COMPOSITE FILLED HOLLOW STRUCTURE

STRUCTURE CREUSE GARNIE DE MATERIAU COMPOSITE

English Abstract

A filled hollow structure (10), such as a fence post, which is constructed
with a hollow member (14) filled with a core (12) to increase its strength.
One aspect of the structure is that the core material normal expands upon
setting, so that, when hardening within the hollow member, the expansion is
restrained by the hollow member and the core is formed into an integral
structure with the hollow member. Further strength is added by constructing
the hollow member of reinforced fiberglass with the fiberglass rovings
oriented at an angle to the axis of the pipe and by using a hard coating (18)
on the outside of the pipe.

French Abstract

L'invention concerne une structure creuse (10) garnie, telle qu'un piquet de barrière. Ladite structure se compose d'un élément creux (14) garni d'un noyau (12) qui augmente sa solidité. Le matériau constituant le noyau se dilate normalement lors de la prise, de sorte que lorsqu'il durcit à l'intérieur de l'élément creux, la dilatation est restreinte par l'élément creux et le noyau forme une structure intégrée à ce dernier. On augmente encore la solidité, en utilisant de la fibre de verre renforcée comprenant des stratifils de verre textile orientés selon un certain angle par rapport à l'axe du tuyau et en utilisant un revêtement dur (18) sur l'extérieur du tuyau.

Claims

1. A filled structure characterized by the combination of high compressive
strength and tensile strength to allow a high bending load, the filled
structure
comprises;
a fiber reinforced resinous hollow structure having fiber rovings throughout
an entire thickness thereof and angled with respect to a longitudinal axis
thereof
so as to have a tensile strength of at least 30,000 psi and having an inside
surface forming a boundry which enclose a space,
a hard core within said space enclosed by the hollow structure, the hard core
having a density of at least 35 pounds per cubic foot and a compressive
strength
of at least 1500 psi, the hard core being formed from a mixture of particulate
cementitious material and liquid, the mixture expanding its volume as it
hardens, expansion of the mixture being restrained by the hollow structure and
the hard core exerting a force against the inside surface of the hollow
structure
such that the hard core is force-fit against the surface.
2. The filled structure of claim 1, wherein the hollow structure is a pipe.
3. The filled structure of claim 1, wherein the hollow structure is a
cylindrical
pipe.
4. The filled structure of claim 1 wherein the mixture from which the core is
formed includes gypsum as part of the particulate material.
5. The filled structure of claim 1 wherein the mixture from which the core is
formed includes an alpha hemihydrate.
6. The filled structure of claim 1 further including a veil attached on the
outside of the hollow structure, the veil comprising a cloth material
impregnated
with resin.
7. The filled structure of claim 1 further including a coating attached on the
outside of the hollow structure with the coating comprising a material which
absorbs ultraviolet radiation.
1

8. The filled structure of claim 1 wherein the hard core has a density of at
least
35 pounds per cubic foot.
9. A method of constructing a filled structure characterized by the
combination
of high compressive strength and tensile strength to allow a high bending load
comprising:
providing a fiber reinforced resinous hollow structure having a tensile
strength of at least 30,000 psi and an inside surface forming a boundary which
encloses a space,
providing a mixture of particulate cementitious material and liquid which
may be hardened into a hard core, said mixture being selected so that the hard
core formed therefrom has a density of at least 35 pounds per cubic foot and a
compressive strength of at least 1500 psi and the mixture expands its volume
as
it hardens,
placing the mixture within the space, and
permitting said mixture to expand and harden into the hard core within the
hollow structure in such a manner that expansion of the mixture is restrained
by
the hollow structure and the hard core exerts a force against the inside
surface of
the hollow structure such that the hard core is force-fit against the inside
surface
to provide said filled structure.
10. The method of constructing a filled structure of claim 9 further including
attaching a veil on the outside of the hollow structure with the veil
comprising a
cloth material impregnated with resin.
11. The method of constructing a filled structure of claim 9 further including
attaching a coating on the outside of the hallow structure with the coating
comprising a material which absorbs ultraviolet radiation.
2

