Wind loads (AS/NZS 1170.2)

The Wind loads wizard (Tools ▸ Wind loads (1170.2), or Cmd/Ctrl-K → "Wind") runs the full AS/NZS 1170.2:2021 wind engine: it turns a building's site data and geometry into the design wind pressure on each surface, for wind blowing across the ridge (0°) and along the building (90°).

Verification build — not yet a design tool

This engine is marked verified: false. Its coefficients are cross-checked against AS/NZS 1170.2:2021 and an independent published worked example, but it is a calculator: it reports pressures, it does not yet apply them to your frame as load cases, and several modelling choices below still need your judgement. Confirm every result against the standard and your design basis before use.

What it computes

Section 2 — site wind speed. Regional speed Vr (Table 3.1, by region + return period), the terrain/height multiplier Mz,cat (Table 4.1(A)), and the Md/Ms/Mt multipliers → Vdes,θ = Vr·Md·(Mz,cat·Ms·Mt) → free-stream dynamic pressure q = 0.5·ρair·Vdes².

Section 5 — aerodynamic shape factors for an enclosed rectangular / portal building:

Surface	Source	Notes
Windward wall	Table 5.2(A)	+0.7 at z=h (h ≤ 25 m), +0.8 if h > 25 m
Leeward wall	Table 5.2(B)	depends on wind direction, roof pitch and d/b
Side walls	Table 5.2(C)	area-averaged over the −0.65 / −0.5 / −0.3 / −0.2 zones
Roof (windward / leeward)	Tables 5.3(A/B/C)	the h/d × pitch grids, incl. the α ≥ 25° b/d formula
Internal Cpi	Table 5.1(A)	enclosed: −0.3 or 0.0; a dominant opening raises it
Area reduction Ka	Table 5.4	per surface type

Each surface's design factor is Cfig,e = Cpe·Ka·Kc·Kl·Kp (Kc = Kl = Kp = 1.0 for main frames), and the net pressure is p = q·(Cfig,e − Cfig,i) — reported for both internal-pressure cases. Roofs carry two design values (uplift and pressure); both are shown (uplift / pressure), because the standard requires designing for both.

Using it

1. Open Tools ▸ Wind loads (1170.2).
2. Set the wind region (from the site's location) and return period (ULS ≈ 500 yr).
3. Choose the terrain category — the roughness of the ground upwind of the building. Hover each option for a plain-language description (TC1 open/over-water … TC4 dense urban).
4. Enter the building span, length, eave height, roof pitch and roof type, or click Fill span/length/eave from model to read them from the current model's bounding box (then check the pitch and eave-vs-apex).
5. Set the dominant-opening ratio (0 = nominally enclosed; > 2 = a dominant windward opening) and the Md/Ms/Mt multipliers if you're not taking them as 1.0.
6. Read the per-surface table: q, the shape factor Cfig,e, the external pressure p_ext, and the two net-pressure cases. Copy exports it as tab-separated text.

Scope and limitations

In scope: enclosed rectangular / portal buildings (gable, monoslope or flat), wind at 0° and 90°, ultimate limit state.

Not yet handled (shown in the wizard's warnings):

• Load-case generation — it does not distribute pressures onto members or build the 1170.0 combinations.
• Along-wind dynamic response (Section 6, Cdyn = 1.0); a warning fires when h > 15 m.
• Table 5.1(B) dominant-opening internal pressure (a representative +0.7 is used); Table 4.1(B) for regions B/C/D at ULS; combination factor Kc < 1.
• Cladding local pressure factors (Kl), free roofs/canopies, non-rectangular geometry.

Verification

Coefficients are confirmed against the AS/NZS 1170.2:2021 tables and reproduce an independent published worked example (a warehouse: Mz,cat = 1.001, leeward wall −0.375, roof upwind −0.888 / −0.394, downwind −0.503) to three decimals. The module stays verified: false pending broader worked-example coverage and an engineer sign-off. See Design checks for the same verification discipline applied to member design.