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Eurocode 1 Wind Peak Velocity Pressure - UK National Annex

Description:
Calculation of peak velocity pressure qp depending on the basic wind velocity from UK National Annex wind map, and the site distance from shoreline and town boundary. The wind action on the structure (forces and pressures) can be derived from the peak velocity pressure. Calculation according to the UK National Annex.
According to:
EN 1991-1-4:2005+A1:2010 Section 4 & UK National Annex to BS EN 1991-1-4:2005+A1:2010
All Calculations
Input
Calculation of the wind action using the exposure factor ce(z) is permitted except for the cases where orography is significant (c0 > 1.0) and the total height above ground is z > 50 m. The calculation of the wind action using the roughness factor cr(z) is general and may be applied for all cases.
m/s
The appropriate value for the examined location is determined on the map given in Figure NA.1 of UK National Annex to EN1991-1-4 (reproduced below).
m
The altitude correction factor calt is determined from the altitude A. Larger value of altitude A give more unfavorable results. Where there is significant orography (c0(z) > 1.0), as defined in Figure NA.2 of UK National Annex, altitude A should be taken as the altitude of the upwind base of the orographic feature along the wind direction considered.
According to Table NA.1 of UK National Annex to EN1991-1-4. The directions are defined by angles measured clockwise from North (0°). The most unfavorable wind direction for the UK is south-westerly to westerly (250°) where cdir = 1.0. Where the wind loading on a building is assessed only for orthogonal load cases, the maximum value of the directional factor cdir for the directions that lie within ±45° either side of the normal to the face of the building is to be used. Conservatively cdir may be taken as 1.0 for all directions.
km
All inland lakes extending more than 1 km in the direction of wind and closer than 1 km upwind of the site should also be treated as Sea. The proximity to shoreline is not relevant for sites where dShore > 100 km. 'Sea Terrain' is considered for structures where dShore ≤ 0.1 km
km
Sites for which the upwind distance inside town terrain is specified less than 0.1 km are treated as 'Country Terrain', otherwise 'Town Terrain' is considered.
m
The appropriate reference height depending on the type of the structure is given in EN1991-1-4 Section 7. For buildings it is generally equal to the height of the building, measured to the top, which may be a ridge or a parapet.
m
For buildings not in town hdis = 0. The displacement height considers the favorable effect of lifting of the wind profile when upwind town terrain exists The appropriate value is specified in EN1991-1-4 §A.5. Conservatively hdis = 0 may be considered for all cases.

Orography factor larger than 1.0 may be applicable over isolated hills and escarpments. See EN1991-1-4 §4.3.3 and §A.3 for more details.
According to Table NA.2 of UK National Annex to EN1991-1-4. In general cseason = 1.0 is applicable for permanent structures that exist for the whole year. For structures that are loaded by the wind only for specific periods of the year a smaller value cseason ≤ 1.0 may be applicable.