[TowerTalk] turnbuckle safety wires

[Patrick Greenlee]

At one time a 1610 ft (490 meter) TV tower at Caprock NM was the tallest 
manmade structure on the planet. The option to put on de-icing 
capability was not taken as it was decided (hoped) there would not be 
enough icing to be a threat. When I was a Senior in High school that was 
the only TV we could get.  An ice storm in the winter of 1960-61 brought 
the tower down.  The ice storm took down 20 miles of overhead power 
distribution poles leaving the town of Tatum NM a national disaster area 
with truck mounted army generators brought in to preserve food in the 
stores.  Gas was pumped by hand from underground tanks into 5 gal cans 
to fuel cars. School was closed until utility power restored (new poles 
installed for 20 miles.)

Moral of the story...  Cutting corners is not always economical

Patrick        NJ5G


On 9/23/2017 7:12 PM, Wes Stewart wrote:
> I had a Cushcraft 80-meter vertical once that broke exactly in half 
> and folded over on itself.  I had guyed it about 2/3 of the way up and 
> apparently caused a resonance that fractured it at one of the swaged 
> joints.  I had noticed some vibration in the mast but ignored it, 
> thinking that the guys would keep it up.  In retrospect, they probably 
> exacerbated the problem.  The uniform, non-tapered diameter probably 
> didn't help either.
>
> The power line people use Stockbridge dampers to reduce wind-induced 
> flutter in their lines and guys.  I saw lots them installed on the 
> guys for what was then the tallest man-made structure on the planet, 
> the 2063' tall tower for KVLY TV.
>
> Wind or vortex shedding is another technique used on some structures. 
> https://en.wikipedia.org/wiki/Vortex_shedding.  (Note the mention of 
> Heard Isl.) Just today I again visited the site of a TopGolf driving 
> range where I've been watching them install a plethora of heroic 
> tubular masts holding up a huge net.  I'm guessing they are at least 
> six feet in diameter at the base and well over 100' tall.  Since the 
> last visit I notice they've installed a helical wrap up the masts.  
> When you start looking for this stuff it's everywhere.  The old-time 
> radio antenna on my 1998 PU and the stubby antenna on the back of my 
> newer car both have helical wraps.
>
> Wes  N7WS
>
>
>
>
>
> On 9/23/2017 6:24 AM, Bob Shohet, KQ2M wrote:
>> There is another potential factor that I have not seen anyone mention 
>> specifically, that of “resonance”. The interplay of wind speed 
>> (constant or intermittent) and direction, wind vortices around the 
>> tower guy and turnbuckle, turnbuckle friction, guy weight, guy length 
>> and guy tension, also contribute to whether or not some form of 
>> resonance may or may not be in play for a given guy and turnbuckle.  
>> This can introduce vibrations into the turnbuckle which can 
>> facilitate additional movement (turning) and fatigue, just as 
>> resonance has been known to destroy element tips, bridges, etc.
>>
>> Movement from resonance can potentially explain “head-scratching” 
>> phenomena related to turnbuckle movement and loosening of untethered 
>> turnbuckles, especially when only one specific turnbuckle seems to be 
>> affected.
>>
>> The bottom line is that as humans, we often unwittingly discount the 
>> very phenomena that can cause a problem and potential catastrophic 
>> failure simply because we can not see physically see the factors at 
>> work that are impacting a future weak point in an installation. Which 
>> is all the more reason to take simple steps to protect against them 
>> when we can; “just in case”. :-)
>>
>> 73
>>
>> Bob  KQ2M
>>
>>
>
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