AS 1720.1 Timber Modification Factors
Calculate k₁, k₄, k₆ and k₉
This calculator determines four common timber strength
modification factors:
k₁ for load duration,
k₄ for moisture,
k₆ for temperature,
and k₉ for strength sharing.
1. Duration of Load Factor k₁
For combinations containing actions of different duration,
use the k₁ corresponding to the shortest-duration action.
2. Moisture Condition Factor k₄
Used only for seasoned timber where annual average
moisture content exceeds 15%.
Used for the AS 1720.1 partial-seasoning condition.
k₄ = 1.00
3. Temperature Factor k₆
Use the regional option only where the location meets
the geographical conditions specified by AS 1720.1.
Normal ambient condition → k₆ = 1.00
4. Strength-Sharing Factor k₉
Single independent member → k₉ = 1.00
Important:
do not automatically use k₉ > 1.0 simply because several
joists exist. The members must form a qualifying strength-sharing
parallel system.
k₁
0.80
k₄
1.00
k₆
1.00
k₉
1.00
Combined modification multiplier
0.800
k₁ × k₄ × k₆ × k₉
Reference Values
| Factor | Typical condition | Value |
|---|---|---|
| k₁ | Floor imposed action – 5 months | 0.80 |
| k₄ | Seasoned timber, average MC ≤ 15% | 1.00 |
| k₆ | Covered, normal ambient environment | 1.00 |
| k₉ | Single independent member | 1.00 |