[TowerTalk] stretched EHS

[Grant Saviers]

Steve,

I got to thinking more about your question - am wondering what you decided.

I assume you measured the small (0.2%) change in length when resetting 
the guy to the initial specified tension.  That would confirm the actual 
inelastic stretch, or some combination of thimble collapse, grip or clip 
slip. Then if there are insulators, those repeated.

Also wondering if there was any slack tension bending deformation at the 
tree impact site on the EHS?  That would be a sign of exceeding the 
yield point of some of the EHS fibers.  Pretty much a "replace it" 
observation.

EHS also having a twist will want to un-twist (apparent stretch) when 
under tension beyond initial setting and suspect at high tension that 
behaves as a one time apparent "stretch" and does not relax when tension 
is removed.  EHS has a slow twist for this reason.  Another variable not 
well defined, and lacking any data I could find for EHS.  Way back for 
my Phillystran guy project, I did come across some info re old straight 
fiber Phillystran vs new twisted which showed the apparent higher 
elasticity of the twisted.

btw comments like "EHS doesn't stretch" are wrong.  The modulus of 
elasticity of soft vs very hard steel is essentially the same, thus for 
a given force a piece of steel stretches the same soft or super hard. 
What is different is the yield point and how sharp and short that 
transition is to the break point.  This is widely misunderstood.

Hope that is helpful.


Grant KZ1W

On 10/12/2022 16:48, Grant Saviers wrote:
> 6" over 360ft = 0.139%.  I think that is less than the spec initial 
> pretension stretch for EHS.  I couldn't find the yield spec or stress 
> strain curve but it's likely around 90% of break.
> 
> However what you don't know is how much this guy was stretched in the past.
> 
> Given the cost to replace vs liability for guy failure, this seems like 
> a time to be conservative and replace the guy.
> 
> Grant KZ1W
> 
> 
> 
> On 10/12/2022 11:29, Steve Maki wrote:
>> I have a question for the materials crew here. I'm writing up a job 
>> report.
>>
>> Our crew went to a site where a huge tree had fallen on the two lower 
>> guys of a 360' tower. We carefully (well as carefully as we could) 
>> slacked off & disconnected one wire at a time, threw it over the tree, 
>> and reconnected it. At that point the site was ready for the tree crew 
>> to come.
>>
>> It was obvious that one of the wires (3/8" EHS) had stretched a few 
>> inches. There were enough unused threads in the turnbuckle to enable a 
>> good snug wire again.
>>
>> I'm recommending that the guy wire be replaced, but was wondering how 
>> much strength in roundabout numbers is lost in this scenario?
>>
>> TIA
>>
>> -Steve K8LX
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