Wind Load Calculation as per Australian Code (AS/NZS 1170.2:2021)

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March 17, 2025

Civil and Structural Design Calculations, Engineering Concepts – Civil & Structural

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Wind loads in Australia are calculated based on AS/NZS 1170.2:2021 – Structural Design Actions, Part 2: Wind Actions. This standard provides guidelines for determining wind loads on buildings and structures based on wind regions, terrain categories, building height, and shape factors.

AS/NZ 1170.2 (2021) is the Australian and New Zealand Standard that specifically addresses wind loads on structures. It outlines the procedures and methodologies for determining the wind loads on various structures.

1. Key Factors in Wind Load Calculation

a. Basic Wind Speed (Vₛ)

Defined for different wind regions (A, B, C, D) in Australia.
Based on a return period of 500 years for ultimate limit state (ULS).
Reference Height: 10m above ground in open terrain.

b. Wind Region Classifications (Refer AS/NZS 1170.2:2021)

Region	Basic Wind Speed (Vₛ in m/s)	Location
Region A	45	Normal Areas (e.g., Sydney, Melbourne)
Region B	57	Higher Risk (e.g., Brisbane, Perth)
Region C	69	Cyclonic Areas (e.g., Townsville, Darwin)
Region D	79	Severe Cyclonic (e.g., North-West WA)

2. Wind Pressure Calculation Formula

The design wind pressure (P) is calculated as:

P=1/2. ρ. V²_d.C_{fig .}C_dyn.C_s.C_dir

Where:

P = Wind pressure (Pa)
ρ = Air density = 1.2 kg/m³
Vₑ = Design wind speed (m/s)
C_fig= Shape factor (based on structure shape)
C_dyn = Dynamic response factor
C_s = Shielding factor (considering surrounding terrain)
C_dir = Directional factor

3. Design Wind Speed Calculation

Vd=V_sM_z, catM_sM_t

Where:

Vₛ = Basic wind speed (m/s)
M_z,cat = Terrain/Height Multiplier
M_s = Shielding Multiplier
M_t = Topographic Multiplier

a. Terrain Categories (AS/NZS 1170.2:2021)

Category	Description	M_z,cat (10m height)
TC1 (Open Terrain)	Coastal, flat land	1.05
TC2 (Suburban Area)	Low-rise buildings, trees	0.9
TC3 (City Center)	Densely built urban areas	0.75

b. Example Calculation (Region B, 10m height, suburban area)

Basic Wind Speed (Vₛ) = 57 m/s
M_z,cat (Terrain Category 2) = 0.9
M_s (Shielding Multiplier) = 0.85
M_t (Topographic Multiplier) = 1.0

Vd = 57 × 0.9 × 0.85 × 1.0

= 43.6m/s

4. Wind Pressure Calculation Example

For a 10m high warehouse in Region B (suburban area):

V_d = 43.6 m/s
C_fig = 1.0 (for walls)
C_dyn = 1.0
C_s = 1.0
C_dir = 1.0

P =12×1.2× (43.6)2×1.0×1.0×1.0×1.0

P =0.6×1902.9

=1141.74Pa =1.14kPa

Thus, wind pressure acting on the walls is 1.14 kPa.

5. Compliance with Australian Standards

✔ AS/NZS 1170.2:2021 – Structural Design Actions (Wind Loads)
✔ AS 4055:2012 – Wind Loads for Housing
✔ AS/NZS 4100 – Steel Structures
✔ AS 3600 – Concrete Structures

6. Download Free Wind Load Calculation Excel & PDF

📥 AS/NZS 1170.2 Wind Load Calculation Excel Sheet
📥 Wind Region Map of Australia (PDF)
📥 Wind Pressure Design Guide for Buildings
📥 Structural Engineering Code Compliance Checklist

7. Conclusion

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Wind load calculation as per AS/NZS 1170.2 ensures that buildings and structures can withstand regional wind speeds, terrain effects, and dynamic forces. Proper design helps in preventing structural failure and ensuring safety.