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Eurocode 1 Wind peak velocity pressure

Description:
Calculation of peak velocity pressure qp depending on the basic wind velocity and the terrain category at the location of the structure. The wind action on the structure (forces and pressures) can be derived from the peak velocity pressure.
According to:
EN 1991-1-4:2005+A1:2010 Section 4
Supported National Annexes:
In addition to countries that adopt the CEN recommended values for NDPs, the following National Annexes are also supported automatically: Finland, Portugal.
All Calculations
Input
m/s
The basic wind velocity is given as vb = vb,0cdircseason where the fundamental value of basic wind velocity vb,0 is defined in EN1991-1-4 §4.2(1)P and its value is provided in the National Annex. Altitude correction may also be specified in the National Annex for EN1991-1-4 §4.2(2)P. The directional and season factors are generally cdir = 1.0 and cseason = 1.0. For particular cases values smaller than 1.0 may be specified in the National Annex for EN1991-1-4 §4.2(2)P.
The terrain categories are illustrated in EN1991-1-4 Annex A (reproduced in the following figure). The transition zones between terrain categories are specified in EN1991-1-4 §A.2.
Wind terrain category 0 Wind terrain category I Wind terrain category II Wind terrain category III Wind terrain category IV
Illustration of Terrain categories reproduced from EN1991-1-4 Annex A
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 above ground, measured to the top, which may be a ridge or a parapet.

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.