DEFORMABLE ENERGY-ABSORBING UTILITY POLE

CROSS-REFERENCE TO RELATED APPLICATION

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

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.

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. 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.

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.

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.

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.

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.

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 (i) illustrates a #6 sectional steel deformable pole (Polefab, Inc.) with a same height insert;

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;

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;

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;

FIG. 6 (i) illustrates a #6 sectional steel deformable pole (Polefab, Inc.) with a half height insert (unattached within the pole);

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;

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;

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;

FIG. 7(
i) illustrates a #6 sectional steel deformable pole (Polefab, Inc.) with an insert having a tri-pillar form;

FIG. 7(
ii) illustrates a #6 sectional steel deformable pole (Polefab, Inc.) with an insert having a grooved form;

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;

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;

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;

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;

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;

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;

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 (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;

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;

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;

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

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

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.

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 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.

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):

V
₁
_x,y=∫₀^t*a_x,ydt (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 HIC₃₆value of 1000 and a HIC₁₅value of 700 are associated with an 18% probability of life-threatening brain injury (Hutchinson, et al., 1998). The HIC₁₅is 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 t₁and t₂are the start and end times (in seconds, s)

$\begin{matrix} HIC = {[\frac{1}{(t_{2} - t_{1})} \int_{t_{1}}^{t_{2}} a (t) \partial t]}^{2.5} (t_{2} - t_{1}) & (Equation 2) \end{matrix}$

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.

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 HIC₁₅showed 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.

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 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, 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.

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 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, (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

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(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).

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.

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).

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

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.

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.

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.

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 3 mm 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 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)).

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.

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 12767:2007-11.

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, Feb. 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.

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.

DEFORMABLE ENERGY-ABSORBING UTILITY POLE

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