U.S. patent application number 11/826405 was filed with the patent office on 2009-02-05 for utility pole.
This patent application is currently assigned to Stelco Inc.. Invention is credited to Peter Badgley, Christian Deveau, Stephen Dunstall, Michael Thorpe.
Application Number | 20090031646 11/826405 |
Document ID | / |
Family ID | 40336820 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090031646 |
Kind Code |
A1 |
Badgley; Peter ; et
al. |
February 5, 2009 |
Utility pole
Abstract
A tubular utility pole for supporting a load, adapted for direct
burial of a preselected end thereof in a soil material. The pole
includes a body having a substantially constant cross-section
substantially along a length thereof. The body includes a steel
tube with holes therein to permit attachment of the load to the
body.
Inventors: |
Badgley; Peter; (Puslinch,
CA) ; Dunstall; Stephen; (Ancaster, CA) ;
Deveau; Christian; (Ancaster, CA) ; Thorpe;
Michael; (Stoney Creek, CA) |
Correspondence
Address: |
VALENTINE A COTTRILL;SUSAN TANDAN
50 QUEEN STREET NORTH, STE. 1020, P.O. BOX 2248
KITCHENER
ON
N2H6M2
CA
|
Assignee: |
Stelco Inc.
Hamilton
CA
|
Family ID: |
40336820 |
Appl. No.: |
11/826405 |
Filed: |
July 16, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60807390 |
Jul 14, 2006 |
|
|
|
Current U.S.
Class: |
52/169.9 ;
52/169.14; 52/741.14 |
Current CPC
Class: |
E02D 27/42 20130101 |
Class at
Publication: |
52/169.9 ;
52/169.14; 52/741.14 |
International
Class: |
E02D 27/42 20060101
E02D027/42 |
Claims
1. A tubular utility pole for supporting a load, the pole being
adapted for direct burial of a preselected end thereof in a soil
material, the pole comprising: a body having a substantially
constant cross-section substantially along a length thereof, and
the body comprising a steel tube with holes therein to permit
attachment of the load to the body.
2. A tubular utility pole according to claim 1 additionally
comprising a bearing plate positioned on the body at the
preselected end, to retard the settlement of the pole into the soil
material.
3. A tubular utility pole according to claim 1 in which said steel
is coated.
4. A tubular utility pole according to claim 3 in which said steel
is coated with a coating selected from the group consisting of
zinc, aluminum, and an alloy of zinc and aluminum.
5. A tubular utility pole according to claim 1 in which the
preselected end of the body is provided with a layer of material
adapted for retarding corrosion of the body.
6. A method of producing the tubular utility pole of claim 1,
comprising: (a) roll-forming a coil of strip steel to a
predetermined configuration such that the strip has at least two
edges adapted to mate with each other; (b) seam welding said at
least two edges together to form the body; and (c) cutting the body
to a predetermined length.
7. A method according to claim 6 additionally comprising: (d)
attaching a bearing plate to the body at the preselected end, to
retard settlement of the pole in the soil material.
8. A method according to claim 7 additionally comprising: (e)
providing the preselected end of the support pole with a layer of
material adapted for retarding corrosion of the body.
Description
FIELD OF THE INVENTION
[0001] This invention is related to a utility pole adapted for
direct burial of an end thereof having a body with a substantially
constant cross-section.
BACKGROUND OF THE INVENTION
[0002] Wooden and steel support poles for supporting electrical
utility transmission lines, telephone and cable wires,
transformers, and the like are known. Wooden support poles have a
number of disadvantages, however. For instance, wooden support
poles tend to rot. To minimize and/or retard rot, wooden poles are
often treated with chemicals. Because of this treatment, however,
the treated poles are generally considered hazardous waste, so that
their disposal is relatively costly. Also, because the wooden poles
originate as natural products, their characteristics vary from one
wooden pole to the next, and in particular, the strength of the
wooden poles can vary from one pole to another. Wooden poles are
generally tapered, due to the natural taper of the tree trunks from
which the poles are formed.
