WO2006093415A1

WO2006093415A1 - Hollow yielding pole structure for use in traffic areas

Info

Publication number: WO2006093415A1
Application number: PCT/NO2006/000059
Authority: WO
Inventors: Kjell Arne Malo; Haavard Ilstad
Original assignee: Euromast As
Priority date: 2005-02-18
Filing date: 2006-02-14
Publication date: 2006-09-08
Also published as: NO20050868L; NO325255B1; EP1848860A1; NO20050868D0

Abstract

Hollow pole construction for the raising of post constructions, guard rails, separating constructions or the like, utilized in connection with arterial traffic, arranged to have significant static strength and rigidity during normal use, while being flexible and energy absorbing when the construction is exposed to local, transverse loads. When subjected to a blow-like impact, the pipe wall of the pole construction will collapse and a 'wave of collapse' is generated, propagating easily in the longitudinal directions of the pole construction. The wave of collapse leaves a flattened cross-sectional profile that will bend easily around a car, for example. A particular combination of material properties and geometrical shapes for the cross-section of the pole is applied, in that the thickness of the pipe wall remains in the range of [formel 1], where the unit for the thickness, t, and diameter, D, is millimeter and the unit for the yield stress for the material is N/mm2, while the diameter, D, to thickness, t, ratio remains in the range of [formel 2], E being the modulus of elastiticity (Young's modulus) and having the same unit as the yield stress, σ0, of the material.

Description

Hollow yielding pole structure for use in traffic areas

The invention concerns a flexible pole construction as disclosed in the preamble of claim 1, utilized during the raising of, for example, traffic or road signs, posters, light signals, portals or semiportals, guard rails or the like pole and post constructions utilized in connection with arterial traffic, and as an energy absorbing construction, center railing or partition, or in connection with, or as a component of, elements that are designed to break or to be flexible and to absorb shock according to selected criteria.

Background of the invention Lamp poles, signs, railings and the like constructions are currently parts of the traffic environment in general. Such constructions are typically mounted on a foundation that consists OF concrete or steel, or they are connected to other constructions, and must be properly dimensioned to be able to carry their own weight, in addition to natural loads such as snow and wind, and other loads. This means that such constructions may involve very demanding properties with respect to rigidity and deformation characteristics when hit by a vehicle or other moving objects. The increasing degree of preference given to traffic safety in many countries has lead one to make efforts to create a traffic environment that provides a passive safety for its users. In this connection a european standard is drawn up for the testing and approval of flexible road equipment: NS-EN 12767 Passive safety of support structures for road equipment. This standard sets up requirements with regard to the flexibility and energy absorbing properties of road equipment. Flexible masts are classified according to their energy absorbing ability as follows:

- HE: High energy absorbing

- LE: Low energy absorbing - NE: Non-energy absorbing

For a structure to be classified as HE, a vehicle must be caught and slowed down controlably to a low velocity of reflection, mainly due to a high energy absorbing ability of the actual road structure. For the LE class, the vehicle must also be slowed down controlably, but the requirements for energy absorbing ability are less, since the corresponding requirements for the velocity of reflection are less strict. If the requirements for velocity of reflection are met, the road structure may subsequently break and/or get catapulted away. Both for the HE and the LE classes it is required that no loose parts are thrown out of, or penetrate into the compartment. According to the NE class the structure I

should break immediately when hit, and then get catapulted away. This is typically refered to as a "break-away" system or a NE flexible structure. Technical problem

The introduction of specific requirements with respect to levels of both acceleration and speed, results in that most of the known configurations of road equipment no longer are, or possess the properties that would qualify it to become, accepted for use in the traffic environment. When, for example, sign poles or lamp poles are installed, it is required that these structures are provided with the rigidity and static strength that will allow them to carry ordinary loads such as wind loads, while a large degree of flexibility and energy absorption will be required in the case of an impact. These characteristics are in principle incompatible. It has turned out that the most demanding property to obtain, in connection with flexible structures, will be the controlled slowing down of the vehicle, where the level of acceleration must be kept under a certain level during the period of contact between the supporting structure and the colliding vehicle. It has been recognized that even the slightest variations in the construction of such structures may result in a significant and unacceptable deflection of the acceleration level. To be able to maintain the risk level with regard to injuries to the driver and passengers in a runaway car at acceptable, low levels, the flexible behavior of, for example, mast constructions must be controlled at all stages during an impact, from the initial impact to the finishing stages of the slowing down of the car. This can be acheived only by maintaining the energy absorbtion, and the transferring of forces from the mast construction to the colliding car, within strict limits. One has heretofore not been able to acheive this in a simple and low-cost pole construction; but as will become apparent from the following description, the present invention has made such an acheivement possible.

