The action of the wind is directly proportional to its dynamic pressure qp, which depends on the square of the wind velocity, the roughness and the shape of the ground, as well as the height above the ground on which it is calculated. Wind forces on a surface can be calculated as global (punctual) or as local (distributed) forces. For this, the peak dynamic pressure qp is multiplied by a force coefficient (punctual) or by a net pressure coefficient (canopy roofs or free-standing walls) or by internal and external pressure coefficients (closed or permeable buildings).

Calculation of the peak velocity pressure

• Fundamental value of the basic wind velocity
  v_b,0 (National Annex)
  depending of the place of construction
• Basic wind velocity
  v_b (EN 1991-1-4 § 4.2(1))
  depending of the place and the period of construction
• Reference mean velocity pressure
  q_b (EN 1991-1-4 § 4.5(1))
  depending of the air density ρ and the basic wind velocity
• Terrain factor
  k_r (EN 1991-1-4 § 4.3.2)
  depending of the terrain category
• Roughness factor
  c_r(z) (EN 1991-1-4 § 4.3.2)
  depending of height above ground
• Orography factor
  c_o(z) (EN 1991-1-4 § 4.3.3 +and+ A.3)
  depending of the relief of the terrain
• Turbulence factor
  k_l (EN 1991-1-4 § 4.4)
• Exposure factor
  c_e(z) (EN 1991-1-4 § 4.5(1))
  depending of the orography factor and the turbulence factor
• Peak velocity pressure
  q_p (EN 1991-1-4 § 4.5(1))

You want to calculate the peak velocity pressure on a building ?

Calculation of wind actions

• Peak velocity pressure
  q_p (EN 1991-1-4 § 4.5(1))
  calculated above
• • Structural factor
    c_sc_d (EN 1991-1-4 § 6 and Annexes B, C, D)
    depending of dynamic behavior and of the shape of the structure
  • External pressure coefficient
    c_pe (EN 1991-1-4 § 7)
    depending of the building sizes
  • Internal pressure coefficient
    c_pi (EN 1991-1-4 § 7.2.9)
    depending of the building permeability
  • Resultant wind force
    F_w (EN 1991-1-4 § 5.3)
    applied perpendicularly to the surface
• • Friction coefficient
    c_fr (EN 1991-1-4 § 7.5 Table 7.10)
    depending of the surface roughness
  • Resultant friction force
    F_fr (EN 1991-1-4 § 5.3)
    applied parallel to the surface