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Topographic Effects (Kzt)

For towers on hilltops, ridges, or escarpments, the topographic factor Kzt amplifies wind speed per TIA-222-H Section 2.6.6.

Default Value​

Kzt = 1.0 for flat terrain (no amplification).

When Kzt > 1.0​

Wind speeds increase when flowing over terrain features:

  • Hilltops — wind accelerates over the crest
  • Ridges — channeling effect increases speed
  • Escarpments — abrupt terrain change creates speed-up

Kzt values typically range from 1.0 to 1.5 depending on the terrain feature's height and the tower's position on it.

Impact​

Since Kzt multiplies the velocity pressure (not the velocity), the effect is direct:

  • Kzt = 1.1 → forces increase by ~10%
  • Kzt = 1.3 → forces increase by ~30%
  • Kzt = 1.5 → forces increase by ~50%
TIA-222-F

TIA-222-F does not include topographic effects. Kzt is always 1.0 under that standard.