Prior art

There exist several different pole constructions that seek the resolution of this problem.

These may preferably be divided into the following main categories:

1) Tubular pole constructions having longitudinal weakenings in the tube wall in the form of grooves or sections having significantly reduced wall thickness or even open, longitudinal slots connected only by way of points. The purpose of the grooves or slots is to weaken the resistance and/or energy absorbtion during an impact, while to a certain degree maintaining static strength. Current variations in this category comprise providing oblong slots or grooves in a pattern transversely or obliquely with respect to the longitudinal axis of the pole construction. The pipe wall of these constructions consists in principle of a solid pipe wall systematically perforated so that the strength of the wall is significantly reduced. The main point here, is the perforation.

2) Pole constructions based on grid constructions or framework consisting of thin rods. Such grid constructions may be manufactured by the use of expanded metal, the latter constituting the framework of the construction. Such constructions may be considered consisting of, in principle, a single- layer "pipe wall" consisting of framework.

3) Pole constructions consisting of internal reinforcement rods fixed to an external covering, or an internal framework/grid construction fixed to an external covering or cover plates.Typically, the external covering in these constructions is much too weak for the pole construction to be able to withstand static loads without the use of reinforcements as indicated. The external covering may provide for an intended stiffening of the grid construction. This construction may be considered to be a dual-layer solution for the pipe wall.

From the relevant prior art, the following is emphasized:

Norwegian Patent 160458 discloses a pole comprising a mantle and rods adapted for static cooperation with one another and which are connected to one another in such a way that the cooperation is terminated when the pole construction is exposed to transverse loads of a predetermined magnitude. The extraordinary aspect of this construction is that the mantle is in the shape of a polygonal body and manufactured by extrusion. Internal grooves are arranged at the corners, which provide for rupture lines, and at least on some of the sides of the mantle there are arranged open channels with tongues extending inwardly. The rods are provided in the channel, preferably preloaded by clamp clips. According to this solution the rods and the mantle will cooperate to support static loads, but these are not intended to have any specific function in the event of an impact. This construction belongs to the main category 3, having features also from main category 1. Lighting pylon from Stahlsund OY, Finland. This construction falls under main category 3.

Lighting pylon from AB Varmforzinking, Sweden type ESV. This construction falls under main category 3.

EP-B 1-001964, where a tubular pole construction is disclosed, having longitudinal, slotted deformation zones arranged along the circumference of the pipe, and an external covering stabilizing the pipe wall. This construction thus comprises features from both of the previously indicated main categories 1 and 3.

WO-A1-97/21872, where a pole construction consisting of expanded metal is disclosed, a part of the pole construction having specific deformation zones. This clearly falls under the main category 2.

DE-A1-2935618, where a tubular pole construction suitable for street lighting is disclosed, the construction not being concerned with deformations and energy absorption, but rather being specifically directed to conditions regarding the hatch. This construction is not considered a potential resolution of the technical problem at hand, and will not be described in further detail.

GB-2268774-A, where a tubular pole construction is disclosed having dual, longitudinally extending deformation zones, comprising slots and solid material alternately, arranged along the circumference of the pipe. This construction clearly falls under main category 1.

