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Re: [TowerTalk] [Fwd: Towers Brought Down!]

Subject: Re: [TowerTalk] [Fwd: Towers Brought Down!]
From: Jim Lux <>
Date: Thu, 18 Jan 2007 10:11:39 -0800
List-post: <>
At 09:37 AM 1/18/2007, wrote:
>In a message dated 1/18/2007 5:21:30 P.M. Greenwich Standard Time,
> writes:
>I use  only three guy anchors for my tower, which has four sets of guys.  It
>would  seem to me higgly unlikely that a guy anchor would fail, but I  have
>seen it happen.
>In most cases you are right.  After hurricane Charley I was in Punta  Gorda
>within 24 hours and had a chance to see the damage first hand. Along  with
>other tower failures I saw two toppled towers, both of them Rohn 25 
>had  sustained
>anchor failures.  Both were in substandard soil conditions..very  wet.  Rohn
>warns about substandard soil this in their catalogue for  specs.

Bringing up an interesting question.. was the soil (and anchor) 
substandard BEFORE the hurricane hit?  And, is "withstand hurricane" 
in the design requirements.. We talk a lot about wind resistance and 
lightning, but there's other things that happen in real disasters, 
like flooding, soil liquefaction, etc.  The tower design might be 
perfectly good for 120 mi/hr winds, but with 20 inches of rain on the 
soil, the anchors might fail. For that matter, now this comes up, I 
remember seeing a series of utility poles that failed near my house 
because the guy anchors were close to a (normally dry) ravine, and 
the combination of lots of water eroding the soil around the anchor 
and the wind blowing in the wrong direction caused the failure.

Similarly, in a seismic event (something that has to be addressed in 
designs in some areas of California), you have to look at the dynamic 
loads on the structure, but also the foundation stability, and, 
although I've not had to do it first hand, I would imagine that one 
would need to look at guy anchors in that context, particularly if 
you were unlucky enough to be in one of the special zones where soil 
stability is questionable.

Jim, W6RMK 


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