Pete wrote:
> But the elongation/stretch of either is pretty much meaningless
> except for precision positioning and even then takes place with
> the initial tensioning. It's doubtful there is much elongation
> associated with wind load unless the tower is overloaded and/or
> the winds are very strong as in approaching the system limits.
Sorry, Pete - elongation/stretch makes a big difference. Please
review the tower studies by K7NV on his web site ...
http://k7nv.com/notebook/towerstudy/towerstudy1.html
Pay particular attention to "Configuration Variation #5" is which
3/16" and 1/4" EHS is replaced by HPTG6700 in a stock 100' tall
Rohn 45 design with 20 sq ft. at the top. Also note that spreading
the 20 sq ft of windload down the tower results in greater stress
at the base of the tower (due to elongation of the lower guys)
than shown in the base case (all 20 sq ft at the top).
Kurt's take away for aramid (Phillystran) cables is:
> These are very strong and lighter than the steel cables. They
> exhibit higher elongation than comparable strength steel guys.
> Since, some guyed towers can be sensitive to cable elongation,
> replacement of steel guys with aramid cannot be only done based
> on strength alone.
>
> Guy elongation must be considered.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Roger (K8RI)
> Sent: Tuesday, September 01, 2009 12:58 PM
> To: n4zr@contesting.com
> Cc: TowerTalk
> Subject: Re: [TowerTalk] Philly installation
>
>
>
>
> Pete Smith wrote:
> > This assumes that elongation of the Phillystran for a given load is
> > the
> > same as EHS. In fact, according to K7NV
> > <http://wiki.contesting.com/index.php/Guy_cable_data>
> 6700-lb Philly
> > elongates about twice as much as 3/16" EHS and almost 4
> times as much as
> > 1/4" EHS which is rated for the same breaking strength.
> >
> But the elongation/stretch of either is pretty much
> meaningless except
> for precision positioning and even then takes place with the initial
> tensioning. It's doubtful there is much elongation associated
> with wind
> load unless the tower is overloaded and/or the winds are very
> strong as
> in approaching the system limits. In practice there is
> probably (I've
> never measured it but I have seen the movement) more give in the
> catenary with EHS than there is with the catenary AND elongation of
> Phillystran. EHS has almost no elongation. What's 4 times almost
> nothing? OTOH the *give* in both is slight unless someone
> runs into your
> guy system with a tractor while you are up there. I know it's
> substantial with EHS at 90 feet.(been there, done that,
> didn't like it
> at all) I'll leave it up to some one else to test the
> Phillystran via
> that method <:-))
>
> Both are good, both have little give, and both are acceptable
> methods of
> guying and even in 30 MPH winds you will not feel the tower
> move. Been
> there and done that too. It was a much more pleasurable (or
> at least far
> less stressful) than having the tractor test run on the guy
> system.<:-))
>
> 73
>
> Roger (K8RI)
> > I have 6700-lb Philly on my top guy set, with steel below,
> tensioned
> > at
> > 400 lb and the tower feels very steady. YMMV.
> >
> > 73, Pete N4ZR
> > New Articles Daily - the Contesting Compendium at
> > http://wiki.contesting.com The World Contest Station
> Database, updated
> > daily at www.conteststations.com The Reverse Beacon Network
> at http://reversebeacon.net
> >
> >
> >
> > Roger (K8RI) wrote:
> >
> >> ...
> >> Yes it's true you do not have a weight of EHS or the massive
> >> catenary.
> >> There is so little catenary in the 4000 and 6000# test
> Phillystran you
> >> really have to look to see it when sighting down the
> cable. However that
> >> means the guys are less likely to be able to cushion shock.
> >>
> >>
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> >
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|