U.S. patent application number 13/908801 was filed with the patent office on 2013-12-26 for deformable energy-absorbing utility pole.
The applicant listed for this patent is Polefab Inc.. Invention is credited to George F. Arnold, Duane S. Cronin, Philip Lockhart.
Application Number | 20130340383 13/908801 |
Document ID | / |
Family ID | 49709210 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130340383 |
Kind Code |
A1 |
Arnold; George F. ; et
al. |
December 26, 2013 |
DEFORMABLE ENERGY-ABSORBING UTILITY POLE
Abstract
The present invention relates to an energy-absorbing deformable
utility pole that comprises a hollow pole, and an insert placed
within the pole. The insert is positioned in an area of the pole
that is most affected by an impacting vehicle and the length of the
insert is such that it substantially includes the affected area of
the pole. During an impact, the utility pole provides for a more
gradual deceleration of the vehicle, compared to previously known
utility poles, resulting in a reduced level of damage to the
vehicle and its occupant(s). The invention also provides for a
process for increasing the energy absorption of a deformable
utility pole by placing an insert composed of a deformable material
within the pole in the area most likely to be affected by an impact
with a vehicle, and wherein the length of the insert substantially
includes the affected area of the pole.
Inventors: |
Arnold; George F.;
(Georgetown, CA) ; Cronin; Duane S.; (Waterloo,
CA) ; Lockhart; Philip; (Waterloo, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Polefab Inc. |
Newmarket |
|
CA |
|
|
Family ID: |
49709210 |
Appl. No.: |
13/908801 |
Filed: |
June 3, 2013 |
Current U.S.
Class: |
52/831 |
Current CPC
Class: |
E01F 9/631 20160201;
E04C 3/30 20130101 |
Class at
Publication: |
52/831 |
International
Class: |
E01F 9/018 20060101
E01F009/018; E04C 3/30 20060101 E04C003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2012 |
CA |
2779209 |
Claims
1. A utility pole comprising: a hollow pole with a top, a bottom
and an inner surface, wherein said pole is composed of a first
material capable of deforming upon impact with a vehicle; a
concentric annular insert that fits within said hollow pole,
wherein said insert has: a top, a bottom, a length, an outer
surface with an area, and an inner surface; wherein the insert is
positioned in a section of the pole that is contacted and affected
by said impact and the length of said insert substantially includes
said section of the pole; and wherein said insert is composed of a
second material capable of deforming upon said impact with the
pole; wherein the bottom of said pole is attached to a surface when
said utility pole is placed in a working position.
2. The utility pole according to claim 1 wherein the outer surface
of said insert is substantially in contact with the inner surface
of said pole.
3. The utility pole according to claim 1 wherein the insert fits
tightly within the hollow pole.
4. The utility pole according to claim 1, wherein the insert is
about 300 to about 600 mm in length.
5. The utility pole according to claim 4, wherein the insert is
about 600 mm in length.
6. The utility pole according to claim 1, wherein the first
material of the hollow pole and the second material of the insert
are the same.
7. The utility pole according to claim 1, wherein the first
material and the second material have a tensile strength of about
50.000 ksi and has a thickness of about 2 mm to about 3 mm.
8. (canceled)
9. The utility pole according to claim 7 wherein the second
material of the insert is about 2 mm in thickness.
10. The utility pole according to claim 1, wherein said insert is
positioned such that the bottom of said insert is around about 300
mm above the surface to which said pole is attached when said pole
is in its working position.
11.-13. (canceled)
14. The utility pole according to claim 1, further comprising a
base to which the bottom of said pole is attached when the utility
pole is placed in its working position, wherein said base provides
for attachment of said utility pole to said surface.
15. A process for increasing the energy absorption of a utility
pole comprising the following steps: providing a hollow pole with a
top, a bottom and an inner surface, wherein said pole is composed
of a first material capable of deforming upon impact with a
vehicle, and wherein said pole is attached to a surface when placed
in a working position; and placing a concentric annular insert that
fits within said hollow pole, wherein said insert has a top, a
bottom, a length, an outer surface with an area, and an inner
surface; wherein the insert is positioned in a section of the pole
that is contacted and affected by said impact and the length of
said insert substantially includes said section of the pole; and
wherein said insert is composed of a second material capable of
deforming upon said impact with the pole.
16. The process according to claim 15 the outer surface of said
insert is substantially in contact with the inner surface of said
pole.
17. The process according to claim 15, wherein the insert fits
tightly within the hollow pole.
18. The process according to claim 15, wherein the insert is around
about 300 to around about 600 mm in length.
19. (canceled)
20. The process according to claim 15, wherein the first material
of the hollow pole and the second material of the insert are the
same.
21. The process according to claim 15, wherein the first material
and the second material have a tensile strength of about 50,000 ksi
and has a thickness of about 2 mm to about 3 mm.
22. (canceled)
23. The process according to claim 21, wherein the second material
of the insert is about 2 mm in thickness.
24. The process according to claim 15, wherein said insert is
positioned such that the bottom of said insert is about 300 mm
above the surface to which said pole is attached when said pole is
in its working position.
25. (canceled)
26. The process according to claim 15, further comprising one or
more attachment members attaching said insert to said utility pole,
wherein said attachment members may be the same or different.
27. (canceled)
28. The process according to claim 15, further comprising a base to
which the bottom of said pole is attached when the utility pole is
placed in its working position, wherein said base provides for
attachment of said utility pole to said surface.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Canadian patent application serial no. 2,779,209, filed Jun. 4,
2012, entitled "DEFORMABLE ENERGY-ABSORBING UTILITY POLE," which is
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a deformable
energy-absorbing utility pole which, in the event of an impact with
a vehicle, provides for a more gradual deceleration of the vehicle,
compared to a rigid (non-energy absorbing) utility pole or a
low-energy absorbing utility pole.
