Barry Kutner wrote:
> On 16 Mar 99,, tgstewart@pepco.com <tgstewart@pepco.com> wrote:
>
> > However, compared to Phillystran, which has most of the same
concerns, it
> > is about 1/3rd the cost for a stronger product.
> >
>
> Another thing to think about is the coefficient of elasticity. That
may
> be the wrong term, but what I mean is how much does it stretch for
> a given load.
> In a recent calculation posted on his Web site, Kurt, K7NV, showed
> that Rohn towers with the bottom section sunk in concrete, rather
> than pier pinned, get pretty close to the 1.0 safety factor, below the
> bottom set of guys, when using Phillystran. This seems to be related
> to a greater stretch per unit force. You need to know how much this
> stuff stretches, and not just ultimate tensile strength, before
deciding
> whether it is acceptable.
> Kurt, correct me if I've run astray here...
> 73 Barry
> --
Hi Barry and all,
Barry is doing well from my perspective mentioning that the elongation
of the
guy material should be considered. The Phillystran example cited above
was for HPTG6700. Larger cable would have resulted in higher safety
margins.
Fiberglass Reinforced Plastic (FRP) certainly meets our requirement for
being non-conductive. There is "fiberglass" (used for highly stressed
aerospace structures) and there is "fiberglass" (used to make your
bathtub), and a lot of stuff in between
Fiberglass:
There are different types of glass filament alloys, some have average
strength
like E-Glass made for electrical applications, and there are high
strength
alloys, like S2 Glass made for high strength applications. There are
also a
multitude of resin systems applied to these fibers in a multitude of
processes
to obtain an even wider variety of properties.
So, when we talk about fiberglass we need to be exceptionally careful to
quantify the constituent materials and their process to get in the right
material properties ballpark.
Add to that, some processors and resin formulators are more clever than
others
and get better properties than the other guys.
I've purchased fiberglass tubing from some suppliers that was not very
impressive. Stuff from others has been exceptional. Guess what the
difference is? Price.
When you go buy a piece of certified G10 Epoxy/glass stock, you know you
are not going to see less than 35000 psi ultimate strength. That's what
the Federal spec requires.
Caution is encouraged when buying "fiberglass" material, get some
values.
I went to the Polygon web site, http://www.polygoncompany.com to see
what
they had. They have a bunch of stuff that says they have lots of
experience in
composites and engineers are standing by to discuss your requirements!
This is
all probably quite true, and there are people there that have a real
grip on
what they do. But, no standard product line material properties are
offered.
Good thing Polygon is not the only outfit that has bought pultrusion
machines
to make these relatively simple solid rods with the pultrusion process.
There
are many of them. Search for pultrusion.
I checked out Glasforms, in San Jose, CA., they do the same thing, and
publish
material properties for their standard product lines.
Tensile modulus = 6.0 MSI for a glass content of 75% By Weight
Tensile strength = 120,000 psi
Density = .073 Lb/ in^3
Another mfgr on the web, Teel Plastics, listed the modulus for their
pultrusions at 2.5 MSI. This is consistent with values I've seen for for
composite laminates that are less axial and more quasi-isotropic.
This would be more usual for rectangular and round tubing sections
This just points out that a wide variety of properties are attainable in
composite materials. That is their appeal! The ability to taylor the
properties for the application.
Is fiberglass rod, from Polygon Company a good thing to use to guy
towers?
It probably is, if 3/8" rod can carry 13000 Lbs as one user stated. This
agrees with rod size and tensile strength given above.
Using the material properties from Glasforms, I get the following:
A 3/8" diameter glass rod made by them is just about equal to the
Phillystran
HPTG11200 aramid cable for elongation. This is because the rod has 3
time the area of the aramid to make up the difference in modulus.
It is stronger by 800 Lbs than the Phillystran HPTG11200.
And it weighs 1.76 times more than the HPTG11200 cable.
The FRP pultruded rod is not controlled or characterized yet by an
industry specification. We need to get the information from the
manufacturers, just like Phillystran.
EHS steel wire rope is usually controlled by ASTM A475. This spec
provides the minimum requirements, so we know what we are getting
without having to ask.
If the other concerns over this material are handled, it should be
useful to many users
--
73, Kurt
K7NV "That's K7 "Nevada" (ex - NI6W)
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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