MasterSeries Blog

Eurocode wind loading on duo-pitched roofs can be a nightmare of Cpe combinations. In this post, we break down how MasterSeries 2024 makes managing these wind pressures easier with new built-in Cpe Sign Patterns.

When designing duo-pitched roofs, wind loading is rarely straightforward. According to the Eurocode, specifically BS EN 1991-1-4, and as highlighted in the MasterSeries 2024 updates, the pressure on windward-facing sloping roof panels, especially at 0° wind direction and on multispan duopitch roofs, can rapidly change between positive and negative values depending on the roof angle. This is particularly true when the roof pitch falls between -5 ° and +45°.The Eurocode suggests considering four cases where the largest/smallest values on the windward face are combined with the smallest values on the leeward face.

What the Eurocode Says

BS EN 1991-1-4:2005+A1:2010 Table 7.4a - Recommended values of external pressure coefficients for duopitch roofs, states:

NOTE 1 At θ = 0° the pressure changes rapidly between positive and negative values on the windward face around a pitch angle of α = -5° to +45°, so both positive and negative values are given. For those roofs, four cases should be considered where the largest or smallest values of all areas F, G and H are combined with the largest or smallest values in areas I and J. No mixing of  positive and negative values is allowed on the same face.

Historically, in MasterSeries (prior to version 2024), users had to manually manage these Cpe signs by creating separate wind directions for each variation, with the wind sign was controlled by a '+/-' input on the wind panel tied to the wind direction. It worked, but it was time-consuming and you could also have run out of wind directions to cover all the patterns you needed to consider.

What’s New in MasterSeries 2024

MasterSeries 2024 introduces a more innovative approach with new Cpe Sign Patterns within the Wind Panel setup to account for these different combinations. You now have a choice of four different Cpe sign patterns for your roof panels, related to the windward and leeward sides, depending on the wind angle.

These patterns allow you to:

• Apply all negative or all positive pressure coefficients
• Alternate positive/negative based on windward/leeward faces
• Automatically generate correct wind load combinations

How to Use Cpe Sign Patterns in MasterSeries

Here's a step-by-step guide on how you can manage Roof Cpe Wind Sign Patterns in MasterSeries:

1. Open your structure in MasterFrame.
2. Navigate to the Wind Directions and Settings. This is found under the Loads menu > Wind Panel Loading
   
3. Define your Wind Directions. Ensure you have activated the "Use MasterKey Wind Loading" option. Specify the angles you want to consider (e.g., 0, 90, 180, 270 degrees). You can set internal pressure and suction coefficients if needed.
   
   
4. Define your Wind Panels. Under the Loads menu > Wind Panel Loading > Wind Panels - Wall and Roof.
5. Select the roof panels you want to apply the Cpe Sign Patterns to.
6. Access the Cpe Sign tab within the Wind Panel setup. This is a new feature in MasterSeries 2024.
7. Choose the appropriate Cpe Sign Pattern for your duopitched roof. You will likely have options like:
   • All negative Cpe values.
   • All positive Cpe values.
   • Alternating negative and positive Cpe values based on windward/leeward sides for different wind angles.
   • Another alternating pattern (refer to MasterSeries documentation for the specific definitions of the four patterns). You'll need to select the pattern that aligns with the Eurocode requirements for your specific roof geometry and wind directions.
     
8. Generate your Wind Loading Cases. Use the automatic load case generation tools, which will now consider the selected Cpe sign patterns when creating load combinations involving wind. This will automatically create the necessary load cases to account for the positive and negative pressure variations on your duopitched roof as per the Eurocode.
   
9. Review the applied wind loads. You can graphically display the wind pressures ('Q') or the external pressure coefficients ('Cpe') on your model to verify the application of the chosen Cpe sign patterns for different wind directions.
   

Key Considerations:

• Design Code: Ensure your MasterSeries project is set to the correct Eurocode standard and UK National Annex.
• Roof Geometry: The specific Cpe values and the need to consider both positive and negative signs heavily depend on the roof pitch angle.
• Wind Direction: The Cpe sign pattern application is linked to the defined wind directions, so ensure these are set up correctly to represent the critical wind scenarios.
• MasterSeries Documentation: Refer to the specific MasterSeries 2024 documentation and technical notes for detailed explanations of the four Cpe sign patterns and their application according to the Eurocode. The MasterSeries website and blog posts are valuable resources for the latest updates.

By utilising the new Cpe sign patterns in MasterSeries 2024, you can more efficiently and accurately account for the Eurocode requirements regarding positive and negative external pressure coefficients on duo-pitched roofs without manually creating numerous wind directions.

Watch the MasterSeries 2024 Release Webinar

See the new Cpe Sign Patterns in action along with other key improvements introduced in MasterSeries 2024.