4.1.7.4. Topographic Factor

(1)

Except as provided in Sentence (2), the topographic factor, C_t, shall be taken as 1.0.

(2)

For buildings on hills or escarpments with slope, H_h /(2L_h), greater than 0.1 (See Figure 4.1.7.4.), the topographic factor, C_t, shall be calculated as follows:

where

where ΔS_max = applicable value from [[b-4.1.7.4.#^table-4174hplca|Table 4.1.7.4.]], x = horizontal distance from the peak of the hill or escarpment, L_h = horizontal distance upwind from the peak to the point where the ground surface lies at half the height of the hill or escarpment, or 2H_h (where H_h is the height of the hill or escarpment), whichever is greater, Z = height above ground, and k and α = applicable constants from [[b-4.1.7.4.#^table-4174hplca|Table 4.1.7.4.]] based on shape of hill or escarpment.

Figure 4.1.7.4. Speed-up of Mean Velocity on a Hill or Escarpment

Forming Part of Sentence 4.1.7.4.(2)

Notes to Figure 4.1.7.4.:

(1) V(z) = wind speed.

Table 4.1.7.4. Parameters for Maximum Speed-up Over Hills and Escarpments

Forming Part of Sentence 4.1.7.4.(2)

Notes to Table 4.1.7.4.:

(1) For H_h /L_h > 0.5, assume H_h /L_h = 0.5 and substitute 2H_h for L_h in the equation for ΔS.