BS 6399 Part 2: A Guide for Wind Loads (PDF)
BS 6399 Part 2 is a British Standard that provides guidelines for assessing wind loads on buildings. This standard is essential for engineers and architects involved in building structural design, ensuring safety and stability against wind forces.
Key Takeaways:
- Purpose of BS 6399 Part 2: Provides methods to determine wind loads on buildings.
- Scope: Applicable to various building types and heights within the UK.
- Methods Included: Standard and directional methods for calculating wind loads.
- Factors Considered: Terrain, building geometry, wind speed, and topography.
- Importance: Ensures structural safety and compliance with building regulations.
What is BS 6399 Part 2?
BS 6399 Part 2 is a section of the British Standard BS 6399, titled “Loading for buildings – Part 2: Code of practice for wind loads.” It offers comprehensive procedures for calculating wind loads that buildings may encounter, facilitating the design of structures capable of withstanding wind pressures.
Scope and Application of BS 6399 Part 2
This standard applies to buildings and structures located in the UK, encompassing various building types and heights. It establishes methods for calculating wind loads by considering factors such as terrain, building geometry, and wind speed.
Methods for Determining Wind Loads
BS 6399 Part 2 provides two primary methods for determining wind loads:
Standard Method
The standard method offers a straightforward approach suitable for most buildings. It involves using predefined factors and coefficients to calculate wind loads based on building dimensions and location.
Directional Method
The directional method assesses wind loading in more detail, considering the directionality of wind and its impact on the structure. While it provides a more precise analysis, it requires increased computational effort and is often implemented using computer software.
Factors Influencing Wind Load Calculations
Several factors influence the calculation of wind loads as per BS 6399 Part 2:
Terrain Categories
The standard defines different terrain categories that affect wind speed profiles:
- Category A: Open-level country with few obstructions.
- Category B: Urban and suburban areas with numerous closely spaced obstructions.
- Category C: City centers with large and tall buildings.
These categories help in determining the appropriate wind speed adjustments for a given location.
Building Geometry
The shape, size, and orientation of a building significantly influence wind load calculations. Factors such as building height, width, and the presence of features like canopies or parapets are considered to assess wind pressure accurately.
Wind Speed
Basic wind speed is determined based on historical meteorological data for a specific location. Adjustments are then made considering altitude, direction, season, and probability to derive the effective wind speed for design purposes.
Topography
The presence of hills, valleys, cliffs, and other topographical features can amplify or reduce wind speeds. BS 6399 Part 2 includes provisions to account for these effects in wind load calculations.
Importance of BS 6399 Part 2 in Structural Design
Adhering to BS 6399 Part 2 ensures that buildings are designed to withstand wind loads appropriate to their location and usage. This compliance is crucial for:
- Safety: Protecting occupants and the public from structural failures due to wind.
- Durability: Ensuring the longevity of the building by preventing wind-induced damage.
- Regulatory Compliance: Meeting legal requirements and building codes within the UK.
Practical Application: Calculating Wind Loads
To illustrate the application of BS 6399 Part 2, consider a building with the following parameters:
- Location: Urban area (Terrain Category B)
- Building Height: 20 meters
- Basic Wind Speed: 25 m/s
Using the standard method, the steps would include:
- Determine Dynamic Pressure: Calculate the dynamic pressure (qs) using the basic wind speed and terrain category.
- Apply Pressure Coefficients: Use external pressure coefficients (Cpe) for the building’s walls and roof based on its geometry.
- Calculate Wind Loads: Multiply the dynamic pressure by the pressure coefficients to obtain the wind loads on different parts of the building.
This process ensures that all relevant factors are considered, leading to a safe and efficient structural design.
Tables for Reference
Here are some key factors and their typical values used in wind load calculations:
Table 1: Terrain Categories and Descriptions
Terrain Category | Description |
---|---|
A | Open level country with few obstructions |
B | Urban and suburban areas with numerous obstructions |
C | City centers with large and tall buildings |
Table 2: External Pressure Coefficients (Cpe) for Vertical Walls
Wall Zone | Cpe Value |
---|---|
A | -0.8 |
B | -0.5 |
C | -0 |
Table 3: Dynamic Pressure (qs) Calculation Formula
Parameter | Formula | Units |
---|---|---|
Dynamic Pressure (qs) | qs=0.613×V2qs = 0.613 \times V^2qs=0.613×V2 | kN/m² |
V (Basic Wind Speed) | Site-specific values | m/s |
Related Questions
Why is wind load analysis important in structural design?
