Steel Buildings in Europe

Part 3: Actions 3 - 27 W d b h Min(2 b ; 4 h ) Figure 8.2 Friction forces The friction forces are obtained from:   fr fr p e fr F c q z A  where: c fr is the friction coefficient. It can be taken equal to: 0,01 for smooth surface (steel, smooth concrete, etc.) 0,02 for rough surface (rough concrete, tar-boards, etc.) 0,03 for very rough surface (ripples, ribs, folds, etc.). q p ( z e ) is the peak velocity pressure at the reference height z e . A fr is the reference area. Friction forces are applied on the part of the external surfaces parallel to the wind A fr , located beyond a distance from the upwind eaves or corners, equal to the smallest value of 2 b or 4 h , b and h as defined in Figure 8.2. 8.2.3 External pressure coefficients on vertical walls The values of the external pressure coefficients, given in tables in the Eurocode are attached to defined zones. The coefficients depend on the size of the loaded area A that produces the wind action in the zone under consideratiion. In the tables, the external pressure coefficients are given for loaded areas of 1 m 2 ( c pe,1 ) and 10 m 2 ( c pe,10 ). In this guide, only the values c pe,10 are taken into account, because they are used for the design of the overall load bearing structure of buildings. Zones for vertical walls are defined in EN 1991-1-4 Figure 7.5 and the external pressure coefficients c pe,10 are given in EN 1991-1-4 Table 7.1. For intermediate values of h / d , linear interpolation may apply. The values of the external pressure coefficients may be given in the National Annex.