One common aspect of all of the prior art solutions is that they are relatively complex constructions requiring rather complicated manufacturing processes. As a consequence, the cost per manufactured unit will be so high that their use for traffic safety purposes will be limited for economical reasons. It is also obvious to a person of ordinary skill in the art, that the use of slots and grids may reduce the durability considerably, since this will make such pole constructions vulnerable to corrosion. The use of extended slots, or framework having few assemblage points, in pole constructions will be of further disadvantage with respect to fatigue properties and may therefore lead to reduced durability due to problems in connection with stress concentration and cracking. The use of slotted constructions also represents a significant drawback in that such constructions very often lack the necessary rigidity to be able to support ordinary loads such as wind and snow, and therefore are liable to be exposed to bending to an unacceptable degree. In addition, slotted constructions, or constructions reinforced by grids, have been known to not be able to provide sufficient torsional rigidity when used in, for example, sign masts.

Objects

The main object of the invention is to provide for a flexible and energy absorbing pole construction that will eliminate, or significantly reduce, one or more of the drawbacks mentioned above. More particularly, an object of the invention is to provide for a hollow pole construction for use in connection with arterial traffic, that in the event of a lateral impact, will respond flexibly and absorb energy yet still have the strength and rigidity necessary to be able to support ordinary loads such as wind and snow. A further object is to provide for a flexible hollow pole construction having properties that are predictable, both regarding flexibility, rigidity and strength, and that will not change over time due to external conditions in the environment. One object in particular, is to provide for a flexible pole construction that is cheap to manufacture, to install and maintain, and that will be durable.

The invention The invention will improve the working characteristics and reduce the manufacturing cost of flexible traffic structures and thus enhance the passive safety along arterial roads. Pole constructions designed according to the invention have undergone full-scale tests and have been found to work according to the intentions of the invention. The invention resolves the technical problem previously described, byutilizing a tubular pole construction not having longitudinal grooves, slots, or internal grids and/or frameworks: The pipe may have a cylindrical, elliptical or polygonal cross section. The specific technical solution has been made possible through a particular combination of the material properties and cross-sectional geometry of the pole. The cross-section of the pole construction does not have to remain constant along the lenght of the construction. The material/geometry combination disclosed below, provides for a sufficient static strength regarding ordinary loads such as wind loads and gravitational loads, while acting flexibly if hit by a car in a way that satisfies the requirements of, for example, EN 12767 Passive safety of support structures for road equipment. According to the invention, a specific tubular cross-sectional geometry will be applied in the section of the pole construction designed for energy absorption, characterized in that:

The thickness of the pipe wall shall remain within the range given by:

while the slimness of the pipe wall remains within the range:

The meaning of the symbols is indicated in the following table:

The formulas apply for most pole constructions made of metal and for pipe cross-sections made of plastic materials or other materials having a certain ductility. The cross-section of the pipe may have local reinforcements in connection with a foundation connection, a hatch opening, pipe connections, if any, and in connection with the fastening of equipment such as fixtures or road signs.

Additionally, it is possible to combine two (or more) different thicknesses of a material, or two (or several) different materials, or two (or more) different thicknesses composed of several different materials. Such combinations can be applied under the condition that the characteristics of the invention (the mode of deformation) are maintained. This condition is automatically satisfied, if all of the combinations of thicknesses and/or materials satisfy all of the conditions of claim 1. If one chooses to construct a section of the pipe wall in the pole construction such that one or several of the conditions according to claim 1 are not met, one has to make specific considerations regarding the location of such sections in the pipe wall. In vertical pole constructions, for example, these sections should be located either facing an impacting car, or at the rear side of the pole. For horizontal railings or road partitions on the other hand, a construction that is more rigid in the vertical than in the horizontal plane may be more desirable. In such cases, one must ascertain that a sufficient part of the cross section of the pipe satisfies the conditions of claim 1, for the pole construction's mode of deformation to be maintained during a collision, while the kinematic conditions of the situation still are acceptable, as disclosed under the headline "function of the invention". In cases where very different directional characteristics are desirable, a more particular choice of construction may be made.

The invention concerns the part, or parts, of a construction designed for flexibility and/or energy absorption. For a pole like construction, for example, situated along an arterial road, this will ordinarily apply for the lower part of the pole, extending in the area of one to two lengths of a car. For railings or a road dividing construction, this may apply for the whole length of the construction, possibly extending several kilometres.

