[TowerTalk] stretched EHS

[Steve Maki]

Grant,

Thanks for thinking about this, really appreciate it.

We did not notice a *bend* in the wire while it was loose - however, our 
main concern was getting all the guys back in service and getting the 
tower straight again before anything Really Bad were to happen. I'm 
looking at my photos which I shot from the anchor looking along the 
wire, and don't see anything.

I'm confident that there was no grip slippage or thimble collapse at 
ground level. Did not get a look at the tower end of the wire. The guys 
have no midspan connections.

Understand about the un-twist phenomenon, which I think is why guys 
loosen up after construction and need to be re-tensioned at least once 
or twice later on.

I'm thinking I'll recommend the guy replacement and after some period of 
time a P&T. All the guy wires seem a little loose - all we did was match 
the existing by feel (which I'm pretty good at after all the years).

Thanks again.

-Steve K8LX

On 10/13/2022 9:08 AM, Grant Saviers wrote:
> 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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