Description

CA 02248804 1998-09-04
WO 97/37093 PCT/LTS96103641
COMPOSITE FILLED HOLLOW STRUCTURE
BACKGROTJND OF THE INVENTION
This invention deals generally with stock
material, and more specifically with filled hollow
structures such as light poles and fence posts and
rails constructed of plastic or fiberglass.
The benefits of plastic and fiberglass for
articles which are used where they are subject to
corrosion are generally well recognized. Structures
using such materials are light weight, strong, and
attractive. They can be made with color integrated
into the material so that they do not need frequent
painting during their use, and possibly their
greatest asset is the inherent chemical resistance
of the materials. A fiberglass or plastic structure
such as a fence post can be expected to last as long
as anyone wants it to, even in the most severe
environment, with no sign of deterioration, and it
will not require any maintenance.
Unfortunately, the major limitation on the
availability of such pole type fiberglass or plastic
structures has been the cost and difficulty involved
in their manufacture. One typical method of
fiberglass construction is the forming of the
fiberglass into a specific shape by wrapping
multiple layers of fiberglass fabric on the outside
of a core and impregnating the fabric with resin or
epoxy, however such manufacturing methods are very
expensive because they involve a great deal of hand
labor.
Another approach, particularly to the
construction of cylindrical structures, is to use
preformed fiberglass or plastic pipe. However, such
pole structures are not strong enough for most

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applications unless the pipe is very thick or the
structure includes wood or metal reinforcing, and
both of these approaches raise the cost of
fiberglass and plastic poles so that they are not o
competitive with conventional metal poles.
One approach to reinforcing fiberglass or
plastic pipe so it can be used as a structural
member has been the use of fillers which are poured
into the inside of the pipe, and then harden into a
core. Fillers have been suggested which include
wood with an adhesive binder (U. S. Patent 4,602,765
by Loper) and rigid foam or concrete (U. S. Patent
3,957,250 by Murphy), but these approachesdo not
furnish strength comparable to metal poles.
SUMMARY OF THE INVENTION
The present invention improves upon the
technique of filling the interior of a hollow member
to reinforce it by using a particular filler
material mixture which produces a structure of
greater strength by creating a stronger core and a
superior bond to the exterior member. This is
accomplished by selecting a material which normally
expands while it is hardening, thereby forming a
strong core with a stressed set and a force fit bond
with the external member.
In the preferred embodiment of the
invention, the material used for the core is a
gypsum based structural material, but one which
would expand as it is setting up except that it is
restrained from expanding by the external member.
The external member selected for the outside of the
pole is selected to have a structural strength which ~

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is greater than the expansion force of the core
~ structural material. Therefore, as the core
material hardens, it forms a plug with a permanent
positive stress and a higher than usual density
within the external member, and this plug is locked
tightly within and virtually bonded to the external
member.
In effect, a compression stressed core
member is formed within and integrated with the
external member, and this gives the filled hollow
structure greater strength than would result from a
core material which does not expand upon hardening,
because a core made of such a non-expanding material
could slide within the external member at the
boundary between the external member and the core.
To derive the full benefit of the filled hollow
structure, the core material must also have great
enough structural strength to add significantly to
the strength of the finished structure.
An additional benefit of the structure of
the preferred embodiment is that the external member
protects the core material from any environmental
factors which might otherwise cause the core
material to deteriorate with exposure.
Two other techniques are also used to
increase the strength of the filled hollow
structure. One, which is available only
for structures which include fiberglass in the
external hollow member, involves the specific
orientation of the rovings of the fiberglass used in
the external member. When the external member is
constructed so that the fiberglass rovings in it are
' essentially angled to the axis of the external

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member, it has greater resistance to splitting than
does a structure in which the rovings are
essentially aligned with the axis or perpendicular
to the axis. While this increase in strength is not '
sufficient to permit the use of an external member
without a strengthened core, it is a beneficial
safety factor for a structure which is already
within the required range of strength.
Another benefit can be secured from the
selection of a proper veil coating on the outside
surface of the external member. Such veil coatings
are often used to protect fiberglass reinforced
products from deterioration caused by exposure to
ultraviolet rays, but the veil coating, in the
proper thicknesses, can also add some structural
strength to the structure.
A final additional coating can also be
added to the pole structure of the present invention
to add particular surface finishes and additional
ultraviolet protection. This coating also adds to
the strength of the finished composite structure.
The present invention therefore furnishes
a highly desirable improvement for fiberglass and
plastic filled hollow structures which makes them
practical to use for such common and cost sensitive
applications as light poles and fence posts and
rails, since they can now be competitive with metal
poles.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is an end view across the axis
of the preferred embodiment of the invention.

