Steel Buildings in Europe

Part 3: Actions 3 - 26 8.2.2.1 External forces The external forces are obtained from:   surfaces ref e s d w,e F c c w A where: c s c d is the structural factor (see 7.2.1.1) w e is the wind pressure acting on the external surface: w e = q p ( z e ) c pe q p ( z e ) is the peak velocity pressure at the reference height z e z e is the reference height for the external pressure (generally, the height of the structure). It depends on the aspect ratio h / b , where h is the height of the building and b is the crosswind dimension. Generally, h is lower than b for single-storey buildings. In this case, z e is taken equal to the height of the building and the velocity pressure q p ( z ) is uniform on the whole structure: q p ( z e ) = q p ( h ). c pe is the pressure coefficient for the external pressure. See §8.2.3 for vertical walls and §8.2.4 for roofs. A ref is the reference area. Here it is the area of the surface under consideration for the design of the structure or the structural component. 8.2.2.2 Internal forces The internal forces are obtained from:   surfaces ref i w,i w A F where: w i is the wind pressure acting on the internal surface: w i = q p ( z i ) c pi z i is the reference height for the internal pressure (generally: z i = z e ) q p ( z i ) is the peak velocity pressure at the height z i (generally: q p ( z i ) = q p (z e )) c pi is the pressure coefficient for the internal pressure, see §8.2.5. 8.2.2.3 Friction forces The friction force results from the friction of the wind parallel to the external surface. Friction is allowed for when the total area of all surfaces parallel to the wind is higher than four times the total area of all external surfaces perpendicular to the wind (windward and leeward), which is the case for long structures.