At 09:37 AM 1/18/2007, Cqtestk4xs@aol.com wrote:
>In a message dated 1/18/2007 5:21:30 P.M. Greenwich Standard Time,
>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
>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.
TowerTalk mailing list