Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~2507~7
This invention relates to poles and their
production, more especially it is concerned with utility or
distribution poles which may be used to support overhead
lines in power transmission and in external lighting of
different kinds, for example, street and highway lighting.
Most oE the utility poles in use are wood poles.
Wood poles are light, easy to erect, have accep-table
durability and are relatively inexpensive.
It is expected that in future, the supply of wood
poles will not meet -the demend for poles. In addition,
while wood poles are satisfactory for use in rural areas,
where they blend with the rural landscape and environment,
and there is an abundance of space for guying, they are
generally considered unsatisfactory in urban areas where
space is limited and where they do not blend
architecturally with the urban landscape and environment.
Concre-te poles have been employed in urban areas,
which poles have an aesthetically pleasing appearance in
the urban landscape and blend in with their surroundings.
lZ5~t~S>7
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Concrete poles are reinforced, typically with steel rods,
to provide adequate strength and deflection
charac-teristics.
The reinforcing steel rods in concrete poles are
subject to the corrosive action of water containing
dissolved components found in the environment such as salts
and acidic gases, which water penetrates through -the pores
oE the concrete.
In view oE this it is necessary to provide a
concrete pole with a thicX concrete wall, typically more
than 60 mm thick, in order to protect the reinforcing rods
against such corrosion, and provide a pole with a
satisfactory life. This need for a -thick concrete wall
resul-ts in a pole which is about twice the weight of a wood
pole of comparable length. The greater weight of the
conventional reinforced conrete poles increases the cost of
installation relative to wood poles and, in particular,
requires the use of more expensive equipment.
Attempts have been made to protect the steel
reinforcing rods without the need for a thick concrete
wall, for example, by galvanizing to provide a sacrificial
coating of zinc on the steel surface. However, the
resulting poles do not have a satisfactory life.
I-t is an objec-t of this invention to overcome the
disadvantages of conventional reinforced concre-te poles,
while a-t the same time providing a pole having the
aesthetic appearance associated with the reinforced
concrete pole.
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- ~ -
It is a further object of this invention to
provide a pole which is light in weight, as compared with a
reinforced concrete pole, and yet is durable and has a long
life.
It is still another object of this invention to
provide a thin walled, tapered, tubular pole having good
deflection characteristics.
It is yet another object of this invention to
provide a method of manufacturing a pole.
It has now, surprisingly, been found, -that a pole
comprising an elongate hollow cone of small diameter wires
embedded in a polymer-containing matrix bonded -to the wires
will form a solid cone wall of relatively low weight per
unit area and which due to the matrix is substantially
impermeable to aqueous corrosive liquids.
In particular the solid cone wall defines a pole
having a weight comparable with a wood pole of similar
dimensions and which can thus be readily transported and
installed using equipment employed for wood poles.
It will be understood that the term "cone" as
employed herein contemplates a truncated cone.
The hollow cone of wires forms the primary
structure of the pole, while the polymer-containing matrix
encapsulates and protec-ts the wires against corrosion,
provides an elongate tubular body of good appearance and
~ZS~)757
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holds the cone wires in a fixed s-tructurally efective
relationship.
According to one aspect of the present invention,
a pole is provided for public utility lines, lighting
apparatus and the like, comprising a pole wall including an
elongate, hollow cone of wires having diameters of about 1
mm to 12 mm, the wires being disposed in a circumferential
layer about 1 mrn to about 12 mm in thickness and arranged
to give equal bending strength in any direction
perpendicular to the longitudinal axis of the cone. The
wires have a yield strength above 550 MPa and a rnodulus oE
elasticity i.n excess of 100 GPa. A polymer containing
matrix is bonded to the wires to form a shell encapsulating
the wires, the matrix having a compression strength in
excess of 1 MN per metre of circurnference and a modulus of
elasticity in excess of 500 M~ per metre of circumference.
The pole wall has a weight less -than 100 Kg/m2 of the
wall.
According to another aspect of -the invention, a
method is provided for producing a pole as described above,
which method comprises the steps of orming the hollow cone
of wires, binding the wires with spiral reinorcement to
hold same in place, molding a moldable polymer concrete
about the cone to form an encapsulating shell wi-th -the
hollow cone embedded therein, and solidifying the cone
wall.