[0003] Various steel tubular utility poles are known in the art.
However, the prior art steel utility poles typically have tapered
tubular bodies (see, e.g., U.S. Pat. No. 3,942,296; Korean Patent
No. 20040020447; and Japanese Patents Nos. 2004211292 and
2005188279), which have relatively high manufacturing costs. U.S.
Pat. No. 6,705,058 discloses a pole that can be directly embedded
into the ground, however, the pole is comprised of telescoping
tubular sections above-ground and an in-ground concrete base.
[0004] For instance, a tapered metal support pole of the prior art
is indicated generally by the reference numeral 10 in FIG. 1. As
can be seen in FIG. 1, the pole 10 has a bottom end 12 with a
preselected diameter and a top end 14 with a much smaller diameter.
The pole 10 is tapered along its length, from the bottom end 12 to
the top end 14.
[0005] A straight (i.e., non-tapered) steel pole which is mounted
on a concrete foundation is also known. For instance, Japanese
Patent No. 08-326356 discloses a straight steel pole positioned on
a concrete foundation for erection. However, this type of pole is
not designed for supporting electrical utility transmission lines,
telephone and cable wires, transformers, and the like. This type of
prior art pole is not suitable for such applications because of the
relatively high costs thereof, and also because such poles are
unable to withstand the loads.
[0006] There is therefore a need for an improved utility pole which
overcomes or mitigates one or more of the disadvantages of the
prior art.
SUMMARY OF THE INVENTION
[0007] In its broad aspect, the invention provides a tubular
utility pole for supporting a load, adapted for direct burial of a
preselected end thereof in a soil material. The pole includes a
body having a substantially constant cross-section substantially
along a length thereof. Also, the body is a steel tube with holes
therein to permit attachment of the load to the body.
[0008] In one of its aspects, the invention additionally includes a
bearing plate positioned on the body at the preselected end, to
retard the settlement of the pole into the soil material.
[0009] In another of its aspects, the invention provides a method
of producing the tubular utility pole. The method includes, first,
the step of roll-forming a coil of strip steel to a predetermined
configuration so that the strip has at least two edges adapted to
mate with each other. Next, the two edges of the strip are seam
welded together to form the body. Finally, the method includes the
step of cutting the body to a predetermined length.
[0010] In another aspect, the method additionally includes the step
of attaching a bearing plate to the body at the preselected end, to
retard settlement of the pole in the soil material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention will be better understood with reference to
the attached drawings, in which:
[0012] FIG. 1 (previously discussed) is a side view of a tapered
utility pole of the prior art;
[0013] FIG. 2A is a side view of an embodiment of a utility pole of
the invention;
[0014] FIG. 2B is a bottom view of an embodiment of a bearing plate
of the invention;
[0015] FIG. 3A shows design constraints and loading used in design
calculations for an embodiment of the pole of the invention;
[0016] FIG. 3B is a cross-section of the pole of FIG. 3A;
[0017] FIG. 4A is a diagram schematically illustrating the results
of finite element modeling conducted to estimate stresses to which
an embodiment of the pole of the invention may be subjected;
and
[0018] FIG. 4B is a contour plot legend for the stresses of the
finite element analysis of FIG. 4A.
DETAILED DESCRIPTION
[0019] Reference is first made to FIGS. 2A and 2B to describe an
embodiment of a tubular utility pole in accordance with the
invention indicated generally by the numeral 20. Preferably, the
utility pole 20 is provided with a bearing plate 21 positioned on a
preselected end 24 of the pole 20, and the end 24 is to be
positioned in soil material 25 (i.e., direct burial), as will be
described. The utility pole 20 includes a tubular body 22 having a
substantially constant cross-section along a length thereof. The
body 22 preferably comprises a steel material, as will be
described. The tubular body 22 preferably includes holes 26
positioned in it, as shown in FIG. 2A, to permit insertion and/or
attachment of one or more members (not shown) for supporting a load
(not shown).