BACKGROUND OF THE INVENTION
[0003] Utility poles are typically placed along road sides and are
used for a variety of functions, such as bearing intersection light
signals, pedestrian signals, road signs, as well as hydroelectric
lines, and telephone lines.
[0004] Vehicle impacts with fixed roadside structures such as
utility poles can result in severe injuries to both vehicle
occupants and people surrounding the scene of the accident. The
damage can be particularly severe if the utility pole falls down
following vehicle impact, and falls upon nearby pedestrians, other
vehicles on the street, or nearby buildings which may have people
within. In addition, due to the small contact area between the
utility pole and the impacting vehicle, the crush structures of the
impacting vehicle are often times not fully engaged upon impact.
This may result in a much more severe damage to the vehicle and its
occupant(s). For example, vehicle impacts with roadside utility
poles have historically accounted for approximately 5% of all
collisions in Waterloo Region, Ontario, Canada, and these
collisions have a 20% fatality rate (Regional Municipality of
Waterloo, 2009).
[0005] There are various types of utility poles available. Rigid
poles are non-energy absorbing poles and are not designed to
control the motion of the vehicle during impact, nor are they
designed with frangible bases, i.e. bases which detach from the
pole upon vehicle impact (FIG. 1 (a)). Many roadside poles are
comprised of concrete, wood or heavy steel and may be buried in the
ground or mounted to a concrete foundation so that they behave as a
rigid structure during an impact with a vehicle. Thus, vehicle
impacts with rigid utility poles can result in significant damage
to the vehicle and the occupant(s) of the vehicle. Further damage
can occur if the force of impact is enough to break the utility
pole, and cause it to be displaced.
[0006] A breakaway pole is a non-energy absorbing pole attached to
a frangible base which is designed to fail on impact (FIG. 1 (b)).
The breakaway pole is thus displaced upon impact and the impacting
vehicle can continue along its trajectory without a depreciable
loss of speed. This reduces the level of damage and potential
injury to occupants of the impacting vehicle. Mak et al. found that
incorporation of a breakaway design into luminaire poles and large
sign supports was effective in reducing the resultant injury
severity for the vehicle occupant (Mak, et al., 1980). However,
breakaway poles may pose a risk to pedestrians, other road users,
and occupants in nearby buildings, who may be injured by the
displaced pole, as well as by any utilities that are carried by the
displaced pole (Sobol, 2012).
[0007] Energy-absorbing poles absorb part of the force of vehicle,
and as such, are designed to affect the deceleration of a vehicle
during impact. Energy-absorbing poles are typically composed of a
deformable material that deforms upon impact (see FIG. 1 (c)). An
example of such a deformable pole is disclosed in WO 2006/093415.
Alternatively, they may comprise an energy absorbing material at or
near the base of the pole.
[0008] There have been attempts to provide a utility pole that has
improved crash response characteristics that reduce the level of
resultant damage to both vehicle occupants and the pole, and also
aid in limiting possible damage to pedestrians and the
surroundings. U.S. Pat. No. 6,305,140 discloses a utility pole that
comprises an inner pole fitted within an outer pole, with a
plurality of lateral supports attaching the inner pole and the
outer pole, and a fill material deposited in the space between the
inner pole and the outer pole. The fill material may be water,
gravel, concrete or sand, and provides energy absorption upon
vehicle impact. As can be appreciated, such a utility pole has
numerous elements and would not be simple to transport or install.
Also, existing poles cannot readily be retrofitted according to the
above-noted design.
[0009] Various pole protective members are also available which are
meant to protect the base of the pole during an impact, and reduce
the amount of damage to the pole and the impacting vehicle. Such
members are typically attached to the outside of an existing pole.
For example, Canadian Patent No. 2,172,104 discloses a pole
protector for protecting a pole against low speed impact,
comprising an outer shell of a tough material and an inner shell of
an impact-absorbing material, wherein the pole protector is wrapped
around the pole and attached to the pole. Also, U.S. Pat. No.
6,477,800 discloses a clamp-like device that locks around a utility
pole, tree or the like, wherein the device comprises a resilient
material such as rubber which provides energy absorption when a
vehicle impacts the pole or tree, and a reflective panel that aids
in improving visibility of the pole to drivers of oncoming
vehicles. As can be appreciated, such pole protective members may
be expensive and time consuming to install and degrade or shift out
of position over time, reducing their effectiveness.
[0010] Accordingly, there is a need for a utility pole which has
improved crash safety characteristics over currently existing
utility poles. Such a utility pole provides for a reduced level of
damage to both the utility pole and the vehicle, and by extension,
to the surroundings which includes pedestrians, other vehicles, and
surrounding buildings. Preferably, such a utility pole is simple
and economical to fabricate, and easy to transport and install.
SUMMARY OF THE INVENTION
[0011] In accordance with a broad aspect of the present invention,
there is provided a utility pole comprising: [0012] a hollow pole
with a top, a bottom and an inner surface, the hollow pole being
composed of a first material capable of deforming upon impact with
a vehicle; and [0013] a concentric annular insert that fits within
said hollow pole, wherein the insert has a top, a bottom, a length,
an outer surface with an area, and an inner surface, and the insert
is composed of a second material capable of deforming upon impact
of a vehicle with the pole.
[0014] The insert is positioned in a section of the hollow pole
that is contacted and affected by an impact with a vehicle and the
length of the insert is such that it substantially includes the
section of the pole that is affected by the impact.
[0015] The bottom of the utility pole is attached to a surface when
the pole is placed in a working position. An example of a working
position is the placement of the utility pole in an upright
position by a roadside. The positioning of the utility pole may be
additionally facilitated by a pole base, wherein the pole base is
adapted to attach securely to a surface, and the hollow pole sits
securely within the pole base.