CA 02248804 1998-09-04
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DETAILED DESCRIPTION OF THE INVENTION
The FIGURE shows an end view across the
axis of pole 10 of the preferred embodiment. Pole
s 10 is formed of four distinct materials, one of
5 which, core 12, takes on a particular significance
because of the manner in which it is formed. Core
12 is encased within pipe 14 which is covered by
veil 16, on top of which is placed protective
surface coating 18. Each of top of which is placed
- 10 protective surface coating the four parts of
composite pole structure 10 adds a particular
characteristic to the pole structure, and together
they furnish a pole of superior strength which can
be produced economically.
The construction of pole 10 is essentially
based upon the filling of pipe 14 with core 12, but
core 12 has unique properties which produce a
non-metallic pole with strength equivalent to that
of steel poles. Core 12 is a gypsum based product
with the important characteristic of normally
expanding as it hardens. It is important that the
core material normally expand in order that it have
a permanent positive stress and produce a force fit
with exterior pipe 14. It is also vital that the
hardened core have significant strength, which is
best indicated by a compressive strength rating of
at least 1500 psi, so that it adds significant
strength to the structure and does not act to merely
fill the interior space of the pipe. The structural
strength of the hardened core must, however, be less
than the structural strength of pipe 14 in order to
prevent the forces produced by the attempted
expansion during hardening of core 12 from

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distorting and weakening pipe 14 as it restrains the
expansion of core 12.
In the preferred embodiment, cylindrical
pipe 14 has a two inch outer diameter with .080 inch
wall thickness and is constructed with a standard
isothalic polyester resin base reinforced with
fiberglass rovings throughout its entire thickness.
Such a material has a tensile strength of at least
30,000 psi. Added bending strength can be attained
if the significant portion of the fiberglass rovings
are oriented to be at an angle of approximately 45
degrees to the axis of the pole.
As with all fiberglass and resin
structures, color pigments may be added during
manufacture of pipe I4 to produce consistent color
throughout the entire pipe.
It is also advantageous to produce veil 16
on the exterior surface of pipe 14 when it is being
manufactured. Veil 16 is a layer of polyester cloth
impregnated with resin. The production of such a
veil is well understood by those skilled in the art
of fiberglass construction. Veil 16 protects the
fiberglass against ultraviolet radiation, protects
against blooming of the surface fibers of the
fiberglass and also adds strength to pole 10.
Core 12 is composed of a mixture of sand,
water and a gypsum based material. In the preferred
embodiment the specific material used is an alpha
hemihydrate such as "Super X Hydro Stone"
manufactured by U.S. Gypsum. This material is
gypsum in calcinated, dehydrated, crystallized,
powder form. One particular mixture used in the

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preferred embodiment has 100 parts "Hydro Stone", 24
parts water and 200 parts 00 silica sand.
When hardened this formula yields a
i compressive strength of 6000 - 9000 psi, but still
has enough flexibility to permit bending of pole 10.
Moreover, this particular formula normally expands
about 0.1 percent upon hardening, and therefore
provides an exceptionally strong force fit with pipe
14. The density of such a core is at least 35
pounds per cubic foot.
Protective coating 18 may also be added to
pole l0, for the purpose of enhancing ultraviolet
protection and corrosion resistance and to produce
a
smooth surface. Such a coating is referred to as a
"hard coat" in industry terminology, and is well
understood by those skilled in coating technology.
It is applied during the manufacture of the pipe and
is at least .001 inch thick. Protective coating 18
is clear, can be made with or without pigments, has
a medium gloss finish, and includes specific
ultraviolet absorbers.
The composite pole of the present
invention furnishes bending strength equal to or
greater than Schedule 40 steel pipe (ASTM F-1083) of
the same diameter, and its inherent corrosion
resistance is far superior to that of steel.
Moreover, the present invention actually furnishes
a
pole which will flex more than twice as far as steel
and still return to its original shape without
failure.
It is to be understood that the form of
this invention as shown is merely a preferred
embodiment. Various changes may be made in the

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function and arrangement of parts; equivalent means
may be substituted fc>r those illustrated and
described; and certa:i.n features may be used
independently from ot=.hers without departing from the
!; spirit and scope of t:.he invention as defined in the
following claims.
For instanc~:e, structures may be produced
without either veil :1.4 or protective coating 16 when
the application does not require ultraviolet
protection. Moreovez-, the diameter and cross
sectional configuration of the external member may,
of course, vary, and the particular formula of the
core could be changed as long as the requirements of
the claims are retained.

Representative Drawing