[TowerTalk] guyed tower reference?

[Michael Keane, K1MK]

On Mon, 06 August 2001, "Leonard Kay" wrote:

> Hi people,
> 
> I'm currently in the process of getting my 
> building permit at my new QTH and have run across 
> a small snag. My building commissioner wants to see 
> some evidence that guyed towers crumple when 
> they fail (not fall over) before he issues me 
> a permit for my 90' tower that is about 70' from 
> the nearest property line. 
> 
> I've searched the archives and the Web and I get
> a lot of hits (a lot of which are from right here), 
> but I haven't found an actual reference to 
> a published study. Can anyone give me a pointer 
> to such a document? I'll call Rohn today too.
> 
> Tnx & 73
> Len K1NU

Hi Len,

A couple of comments:

1) Here is a reference to a study of tower failures due to icing 
which is one of the common causes for tower failure here in the
northeast (and elsewhere): 

Atmospheric Icing and Tower Collapse in the United States
N. D. Mulherin, U.S. Army Cold Regions Research and Engineering Laboratory
http://www.crrel.usace.army.mil/techpub/CRREL_Reports/reports/Mulherin_Atmos_Icing.pdf

Quote: 

"...the data show that when towers fall, the debris is
usually contained within a radius of 50% of the tower’s
height agl...The mean and median collapse radii for the
40 cases were 31 and 20%, respectively, and the 
standard deviation was 23%. Only six towers had a
fall radius larger than 50%, and those were generally the
result of unusual circumstances."

2) It should be easy to have a PE write you a letter noting (if true) 
that for the specific design being proposed, the tensile 
strength of the guy system sufficiently exceeds the
compressive strength of the tower legs such that the 
failure mode will be  buckling of the tower's legs. 
In the event of such a failure, any debris would remain within
a specified  radius if the guy system remains sufficiently intact;
that caveat (sufficiently intact) is a big catch.

3) If a common anchor for each set of guys is used, then the tower is 
vulneable to the single-point failure of an anchor, equalizing plate 
etc. This could result in the tower laying out its to full length.
This failure mode can be addressed by using multipole, independent 
anchors on each set of guys and then sizing the guy system so the 
tower will pancake rather than lay out should any one anchor fails. 

Usually this means putting the top guys on a separate anchor and 
oversizing the top set of guys so they have sufficient tensile strength
by themselves  to cause the tower to buckle.

73 & KB,
Mike K1MK      

Michael Keane K1MK
k1mk@arrl.net
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