Steel Buildings in Europe

Part 3: Actions 3 - 14 b d h W W indicates the wind direction Figure 8.1 General dimensions of a building The following procedure is proposed: 1. The roughness length z 0 and the minimum height z min These values are obtained from EN 1991-1-4 Table 4.1, depending on the terrain category. 2. The reference height z s z s = 0,6 h ( h is the height of the multi-storey building) But z s should not be taken lower than z min . 3. The orography factor c o ( z s ) According to EN 1991-1-4 § 4.3.3, the effects of orography may be neglected when the average slope of the upwind terrain is less than 3°. Then: c o ( z s ) = 1,0 Otherwise, this factor can be determined either from EN 1991-1-4 §A.3, or from the relevant National Annex. 4. The roughness factor c r ( z s ) c r ( z s ) has to be calculated for the reference height according to EN 1991-1-4 § 4.3.2: If z min ≤ z s ≤ z max c r ( z s ) = 0,19 ( z 0 / z 0,II ) 0,07 l n ( z s / z 0 ) Else, if z s < z min c r ( z s ) = c r ( z min ) where: z 0,II = 0,05 m and z max = 200 m 5. The turbulence factor k l It may be defined by the National Annex. The recommended value is: k l = 1,0