Calculation of wind loads on duopitch canopies

Eurocode 1 Wind load on duopitch canopies (net pressure coefficients and overall force coefficient)

Description:

Calculation of wind load action effects on duopitch canopies (i.e. roofs of structures not enclosed with permanent side walls). The net effect of the wind pressure on the upper and lower surface for zones A, B, C, D on the roof surface are calculated from the corresponding net pressure coefficients. The overall effect of the wind action on the structure is also calculated from the corresponding force coefficient.

According to:

EN 1991-1-4:2005+A1:2010 Section 7.3

Applicable for:

Roofs of structures not enclosed with permanent side walls such as petrol stations, dutch barns etc. Duopitch slope between -20° and +30°

Supported National Annexes:

A) Calculation of pressure coefficients: Only countries that adopt CEN recommended values for section 7.3 of EN1991-1-4 are supported. B) Peak velocity pressure: The value of the peak velocity pressure can be specified manually. Otherwise automatic calculation of peak velocity pressure is supported, in addition to countries that adopt the CEN recommended values for NDPs, also for the following National Annexes: Finland, Portugal. The National Annexes of Germany, Norway, Spain, Sweden, Switzerland are NOT supported (enter peak velocity pressure manually).

Hint: Select 'Custom peak velocity pressure' in the terrain category dropdown in order to manually specify the peak velocity pressure.

Terrain category

The terrain categories are illustrated in EN1991-1-4 Annex A. The transition zones between terrain categories are specified in EN1991-1-4 §A.2. For a description of the terrain categories 0, I, II, III, IV see Calculation of peak velocity pressure.

Basic wind velocity

v_b

m/s

The basic wind velocity is given as v_b = v_b,0⋅c_dir⋅c_season where the fundamental value of basic wind velocity v_b,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 c_dir = 1.0 and c_season = 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.

Peak velocity pressure at reference height

q_p(z_e)

kPa

Horizontal dimension of rectangular plan parallel to the wind direction

Horizontal dimension of rectangular plan perpendicular to the wind direction (crosswind dimension)

Height of canopy from ground up to the maximum roof level

Roof pitch angle

The pitch angle value is positive for typical duopitch roofs with roof surfaces sloping downwards towards the exterior of the building. Negative values of the pitch angle correspond to duopitch roofs with roof surfaces sloping downwards towards the interior of the building (central trough instead of ridge).

Degree of blockage under the canopy roof

The ratio of the area of feasible, actual obstructions under the canopy divided by the cross sectional area under the canopy, both areas being normal to the wind direction. A value of φ=0 represents an empty canopy, and φ=1 represents the canopy fully blocked with contents to the down wind eaves only (this is not a closed building). See figure below.

Definiton of blockage factor for canopy roofs (see also EN1991-1-4 Figure 7.15)

Orography factor at reference height z_e

c₀(z_e)

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.

Structural factor

c_sc_d

Structural factor c_sc_d in accordance with EN1991-1-4 Section 6. A value of c_sc_d = 1.0 is generally conservative for small structures not-susceptible to wind turbulence effects such as buildings with height less than 15 m.