As1170 Wind Calculations Excel

Calculate wind loads according to Australian Standard AS1170.2 with this precise engineering tool

Comprehensive Guide to AS1170 Wind Calculations in Excel

The Australian Standard AS1170.2 provides the minimum requirements for wind loads on structures in Australia. This guide explains how to perform these calculations manually and implement them in Excel for efficient structural design.

Understanding AS1170.2 Wind Load Basics

AS1170.2 uses a probabilistic approach to determine wind loads based on:

• Wind region (A-D) based on geographical location
• Terrain category (1-4) based on surface roughness
• Building height and dimensions
• Importance level (1-4) based on building use
• Topographic effects and shielding

Key Parameters in Wind Load Calculation

Parameter	Description	Typical Values
VR	Regional wind speed (m/s)	33-66 depending on region
Md	Wind directional multiplier	0.9-1.0
Mz,cat	Terrain/height multiplier	0.6-1.8
Ms	Shielding multiplier	0.8-1.0
Mt	Topographic multiplier	0.7-1.4

Step-by-Step Calculation Process

1. Determine Regional Wind Speed (V_R)

   Select the appropriate wind region from AS1170.2 Figure 3.1 based on your location. Region D has the highest wind speeds (66 m/s), while Region A has the lowest (33 m/s).

2. Calculate Design Wind Speed (V_des)

   Use the formula: V_des = V_R × M_d × M_z,cat × M_s × M_t

   Where:

   • M_d = 1.0 for most cases (0.9 for certain directions)
   • M_z,cat depends on terrain category and height (Table 4.1)
   • M_s = 0.8 for shielded, 1.0 for unshielded
   • M_t depends on topography (1.0 for flat terrain)
3. Determine Wind Pressure (p)

   Calculate using: p = 0.5 × ρ × (V_des)² × C_fig

   Where:

   • ρ = air density (1.2 kg/m³ at sea level)
   • C_fig = aerodynamic shape factor (from AS1170.2 Section 5)

Implementing AS1170 in Excel

To create an Excel spreadsheet for AS1170 calculations:

1. Input Section

   Create cells for:

   • Wind region (dropdown: A, B, C, D)
   • Terrain category (dropdown: 1, 2, 3, 4)
   • Building height, width, length
   • Importance level (dropdown: 1, 2, 3, 4)
   • Topography (dropdown: flat, hill, escarpment, etc.)
   • Shielding (dropdown: shielded, unshielded)
2. Lookup Tables

   Create tables for:

   • Regional wind speeds (Table 3.1)
   • Terrain/height multipliers (Table 4.1)
   • Topographic multipliers (Table 4.2)
   • Aerodynamic shape factors (Section 5)

   Use VLOOKUP or XLOOKUP functions to reference these tables.

3. Calculation Section

   Create formulas for:

   • Design wind speed: =V_R*M_d*M_z*M_s*M_t
   • Wind pressure: =0.5*1.2*(V_des^2)*C_fig
   • Intermediate calculations for each multiplier
4. Output Section

   Display results with clear labeling:

   • Design wind speed (m/s)
   • Wind pressure (kPa)
   • Critical wind directions
   • Recommended structural requirements

Advanced Considerations

For complex structures, consider these additional factors:

Factor	When to Apply	Calculation Method
Dynamic Response	Buildings > 50m tall or with unusual shapes	AS1170.2 Section 6 or specialist software
Local Pressure Effects	Roof corners, parapets, canopies	Section 5.4 with appropriate Cfig values
Internal Pressures	Buildings with dominant openings	Section 5.3 with Cpi values
Debris Impact	Cyclonic regions (Region D)	AS1170.2 Appendix E

Common Mistakes to Avoid

• Incorrect terrain category: Category 2 (suburban) is most common, but verify with site photos
• Ignoring importance level: Level 4 buildings require 20% higher wind speeds
• Wrong shape factors: Always check Section 5 for the correct C_fig values
• Missing topographic effects: Even small hills can increase wind loads by 30%
• Excel rounding errors: Use sufficient decimal places in intermediate calculations

Verification and Validation

Always verify your Excel calculations against:

1. Manual calculations for simple cases
2. Established structural engineering software
3. The worked examples in AS1170.2 Appendix F
4. Peer review by another qualified engineer

For critical structures, consider:

• Wind tunnel testing for complex shapes
• CFD analysis for unusual terrain
• Third-party certification of your Excel spreadsheet

Excel Implementation Tips

To create a robust Excel calculator:

• Use named ranges for all input cells
• Implement data validation for all dropdowns
• Add conditional formatting to highlight invalid inputs
• Create a summary dashboard with key results
• Include a printable report section
• Add version control and change tracking
• Document all assumptions and limitations

Important Disclaimer: This calculator provides preliminary estimates only. For actual structural design, always consult a qualified structural engineer and refer to the current version of AS1170.2. The authors accept no liability for any consequences arising from the use of this information.

Authoritative Resources

For official information and detailed guidance:

• Standards Australia – AS/NZS 1170.2
• Geoscience Australia – Wind Hazard Information
• Bureau of Meteorology – Climate Data Services