AS 1720.1 Timber Beam Bending Capacity Calculator
Complete F-grade rectangular sawn timber beam design
Automatic design calculation:
Timber grade → f′b → φ → k₁ → k₄ → k₆ → k₉ → S₁ → ρb → k₁₂ → Z → Md → PASS / FAIL
Timber grade → f′b → φ → k₁ → k₄ → k₆ → k₉ → S₁ → ρb → k₁₂ → Z → Md → PASS / FAIL
1. Timber Grade and Condition
2. Structural Application Category
Category 1 = house members with limited consequence
or secondary members.
Category 2 = primary structural members.
Category 3 = essential-service / post-disaster primary members.
Category 2 = primary structural members.
Category 3 = essential-service / post-disaster primary members.
3. Rectangular Beam Geometry
Z = bd² / 6
For an F-grade rectangular beam with d > 300 mm:
f′b,design = f′b,H2.1 (300/d)0.167
For an F-grade rectangular beam with d > 300 mm:
f′b,design = f′b,H2.1 (300/d)0.167
4. Duration of Load Factor k₁
For a load combination containing actions of different duration,
select the effective duration associated with the shortest-duration
action in the combination.
Calculated k₁ =
0.80
5. Moisture Condition Factor k₄
k₄ = 1.00
6. Temperature Factor k₆
Calculated k₆ =
1.00
The northern-region reduction applies to seasoned timber in
the geographical regions specified by AS 1720.1 Clause 2.4.3.
7. Strength-Sharing Factor k₉
Number effectively fastened together in one group.
Number of discretely spaced parallel members.
Single beam → k₉ = 1.00
Important:
k₉ > 1.0 is only appropriate when the members actually form
a qualifying strength-sharing structural system.
8. Lateral Stability – S₁ and k₁₂
If lateral restraints occur only at the two beam ends,
enter the actual distance between those restraint points.
When selecting a continuous restraint option,
the designer must confirm that the restraint system satisfies
the AS 1720.1 requirements for an effective continuous
lateral restraint system.
9. Applied Design Bending Moment
f′b
—
φ
—
k₁
—
k₄
—
k₆
—
k₉
—
S₁
—
k₁₂
—
Design Bending Capacity Md
—
Md ≥ M*
—
10. Complete Calculation
| Parameter | Value | Source / Calculation |
|---|---|---|
| Grade | — | User selection |
| f′b base | — | Table H2.1 |
| f′b design | — | — |
| φ | — | Table 2.1 |
| Z | — | Z = bd² / 6 |
| k₁ | — | Duration of load |
| k₄ | — | Moisture condition |
| k₆ | — | Temperature / location |
| k₉ | — | Strength sharing |
| ρb | — | Table 3.1 |
| S₁ | — | Beam restraint condition |
| ρbS₁ | — | ρb × S₁ |
| k₁₂ | — | Stability factor |
| Combined kmod | — | k₁k₄k₆k₉k₁₂ |
| Md | — | φk₁k₄k₆k₉k₁₂f′bZ |
| M* | — | Applied design moment |
| Utilization | — | M* / Md |
Scope:
This calculator is for a straight,
solid rectangular F-grade sawn timber beam
bending about its major axis.
It is intentionally not applying the same F-grade rules to
MGP, A17, LVL or glulam because those products have separate
property and modification provisions in AS 1720.1.