CA1250757A - Utility pole - Google Patents
Utility poleInfo
- Publication number
- CA1250757A CA1250757A CA000495188A CA495188A CA1250757A CA 1250757 A CA1250757 A CA 1250757A CA 000495188 A CA000495188 A CA 000495188A CA 495188 A CA495188 A CA 495188A CA 1250757 A CA1250757 A CA 1250757A
- Authority
- CA
- Canada
- Prior art keywords
- pole
- wires
- polymer
- cone
- hollow cone
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04H—BUILDINGS OR LIKE STRUCTURES FOR PARTICULAR PURPOSES; SWIMMING OR SPLASH BATHS OR POOLS; MASTS; FENCING; TENTS OR CANOPIES, IN GENERAL
- E04H12/00—Towers; Masts or poles; Chimney stacks; Water-towers; Methods of erecting such structures
- E04H12/02—Structures made of specified materials
Landscapes
- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Wood Science & Technology (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Reinforcement Elements For Buildings (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A tubular elongate pole comprises a pole wall having an elongate hollow cone of small diameter wires embedded in a polymer-containing matrix bonded to the wires to form an encapsulating shell of relatively low weight and which is substantially impermeable to aqueous corrosive liquids.
A tubular elongate pole comprises a pole wall having an elongate hollow cone of small diameter wires embedded in a polymer-containing matrix bonded to the wires to form an encapsulating shell of relatively low weight and which is substantially impermeable to aqueous corrosive liquids.
Description
~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 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.
v~
- ~ -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 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 ~Z~5~
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 lZ~7S7 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.
~Z5~57 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 ~25q~7~
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.
~ZSV ~57 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 ~ ~Z5~57 100 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.
~ZS~75~7 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, ~l2S~7S7 ~ 13 -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 ~2s~ j7-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, ~ZS~75~
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.
~LZSU7S7 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 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 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.
lZS~7S~
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 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.
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 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.
v~
- ~ -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 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 ~Z~5~
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 lZ~7S7 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.
~Z5~57 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 ~25q~7~
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.
~ZSV ~57 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 ~ ~Z5~57 100 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.
~ZS~75~7 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, ~l2S~7S7 ~ 13 -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 ~2s~ j7-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, ~ZS~75~
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.
~LZSU7S7 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 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 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.
lZS~7S~
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 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.
Claims (17)
1. A pole 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 about 12 mm, the wires being disposed in a circumferential layer about 1 mm to about 12 mm in thickness and arranged to give equal bending strength in any direction perpendicular to the longitudinal axis of the cone, said wires having a yield strength above 550 MPa and a modulus of elasticity in excess of 100 GPa, a polymer containing matrix 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 circumference and a modulus of elasticity in excess of 500 MN per metre of circumference, and the pole wall having a weight less than 100 kg/m2 of the wall.
an elongate, hollow cone of wires having diameters of about 1 mm to about 12 mm, the wires being disposed in a circumferential layer about 1 mm to about 12 mm in thickness and arranged to give equal bending strength in any direction perpendicular to the longitudinal axis of the cone, said wires having a yield strength above 550 MPa and a modulus of elasticity in excess of 100 GPa, a polymer containing matrix 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 circumference and a modulus of elasticity in excess of 500 MN per metre of circumference, and the pole wall having a weight less than 100 kg/m2 of the wall.
2. A pole according to claim 1, wherein said polymer-containing matrix is a polymer concrete comprising mineral aggregate and polymer.
3. A pole according to claim 1, wherein said polymer-containing matrix is a polymer impregnated concrete comprising a Portland Cement concrete impregnated with polymer.
4. A pole according to claim 1, wherein the wires of the hollow cone are arranged in the axial direction of the pole such that the bending strength decreases along the pole axis towards the tip of the pole.
5. A pole according to claim 1, wherein said wires of said cone are spaced in a symmetrical array about the longitudinal axis of the pole.
6. A pole according to claim 5, wherein the array comprises groups of circumferentially spaced apart wires, the wires within a group being in side-by-side relationship.
7. A pole according to claim 1 or 4, wherein said hollow cone is formed of a plurality of wires of varying lengths, at least some of which extend the full length of the pole.
8. A pole according to claim 1 wherein the hollow cone of wires is formed of wires having diameters between 5 and 10 mm.
9. A pole according to claim 1, 4, or 5 wherein there are more wires at the base of the pole than at the top of the pole.
