3-D AXISYMMETRICAL HILL

wind speed: Normal
Kzt = (1 + K₁K₂K₃)² Speed-up Zone K₁ = 0.21 x (Upwind) x (Downwind) H Lh H/Lh ≥ 0.2 Upper 1/2 Flow Around Sides 3-D AXISYMMETRICAL HILL

3-D Hill Characteristics (K₁ = 0.21):

Dispersed Flow: Wind can flow around the sides as well as over the top

Lower Speed-up Effects: Peak acceleration is reduced due to flow dispersion

Side Flow Patterns: Multiple flow paths reduce concentrated acceleration

Gradual Transitions: Smoother changes in wind speed and direction

Topographic Factor Requirements:

Structure: Must be in upper half of hill/ridge

H/Lh ≥ 0.2: Height to length ratio requirement

Height: H ≥ 15 ft (Exposure C,D) or 60 ft (Exposure B)

Isolation: No similar upwind obstructions within 100H or 2 miles

Formula: Kzt = (1 + K₁K₂K₃)² where K₁ = shape factor, K₂ = distance factor, K₃ = height factor