According to yet another aspec-t of the invention,
a method is provided or producing a pole as described
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above, which method comprises the steps of forming the
hollow cone of wires, binding the wires with spiral
reinforcement to hold same in place, casting a Portland
Cement concre-te about the cone to form an encapsulating
shell, solidifying the encapsulating shell, impregnating
the shell with a polymer, and curing the polymer.
The invention is illustrated in particular and
preferred embodiments by reference to the accompanying
drawings, in which:
Figure 1 illustrates schematically a pole of the
invention.
Figure 2 shows a cross-section of a pole of the
invention in one embodiment;
Figure 3 shows a cross-section of a pole of the
invention in another embodiment; and
Figure ~ shows a cross-section of a pole of the
invention in yet another embodiment.
With reference to Figure 1, a tubular pole 10 has
a tip 12 and a base 1~.
Pole 10 has an inner tubular surface 18 and an
outer tubular surface 20. A tubular passage 2~ provides a
housing for the electrical wiring. A port 26 in base 14
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provides an entry for underground wiring. Access port 22
provides access to the wiring for maintenance and repair.
The pole 10 is installed in ground 16 with a height "h"
above ground 16 typically between 10 and 20 metres and a
depth "b" below ground 16 of about 2 metres. The usual
total length of poles 10 is about 15 metres.
With further reference to Figure 2, a tubular
pole 100 comprises a cone wall 102 having embedded therein
a plurality of spaced apart, symmetrically arranged wire
groups or bundles 104 extending axially of pole 100 and
~orming a hollow cone.
Cone wall 102 includes an outer solid shell 108
of polymer-containing matrix and an inner shell 110 of the
matrix. A structural steel or stainless steel spiral 114
is located inside the inwardly facing surfaces of bundles
104 primarily to hold the bundles in place during
construction of pole 100. A spiral 112 of an inert plastic
such as "Kevlar" fibre is wound around the ou~wardly facing
surfaces of bundles 104. Kevlar is a trade mark of E.I.
duPont de Nemours and Co.
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The groups 104 each comprise four identical wires
115 in side-by-side relationship, although dif~erent
numbers and sizes of wires could be used as discussed
further below.
The pole 100 has a tubular inner surface 118 and
a -tubular outer surface 120.
In a particular embodiment the cone wall 102 has
a thickness "a" of 22 mm and the wires 115 have diameters
of 7 mm. The inner shell 110 has a thickness of S mm, thus
the dis-tance "c" between groups 104 and -the ouker surface
120 is 10 mm.
In pole 100, the zones in which the bundles 104
forming the hollow cone of wires are located, are not
readily apparent from a visual inspection. Therefore,
plugs 126 are used in the cone wall at predetermined
locations to provide attachment points Eor hardware, etc.
Alternatively, a special instrument can be used to detect
the location of the wires 104 so that holes for attachments
can be drilled between groups 104 and hitting or exposure
of the wires can be avoided.
With further reference -to Figure 3, there is
shown a pole 200, In so far as the pole 200 has parts
corresponding to those of the pole 100 of Figure 2, the
same reference numerals have been employed, but increased
by 100.
The pole 200 has an outer shell 230 which defines
an outer surface 232 of eight flat sides 234. In this way
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the amount of polymer-containing matrix in the pole 200 is
reduced where it is not needed to cover wires, thereby
`decreasing both the cost and the weight, and the minimum
thickness "e" of cone wall 202 is reduced to about 16 mm.
Pole 200 has embedded therein a plurality of
spaced apart, symmetrically arranged wire bundles 206, each
comprising two wires 217 of the same diameter and a larger
diameter wire 219 therebetween. This provides for a
uniform -thickness of matrix or cover over wires 206 while
allowing the use of larger diameter wires than are used in
pole 100 of Figure 2.
Pole 200 has the advantage that the locations of
the bundles 206 can be readily determined visually and the
locations for drilling holes for attachmen-ts can be readily
located centrally of sides 234 without the danger of
hitting or exposing the wires of bundles 206.
Wi-th further reference to Figure 4 there is shown
a pole 300. In so far as the pole 300 has parts
corresponding -to those of the pole 100 of Figure 2, the
same reference numerals have been employed but increased by
200.