[0020] As noted above, the pole 20 preferably includes the bearing
plate 21. It is preferred that the bearing plate 21 is mounted on
the body 22 at the end 24. The bearing plate 21 is for retarding
settlement of the pole 20 into the soil material 25.
[0021] It is preferred that the steel material of which the pole 20
is made is coated. For the purposes hereof, "coated" refers to any
coatings (such as those resulting from galvanizing or
galvannealing) added after the steel has been made, to protect the
steel from corrosion. Preferably, the coating is selected from a
group consisting of zinc, aluminum, and an alloy of zinc and
aluminum. It is also preferred that the steel is pre-coated, i.e.,
the steel is coated shortly after the steel has been made, and
before the steel has been formed into the body 22. However, the
steel may also be post-coated. "Post-coated" refers to any coating
(e.g., such as those resulting from galvanizing) added after the
body 22 has been formed, i.e., manufactured.
[0022] In addition, it is preferred that the preselected end 24 of
the body (i.e., the end to be inserted into the soil material 25)
is provided with a material (not shown) adapted for retarding
corrosion of the body. Such material preferably is a layer of an
organic material such as epoxy, or any suitable polymer, as would
be known to one skilled in the art. It will be understood that, for
the purposes hereof, "soil material" refers to any suitable soil or
aggregate material in which the end 24 of the body 22 is
positioned.
[0023] Preferably, the holes 26 are provided in the body 22 to
facilitate the attachment of members on which the load is supported
(or otherwise to permit attachment of the load to the pole)
generally towards an upper end 28 of the body 22. Preferably, the
holes 26 are spaced apart from the end 24 by predetermined
distances. As indicated above, the load may be, for example,
electrical utility transmission lines, telephone and cable wires,
transformers, and the like, and also may include related gear, such
as members inserted in the holes 26 (FIG. 2A).
[0024] To form the steel utility pole 20, the following steps are
taken. First, a coil of strip steel is roll-formed in a continuous
rolling mill to a predetermined configuration, so that the strip
has two or more edges which are adapted to mate with each other.
Next, the two edges are seam welded together to form the body 22.
Next, the body 22 is cut to a predetermined length, as required for
the application. The bearing plate 21 is also attached by any
suitable means.
[0025] As noted above, the pole is adapted for direct burial of the
end 24 thereof. As is known, a hole is dug in the soil, in which
the end 24 is receivable, to the depth required. Before burial of
the end 24 in soil, the preselected end 24 of the utility pole 20
preferably is provided with a layer of material (i.e., whether a
polymer or epoxy) which is adapted for retarding corrosion of the
body 22. The end 24 is subsequently inserted and/or buried directly
in the soil material, being such suitable material as may be
available. After the end 24 is positioned in the hole, soil
material is backfilled, i.e., positioned around the pole in the
space remaining in the hole, and such material is tamped down or
compressed, to a suitable extent, to hold the end 24 so that the
pole remains substantially vertical.
Engineering and Design Principles
[0026] There are three major factors to be considered in designing
the steel pole of the invention. The factors are: expected
strength, expected life, and expected performance.
[0027] 1) Expected Strength: The primary structural component, the
body 22, is subjected to transverse wind and ice loading. Its
resistance is characterized by a bending-strength at groundline
(GL) (FIGS. 2A, 3A). However, the pole bending capacity could be
limited by local buckling, depending on pole diameter (D) and
thickness (t) ratio, D/t. Steel pole manufacturers would typically
provide a nominal strength P.sub.n (or a minimum guaranteed
strength f.sub.ymin) to determine the moment capacity, and an
ultimate vertical load P.sub.u (or the buckling critical load based
on Euler's formula).
[0028] The many sources of uncertainty in observed pole strength
include inherent material property variability, manufacturing
effects, and variation in testing methods. Thus, the current
practice requires that the strength of the pole must be
characterized by a probability density function (normal
distribution type) with a mean value and a coefficient of variation
(COV). For steel towers the standards assume that nominal strength
P.sub.n has an exclusion limit in the range of 5% to 10% and COV is
in the range of 10% to 20%.