Function of the invention A tubular pole construction according to the invention will comprise a cross-sectional profile that will provide the strength necessary for supporting ordinary loads such as gravitational loads and for wind loads so that the cross-sectional profile (pipe wall) will not break down and collapse. During an impact from, for example a colliding car, the car will push in the pipe wall and press the walls together so that the cross-section of the pipe approaches an approximately flat, oval geometric shape, or a figure-eight like geometric shape. The flat cross-sectional shape of the pipe section provides, as a consequence, a pole construction that relatively easily may be bent around the front of a colliding car. If the conditions according to claim 1 of the invention are met, this collapsing of the cross-sectional profile will behave like a deformation wave, easily propagating in the longitudinal direction of the energy absorbing part (or parts) of the pole construction. The energy consumption which this flattening of the cross-sectional profile of the pipe, and the bending of the pole construction around a colliding car, requires, will result in a suitable reduction of the kinetic energy for, and a corresponding slowing down of, the colliding car. The cross-sectional profile of a pole construction according to the invention will collapse initially, in the event of a sudden sideways, blow-like impact, as when hit by a car. As long as the energy is sufficiently large, this "wave of collapse" (deformation wave) will easily propagate in the longitudinal directions of the pole construction until the external energy reaches an insignificant level, or the deformation wave reaches a section of the pole construction not satisfying claim 1 of the invention. The deformation wave will then come to a stop. Applying the invention in for example conical lamp poles, this will have as a result, in the event of a sideways, blow-like impact, that the deformation wave will come to a stop at for example a foundation point, where the cross-sectional profile is provided with a local reinforcment and, in addtion, at some point further up in the conical pole construction where the deformation wave reaches a section not satisfying the conditions of claim 1.

Examples of geometrical shapes of the pole construction: The invention will now be described in more detail, with reference to the drawings, where: Figure 1 shows a vertical, hollow and conical pole utilized as a lamp pole, Figure 2 shows a section of the deformation zone in a vertical, hollow pole having a circular cross-section, the pole having been exposed to a sideways, blow-like impact resulting in the pipe wall having caved in, and illustrates how the front of the deformed zone (the deformation wave) propagates further up in the longitudinal direction of the pole construction, leaving an approximately flat, collapsed cross-sectional profile behind the deformation front,

Figure 3 shows a circular cross-section of a hollow pole construction and illustrates the principle for determining the diameter D and the thickness of the pipe wall t, Figure 4 shows an elliptic cross-section of a hollow pole construction, Figure 5 shows a quadratic cross-section having rounded corners, Figure 6 shows a polygonal cross-section, the pipe wall having uniform thickness, Figure 7 shows a polygonal cross-section of a hollow pole construction, with the pipe wall having varying thicknesses.

In Figure 1 a conical lamp pole is shown. The section closest to the ground is designed for flexibility and energy absorption and satisfies the conditions of claim 1, the length of this section typically extending between one and two car lengths. The remaining part of the lamp pole serves no function regarding flexibility and energy absorption, but serves to give the lamp of the lamp pole sufficient height above the ground. Consequently, it is not necessary to set specific requirements regarding flexibility for this upper section; requirements may exist, however, with respect to strength and rigidity, and limitations regarding the total weight of the upper section of the pole may exist as well. The conical lamp pole of Figure 1 may for example comprise a circular cross-section having a diameter D, measured from the center plane of the cross-section, and a wall thickness t, (see Figure 3). For a conical, hollow pole, the slimness DIt of the pipe wall thus varies along the longitudinal axis of the pole construction, and the diameter and thickness of the pipe wall must, in the flexible and energy absorbing section, both be selected according to claim 1 , for the object of the invention to be acheived.

Hollow pole constructions according to the invention, will provide for a significantly smoother and more flexible behavior than conventional hollow poles in the event of a sideways, blow-like impact. The reason for this is that in the event of being hit by a car, for example, the specific mode of deformation provided for in the hollow pole construction, will have a particularly advantageous effect. Hitting the pole construction, the car will force in the pipe wall and, given that the conditions of claim 1 are satisfied, a "wave of collapse" is generated, propagating easily in the longitudinal directions of the pole construction, the wave leaving a flattened cross-sectional profile that will bend easily around a car. The forces between the car and the pole will thus be of a limited magnitude and ensure a controlled slowing down of the car. Figure 2 shows a section of the pole construction illustrating this mode of deformation, the deformation front, in this particular example, propagating upwards. Figure 2 clearly shows how the wave is propagating in the upward longitudinal direction of the pole construction, leaving a hollow, but flattened cross- sectional profile behind the deformation front.

