(1) For the application of the Dynamic Procedure, the provisions of Article 4.1.7.3. shall be followed, except that the exposure factor, Ce, shall be as prescribed in Sentences (2) and (3), and the gust effect factor, Cg, shall be as prescribed in Sentence (4), when determining the wind loads on the main structural system.
(2) For buildings in open terrain as described in Clause 4.1.7.3. (5) (a), the value of Ce for the design of the main structural system shall be calculated as follows:
Ce = (h/10)0.28, but 1.0 ≤ Ce ≤ 2.5
(3) For buildings in rough terrain as described in Clause 4.1.7.3. (5) (b), the value of Ce for the design of the main structural system shall be calculated as follows:
Ce = 0.5(h/12.7)0.5, but 0.5 ≤ Ce ≤ 2.5
(4) For the design of the main structural system, Cg shall be calculated as follows:
Cg = 1 + gp(δ/μ)
where,
gp =peak factor calculated as, √(2 ln(ν·T)) + 0.577 / √(2 ln(ν·T)) and
δ/μ = √((K / C_eH) · (B + sF / β)),
where,
υ =average fluctuation rate calculated as f_nD · √(sF / (sF + βB)),
T =3 600 s,
K =0.08 for open terrain and 0.10 for rough terrain,
CeH =exposure factor evaluated at reference height h = H,
B =background turbulence factor, a function of w/H determined from Figure 4.1.7.8.,
s =size reduction factor calculated as π/3 · (1 / (1 + 8 f_n H / (3 V_H))) · (1 / (1 + 10 f_n w / V_H)),
F =gust energy ratio calculated as x_0^2 / (1 + x_0^2)^{4/3}, where x0 = (1 220 fn/VH), and
β =damping ratio, which shall be determined by a rational method or may be taken to be 0.01 for steel structures, 0.02 for concrete structures and 0.015 for composite structures,
where,
fnD =natural frequency of vibration of the building in the along-wind direction, in Hz,
fn =lowest natural frequency of the building, in Hz, as described in Sentences 4.1.7.2. (2) and (3),
H =height of the building,
w =effective width of windward face of the building calculated as Σ h_i w_i / Σ h_i, where wi = width normal to wind direction at height hi, and
VH =mean wind speed at the top of the structure, in m/s, calculated as V̄ · √(C_eH),
where,
=reference wind speed at a height of 10 m, in m/s, calculated as √(2 · I_w · q / ρ),
where,
Iw =importance factor,
q =reference velocity pressure, in Pa, and
ϱ =air density = 1.2929 kg/m3.