[0029] 2) Expected Life: A steel pole of the invention has a
service life of up to approximately 80 years (i.e., more than twice
the typical service life of a wooden utility pole). Steel utility
poles of the invention can be coated with zinc or made from
weathering steel. (Weathering steel poles of the invention can
provide the same benefits as galvanized steel poles.) Accordingly,
the steel pole of the invention is an economically viable
alternative to traditional wood poles. Preferably, and as noted
above, an organic, epoxy material (not shown) is applied at the end
24 of the pole, to further protect the directly embedded end of the
pole. Various epoxy materials may be suitable. All serve the same
purpose of protecting the steel from aggressive corrosion
conditions that sometimes exist in the environment.
[0030] 3) Expected Performance: The following three factors are to
be taken into consideration when assessing expected performance:
[0031] a. Groundline Deflection; [0032] b. Handling; and [0033] c.
Field Use.
[0034] Preferably, the utility pole of the invention is designed to
various diameters that vary in steel grades, strength, and
thicknesses (gauge), depending on the application, i.e., depending
on the dimensions and the load. The steel utility poles of the
invention are manufactured and tested to stringent quality and
performance requirements. In general, the utility poles of the
invention do not fail catastrophically. They exhibit forms of
material yielding when damaged, often allowing the utility line to
remain in service and providing enough time for utility workers to
replace or repair the pole without causing any major service
interruption. Additionally, the steel utility poles of the
invention can be designed for applications where wood poles are
required to be guyed, i.e., the pole of the invention is usable in
such circumstances without a guy. The steel utility poles of the
invention provide a solution for tight spacing requirements and
need not be guyed or otherwise exteriorly supported.
Installation
[0035] In the present invention, utility poles are installed in a
very similar fashion to wood poles and conventional tapered steel
utility poles with direct burial in the soil material (FIGS. 2A,
3A). Utility poles are also relatively lightweight and easier to
install and manoeuvre than wooden poles. Due to the increased
strength and engineered dimensional stability, utility poles can be
smaller in diameter than prior art wooden poles and can also
utilize smaller-sized auger equipment. (This is especially
advantageous because only one auger size needs to be selected
whereas wood poles can differ in diameter sizes and require more
auger sizes to be required). Changing augers can increase
installation times when a series of poles is being installed. With
more control over pole diameters, backfill practices are
minimized.
[0036] Among other advantages, the utility poles of the invention
require less maintenance, resulting in fewer risks for utility
linemen.
Storing and Handling
[0037] Utility poles preferably are shipped as single pieces due to
their length (less than approximately 60 feet). Since the utility
poles of the invention are lighter than wood poles, the number of
poles per truckload is governed by volume, not weight. Utility
poles are also easier to nest tightly together than the
conventional tapered steel utility poles. When traditional wood
poles are transported to the holding site, cribbing practices must
be in place in order to avoid storage stains. Unlike wood poles,
steel poles do not require periodic rotation while in storage to
avoid potential moisture problems.
Testing
[0038] Steel utility poles of the invention preferably are tested
to verify the maximum load carrying capacity by bending tests,
whereas wood poles are tested to determine the mean rupture
strength.
HSS Utility Pole Examples
EXAMPLE 1
[0039] In the present invention, the utility pole is dipped in zinc
for corrosion prevention. Preferably, and as described above, the
buried portion of the pole (i.e., the end 24) is further coated
with an organic material prior to burial.
[0040] According to American National Standards Institute (ANSI)
standards and, in general, the typical standards of hydro utilities
in North America, utility poles are defined by height above ground
and class, where the class identifies the load-bearing capacity
(see Table 1). Body 22 behaves as a cantilever beam, with end 24
fixed at groundline (GL) and a transverse load P, depending on the
service class. In accordance with such standards, the prescribed
load is applied 2 feet below the pole top and is intended to
represent the applied force from service equipment, wires, and the
like mounted to the pole. The groundline is assumed to be at a
distance from the pole bottom which is approximately ten percent of
the pole length, plus 2 feet (FIG. 3A).
