Hi Jim,
I don't have any experience with kevlar or fiberglass
kuys other than admiring it on other peoples towers. If
you look at Kurt's website, however, it looks like for the
same 3000 lb tensile load that Phylistran elongates
about 2x as much as EHS with the same ultimate
strength. Likewise the fiberglass guys seems to have a
higher (~2X) tensile modulus compared with EHS.
Kurt is careful to note, however, that you can't generalize
too much as to the properties of fiberglass composites
as they can vary significantly across different resin
systems and manufacturing processes.
If you look at Kurt's tower study (you need to read
down toward the end to see the phylistran case) you
can see that the additional stretchiness of composite
guys can bite you if the base of the guyed tower is
over-constrained (e.g. 3 legged rigid mounting). With
a pier pin, it doesn't matters as the tower just leans a
little more in the wind when the composite guys are
used.
73 de Mike, W4EF.................
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
> And, I'll add some of my own experience. I've built a fair amount of
> stuff
> with structural steel, structural aluminum, and pultruded fiberglass
> (Extren
> 550). From a strength standpoint, the aluminum and Extren are about the
> same
> (in bending, tension, compression, but not shear.. Fiberglass is quite
> weak
> in shear). However, the Extren is about twice as flexible as aluminum
> (that
> is, a 2x2" box tube of aluminum will bend about half as much as the same
> size tube in Extren, with a "less than failure" load.
>
> Aramids are substantially stiffer and stronger than glass fibers (in
> composites, the resin just keeps the fibers in place, and doesn't
> contribute
> to the strength). However, that greater stiffness makes them more
> brittle.
> You're not as likely to see a Kevlar/Epoxy spring as a Glass/Epoxy spring.
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|