The pole 300 has an outer shell 340 forming a
plurality of protuberances 342 spaced apart by flat sides
344. The protuberances 342 are located radially outwardly
of the wire bundles 304 and 306 and thus the thickness of
outer shell 340 between the groups 304 and 306 is
significantly reduced thereby reducing -the cost and weight
of pole 300.
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It will be apparent that both types of wire
bundles 304 and 306 are used in pole 300. These are
alternatives, and in fact, either type of wire bundle can
be used in the poles 100 and 200 of Figures 2 and 3 as
desired, provided sufficient thickness of matrix or cover
is provided for -the wires.
As in -~he case of the pole 200 of Figure 3, the
location of groups 304 and 306 is readily apparent.
Further description of the preferred embodiments
is as follows:
a) Hollow Cone of Wires
The hollow cone Eormed from a plurality of small
diameter wires provides the primary structure of the pole
and supplies most of the bending strength of the pole.
Wires having a diameter of about 1 to about 12
mm, preferably 5 to 10 mm, disposed circumferentially
about, and extending in the direction of the longitudinal
axis, and which have a yield strength above 550 MPa and a
modulus of elasticity above about 100 GPa are found to meet
the strength and deflection requirements of the pole.
The wires are disposed in a circumferential
layer having a thickness of not more than 12 mm. In this
way the wires can be embedded in the polymer-containing
matrix to produce a relatively thin, light-weight pole
wall.
~etal wires are particularly suitable, especially
steel wires. Cold drawn steel wires with a yield strength
over 550 MPa and a modulus of elasticity in excess of
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100 GPa are preferable, with wires having a yield strength
over 1100 MPa and a modulus of elasticity of 200 GPa being
especially suitable.
The plurality of wires is suitably spaced in a
symmetrical array. It is especially preferred to dispose
the wires in a symmetrical array comprising the groups or
bundles of wires 104, 206, 304 and 306, the bundles being
circumferentially spaced apar-t, and the wires within the
bundles being in side by side relationship.
It is nvt necessary that -the bundles or groups of
wires be identical, although it is preferred that the
groups be arranged and spaced apart in -the aforementioned
symmetrical array. In this way the pole has the same
bending strength in all directions perpendicular to the
longitudinal axis.
The bundles of wires may con-tain wires of
varying lengths, at least some of which ex-tend the full
height of the cone. There may be more wires in -the bundles
at the base of the pole and less wires at the tip of the
pole, so that this bending strength of the pole decreases
along the pole axis towards the tip of the pole.
b) Matrix
~s mentioned above, the wires are encapsulated in
a matrix. This is a polymer-containing matrix which is an
impermeable polymer concrete or polymer impregnated
concrete.
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A polymer concrete is formed from a mixture of a
polymer and mineral aggrega-te; a polymer impregnated
concrete is a concre-te formed from a mixture of Portland
Cemen-t and mineral aggrega-te, impregnated wi-th a polymer to
fill the pores and render it substan-tially impermeable to
corrosive aqueous liquids.
A polymer concrete comprises about 7 -to 20%,
typically abou-t 10 to 15%, by volume of the polymer;
whereas a polymer impregnated concrete comprises about 3 to
about 5~, generally about ~%, by volume of polymer.
The mineral aggrega-te in both polymer concre-te
and polymer impregnated concrete may comprise coarse and
fine aggregate as well as fines.
The selection of a suitable polymer is within -the
skill of persons in the ar-t having regard to -the particular
characteristics required.
In the case of the polymer concrete, the polymer
should form a satisfactory bond wi-th the wires and the
polymer concrete must, of course, have sufficient streng-th
when molded about the hollow cone to suppor-t the wires of
the cone in their cone-forming shape and to force the wires
to perform structurally as a group.
In order -to provide durability the polymer both
for the polymer concrete and the polymer impregnated
2S concrete should be chemically inert both -to -the wires and
aqueous corrosive liquids encountered by the pole in use.
Although the hollow cone of wires provides the
primary s-treng-th and deflection characteristics of -the pole,
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the matrix should be stiff enough to provide a stifening
effec~, at least until the load reaches 25~ of the breaking
strength of the pole, in orde,r to decrease the deflection
and stress fluctuations under all except high loading,
which is rarely experienced.