Wind load analysis ensures that structures can withstand wind pressures without experiencing structural failures. It minimizes risks to occupants, preserves building integrity, and avoids costly damages.
How does BS 6399 Part 2 compare to Eurocode standards?
BS 6399 Part 2 is a UK-specific standard, while Eurocode 1 offers a broader European framework. Eurocode is more flexible and complex, with provisions applicable across multiple European countries. For UK-specific projects, BS 6399 may be preferred due to its simpler application for local wind conditions.
Can BS 6399 Part 2 be applied outside the UK?
No, BS 6399 Part 2 is designed specifically for the UK’s climate and wind conditions. For projects outside the UK, local standards such as ASCE 7 (USA) or Eurocode 1 should be used.
Are there any limitations of BS 6399 Part 2?
While effective, BS 6399 Part 2 may not address modern wind design challenges as comprehensively as newer standards like Eurocode. Its simpler methods may result in less precise calculations for highly complex structures.
Advanced Considerations in BS 6399 Part 2 Applications
Wind Load on Complex Structures
Complex structures, such as bridges, stadiums, or high-rise towers, require advanced wind load assessments beyond standard BS 6399 Part 2 calculations. Computational Fluid Dynamics (CFD) simulations and wind tunnel testing are often employed for these structures to evaluate:
- Vortex shedding effects
- Dynamic wind-induced oscillations
- Localized pressure differences
These methods supplement BS 6399 Part 2 to achieve more accurate results for intricate designs.
Incorporating Wind Directionality
BS 6399 Part 2 emphasizes the directionality of wind forces, especially for buildings with irregular geometries. By using the directional method, engineers can:
- Account for wind pressures from prevailing wind directions.
- Apply varying external pressure coefficients to different building zones.
- Optimize building orientation to reduce wind impact.
This approach is crucial for regions with highly directional wind patterns.
Combining Wind Loads with Other Loads
Buildings are designed to handle combined loading scenarios, where wind loads interact with:
- Dead loads (weight of structural elements).
- Live loads (temporary or movable loads like furniture and occupants).
- Seismic loads (if applicable).
Practical Example: Wind Load Calculation for a Warehouse
Building Specifications
- Location: Open country (Terrain Category A)
- Dimensions: 40m length, 20m width, 10m height
- Basic Wind Speed: 28 m/s
Step-by-Step Calculation

Tables and Data for Reference
Table 4: Pressure Coefficients (Cpe) for Roof Zones
Roof Zone | Angle (°) | Cpe Range |
---|---|---|
Windward Slope | 0–30 | -1.2 to -0.6 |
Leeward Slope | 30–60 | -0.8 to -0.4 |
Table 5: Load Combination Factors
Load Type | Factor |
---|---|
Dead Load (G) | 1.35 |
Live Load (Q) | 1.5 |
Wind Load (W) | 1.5 |
Related Questions and Answers
How does terrain affect wind load calculations?
Terrain directly impacts wind speed profiles. Open terrains allow for higher wind speeds and increasing loads, while urban areas experience reduced wind speeds due to obstructions.
What tools can assist in wind load analysis?
Modern tools like ETABS, STAAD.Pro and CFD software provide advanced wind load simulations and analyses, complementing BS 6399 Part 2.
When should wind tunnel testing be conducted?
Wind tunnel testing is ideal for large-scale or unconventional designs, such as stadiums, skyscrapers, and bridges, where standard calculations may not capture complex wind interactions.
FAQs on BS 6399 Part 2: A Guide for Wind Loads
What is the difference between BS 6399 Part 2 and Eurocode 1 for wind loads?
BS 6399 Part 2 is tailored for UK-specific conditions, focusing on simplified calculations for most building types.
Eurocode 1, on the other hand, provides a more detailed and adaptable framework applicable across Europe, with broader considerations for varying climatic zones.
Why is wind load safety important in construction?
Wind load safety ensures buildings can:
Resist extreme wind events like storms or hurricanes.
Protect occupants and contents from damage or collapse.
Comply with local building codes and standards to avoid legal issues.
Failing to design for appropriate wind loads can lead to catastrophic failures, as observed in poorly engineered structures during extreme weather events.
How does BS 6399 Part 2 address wind-borne debris?
The standard provides indirect guidance by emphasizing robust designs that minimize damage from wind-borne debris. However, unlike newer codes like ASCE 7-16 in the US, it does not explicitly cover debris impact.