SURFACE WIND LOAD
DYNAMIC CLASSIFICATION
;
Actual height of building above ground; H = 6.8 m
Building type factor (Table 1);
Kb = 1.0
BS6399:Pt 2:Cl 1.6.1
Dynamic augmentation factor (simple equation)
Cr = [Kb (H/(0.1 m))0.75] / (800 log(H/(0.1 m))) = 0.02
Standard/Hybrid Method applicable
BS6399:Pt 2:Cl 1.6.2 and Annex C
Maximum height of building above ground level; Hr = 8.0 m
Town terrain
;
Average height of roof tops of surrounding buildings; Ho = 3.0 m
Upwind spacing of surrounding buildings; Xo = 20.0 m;
Displacement height;
Hd = if(Xo (2Ho), 0.8Ho , if (Xo < (6Ho), 1.2Ho-0.2Xo, 0 m)) = 0.000 m
Effective height of building;
He = max(Hr - Hd , 0.4Hr) = 8.000 m
BS6399:Pt 2:Cl 1.7.3.3
Basic wind speed
;
Vb = 20.0 m/s
BS6399:Pt 2:Cl 2.2.1
Altitude factor - topography not considered
;
Site altitude; S = 76.0 m
Sa = 1 + (0.001 m-1) S = 1.08
BS6399:Pt 2:Cl 2.2.2.2.2
Direction factor; Sd = 1.0;
Seasonal factor; Ss = 1.00 ;
Probability factor; Sp = 1.0
Site wind speed
Vs = Vb Sa Sd Ss Sp = 21.52 m/s
BS6399:Pt 2:Cl 2.2
Determine terrain and building factor
Effective height; He =8.0 m
;
Upwind distance from sea to site; dsea = 150.0 km
Upwind distance from edge of town to site; dtown = 20.0 km
Table = "BS 6399 : Part 2 : 1995 ..... Table 22"
From BS 6399 : Part 2 : 1997 ..... Table 22
For; He = 8.0 m ; dsea = 150.0 km
Fetch factor; Sc = 0.953
Turbulence factor; St = 0.184
Table = "BS 6399 : Part 2 : 1995 ..... Table 23"
From BS 6399 : Part 2 : 1997 ..... Table 23
For; He = 8.0 m ; dtown = 20.0 km
Fetch adjustment factor; Tc = 0.733
Turbulence adjustment factor; Tt = 1.564
Terrain and building factor - town terrain
Sb = Sc Tc ( 1+ 3.44 St Tt ) =1.39
BS6399:Pt 2 Cl 2.2.3.3
Effective wind speed
Ve = Vs Sb = 29.89 m/s
BS6399:Pt 2 Cl 2.2.3.1
Dynamic pressure
qs = (0.613 kg/m3) Ve2 = 0.55 kN/m2
BS6399:Pt 2 Cl 2.1.2.1
External surface pressures
;
Dynamic wind pressure; qs = 0.55 kN/m2
External pressure coefficient; Cpe = 0.40
Size effect factor
;
Diagonal dimension of building for external size effect factor; ae = 5.0 m
Curve to be used for size effect factor (figure 4); Curve = "B"
set up curve equation
a = if(Curve=="A",1.1006, if(Curve=="B",1.1228,1.1478)) = 1.123
b = if(Curve=="A",-0.1422, if(Curve=="B",-0.1736,-0.2089)) = -0.174
Cae = min(1.0, a + b log(ae/(1 m))) = 1.00
BS6399:Pt 2 Cl 2.1.3.4
External surface pressure
pe = qs Cpe Cae = 0.22 kN/m2
BS6399:Pt 2 Cl 2.1.3.1
Internal surface pressures
;
Internal pressure coefficient; Cpi = -0.3
Size effect factor
;
Internal volume for internal size effect factor; Voli = 0.1 m3
Internal diagonal dimension; ai = 10 ( Voli )1/3 = 5.0 m
Curve to be used for size effect factor (figure 4); Curve = "B"
set up curve equation
a = if(Curve=="A",1.1006, if(Curve=="B",1.1228,1.1478)) = 1.123
b = if(Curve=="A",-0.1422, if(Curve=="B",-0.1736,-0.2089)) = -0.174
Cai = min(1.0, a + b log(ai/(1m))) = 1.00
BS6399
:Pt 2 Cl
2.1.3.4
Internal surface pressure
;
pi = qs Cpi Cai = -0.16 kN/m2
BS6399
:Pt 2 Cl
2.1.3.2
Net surface pressure
p = pe - pi = 0.38 kN/m2
BS6399
:Pt 2 Cl
2.1.3.3
