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The structural factor takes into account the absence of pressures simultaneity to the surface of the construction and of vibration of the structure caused by the turbulence.

The c_{s}c_{d} calculation is based on the building dimensions, construction location and the terrain's categories.

A minimum approved value of c_{s}c_{d} = 0.85 is indicated in Appendix D.

EN 1991-1-4 §6.3.1 - Detailed procedure for structural factor c_{s}c_{d}

EN 1991-1-4 Annex B - Procedure 1 for determining the structural factor c_{s}c_{d}

In France (NF EN 1991-1-4/NA clause 6.3.1 (1) NOTE 3):

The procedure to use is the procedure 1 described in Annex B. Annex B is normative; Annex C does not apply.

In Belgium (NBN EN 1991-1-4 ANB §6.3.1 (1) NOTE 3):

The procedure 1 of Annex B recommended to calculate c_{s}c_{d} is normative.

In United Kingdom (BS EN 1991-1-4 NA.2.21):

The recommended procedure given in BS EN 1991-1-4:2005 Annex B should be used.

An approched value of the structure's fundamental frequency can be calculated from:

- for a building height up to 28m, equation 4.6 of Eurocode 8 - Earthquakes:

This expression takes into account the nature of the structure (C_{t}) and its free vibration height (H). - for construction height upper than 28m, equation F.1 of Eurocode 1 part 1-4 - Wind:

This expression only takes into account the free vibration height (H) of the structure.

This is the standard deviation of wind turbulence divided by the average wind speed. It gives a mesure of the wind in the form of gusts. The recommended calculation procedure is given in EN1991-1-4 4.4(1) and the national annexes.

This coefficient reflects the lack of pressure correlation on the construction. The recommended calculation procedure is given in EN1991-1-4 B.2(2) and the national annexes:

with:

- h = total height of the building (in m)
- b = perpendicular dimension of the building to the wind (in m)
- L(z
_{s}) = turbulence scale according to EN1991-1-4 B1(1):- Lt = reference scale (300m)
- zt = reference height (200m)

This coefficient reflects the effect of turbulence in resonance with the considered vibration mode of the building. The recommended calculation procedure is given in EN1991-1-4 B.2(5) and the national annexes:

with:

- δ = logarithmic decrement of damping according to EN1991-1-4 Equation F.15:
- δs = logarithmic decrement of structural damping (0.05 for steel building, 0.06 for timber building, 0.10 for reinforced concrete buildings)
- δa = logarithmic decrement of aerodynamic damping for the fundamental mode (can be securely taken to 0)
- δd = logarithmic decrement of damping due to special devices (0 if no special device)
- S
_{L}(z_{s},n_{1,x}) = non-dimensional power spectral density function according to EN1991-1-4 B.1(2): - f
_{L}(z_{s},n_{1,x}) = non-dimensional frequency according to EN1991-1-4 B.1(2): - R
_{h}and R_{b}= aerodynamic admittance functions according to EN1991-1-4 B.2(6).

This factor is the ratio of the maximum value of the fluctuating part of the response to its standard deviation. The recommended calculation procedure is given in EN1991-1-4 B.2(3) and the national annexes:

with:

- ν = up-crossing frequency
- T = averaging time for the mean wind velocity, T=600 seconds.

The recommended calculation procedure is given in EN1991-1-4 6.3.1(1) and the national annexes:

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