[0016] In an embodiment of the present invention, the outer surface
of said insert is substantially in contact with the inner surface
of said pole. Preferable, the insert fits tightly or snugly within
the hollow pole.
[0017] In another embodiment of the present invention, the insert
is around 300 to around 600 mm in length. In a preferred
embodiment, the insert is around 600 mm in length.
[0018] The first material of the hollow pole and the second
material of the insert may be the same or different. For
convenience and ease of manufacturing, the material of the hollow
pole and the material of the insert may be the same.
[0019] In an embodiment of the invention, the material of the
hollow pole has a tensile strength of around 50,000 ksi, and a
thickness of around 2 mm to around 3 mm. Preferably, the material
of the hollow pole is 44W steel. As noted above, the insert may be
composed of the same material as the hollow pole. Thus, the insert
may also be composed of a material with a tensile strength of
around 50,000 ksi and a thickness of around 2 mm to around 3 mm. In
a preferred embodiment, the material of the insert is 44W steel.
Preferably, the material of the insert is around 2 mm in
thickness.
[0020] In another embodiment of the invention, the insert is
positioned such that the bottom of said insert is around 300 mm
above the surface to which the utility pole is attached when in its
working position.
[0021] In yet another embodiment of the invention, the insert may
further comprise one or more tabs placed at near the bottom edge of
its inner surface, which aid in positioning and placement of the
insert within the hollow pole.
[0022] The utility pole may also further comprise one or more
attachment members attaching the insert to said utility pole. The
attachment members may be the same or different. Suitable
attachment members include a bolt and a screw.
[0023] The utility pole may further comprise a base to which the
bottom of said pole is attached when the utility pole is placed in
its working position, wherein said base provides for attachment of
the utility pole to the surface.
[0024] According to another aspect of the present invention, there
is provided a process for increasing the energy absorption of a
utility pole comprising the following steps: [0025] (a) providing a
hollow pole with a top, a bottom and an inner surface, wherein said
pole is composed of a first material capable of deforming upon
impact with a vehicle, and wherein said pole is attached to a
surface when placed in a working position; and [0026] (b) placing a
concentric annular insert that fits within said hollow pole,
wherein said insert has a top, a bottom, a length and an outer
surface; wherein the insert is positioned in a section of the pole
that is contacted and affected by said impacting vehicle and the
length of said insert is such that the insert substantially
includes the affected area of the pole; and wherein said insert is
composed of a second material capable of deforming upon impact of
said vehicle with the pole.
[0027] In this aspect of the present invention, the process
comprises a utility pole described according to any of the
above-noted embodiments.
[0028] An advantage of the present invention is providing a utility
pole that, in the event of an impact with a vehicle, deforms upon
impact and absorbs the energy of impact, and provides a more
controlled and smoother deceleration of the impacting vehicle when
compared to a previously known deformable utility pole. As a
result, the level of injury to the vehicle occupant and damage to
the vehicle is reduced. In addition, the potential for damage to
the surroundings (e.g. pedestrians, nearby vehicles, nearby
buildings, etc.) is also reduced.
[0029] Another advantage of the present invention is that the
utility pole is simple and economical to manufacture, transport and
install. The insert is also simple and economical to manufacture
and install.
[0030] Yet another advantage of the present invention is that
pre-existing, unmodified poles may be modified to become the
utility pole of the invention, by insertion of the above-noted
insert, and provided that the resultant utility pole meets the
requirements noted above. Thus, in situ poles may be removed, the
insert installed, and the thus-modified pole returned to its
working position.
[0031] Other and further advantages and features of the invention
will be apparent to those skilled in the art from the following
detailed description of an embodiment thereof, taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The present invention will be further understood from the
following detailed description of an embodiment of the invention,
with reference to drawings in which:
[0033] FIG. 1 illustrates a simulated impact of a typical North
American mid-sized sedan vehicle, moving at 50 km/h, with (a) a
rigid pole, (b) a rigid pole with a breakaway base, and (c) an
energy absorbing, deformable pole (e.g. #6 sectional steel pole by
Polefab Inc., Newmarket, Ontario);
[0034] FIG. 2 illustrates the simulated acceleration response of a
vehicle impact with a #6 sectional steel pole (Polefab, Inc.) at
various speeds, and the Ride Down Acceleration threshold of 20.49
g;
[0035] FIG. 3 illustrates normalized impact responses for a
deformable pole (e.g. #6 sectional steel pole by Polefab Inc.);
[0036] FIG. 4 illustrates a computer simulation model of (a) an 841
kg pendulum, and (b) and (c), a finite element model of a
deformable utility pole;
[0037] FIG. 5 (i) illustrates a #6 sectional steel deformable pole
(Polefab, Inc.) with a same height insert;
[0038] FIG. 5 (ii) (a) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a same height insert at 30 km/h;
[0039] FIG. 5 (ii) (b) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a same height insert at 50 km/h;
[0040] FIG. 5 (ii) (c) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a same height insert at 70 km/h;
[0041] FIG. 6 (i) illustrates a #6 sectional steel deformable pole
(Polefab, Inc.) with a half height insert (unattached within the
pole);
[0042] FIG. 6 (ii) (a) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a half height insert (unattached within the pole), at 30
