Wind Loading p Background p Standards p Design

Wind Loading

Wind Loading p CP 3: Chapter V: Part 2 p Code of basic data for the design of buildings Chapter V. Loadings Part 2. Wind loads p BS 6399 -2: 1997 p Loadings for buildings Part 2: Code of practice for wind loads

Wind Loading - CP 3 p Wind Speed - 3 second gust p Exposure p Open Country, scattered wind breaks p Small towns, outskirts of cities p City centres p Building Height

Wind Loading - BS 6399 p Wind Speed - hourly mean p Height above sea level p Distance from sea p Exposure p Town p Country p Building height

Wind Loading - BS 6399 p Standard Method p Directional Method

Wind Loading - BS 6399 p Site Wind Speed Vs = V b x S a x S d x S s x S p p Vb – Basic wind speed p Sa – Altitude factor p Sd – Direction factor p Ss – Seasonal factor p Sp – Probability factor

Wind Loading - BS 6399

Wind Loading - BS 6399 p Altitude factor Sa = 1+ 0. 001 x Height above sea level If topography not significant p As a generalisation any building more than half-way up a hill, or an on a ridge or cliff will have increase wind loading and a more detailed calculation of Sa will be required

Wind Loading - BS 6399

Wind Loading - BS 6399 p Sd – Direction factor

Wind Loading - BS 6399 p Ss – Seasonal factor = 1 p Sp – Probability factor = 1 1 in 50 years storm

Example calculation Vs = V b x S a x S d x S s x S p Sa =1. 005 Sd =1 Ss = 1 Sp = 1 Vs = 16. 63 x 1. 01 x 1 x 1 = 16. 80 m/s Page 15

Wind Loading - BS 6399 p Effective wind speed Ve = V s x S b Sb = Terrain & Building Factor p Site in town or country p Distance from the sea

Wind Loading - BS 6399

Example calculation Building size: H = 26. 2 m L = 44. 3 m Ve = Vs x Sb Sb = 1. 97 for distance 30 km from sea and He = 26. 2 m Ve = Vs x Sb = 16. 80 x 1. 932 = 32. 5 m/s Page 18

Wind Loading - BS 6399 p Dynamic Pressure qs = 0. 613 x Ve 2 qs = 0. 613 x (32. 5)2 = 647. 5 N/m 2 = 0. 65 k. N/m 2

Wind Loading - BS 6399 p Pressure to structure p External pressure pe = qs x Cpe x Ca Cpe is the external pressure coefficient Ca is the size effect factor = 1