Steel Buildings in Europe

Title Appendix A Worked Example: Wind action on a multi-storey building 7 of 18 3 - 28 3.2. Structural factor 3.2.1. General The structural factor c s c d is calculated from the following equation, for wind on the long side and for wind on the gable: 1 7 ( ) 1 2 ( ) . v s 2 2 p v s s d I z k I z B R c c     The calculation is performed according to the procedure given in Section 8.2 of this guide. EN 1991-1-4 § 6.3.1 3.2.2. Wind on the long side Dimensions: b = 120 m and h = 35 m 1 The terrain category is III. Then: z 0 = 0,30 m and z min = 5 m EN 1991-1-4 Table 4.1 2 Reference height: z s = 0,6 h = 0,6 × 35 = 21 m (> z min = 5 m) EN 1991-1-4 Figure 6.1 3 Orography factor Since the slope of the upwind terrain is less than 3°, c 0 (z s ) = 1,0 EN 1991-1-4 § 4.3.3 4 Roughness factor Since z min ≤ z s ≤ z max (= 200 m) c r ( z s ) = 0,19 ( z 0 / z 0,II ) 0,07 l n ( z s / z 0 ) = 0,19 × (0,3 / 0,05) 0,07 × ln(21/0,3) = 0,915 EN 1991-1-4 § 4.3.2 5 Turbulence factor (recommended value): k l = 1,0 EN 1991-1-4 § 4.4(1) 6 Turbulence intensity Since z min ≤ z s ≤ z max (= 200 m) I v ( z s ) = k l / [ c 0 ( z s ) ln( z s / z 0 ) ] = 1,0 / [1,0 × ln(21 / 0,3)] = 0,235 EN 1991-1-4 § 4.4(1) 7 Turbulent length scale Since z s > z min : L ( z s ) = L t ( z s / z t )  L t = 300 m z t = 200 m  = 0,67 + 0,05 ln( z 0 ) = 0,67 + 0,05 ln(0,30) = 0,61 Then: L ( z s ) = 300 × (21/200) 0,61 = 75,9 m EN 1991-1-4 § B.1(1)