Design timber wall studs to AS 1720.1. Go beyond the limits of AS 1684 and engineer tall walls, jamb studs, and high-wind framing using MGP10, MGP12, and F-grades.
For standard houses, AS 1684 (Residential Timber Framed Construction) is the bible. But modern architecture—with high ceilings, large window openings, and extreme wind categories—often pushes framing beyond the scope of the standard tables.
The SPEC Toolbox Stud Wall Calculator performs a first-principles engineering analysis to AS 1720.1. It allows you to verify studs for specific heights (e.g., 3.6m), localized wind pressures, and heavy point loads that simplified span tables simply cannot handle.
This tool analyzes a vertical timber stud as a structural Beam-Column under combined Gravity (Roof/Floor) and Lateral (Wind) loads. It verifies:
1. Buckling Stability ($k_{12}$)
In AS 1720.1, the capacity of a stud is defined by its “Slenderness.”
The calculator determines the Slenderness Coefficients ($S_3, S_4$) for:
2. Combined Actions Equation
When a stud supports a roof truss and resists a wind gust, it is stressed in two ways.
We apply the AS 1720.1 interaction formula (Clause 3.3.3):
$$\left(\frac{N^*}{N_d}\right) + \left(\frac{M^*}{M_d}\right)^2 \le 1.0$$
Note: For slender studs ($S > 20$), the bending term is squared, meaning even small wind loads can drastically reduce the axial load the stud can carry.
3. MGP vs. F-Grades
The Australian market is dominated by Machine Graded Pine (MGP).
The calculator includes the latest characteristic values for all these grades.
Design Capacity ($N_d$):
$$N_d = \phi \cdot k_1 \cdot k_4 \cdot k_6 \cdot k_{12} \cdot f’_c \cdot A_c$$
Bearing Check ($k_7$):
$$N_{p,d} = \phi \cdot k_1 \cdot k_7 \cdot f’_p \cdot A_p$$
The tool applies the $k_7$ bearing factor. For a standard 35mm or 45mm stud on a continuous plate, this factor enhances bearing capacity, accounting for the load spreading through the plate fibers.
Yes. While AS 1684 is a “Deemed-to-Satisfy” manual, a design to AS 1720.1 (which this tool produces) is a primary reference standard in the NCC and is fully accepted for certification.
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