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[TowerTalk] Paranoid vs. Overkill

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Subject: [TowerTalk] Paranoid vs. Overkill
From: (Michael Keane, K1MK)
Date: 11 Sep 2001 05:24:19 -0700
On Tue, 11 September 2001, "Barry " wrote:

> Correct me if I'm wrong, but the Rohn specs are for SUSTAINED 
> wind speeds, not gusts. Big difference!
> Barry W2UP

The EIA-222 standard & the Rohn specs are for wind zones that are designated
by the speed of the fastest mile of wind at 10 meter height having a 50-year 
return period on average. 

The force that results from the calculation of the wind loading is not simply 
the stagnation pressure of the wind speed that desigates the wind zone. 

The wind load includes both a height dependent exposure term (designated 
Kz in EIA-222) and a gust factor (Gh in EIA-222) that depends on both the 
height and structure design.

At a height of 100' the spec wind load in a wind zone designated as 70 Mph
corresponds to the force resulting from an instantaneous gust of about 
88 Mph.

Mike K1MK

Michael Keane K1MK
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