km/h;
[0043] FIG. 6 (ii) (b) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a half height insert (unattached within the pole), at 50
km/h;
[0044] FIG. 6 (ii) (c) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with a half height insert (unattached within the pole), at 70
km/h;
[0045] FIG. 7(i) illustrates a #6 sectional steel deformable pole
(Polefab, Inc.) with an insert having a tri-pillar form;
[0046] FIG. 7(ii) illustrates a #6 sectional steel deformable pole
(Polefab, Inc.) with an insert having a grooved form;
[0047] FIG. 7 (iii) (a) illustrates a computer simulation model of
a vehicle impact with a #6 sectional steel deformable pole
(Polefab, Inc.) with an insert having a tri-pillar form at 30
km/h;
[0048] FIG. 7 (iii) (b) illustrates a computer simulation model of
a vehicle impact with a #6 sectional steel deformable pole
(Polefab, Inc.) with an insert having a tri-pillar form at 50
km/h;
[0049] FIG. 7 (iii) (c) illustrates a computer simulation model of
a vehicle impact with a #6 sectional steel deformable pole
(Polefab, Inc.) with an insert having a tri-pillar form at 70
km/h;
[0050] FIG. 7 (iv) (a) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with an insert having a grooved form at 30 km/h;
[0051] FIG. 7 (iv) (b) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with an insert having a grooved form at 50 km/h;
[0052] FIG. 7 (iv) (c) illustrates a computer simulation model of a
vehicle impact with a #6 sectional steel deformable pole (Polefab,
Inc.) with an insert having a grooved form at 70 km/h;
[0053] FIG. 8(i) illustrates a side cross-sectional view of a
utility pole comprising a ring insert of length (a) about 300 mm,
and (b) about 600 mm;
[0054] FIG. 8(ii) illustrates an embodiment of the utility pole
comprising (a) a side cross-sectional view of a hollow pole 11
(e.g. #6 sectional steel pole; Polefab Inc., Newmarket, Ontario)
with a hand hole, positioned in a base comprising a collar 21 and a
base plate 22, (b) a side cross-sectional view of a 600 mm insert
20 with tabs 23, (c) a side cross-sectional view of the hollow pole
11 with the insert 20 in place, showing the lower end of the insert
around 300 mm above the bottom of the base plate 22, and (c) top
view of the utility pole with the insert in position.
[0055] FIG. 9 (a) illustrates a computer simulation model of a
vehicle impact with a deformable pole (#6 sectional steel pole,
Polefab, Inc.) with a (i) 600 mm ring insert, 2 mm wall thickness,
and (ii) 600 mm ring insert, 3 mm wall thickness, at 30 km/h;
[0056] FIG. 9 (b) illustrates a computer simulation model of a
vehicle impact with a deformable pole (#6 sectional steel pole,
Polefab, Inc.) with a (i) 600 mm ring insert, 2 mm wall thickness,
and (ii) 600 mm ring insert, 3 mm wall thickness, at 50 km/h;
[0057] FIG. 9 (c) illustrates a computer simulation model of a
vehicle impact with a deformable pole (#6 sectional steel pole,
Polefab, Inc.) with a (i) 600 mm ring insert, 2 mm wall thickness,
and (ii) 600 mm ring insert, 3 mm wall thickness at 70 km/h;
[0058] FIG. 10 (a) illustrates the calculated energy absorbed by
(i) an unmodified deformable pole (#6 sectional steel pole,
Polefab, Inc.), (ii) the pole with a 600 mm insert with 3 mm wall
thickness, during a vehicle impact at 50 km/h; and
[0059] FIG. 10 (b) illustrates the calculated energy absorbed by
(i) an unmodified deformable pole (#6 sectional steel pole,
Polefab, Inc.), (ii) the pole with a 600 mm insert with 3 mm
thickness, during vehicle impact at 70 km/h.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0060] In the event of an impact of a vehicle with a utility pole,
two primary safety issues are protection of vehicle occupants, and
the protection of pedestrians who may be impacted by the vehicle or
pole. Conventional design has focused on utility poles that are
relatively rigid, such that they can withstand lower speed impacts
and the incorporation of frangible bases to protect vehicle
occupants at higher speeds; however, this does not address the
issue of pedestrian safety or reducing the level of damage to the
surroundings.
[0061] Hollow poles composed of steel are widely used along roads
due to their ease of manufacture, transportation and handling.
These poles may be sectional to increase the ease of manufacturing,
storage, transportation, handling and on-site or in situ assembly.
Hollow steel poles may be attached to a frangible base to form a
breakaway pole, thus providing for improved crash safety as hollow
steel poles are generally lighter and less rigid than a wooden or
concrete pole of comparable. It was thought that the design of such
a pole could be improved to reduce the amount of damaged sustained
by the vehicle and the occupants of the vehicle.
Evaluation of Utility Pole Impact Tests: Test Standards
[0062] In North America, the evaluation of utility pole impact
tests involves a number of factors, but the principle analytical
measure used in these tests is the "Occupant Impact Velocity"
(OIV). For breakaway utility poles, both the OIV and "Occupant Ride
Down Acceleration" (RA) must be measured. The current North
American test standard, NHCRP 350 (Sicking, et al., 2007), uses an
1100 kg target vehicle with initial velocities of 30 km/h, 50 km/h,
70 km/h, and 100 km/h, depending on the test level being evaluated.
The various test levels recognizes that some roadside structures
may be used in high speed applications (such as freeway sign
markers) and some for lower speed applications such as urban
intersections.
[0063] The European test standard (British Standard Institute,
2010) utilizes similar evaluation criteria; the Acceleration
Severity Index (AST) and Theoretical Head Impact Velocity (THIV).
The test standard (EN 12767) (European Committee for
Standardization, 2007) defines three levels of energy absorption
for pole structures, based on how well they decelerate the
impacting vehicle. These three levels of energy absorption are: (1)
High Energy Absorbing, (2) Low Energy Absorbing and (3) Non-Energy
Absorbing. Support structures with no performance requirements for
passive safety are considered Class 0; wooden and concrete utility
poles can be considered part of this class.
