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Wind load

The calculations are performed in accordance with the standard EN 1991-1-4. These procedures are included:

Peak velocity pressure

The calculation of the peak velocity pressure is performed in accordance with chapter 4 of EN 1991-1-4.

The basic wind velocity vb is calculated using formula (4.1):

where is:

vb

  • The basic wind velocity defined at 10m above ground of the terrain category II

cdir

  • The directional factor

Cseason

  • The season factor

vb,0

  • The fundamental value of the basic wind velocity (entered manually or selected from the map of wind regions)

The mean wind velocity vm(z) at the height z above the terrain is calculated using following formula:

where is:

cr(z)

  • The roughness factor

co(z)

  • The orography factor calculated in accordance with annex A.3 of EN 1991-1-4

vb

  • The basic wind velocity defined at 10m above ground of the terrain category II

For the interval

the roughness factor cr(z) is calculated using formula

For

the following formula is used:

where is:

z0

  • The roughness length according to the table 4.1 of EN 1991-1-4

zmin

  • The minimum height according to the table 4.1 of EN 1991-1-4

zmax

  • The maximum height 200m

kr

  • The terrain factor

The terrain factor kr is calculated using formula:

z0,II

  • The roughness length for the terrain category II

The turbulence intensity Iv(z) shall be calculated for the interval

using formula

For

the following formula is used:

where is:

kI

  • The turbulence factor, the value is 1.0

c0

  • The orography factor

z0

  • The roughness length according to the table 4.1 of EN 1991-1-4

The peak velocity pressure qp(z) is calculated using formula (4.8):

where is:

ρ

  • The air density

Wind pressure on surfaces

The wind pressure we acting on the external surfaces is calculated using following formula:

where is:

qp(ze)

  • The peak velocity pressure

ze

  • The reference height

cpe

  • The pressure coefficient

The pressure coefficient cpe depends on the loading are A. The values cpe,1 for members with loaded area of 1m2 or less and cpe,10 for members with loaded area of 10m2 or larger are defined in the standard. The linear interpolation is used for members with loaded area between 1m2 and 10m2:

Pressure coefficients for roofs

The pressure coefficients for roofs are selected in accordance with chapters 7.2.3 (flat roofs), 7.2.4 (mono-pitched roofs), 7.2.5 (duo-pitched roofs) and 7.2.6 (hip roofs) of EN 1991-1-4. The most unfavourable value is used for the roofs with undeterminable topology (for example the rectangular building with one hip and one gable).

Pressure coefficients for roofs

The pressure coefficients for walls are selected in accordance with chapter 7.2.2 of EN 1991-1-4.

Pressure coefficients for vaulted roofs and domes

Pressure coefficients for vaulted roofs and domes are selected in accordance with chapter 7.2.8 of EN 1991-1-4.

Pressure and force coefficients for vertical cylinders

Pressure coefficients for cylinders are selected in accordance with chapter 7.9.1 of EN 1991-1-4. Force coefficients for cylinders are selected in accordance with chapter 7.9.2 and 7.9.3 of EN 1991-1-4.

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