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Meteodyn EC1: Automatic calculations for wind design according to Eurocode 1.
The design of structures and buildings must take into account extreme wind conditions.
The wind design of structures is governed by Eurocode 1 (1): ‘Actions on structures’, specifically the section on ‘Wind actions’.
It is supplemented by its National Annex (2), which specifies certain parameters specific to France.
The local wind speed depends on the location, height above ground level, terrain shape, and ground obstructions in its path. While the first two elements are easy to consider, roughness (type of obstacle) and orography (terrain shape) are much more challenging.
The roughness effect is easily modeled, but depends on a parameter z0 (roughness length) that is difficult to define accurately: the user must compare aerial photographs of the site to a tabulated roughness scale based on five classes. It’s a delicate step, open to interpretation.
As for the orography, the formulas proposed by the Eurocode are quite difficult to implement, especially since the shape of the terrain is rarely known with precision! One would need to obtain elevation maps and calculate local slopes around the site to estimate the orography factor co.
Meteodyn offers an online application at https://ec1.meteodyn.com that answers all these questions.
All you have to do is enter the location and height of the building, and the application takes care of the rest!
Regional parameters Vb and co are extracted from the maps in the National Annex (2) based on the geographic coordinates of the location. The application uses the CORINE Land Cover map provided by the European Copernicus program.
By assigning a specific roughness to each type of land use (compatible with the Eurocode scale) and using the statistical calculation of aerodynamic drag, the roughness z0 is deduced for each wind sector.
The orography is from publicly available NASA data, SRTM at 3 second arc resolution. This altimetric map allows the computation throughout the territory of the relative altitude AC.
This parameter is then used in a formula given in the French National Annex to directly compute the orographic coefficient:
If the orography coefficient co is greater than 1.15, the application considers the site too mountainous to use the method.
You now have a fast and user-friendly tool that takes into account all the parameters that influence the reference wind speed for sizing your structures.
Simply enter the location of your project by its address or GPS coordinates and the desired height. The application automatically determines the roughness and orography coefficients and then calculates the reference dynamic pressure to be used for sizing your structure.
Your final and intermediate results are simply displayed on the map background, with the most penalizing direction highlighted.
Documents used to design the application
(1) Eurocode
- NF EN 1991-1-4 (Nov. 2005)
- NF EN 1991-1-4/A1 (Oct. 2010)
(2) National Annex
- NF EN 1991-1-4/NA (March 2008)
- NF EN 1991-1-4/NA/A1 (July 2011)
- NF EN 1991-1-4/NA/A2 (Sept. 2012)
More advanced approaches are needed to refine the calculation and attempt to reduce the orography coefficient.
Meteodyn offers a Computational Fluid Dynamics (CFD) reference wind speed assessment service dedicated to wind computation in complex terrain.
It responds perfectly to the needs, taking into account the roughness and orography of the terrain.
It is compatible with the Eurocode and supports the restrictions of clause 1.5(2) of the National Annex.