Indices for Measuring Severity of a Vehicle Impact
[0064] The National Cooperative Highway Research Program (NCHRP)
Report 350 (Sicking, et al., 2007) describes the test conditions
and criteria for qualifying roadside structures. The occupant risk
is assessed using two measures, the "Occupant Impact Velocity"
(OIV) and the "Ride Down Acceleration" (RA). These criteria are
based on the response of a hypothetical, unrestrained, front seat
occupant that behaves as a point mass, under the assumption that
the motion of the occupant is tied to the vehicular acceleration.
During impact, the occupant is assumed to strike the instrument
panel, windshield or side structure and remain in contact with the
interior surface.
[0065] The Ride Down Acceleration (RA) is defined as the highest
lateral and longitudinal component of resultant vehicular
acceleration averaged over any 10 ms interval for the collision
pulse subsequent to occupant impact. The threshold limits for the
RA is 20.49 g, with a preferred limit of 15 g (wherein
g=(acceleration of the vehicle in m/s.sup.2)/9.80665 m/s.sup.2). It
is desired that the occupant risk criteria be less than the
preferred limit and that they not exceed the maximum values.
[0066] The Occupant Impact Velocity (OIV) is taken as the velocity
of the vehicle's centre of gravity at the time when the
displacement is either 0.6 m forward or 0.3 m lateral, whichever is
smaller (t*). The expression to calculate OIV is as follows,
wherein a is acceleration (m/s.sup.2) and t is time (s):
V.sub.1.sub.x,y=.intg..sub.0.sup.t*a.sub.x,ydt (Equation 1)
[0067] For roadside support structures such as utility poles, the
OIV has a preferred limit of 3 m/s and a maximum limit of 5 m/s. If
the pole is evaluated as a breakaway utility pole, the OIV limits
are 9.1 m/a and 12.2 m/s for the preferred and maximum limits
respectively (Sicking et al., 2007).
[0068] The Head Injury Criterion (HIC) uses the resultant linear
acceleration of the head to calculate a value which is then related
to a tolerance value for injury (SAE, 2003). There are two
different tolerance levels depending on the duration of the
"window" used for calculating the HIC: HIC.sub.15=700 (15 ms
window; ms is milliseconds) and HIC.sub.36=1000 (36 ms window). For
a 50th percentile male, a HIC.sub.36 value of 1000 and a HIC.sub.15
value of 700 are associated with an 18% probability of
life-threatening brain injury (Hutchinson, et al., 1998). The
HIC.sub.15 is the injury metric utilized by CMVSS 208 (Transport
Canada, 2011) to assess head injury in an automotive crash, where a
is acceleration (m/s.sup.2), and t.sub.1 and t.sub.2 are the start
and end times (in seconds, s)
HIC = [ 1 ( t 2 - t 1 ) .intg. t 1 t 2 a ( t ) t ] 2.5 ( t 2 - t 1
) ( Equation 2 ) ##EQU00001##
[0069] Steel poles with a relatively thin wall in comparison to its
diameter are deformable and will absorb some of the energy of
impact with a vehicle by deformation. Thin-walled poles composed of
steel or other materials of similar tensile strength would fall
into the high energy absorbing category for pole structures
described above (test standard EN 12767, European Committee for
Standardization, 2007). In such thin-walled utility poles have a
high ratio of pole diameter to wall thickness. An example of such a
pole is the #6 sectional steel pole by Polefab Inc., composed of
44W steel of 50,000 ksi tensile strength, and a wall thickness of
2.15 mm, with an inner diameter of about 319 mm at about 300 mm
from the lower end of the pole (the #6 pole tapers gradually in
diameter from the lower end to the upper end). The crash response
of the #6 sectional steel pole by Polefab, Inc. is typical of other
hollow, thin-walled steel poles that are presently available.
[0070] In computer simulated impacts between a vehicle and a
deformable utility pole (e.g. the #6 sectional steel pole), it was
observed that there is a large spike in acceleration during impact
which results in high values for both the RA and HIC.sub.15 (FIG.
2). It was also was noted that at higher impact speeds (e.g. above
30 km/h), the occupant response does not follow the same trend as
the vehicle response, wherein HIC.sub.15 showed a steep increase
with increasing impact velocity, while RA showed a slight decrease
with increasing impact velocity (FIG. 3). This meant that
improvements could be made to occupant response which would still
allow the utility pole to meet the gross vehicle kinematic response
requirements. The objective was to reduce the two measurable
parameters, the ride-down acceleration (RA) and the occupant
response (i.e. Occupant Impact Velocity, or OIV), upon vehicle
impact with a breakaway pole composed of a sectional steel pole and
a base to which the pole is affixed.
[0071] Improvements to an existing deformable pole (#6 sectional
steel pole; Polefab Inc., Newmarket, Ontario; composed of 44W
carbon steel, tensile strength about 50,000 ksi, 2.156 mm
thickness) were investigated with the goal of improving the
response of the pole during impact while maintaining occupant and
vehicle metrics below the preferred threshold limits. The main
parameter that was targeted for reduction was the acceleration of
the vehicle. In a computer simulated impact of a vehicle with the
#6 pole, the vehicle shows a large spike in acceleration during
impact (FIG. 2), which results in high values for both the RA and
HIC.sub.15. As noted above, it was thought that improvements could
be made to the occupant response (e.g. as measured with
HIC.sub.15), which would still allow the pole to meet gross vehicle
kinematic response requirements.
[0072] Surprisingly, it has now been found that a deformable
energy-absorbing utility pole comprising a concentric or annular
insert, composed of a material that also deforms upon impact and
positioned in the zone of impact of the pole, exhibits
significantly increased energy absorption upon impact with a
vehicle, when compared to an unmodified deformable utility pole.
The insert fits within the pole such that the outer surface of the
insert is in contact with the inner surface of the utility pole.
