Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02779209 2012-06-04
Deformable Energy-Absorbing Utility Pole
Field of the Invention
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
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.
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).
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.
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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).
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.
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.
United States
Patent 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.
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,
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United States Patent 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.
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
In accordance with a broad aspect of the present invention, there is provided
a utility pole
comprising:
- 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
- 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.
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.
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.
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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.
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.
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.
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.
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.
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.
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.
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.
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CA 02779209 2012-06-04
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:
(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
(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.
In this aspect of the present invention, the process comprises a utility pole
described
according to any of the above-noted embodiments.
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.
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.
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.
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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
The present invention will be further understood from the following detailed
description
of an embodiment of the invention, with reference to drawings in which:
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);
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;
Fig. 3 illustrates normalized impact responses for a deformable pole (e.g. #6
sectional steel pole
by Polefab Inc.);
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;
Fig. 5 illustrates a computer simulation model of a vehicle impact with a #6
sectional steel
deformable pole (Polefab, Inc.) with a same height insert, at (a) 30 km/h, (b)
50 km/h and (c) 70
km/h;
Fig. 6 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 (a) 30
km/h, (b) 50 km/h and (c) 70 km/h;
Fig. 7(i) 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
(a) 30 km/h, (b) 50
km/h and (c) 70 km/h;
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Fig. 7(ii) 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 (a)
30 km/h, (b) 50 km/h
and (c) 70 km/h;
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;
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.
Fig. 9 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 (a) 30 km/h, (b) 50 km/h and (c)
70 km/h (wherein
all measurements of the ring insert are approximate); and
Fig. 10 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 (a) 50 km/h and (b) 70 km/h (wherein all
measurements of the ring
insert are approximate).
Detailed Description of Embodiments of the Invention
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.
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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
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.
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
The National Cooperative Highway Research Program (NCHRP) Report 350 (Sicking,
et
al., 2007) describes the test conditions and criteria for qualifying roadside
structures. The
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occupant risk is assessed using two measures, the "Occupant Impact Velocity"
(01V) 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.
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/s2) / 9.80665 m/s2). It
is desired that the occupant risk criteria be less than the preferred limit
and that they not exceed
the maximum values.
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/s2) and t
is time (s):
t*
V = a dt
x,37
= 0
(Equation 1)
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).
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: HIC15=700 (15 ms window; ms is milliseconds) and HIC36=1000 (36 ms
window). For a
50th percentile male, a HIC36 value of 1000 and a HIC15 value of 700 are
associated with an 18%
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probability of life-threatening brain injury (Hutchinson, et al., 1998). The
HIC15 is the injury
metric utilized by CMVSS 208 (Transport Canada, 2011) to assess head injury in
an automotive
crash, where a is acceleration (m/s2), and t1 and t2 are the start and end
times (in seconds, s)
HC ¨2 ti t2 2.5
a(t)dti (t2 t1)
(t-ti)-
(Equation 2)
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
2.15mm, 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.
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 HIC15 (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 HIC15 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 01V), upon vehicle impact with a breakaway pole
composed of a
sectional steel pole and a base to which the pole is affixed.
CA 02779209 2012-06-04
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
HIC15. As noted above,
it was thought that improvements could be made to the occupant response (e.g.
as measured with
HIC15), which would still allow the pole to meet gross vehicle kinematic
response requirements.
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.
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.
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
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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.
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/m2; 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.
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).
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,
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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.
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.
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.
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.
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.
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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.
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
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).
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.
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.
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
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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
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.
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
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, (a), (b) and (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 (c)).
CA 02779209 2012-06-04
(b) Pole insert of approximately half height
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, ¨1 m and pole
height ¨2 m) was tested for crash response (Fig. 6). 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(b),
simulated impact at
50 km/h).
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
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(i) (b),
simulated impact at 50
km/h).
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
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CA 02779209 2012-06-04
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(ii)(b)).
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
Ring insert designs were investigated using concentric tubes placed at a
height of
The #6 steel pole tapers from bottom to top, and the ring inserts were
designed to fit
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CA 02779209 2012-06-04
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.
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.
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).
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)).
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 3mm thick insert resulting in the highest reduction in
acceleration (Fig. 9
(b)).
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)).
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 3rnm 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)).
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CA 02779209 2012-06-04
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.
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.
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.
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.
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.
References
1. British Standard Institute. "BS EN 1317-1: 2010, Road Restraint System Part
1:
Terminology and General Criteria for Test Methods" [Report]. London: BSI
British
Standards, 2010.
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CA 02779209 2012-06-04
2. Eskandarian, A., Marzougui D. and Bedewi N. E. "Finite element model and
validation
of a surrogate crash test vehicle for impacts with roadside objects."
[Journal] //
International Journal of Crashworthiness. 1997. Vol. 2:3, pp. 239-258.
3. European Committee for Standardization. "Passive safety of support
structures for road
equipment - Requirements, classification and test methods." [Report]. Vienna:
Austrian
Standards Institute, 2007. EN 12767:2007-1 1.
4. Hutchinson, J., Kaiser, M. and Lankarani, H. The Head Injury Criterion
(HIC) functional
[Journal] // Applied Mathematics and Computation. [s.1.] : Elsevier Science
Inc., 1998.
Vol. 96. PIT: S00963003(97) 10106-0.
5. Mak, King K. et al. "Accident analysis: breakaway and non-breakaway poles
including
sign and light standards along highways" [Book]. 1980.
6. Ontario Provincial Standard Specification Material Specification for Steel
Poles, Base
Mounted [Report]. 2010. OPSS 2423.
7. Opiela, K. S. "Finite element model of Ford Taurus" [Online] // FHWA /
NHTSA Finite
Element Model Archive. - 2008. - November 2011.
http://www.ncac.gwu.edu/vml/archive/ncac/vehicle/taurus-v3.pdf
8. Regional Municipality of Waterloo. "2009 Collision Report [Report] /
Transportation &
Environmental Services Department." Waterloo, Ontario: [s.n.], 2009.
9. Sicking, D. L. et al. "Recommended Procedures for the Safety Performance
Evaluation of
Highway Features" [Report] [s.1.] : National Highway Research Program Project,
2007.
22-14(2) Draft Final Report.
10. Sobol, R. "City lights pole falls, hits pedestrian during NW Side crash"
[Online] Chicago
Tribune, February 24, 2012. March 2012.
http://www.chicagotribune.com/news/local/breaking/chi-city-lights-pole-falls-
hits-
pedestrian-during-nwside-crash-20120224,0,3237320.story.
CA 02779209 2012-06-04
10. Transport Canada. "Occupant Restraint Systems in Frontal Impact" (Standard
208)
[Online]. - 2011. http://www.tc.gc.ca/eng/acts-regulations/regulations-cre-
c1038-sch-iv-
208.htm.
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.
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