Cpe Sign Tab
Roof Cpe Signs for Duopitched Roofs (MasterSeries 2024+)
This section details the use of the dedicated Cpe Sign Patterns feature, introduced in MasterSeries 2024, designed to manage the numerous load cases required for highly sensitive roof geometries, particularly when designing to Eurocode wind provisions.
Background: The Necessity for Cpe Sign Patterns
The determination of wind loading coefficients on sloping roof surfaces is complex, specifically for duo-pitched roofs designed to the Eurocode (BS EN 1991-1-4:2005+A1:2010).
For a wind direction normal to the eaves, the external pressure coefficients (Cpe) on the windward face (Zones F, G, H) change rapidly between positive (pressure) and negative (suction) values when the roof pitch angle falls between 5 and 45 degrees.
The Eurocode mandates that, for these critical pitch angles, four distinct load cases must be considered, combining the largest or smallest calculated values across the windward areas (F, G, H) with the largest or smallest values on the leeward areas (I, J). Crucially, the code requires that no mixing of positive and negative values is permitted on the same face.
Historically (prior to MasterSeries 2024), achieving these four combinations required manually managing the Cpe signs by creating multiple, separate wind directions, which was time-consuming and prone to error. The new Cpe Sign tab simplifies this by assigning up to four patterns per panel, which are then referenced by the automated Load Case Generator.
Accessing the Cpe Sign Tab
The Cpe Sign settings are accessed within the Wind Panel setup (Loads menu > Wind Panel Loading > Wind Panels - Wall and Roof) after defining your wind directions.
Tooltip for Selection Option:
"Where a choice of C_pe sign is given in roofs and canopies, patterning of signs may be considered. The wind sign for the current panel can be used in up to four patterns. The pattern number is then set in the loading case combination."
The Four Available Cpe Sign Patterns
MasterSeries 2024 introduces four distinct Cpe sign patterns (Pattern 1, Pattern 2, Pattern 3, and Pattern 4) that the program calculates automatically where a choice of sign is applicable (e.g., on sloping roof faces or canopies):
| Pattern | Description | Application | Notes |
| Pattern 1 | -/ \- All negative (fixed) | Forces the external pressure coefficient to be the most negative (suction) value applicable to that zone. | This pattern is fixed (always negative). |
| Pattern 2 | +/ \+ All positive (fixed) | Forces the external pressure coefficient to be the most positive (pressure) value applicable to that zone. | This pattern is fixed (always positive). |
| Pattern 3 | -/ \+ Positive or negative | Applies a predetermined alternation pattern (e.g., negative on the current panel face) to accommodate asymmetric load requirements. | The definition for Pattern 3 (negative/positive) automatically sets Pattern 4 as the reciprocal sign pattern. |
| Pattern 4 | +/ \- Negative or positive | Applies the reciprocal alternation pattern to Pattern 3 to ensure all required asymmetric load cases are covered. | Pattern 3 and 4 cannot both be simultaneously positive or negative; they are automatically set to be opposite signs. |
Integration with Load Case Generation
The main advantage of assigning these patterns to your roof panels is how they interact with the automatic Load Case Generator. See also 🎥 📺MasterFrame Automatic Load Case Generator
- Panel Assignment: You assign the relevant roof panels to support these four patterns via the new dedicated tab.
- Combination Creation: When you use the automatic Load Case Generator, you instruct it to include the wind sign patterns (1, 2, 3, and 4).
- Resulting Load Cases: The system uses these selected Cpe Sign Patterns when generating the loading case combinations. For wind directions where a sign choice exists (like θ=0∘ on duo-pitched roofs), the program automatically generates the necessary permutations of ultimate and service load cases corresponding to all four required sign patterns, rather than forcing the user to create separate wind directions for each variation.
- Review: After generation, you can review the applied loads graphically, displaying the pressures ('Q') or the external pressure coefficients ('C_pe') to verify the application of the chosen sign pattern for each load case.
This updated methodology ensures that the comprehensive load requirements for duopitch roofs under Eurocode are efficiently and accurately incorporated into the analysis.