Preferably, the insert is of a shape to fit snugly within the
hollow body of the pole. The insert is of an appropriate length to
substantially include the area of the pole that would be expected
to come in contact with and be affected by a vehicle during an
impact. The length of the insert may vary, and would depend on a
number of factors. Examples of such factors affecting the length of
the insert may include the end use of the utility pole (e.g. by a
suburban roadside, or by a highway), what types of vehicles would
typically frequent the roadway where the utility pole is to be
used, and the average velocity of the vehicles in that roadway.
[0073] Even more surprisingly, the deformable utility pole
comprising the concentric insert noted above exhibits more
significantly controlled deformation and buckling upon impact, when
compared to an unmodified utility pole. As a result, a deformable
pole comprising the insert provides more controlled deceleration of
the vehicle, thereby reducing the level of potential injury to the
occupant.
[0074] Preferably, the insert is of a thickness that is around 1:1
with the thickness of the pole itself. Also, the length of the
insert is such that it substantially includes the zone of impact
between a typical vehicle and the pole, when the pole is placed in
a normal working position. On initial impact, the insert provides
localized increased rigidity of the pole, which results in crushing
of the vehicle to decelerate the vehicle. As the impact progresses
in time, the pole begins to buckle within and outside the area
supported by the insert, absorbing additional energy.
[0075] The above-noted utility pole comprises a hollow pole and
optionally a base for securing the pole to the ground for placement
of the utility pole in a working position (e.g. upright, by the
side of a road). The pole is preferably composed of steel with a
thickness of approximately 2 mm, with a tensile strength of about
50,000 ksi. In an embodiment of the invention, the steel is
preferably 44W carbon steel with a tensile strength of about 50,000
ksi (344 737 864 N/m.sup.2; 345 MPa), and a thickness of
approximately 2 mm. Upon impact, the pole would absorb part of the
force of impact and deform in a controlled manner. Depending on the
amount of force applied, the pole may detach from the base. For
example, with a pole composed of 44W carbon steel as noted above,
an impact with a vehicle of about 1240 kg will cause detachment of
the pole from the base at a minimum speed of 65-68 km/h.
[0076] In an embodiment of the invention, the insert is concentric
with the inner surface of the utility pole such that the lower end
of the insert (closer to the ground) abuts the inner surface of the
utility pole at a height such that the insert is positioned within
the zone of impact if the pole were to be impacted by a typical
vehicle, wherein the impact zone is the section of the pole that
would be expected to be contacted and affected by a typical
passenger vehicle in the event of an impact. The length of the
insert is such that it substantially includes the impact zone of
the pole, as described above. Thus, the insert provides a localized
increase in the rigidity of the pole, which results in a more
controlled deformation of the pole and a more gradual deceleration
in the impacting vehicle, compared to an unmodified utility pole.
The crash response is thus improved over previously existing
deformable utility poles and high-energy absorbing poles, as well
as other types of poles such as low energy-absorbing poles and
rigid poles (European test standard test standard EN 12767,
European Committee for Standardization, 2007).
[0077] The insert is positioned within the pole such that it is
placed in the section of the utility pole that is most likely to be
contacted and affected by an impacting vehicle. This would depend
on a number of factors, such as where the utility pole is to be
used (e.g. by a suburban roadside, or by a highway), and in what
jurisdiction the pole will be deployed in. In North America, the
bumper height of passenger vehicles is around 400 to around 510 mm.
As such, for utility poles deployed in North America, the insert is
placed at a height such that the lower end of the insert is about
300 mm above the surface to which the pole is attached, when the
utility pole is placed in its working position. For example, the
bottom of the pole may be at the same level as the ground to which
the pole is attached. It is also possible that the bottom section
of the pole may be buried in the ground, in which case, the insert
would be positioned within the pole such that the lower end of the
insert is about 300 mm above the ground.
[0078] In an embodiment of the invention, the insert fits tightly
within the hollow pole, i.e. the outer surface of the insert is in
substantial contact with the inner surface of the pole. In such a
configuration, the insert is slid into place and the insert jams
into position within the hollow body of the pole, such that the
lower end of the insert is positioned around 300 mm above the
surface to which the utility pole is attached, when the utility
pole is in its working position. The insert is preferably composed
of steel, and even more preferably, it is composed of the same
steel as used to manufacture the pole, with a thickness from around
2 mm to around 3 mm. In yet another preferred embodiment, the
insert is around 2 mm in thickness.
[0079] The insert may be rotated within the hollow pole until the
outer wall of the insert best matches the inner wall of the hollow
pole, such that there is a snug fit between the outer wall of the
insert and the inner wall of the hollow pole.
[0080] In yet another embodiment of the invention (see FIG.
8(ii)(b)), the positioning of the insert within the hollow pole may
be aided by one or more tabs 23 which are attached at or near the
bottom edge of the inner surface of the insert. When the insert is
rotated within the hollow pole until a snug fit is achieved, the
points on the insert where the tabs are located act as brace points
when force is applied to lodge or jam the insert into a tight fit
against the inner wall. The tabs may thus aid in positioning the
insert in the area of the hollow pole that would come in contact
with an impacting vehicle.
[0081] The insert may be further secured to the pole with one or
more attachment members, such as a bolt or a screw. The attachment
members may be the same or different.
[0082] When positioning the utility pole in its working position,
the utility pole may be attached directly to a surface, e.g. by
burying the lower end of the pole in the ground. Alternatively, the
positioning of the utility pole in its working position may be
facilitated with a pole base which aids in securing the utility
pole to a surface (e.g. concrete) (see FIG. 8(ii) (a)). The pole
base may be composed of a collar 21, and a base plate 22 attached
to the collar. The collar 21 of the pole base is adapted such that
the hollow pole 11 fits securely in it.