10. A pole according to claim 2, 3 or 6, wherein said encapsulating shell has a thickness of less than 25 mm, said pole having a taper of about 1.5%, a base diameter about 2.5% of the pole length and a deflection of not more than 3% of the height under a load of 25% of the ultimate strength.
11. A pole according to claim 6, further including elongate reinforcing elements wound spirally on said hollow cone.
12. A pole according to claim 11 wherein said reinforcing elements are steel spirals wound on the inside of the wires.
13. A pole according to claim 11 hwerein said reinforcing elements are inert plastic spirals.
14. A pole according to claim 12 wherein the reinforcing elements further include inert plastic spirals wound on the outside of the wires.
15. A pole according to claim 11 wherein the pole has strong spirally wound reinforcing elements at the top of the pole and inert, durable spirally wound reinforcing elements at the base of the pole.
16. A method of producing a pole as defined in claim 1, which comprises:
forming said hollow cone of wires, binding the wires with spiral reinforcement to hold same in place, molding a moldable polymer concrete about said cone to form an encapsulating shell with said hollow cone embedded therein, and solidifying the cone wall.
forming said hollow cone of wires, binding the wires with spiral reinforcement to hold same in place, molding a moldable polymer concrete about said cone to form an encapsulating shell with said hollow cone embedded therein, and solidifying the cone wall.
17. A method of producing a pole as defined in claim 1, which comprises:
forming said hollow cone of wires, binding the wires with spiral reinforcement to hold same in place, casting a Portland Cement concrete about said cone to form an encapsulating shell, solidifying the encapsulating shell, impregnating said shell with a polymer, and curing the polymer.
forming said hollow cone of wires, binding the wires with spiral reinforcement to hold same in place, casting a Portland Cement concrete about said cone to form an encapsulating shell, solidifying the encapsulating shell, impregnating said shell with a polymer, and curing the polymer.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000495188A CA1250757A (en) | 1985-11-13 | 1985-11-13 | Utility pole |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000495188A CA1250757A (en) | 1985-11-13 | 1985-11-13 | Utility pole |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1250757A true CA1250757A (en) | 1989-03-07 |
Family
ID=4131874
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000495188A Expired CA1250757A (en) | 1985-11-13 | 1985-11-13 | Utility pole |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1250757A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2878551A1 (en) * | 2004-11-30 | 2006-06-02 | Acome Soc Coop Travailleurs | CARRIER ELEMENT RESISTANT TO HIGH LOADS AND METHOD OF MAKING SAME |
| WO2007136676A2 (en) * | 2006-05-18 | 2007-11-29 | Williams Donald S | Pultruded utility structures |
| US8322105B2 (en) | 2006-05-18 | 2012-12-04 | Duratel, Llc | Pultruded utility support structures |
| US8359814B2 (en) | 2006-05-18 | 2013-01-29 | Duratel, Inc. | Pultruded/extruded utility lighting, mounting and climbing structures |
| CN106869573A (en) * | 2017-01-24 | 2017-06-20 | 上海必立结构设计事务所有限公司 | Smoke exhaust barrel supporting arrangement |
-
1985
- 1985-11-13 CA CA000495188A patent/CA1250757A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2878551A1 (en) * | 2004-11-30 | 2006-06-02 | Acome Soc Coop Travailleurs | CARRIER ELEMENT RESISTANT TO HIGH LOADS AND METHOD OF MAKING SAME |
| WO2007136676A2 (en) * | 2006-05-18 | 2007-11-29 | Williams Donald S | Pultruded utility structures |
| WO2007136676A3 (en) * | 2006-05-18 | 2008-04-17 | Donald S Williams | Pultruded utility structures |
| US8024908B2 (en) | 2006-05-18 | 2011-09-27 | Williams Donald S | Pultruded utility structures |
| US8322105B2 (en) | 2006-05-18 | 2012-12-04 | Duratel, Llc | Pultruded utility support structures |
| US8359814B2 (en) | 2006-05-18 | 2013-01-29 | Duratel, Inc. | Pultruded/extruded utility lighting, mounting and climbing structures |
| CN106869573A (en) * | 2017-01-24 | 2017-06-20 | 上海必立结构设计事务所有限公司 | Smoke exhaust barrel supporting arrangement |
| CN106869573B (en) * | 2017-01-24 | 2023-12-29 | 上海必立结构设计事务所有限公司 | Support device for smoke exhaust tube |
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