4.1.7.8. Dynamic Procedure

(1)

For the application of the Dynamic Procedure, the provisions of Article 4.1.7.3. shall be followed, except that the exposure factor, C_e, shall be as prescribed in Sentences (2) and (3), and the gust effect factor, C_g, shall be as prescribed in Sentence (4), when determining the wind loads on the main structural system.

(2)

For buildings in open terrain, as defined in Clause 4.1.7.3.(5)(a), the value of C_e for the design of the main structural system shall be calculated as follows:

(See Note A-4.1.7.8.(2) and (3))

(3)

For buildings in rough terrain, as defined in Clause 4.1.7.3.(5)(b), the value of C_e for the design of the main structural system shall be calculated as follows:

(See Note A-4.1.7.8.(2) and (3))

(4)

For the design of the main structural system, C_g shall be calculated as follows:

where g_p = peak factor calculated as

, and

σ /μ =

,

where

= average fluctuation rate calculated as

, T = 3 600 s, K = 0.08 for open terrain and 0.10 for rough terrain, C_eH = 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,

F = gust energy ratio calculated as

, where x₀ = (1 220f_nD /V_H), 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 f_nD = natural frequency of vibration of the *building* in the along-wind direction, in Hz, f_n = 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

, where w_i = width normal to wind direction at height h_i, and V_H = mean wind speed at the top of the structure, in m/s, calculated as

, where,

= reference wind speed at a height of 10 m, in m/s, calculated as

, where I_w = importance factor for wind load, as provided in Table 4.1.7.3., q = reference velocity pressure, in Pa, and

= air density = 1.2929 kg/m3.

(See Note A-4.1.7.8.(4))

Figure 4.1.7.8.

Background Turbulence Factor, B

Forming Part of Sentence 4.1.7.8.(4)