400) | mm |
| Natural frequency (dead load) | 8.9 | Hz |
- ✓ Bending, permanent (1.35G) — 22 %
- ✓ Bending, G + Q — 45 %
- ✓ Shear
- ✓ Long-term deflection ≤ L/300
- ✓ Live-load deflection ≤ L/360
- ✓ Frequency ≥ 8 Hz (floors)
Method, formulas and assumptions
- φMd = φ·k1·k4·k6·k9·k12·f′b·Z with k4 = k6 = k9 = 1 (dry, normal temperature); shear φ·k1·f′s·As with As = 2bd/3.
- k12 (Cl 3.2.4): S1 = 1.25(d/b)(Lay/d)^½ for discrete restraint of the compression edge; ρb = 14.71(E/f′b)^−0.48·r^−0.061; k12 = 1 (ρbS1 ≤ 10), 1.5 − 0.05ρbS1 (≤ 20), 200/(ρbS1)².
- Grade properties are typical (AS/NZS 1328 glulam, proprietary LVL): use the manufacturer's published values for design.
- Floor vibration: f = (π/2L²)√(EI/m) under the permanent load; ≥ 8 Hz is a common target for timber floors.
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.