[0083] Further details of the preferred embodiments of the
invention are illustrated in the following Examples which are
understood to be non-limiting with respect to the appended
claims.
Example 1
Impact Simulation Test
[0084] To test the performance of modified utility poles and to
compare against unmodified utility poles, a computer simulation was
used to model impacts and to calculate the theoretical acceleration
response of the impacting object, and the energy absorption of the
pole upon impact. A finite element model of a standard energy,
absorbing pole, in this case, Polefab Inc.'s #6 sectional steel
pole, was developed and subjected to simulated impacts with an 841
kg deformable pendulum model (FIG. 4) and a mid-sized automobile
(FIG. 1 (c)). A description of the pendulum model test is provided
in Eskandarian et al., 1997. The vehicle model used for this study
was a 1635 kg 2001 model year Ford Taurus, a typical North American
mid-sized sedan. (Opiela, 2008).
[0085] The #6 sectional steel pole by Polefab Inc. is composed of
44W carbon steel with a thickness of 2.156 mm and tensile strength
about 50,000 ksi.
[0086] The simulation test was validated with a standard sectional
steel pole (Polefab #6 pole, Polefab Inc., Newmarket, Ontario). The
pendulum provides a 30 km/h impact, and the impact was filmed using
high speed video which was used in conjunction with the impactor
accelerometer data.
[0087] In a real life crash, the utility pole can sometimes detach
partially or completely from its attachment point (e.g. the base of
the pole which is secured to the ground). The computer simulation
model takes into account the possibility of the pole detaching
partially or completely from its attachment point to the surface
following an impact with a vehicle. That is, in the simulation, the
utility pole may detach completely if the impact velocity is
greater than around 65 km/h, and the utility pole may also detach
partially at lower impact velocities.
Example 2
Modifications to Pole to Increase Energy Absorption
[0088] It was thought that a concentric tube inserted within a
utility pole may potentially aid in improving the crash response of
the pole (i.e. by reducing the level of damaged sustained by an
impacting vehicle and to its occupant(s)). Another design
constraint considered involved the fabrication and ease of
introduction to existing production facilities and processes, as
well as ease of implementation. The designs considered were all
concentric ring shaped inserts that could be inserted into the pole
via the base of the pole, without blocking the inner wiring channel
or hand hold for the pole.
[0089] The modified poles (i.e. poles comprising an insert), were
then subjected to the pendulum impact test described above, and the
acceleration response of the pendulum (upon impact with the pole)
was measured over time. The acceleration response is taken as the
Ride Down Acceleration (RA), as defined above.
(a) Pole Insert of Same Height
[0090] The first design considered was a concentric hollow pole
insert of 1 mm thickness that was the same height as the #6
sectional pole, which is approximately 2 m in height. The
concentric hollow pole insert 12 fitted snugly within the hollow
body of the #6 pole 11 (FIG. 5). Two variations of this design were
investigated: (1) insert not attached to the pole, and (2) insert
attached at the top and bottom to the pole. It was found that this
design increased the acceleration profile of the impacting vehicle,
for both the attached and unattached configurations as compared to
the unmodified pole (see FIG. 5, (ii) (a), (ii) (b) and (ii) (c)).
The presence of the same height insert within the pole also
introduced a sharp acceleration spike at the end of the impact at
70 km/h, compared to the unmodified pole (FIG. 5 (ii) (c)).
(b) Pole Insert of Approximately Half Height
[0091] Next, a #6 steel pole 11 comprising a concentric insert 13
of 1 mm thickness with a height approximately half that of the #6
sectional steel pole (i.e. insert height, .about.1 m and pole
height .about.2 m) was tested for crash response (FIG. 6(i)). In
this design, the insert was not attached to the pole. As seen in
FIG. 6, the acceleration response upon impact of the pole
comprising the half pole insert was very close to that of the pole
with the same height insert. In addition, the acceleration response
with the pole comprising the half height insert exhibited a spike
at the end of the impact (see for example, FIG. 6 (ii) (b),
simulated impact at 50 km/h).
[0092] An analysis of the impact tests of the poles comprising the
half height insert and the same height insert indicated that the
deformation of the pole was initiating later in time as a result of
the overall increased wall thickness, i.e. due to the combined wall
thicknesses of the hollow pole and the insert acting together.
(c) Pole Inserts with Material Removed: Tri-Pillar and Tri-Groove
Designs
[0093] To help initiate the initial buckling of the pole, two
designs were investigated that had material removed in vertical
strips from the insert. The first design that was considered with
this concept had material removed from the insert to create three
equally spaced strips or "pillars" 15, attached via a ring 16 at
the top and a ring 17 at the bottom of the insert (FIG. 7 (i)). In
FIG. 7(i), the insert is also shown with the pole base 14 for the
utility pole. In this example, the insert was designed to fit
snugly within the pole such that the lower end of the pole was
positioned about 300 mm above the surface to which the pole was
attached. During the simulated impact test with a utility pole
comprising this insert, a prolonged acceleration plateau at the
lower impact speed was observed but the same spike in acceleration
occurred at the end of the impact, similar to the impacts observed
with the poles comprising the full and half pole inserts (see FIG.
7(iii) (b), simulated impact at 50 km/h).
[0094] Another design of the insert had equally spaced grooves 18
(in one case, 3 grooves, in another case, 4 grooves) of 0.5 mm
depth cut into the full height pole insert described earlier in
Example 2(a) (see FIG. 7 (ii)). In the impact simulation test, both
of the grooved designs exhibited a similar plateau to the
tri-pillar design for the 30 km/h impact but also exhibited much
higher spikes in acceleration at the higher speed impacts than any
of the previously considered designs (see for example FIG.
7(iv)(b)).