[0041] Table 2 shows three design cases according to the current
invention. The parameters are illustrated in FIGS. 3A and 3B. These
designs were arrived at following the design steps as per ANSI 05.1
Utility Distribution Pole Class Design Requirements.
[0042] 1) Calculate pole nominal bending moment M.sub.nom at
GL:
M.sub.nom@GL=P*[L-(0.1L+2)-2]*12, [in-Ibf]
[0043] 2) Calculate pole section modulus, S.sub.nom:
S.sub.nom=D.sub.n.sup.4-(D-2t.sub.n).sup.4)/32D.sub.n,
[in.sup.3]
[0044] 3) Calculate nominal bending stress f.sub.bnom:
f.sub.bnom=M.sub.nom/S.sub.nom, [psi]
[0045] 4) Select material minimum yield, f.sub.y:
f.sub.ymin=f.sub.bnom
[0046] 5) Check for buckling limitations, as per ASCE manual 72,
with a strength factor, .phi.=1:
D/t.ltoreq.6,000.phi./f.sub.y then allowable bending stress
f.sub.ba=f.sub.ymin, [ksi]
6000/f.sub.y<D/t<12000.phi./f.sub.y then allowable bending
stress f.sub.ba=0.7f.sub.y+800/(D/t)
[0047] 6) Calculate Euler's critical buckling load P.sub.u (for a
column of length L.sub.B, fixed at the base and free at the
top):
P.sub.u=.pi..sup.2EI/4L.sub.B.sup.2, [Ibf] [0048] I=section moment
of inertia, [in.sup.4] [0049] L.sub.B=distance from GL to 2 ft from
the top of pole, [in]
[0050] The three design solutions described above and in Table 2
were verified through finite element modeling (FIGS. 4A, 4B).
TABLE-US-00001 TABLE 1 Utility Distribution Poles ANSI 05.1 Class
Requirements** Working Wood Horizontal Equivalent Steel Class Load
(lbs) Load (lbs)* 4.times. Load (lbs)* 2.5.times. ("X") ("Y")
Safety Factor Safety Factor 2 925 3,700 2313 3 750 3,000 1875 4 600
2,400 1500 5 475 1,900 1188 6 375 1,500 938 *Point load located
2-ft below top of pole based on requirements for new and replaced
Grade C Structures (NESC) **Table from American Iron and Steel
Institute (AISI)
TABLE-US-00002 TABLE 2 Examples in Table Format Design Calculations
Bending Bending Design Section Moment Stress, Stress.sup.2, Steel
Ultimate O.D. Thickness Length Weight Pole Load Modulus @GL
Calculate FEA Grade Vertical Load D, [in] t, [in] L, [ft] [lbf]
Class.sup.1 P, [lbf] S.sub.nom, [in.sub.3] D/t M.sub.nom, [in-lbf]
f.sub.bnom, [ksi] f.sub.bFEA, [ksi] [ksi] P.sub.u, [kips] 9.625
0.188 40 757.1 3 1875.0 12.90 51.2 720,000.0 55.8 58.0 80 301.2
9.625 0.188 40 757.1 4 1,500.0 12.90 51.2 576,000.0 44.7 47.0 60
301.2 9.625 0.188 40 757.1 5 1,187.5 12.90 51.2 456,000.0 35.4 37.0
50 301.2 .sup.1per ANCI05.1-NESC Type C Construction
.sup.2Predicted results from a 1st order linear finite element
model.
[0051] Any element in a claim that does not explicitly state "means
for" performing a specified function, or "step for" performing a
specific function, is not to be interpreted as a "means" or "step"
clause as specified in 35 U.S.C. .sctn.112, paragraph 6.
[0052] It will be appreciated by those skilled in the art that the
invention can take many forms, and that such forms are within the
scope of the invention as claimed. Therefore, the spirit and scope
of the appended claims should not be limited to the descriptions of
the preferred versions contained herein.
* * * * *