It is found that an appropriate stiffening effect
is provided by a matrix having a compressive strength in
excess of 1 MN (Mega Newton) per meter of perimeter or
circumference, and a modulus of elasticity in excess of 500
MN per meter of pole perimeter.
It will be understood that the reference to
"circumference" is not intended to restrict the invention
-to poles of circular cross-section, and poles of non-
circular cross-section, for example, poles having a
polygonal peripheral surface, such as poles 200 and 300,
are also conte~plated by the invention. As employed herein
the term "circumference" is to be understood as extending
to the imaginary circumference or the circumference of an
imaginary circle extending about the peripheral surface of
a pole of non-circular cross-section.
The matrix should have a density such -that the
cone wall formed by the matrix and the embedded hollow cone
of wires has a weight of no more than 100 kg/m2 of
cone wall for poles having a length oE up to 20 m. and a
proportionally larger weight for larger poles.
The matrix should form a relatively smoo-th molded
or cas~ surface having a hardness comparable to that of
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steel, stone or glass; and should preEerably form a molded
or cast surface of substantially uniform colour,
particularly a whitish grey colour.
The solid tuhular wall should be rela-tively
resistant to staining.
The polymer is most suitably a thermosetting
resin, and acrylate polymers and coplymers, especially the
methacrylates, for example polymethyl-methacryla-te, have
been found to provide particularly good resul-~s both in
polymer concretes and polymer impregnated concretes. Cone
walls having an outer thickness "c" i.e., the thickness of
cone wall from the outer ace of the layer of wires to the
external surface of the pole, of about 10 mm and total cone
wall thicknesses o less than 25 mm have been achieved
using these polymers.
Polymer concretes are suitably made by mixing the
mineral aggregate and the unpolymerized polymer ingredients
and effecting partial polymerization or curing, by heat or
catalysts, during the mixing to form a moldable or plastic
mixture and solidifying the mix-ture by comple-ting the
polymerization or curing after molding.
Thus the moldable mix-ture is molded about the
hollow cone oE wires, whereafter the polymerization or
curing is completed. The preferred method of molding is
centrifugal casting, but injection molding and extrusi
processes could be used as well.
Polymer impregnateed concretes are suitably made
by forming and shaping, for example by centrifugal casting,
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Portland Cement concrete -to the desired shape, curing the
concrete, drying the shaped concrete -to remove water from
the pores and voids, impregnating the porous concrete with
the polymer-forming monoMers and any polymerization
additives such as curing agents or catalysts to fill the
pores, and polymerizing or curing, for example, by
heating.
Thus the Portland Cement concrete is shaped about
the hollow cone and allowed to cure, wherea.fter it is dried
and impregnated and the polymerization is eEfec-ted.
c) Pole
The pole which includes the hollow cone of wires
encapsulated in its matrix, is typically formed as an
elongate member with a slight taper from base to -tip. In
one embodiment the pole 100 is of generally circular cross-
section and has the form o~ an elongate, truncated cone.
Other cross-sections, for example, polygonal cross-sections
such as poles 200 and 300 are also possible.
Poles which have a plurality of flat side walls
provide some advantages in that the location of wire free
zones can be more readily located for mounting attachments
and hardware, otherwise plugs 126 are used as shown in
Figure 2.
In general, the taper of -the pole is about 1.5~
with the base having a diameter of about 2.5% of the length
and the tip a diameter of 1 -to 1.25% of the length.
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In providing an acceptable pole for urban use it
is important that the poles remain substantially straight
under everyday loadings.
The poles of the invention suitably have a
deflection oE not more than about 3% of the height under a
load of 25% of the ultimate strength, and thus are
substantially straight most oE the time.
Suitably the poles exhibit a permanent set of not
more than 0.5~ of the length after application of a load oE
60~ of the ultimate strength.
The loads applied to most poles can be
approximated by applying a shear and torsion at the tip oE
the pole while the butt of the pole is rigidly clamped.
The major structural forces resulting from this load are
the bending forces near the base of the pole. The hollow
cone of wires provides the major resistance to these forces
by supplying axial tension and compression forces of
approximately equal magnitude on opposite sides of the pole
centre line.
In addition to the axial forces there are shear
stresses at the base due to the applied torsion and shear.
However, the shear stresses are much less than the bending
stresses and can be resisted by a material less strong than
high streng-th steel wire.
