High velocities of wind are observed more frequently in some sectors directions; the directional factor allows a reduction when the wind comes from a direction where the probability of occurrence of severe winds is lesser.
« Wind direction » means the direction from which the wind comes. By convention, this direction is identified by the angle it forms with the North, increasing from 0° to 360° clockwise.
For the calculation of wind actions, only a few wind directions are considered; for example the normal directions to the facades in the case of buildings.
In Belgium, you can use the values of cdir defined by the table below.
| Wind direction | 0° ( North ) | 22.5° | 37.75° | 45° | 56.25° | 90° ( East ) | 120° | 150° | 180° ( South ) | 270° ( West ) |
|---|---|---|---|---|---|---|---|---|---|---|
| Directional factor cdir | 1.0 | 1.0 | 0.95 | 0.90 | 0.85 | 0.85 | 0.90 | 0.95 | 1.0 | 1.0 |
In Metropolitan France, you can use the values of cdir defined by the map below, provided that the nominal angular sector including the wind directions associated with the pressure or force coefficients used in the calculations, is entirely contained by the interval.
| Zone | 1 | 2 | 3 |
|---|---|---|---|
| Nominal angular sector included in the interval (North at 0°) | 10° - 150° | 70° - 150° | 50° - 250° |
| Directional factor cdir | 0.7 | 0.7 | 0.85 |
Zoning map of the directional factor of Metropolitan France (2011-2024)
The rotary nature of tropical cyclones which affect certain Overseas Departments does not allow any reduction for the effect of management in these departments.
In Italy, the recommended value is 1.0 (no reduction is allowed).
