Wind Bracing Design

How it calculates

The calculator works through four sequential steps: determining design wind pressure for each wind direction, calculating the racking demand on each wall face, tallying the bracing capacity provided, and checking that capacity meets demand. Each step is performed independently for the long-side (wind on side) and short-side (wind on end) of the building.

Step 1 — Design wind pressure from AS 4055:2021

Wind pressure depends on how the wind approaches each face of the building.

For vertical surfaces (flat gable ends, skillion ends, and walls presenting a flat face to the wind), the calculator looks up the design wind pressure directly from Table 5.2(A) of AS 4055:2021 using the wind classification. The values for non-cyclonic sites are:

• N1: 0.66 kPa
• N2: 0.92 kPa
• N3: 1.44 kPa
• N4: 2.14 kPa

For sloped roofs (hip roofs and side wind on gable or skillion roofs), the calculator interpolates across Tables 5.2(B)–(I) of AS 4055:2021 using both roof pitch (0–35°) and building width as inputs. Wind class and storey level (single storey / upper storey versus lower storey of a two-storey building) determine which sub-table governs. Because the sloped-roof pressure depends on building width, the long-side and short-side of the same building may produce different pressures even at the same wind class.

Roof pitch must be between 0° and 35° (70:100 slope), and building width must be less than 16 m — both are enforced by the calculator in accordance with the scope of AS 4055:2021.

Step 2 — Racking demand from area of elevation

The racking demand (kN) acting on each wall face is the product of the design wind pressure and the area of elevation facing that wind direction, per AS 1684.2:2021 Cl 8.3.4:

F* = p_u × A

The area of elevation can be entered in two ways. When auto-calculation is selected, the calculator derives the long-side area from wall height and building length, adding the gable or hip triangle contribution using roof pitch. The short-side area is derived similarly using building width. When custom areas are selected, the user supplies the projected areas directly — required for L-, H-, or U-shaped plans, buildings with enclosed verandahs, or any geometry where the standard formula would not capture the true exposed surface.

Step 3 — Bracing capacity from AS 1684.2:2021

Bracing capacity is assembled from up to three sources for each wall direction.

Structural wall bracing is chosen from the 18 bracing types listed in Table 8.18 of AS 1684.2:2021. Unit capacities range from 0.8 kN/m for type (a) two diagonally opposed timber/metal angle braces up to 7.6 kN/m for type (i) 7 mm F11 plywood and type (m) Hardboard Type C. The user nominates the bracing type and total installed length; the calculator multiplies these to obtain the bracing capacity for each row and sums across all rows.

Two adjustments modify the raw table values:

• Wall height multiplier (Table 8.19, Cl 8.3.6.4): For wall heights greater than 2.7 m, all bracing capacity is scaled down by the ratio 2700 mm / H_w. A 3.6 m wall, for example, attracts a multiplier of 0.75.
• Joint group uplift (Cl 8.3.6.3): If the timber framing is JD4 rather than the default JD5, the capacity of sheet bracing types (g) to (k) is increased by 12.5% and types (l) to (n) by 16%.

Nominal wall bracing (Cl 8.3.6.2) represents sheet lining fixed to the framing without purpose-fitted bracing hardware. One-side-sheeted walls contribute 0.45 kN/m and two-side-sheeted walls contribute 0.75 kN/m. The total nominal bracing capacity credited to the design is capped at a user-controlled percentage of the racking demand — by default 50% per the standard, but this can be set lower.

Custom bracing allows users to enter proprietary or non-standard bracing products not listed in Table 8.18, supplying their own unit capacity (kN/m) and installed length. The wall height multiplier can be toggled on or off for each custom row, accommodating products where the manufacturer's capacity already accounts for wall height variation.

Total racking capacity for each direction is the sum of structural bracing capacity, nominal bracing capacity (capped), and any custom bracing capacity.

Step 4 — Pass/fail check

The calculator compares total racking capacity against the racking demand for both the long-side and short-side walls independently. The design passes when:

F_total ≥ F*

If capacity is insufficient, a clear failure message identifies which wall direction needs additional bracing. Because eccentricities in wind loading and plan irregularities are excluded from scope, this is a global check — total capacity across the wall face versus total demand — consistent with the simplified approach in AS 1684.2:2021.