# When generating wind loads, some external pressure coefficients have a value of 0. What is the reason for this?

For duopitch roofs with a roof inclination of > 5°, the roof areas F, G, H, I and J have to be separately classified according to the windward and leeward side. For the wind direction of 0° (wind in longitudinal direction), positive as well as negative aerodynamic coefficients have to be taken into account for roof inclinations of up to 45°.
For these cases, this results in a total of 4 possible wind combinations, depending on the building side (see Figure 1).
For the direction of flow of 90 ° (wind on the gable side), however, there are no positive external pressure coefficients. Thus, for a building with a roof inclination of 45 °, 10 possible wind load cases would be obtained (0 ° = 4 · 2; 90 ° = 1 · 2).

LC w+:

Only positive (pressure) aerodynamic coefficients per roof area are used.

LC w-:

Only negative (suction) aerodynamic coefficients per roof area are used.

LC w-/+:

Negative (suction) aerodynamic coefficients for the windward side and positive (pressure) coefficients for the leeward side of the roof are used.

LC w+/-:

Positive (pressure) aerodynamic coefficients for the windward side and negative (suction) coefficients for the leeward side of the roof are used.

If there are, for example, only negative coefficients for a load position, then only negative loads are applied to the roof surface. Consequently, there is no pressure -> therefore these values are set to 0. A load case, which thus contains only values with the size 0, could also be deselected during the generation.

For example, this is always possible, as already described, for the LC w + with a wind direction of 90° (gable-sided wind) and a roof inclination of > 15°.