The strength requirements of a pole change for
pole locations above the base. In the case of t~e hollow
tubular pole of the invention, the section modulus of the
wire cone, which provides the bending strength, decreases
125C~757
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linearly as the radius of the cone decreases and linearly
as the total area of wire in -the section decreases. In -the
case of -the preferred tapered poles, the radius decreases
linearly with height but is not zero at the tip. The
bending moment, on the o-ther hand, decreases linearly with
height, and is zero at the tip. Typically, therefore, the
radius decreases more slowly than the bending moment and
for any given strength of wire it is possible to reduce the
area of wlre progressively towards the tip. This is done
by using wires of differen-t lengths so that fewer wires are
provided near the tip~
Shear and -torsional forces are approximately
constant from -tip to ground line. They are resisted
primarily by the matrix material.
Shear stresses on the matrix at any point along
its Iength, are inversely proportional to the total
cross-sectional area at the point, while those due to
torsion are inversely proportional to the cross-sectional
area multiplied by the radius of the wall. Shear strength,
therefore, decreases linearly for tubular poles of the
invention having a cons-tant cone wall thickness. The
torsional strength decreases approximately as the square of
the radius of the tubular pole.
Shear and torsion almost never govern pole
strength at the base, but they do become significant a-t the
tip. The preferred matrix materials are, coincidentally
weaker in tension than compression. Consequently, the use
of generally circumferentially extending reinforcing
~ lZSU~57
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elements, having a high tensile strength, is advantageous
at the tip of the pole.
d) Spiral Reinforcing Elements
In an especially preferred embodiment the
circumferentially extending reinforcing elemen-ts are
spirally wound about the outer and inner faces of the
hollow cone of wires. In addition to increasing the shear
strength of the matrix, especially at the tip of the pole,
the reinforcing elements particularly those wound on the
inner face of the hollow cone, assist in holding the axial
wires of the hollow cone in place during formation of the
pole.
The spiral reinforcing elements may, in
particular, be structural steel wires, stainless steel
wires or inert, plastic, wire-like extruded members, for
example, fibres of Kevlar. Steel reinforcing elements are
particularly strong and for the purposes of this disclosure
are referred to as strong reinforcing elements. Kevlar
reinforcing elements are particularly inert and durable,
for the purposes of this disclosure are referred to as
inert, durable reinforcing e~ements.
For the upper part of the pole, the spiral
reinforcing elements may conveniently comprise wires of the
same type of material as employed for the hollow wire cone,
since the requirement for strength is greater and the
exposure to corrosive elements is less than at the butt or
base of the pole.
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Structural reinforcement -to provide shear and
torsional strength is less important at the bottom of the
pole where the cross-section is larger. On the o-ther hand,
the effec-t of salt splash and freez.e/thaw cycles in
Northern climates; the effect of salt spray driven by
hurricane force winds in sub-tropical climates, and the
effect of insects, bacteria and ground born chemicals at
and below grade levels may all dictate tha-t the base end
desirably be o.f grea-t durability. The use oE -the spiral
reinforcing elements at the base end of the pole also
prevents or hinders splitting of the matrix along -the axis
of the hoLlow cone. For this purpose the coils of the
spiral are desirably closely spaced to control crack size
and formation and the elements are selec-ted for durability
rather than strength at the base of the pole. Suitably
inert, plastic fibres, Eor example, of Kevlar, rather than
steel wires are particularly good at the base of the pole.
Accordingly, in some applications, it is
desirable to have steel spiral reinforcing elements at the
top end of the pole for strength and inert plastic
reinforcing elements at the base of the pole for
durability.
Finally, in some climates, such as dessert
climates, where corrosion of the cone of wires is no-t much
of a problem, a more permeable matrix may be used.
S.imilarly in extremely corrosive environments, pre-coati.ng
the wires of the cone of wires may also be employed to
75~7
- 20 -
provide greater protection. A suitable pre-coating
material as would be apparent to those skilled in the ar-t
would be used which would work wi-th the matrix to provide
even greater protec-tion than either the coating or the
matrix would provide alone. Alternatively, the ma-trix
could be thicker at the base of the pole than at the top to
provide more protection, in which case the cover would
still taper uni~ormly to the -top.