Example 3
Optimized Pole Insert
[0095] Review of initial modifications to a standard hollow
sectional steel pole (#6 pole, Polefab Inc., Newmarket, Ontario)
showed that the key portion of the pole for impact performance was
the lower portion of the pole just above the base ring. This
section of the pole is where a typical passenger vehicle would be
expected to impact, in a crash scenario where the vehicle runs into
the pole. Deformation of this area allowed for initialization of
controlled deceleration. However, it was thought that by thickening
the area or section of the pole where a standard passenger vehicle
would expect to impact, more energy could be absorbed,
theoretically reducing the acceleration peak and producing a more
gradual deceleration of the impacting vehicle.
[0096] Ring insert designs were investigated using concentric tubes
placed at a height of 300 mm from the base of the pole (i.e.
approximately 300 mm above the ground when the pole is placed in
its working position). As noted above, the length of the insert and
the placement of the insert was an issue, as a typical North
American passenger vehicle has a bumper height of about 400 to
about 510 mm. The insert had to be of an adequate length to cover
the area of the pole that would most likely be contacted and
affected by a vehicle during any impact. As shown in FIG. 8(i), a
ring insert 19 of height (length) 300 mm and a ring insert 20 of
height (length) 600 mm, were investigated. The ring insert 20 of
length 600 mm was created after initial simulations showed the
vehicle riding over the top of the shorter insert during the higher
speed impacts.
[0097] The #6 steel pole tapers from bottom to top, and the ring
inserts were designed to fit snugly within the pole such that the
insert would be reside within the main impact zone of the pole,
i.e. the section of the pole that would be expected to be contacted
and affected by a typical passenger vehicle in the event of an
impact. As a typical passenger vehicle in North America has a
bumper height of around 400 to around 510 mm, the inserts were
placed within the pole such that the lower end was about 300 mm
from the bottom of the pole. In this instance, the bottom of the
pole was considered to be at the same level as the ground to which
the pole was attached. However, it is possible that the bottom
section of the pole may be buried in the ground, in which case, the
insert would be positioned within the pole such that the lower end
of the insert is about 300 mm above the ground.
[0098] In a preferred embodiment, the insert has an outer diameter
of 319.12 mm at its lower end and an outer diameter of 304.32 mm at
the upper end, with a wall thickness of 2.15 mm.
[0099] Two insert thicknesses of about 2 mm and about 3 mm were
investigated for the 600 mm insert, using the full vehicle impact
model (FIG. 9).
[0100] No differences were seen between the two thicknesses for the
low speed impact at 30 km/h, but a small increase was seen in the
acceleration response when compared to the unmodified pole,
however, it was still below the RA threshold limit (FIG. 9
(a)).
[0101] The following two ring inserts, (1) 600 mm, 2 mm wall
thickness and (2) 600 mm, 3 mm wall thickness, showed a slight
increase in vehicle acceleration response for the first
acceleration peak for the 50 km/h impacts (FIG. 9 (b)). In
comparison to the unmodified pole, the second acceleration peak was
attenuated by the addition of the insert, with the 3 mm thick
insert resulting in the highest reduction in acceleration (FIG. 9
(b)).
[0102] By examining the energy absorbed by the pole, it could be
seen that the addition of the inserts allowed the pole to absorb
approximately the same amount of energy as the unmodified pole for
the 50 km/h impact (FIG. 10 (a)), but in the case of the 2 mm thick
600 mm insert, significantly more energy for the 70 km/h impact
(FIG. 10(b)).
[0103] The 3 mm thick insert (length 600 mm) was thought to
increase the overall rigidity of the pole. That is, the pole
comprising the 3 mm insert did not absorb as much energy as the
pole comprising the 2 mm thick insert. The increased rigidity also
resulted in the pole breaking away at the base during the 50 km/h
impact for the 3 mm thick insert. A simulated impact with the pole
with the 2 mm insert resulted in a longer acceleration pulse which
was still below the maximum RA limit for a 70 km/h impact (FIG. 9
(c)).
[0104] In view of the foregoing, an optimal design for reducing
ride-down acceleration upon impact with the #6 steel pole was
determined to be a concentric, annular insert approximately 600 mm
tall, with a wall thickness of about 2 mm, with the lower end of
the insert set at about 300 mm above the surface to which the pole
is attached.
[0105] As noted above, the insert was preferably designed to fit
snugly within the pole such that it is positioned within the main
impact zone of the pole (if the pole were to be contacted by an
oncoming vehicle) and would not slip out of place.
[0106] In an embodiment of the utility pole (FIG. 8(ii)), two tabs
23 were welded to the lower end of the interior of the insert (in
this example, the 600 mm insert 20) to act as points upon which
force could be applied. The presence of the tabs 23 was to further
ensure that the insert did not shift out of place within the pole.
When the insert was rotated within the hollow pole until a snug fit
between the outer wall of the insert and the inner wall was
achieved, the points on the insert where the tabs are located acted
as brace points when force was applied, helping to lodge or jam the
insert in place. An optional hand hole 24 in the wall of the hollow
pole 11 allowed an operator to manually fit the insert into the
pole. If a hand hole is present, a cover 25 may be used to cover
the hand hole to protect the interior of the utility pole.
[0107] In yet another embodiment of the utility pole (FIG. 8(ii)),
two screws 26 were inserted through the wall of the hollow pole and
the wall of the insert, thus attaching the insert to the pole. The
presence of the screws helped to keep the insert from twisting or
shifting within the pole.
[0108] It was noted that the presence of the tabs and/or the screws
was optional, and merely to further ensure that the insert was
properly positioned within the pole, without affecting the working
properties of the utility pole.
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[0120] Numerous modifications, variations and adaptations may be
made to the particular embodiments of the invention described above
without departing from the scope of the invention, which is defined
in the following claims.
* * * * *
References