If the pole construction according to the invention is provided with mainly symmetrical cross-sectional profiles, a circular cross-section, as illustrated in Figure 3, or a polygonal cross-section, as shown in Figure 6, then a hollow pole construction, having substantially the same deformation properties in all directions, will be obtained. If directional or different deformation properties are desirable, an elliptical cross-section as shown in Figure 4 may be chosen, or som eother variant, like, for example, one of the variants shown in Figures 5, 6 or 7. Choosing a cross-sectional profile that is not rotationally symmetrical, directional static strength and rigidity properties could be provided for, in addition to directional deformation properties. The diameter D is given by the circumference of the middle plane of the cross-section of the hollow pole construction divided by π (3.14).

Figure 7 illustrates an octagonal cross-section with the pipe wall having different thickness along the profile. If the pipe section is manufactured from one type of material, at least one of the two thicknesses (ti or ti) must satisfy claim 1 of the invention, for the deformation pattern (the deformation wave) to be obtained. The section supplied with the second thickness may have a limiting effect, and it must be ensured that the deformation pattern (deformation wave) is not being restrained to a too large an extent. The part of the pipe wall being allowed to not satisfy claim 1, will therefore be limited. On the other hand, if this pipe section is manufactured from two types of material, one type with a thickness of ^₁ (with E₁ and σ_Ojl) and a second type with a thickness of ^₂ (with E₂ and σ_Oj2), each giving approximately the same values using the formulas of claim 1, then the pipe section will have substantially the same deformation properties as if it was manufactured from only one of these materials, the thickness then adjusted accordingly.

Examples of materials applied in hollow pole construction

All of the examples of materials applied in a hollow pole conastruction according to the invention are, for the sake of simplicity, given in relation to Figure 3, which shows a circular cross-section of a hollow pole construction having diameter D and pipe wall thickness t.

A low-grade steel like S235 where E= 210000 and σo= 235. According to the requirements of claim 1, the allowed thickness for the pipe wall will be in the range of 1.7≤t≤2.5 mm. Hollow pole constructions made of steel, and according to the invention, generally have thinner pipe walls than conventional poles, utilized for example as lamp poles.

Aluminium alloy AA6083.T6 where E= 70000 and σo= 255. According to the requirements of claim 1 , the allowed diameter for the pipe will be in the range of 60<D<210 mm. According to the invention, it will not be possible, utilizing this material, to use a cross- section having a diameter beyond this rangr, no matter what the size of the thickness of the pipe wall might be. For a hollow pole construction made of this material, having a diameter D=I 80 mm, the allowed thickness for the pipe wall will be in the range of 2.2<t≤2.7 mm, for the characteristics of the invention to be obtained.

A plastic compound such as polyethylene, where typically E= 1200 and σ_o= 23. According to the requirements of claim 1 , for a hollow pole construction made of this material, having a diameter D=250 mm, the allowed thickness for the pipe wall will be in the range of 7<t<12 mm.

A composite containing polyproylene and having a glass fibre content of about 30%, where typically E= 5500 and σ_o= 65. According to the requirements of claim 1, for a hollow pole construction in this material, having a diameter D=200 mm, the allowed thickness for the pipe wall will be in the range of 4.5<t<6.5 mm.

It will be obvious to a person of ordinary skill in the art, that the selection of thickness for the pipe wall, according to the conditions stated in the claims, is related to the static loads prevalent at the site of installation, as well as the desired classification regarding flexibility and energy absorption.

Claims

Claims:

1. Hollow pole construction for the raising of, for example, lighting, signs, posters, light signals, portals or semiportals, guard rails or the like mast and post constructions utilized in connection with arterial traffic, and other components that are designed to break or to be flexible and to absorb shock according to selected criteria, and which is designed to be flexible if the construction is exposed to local transverse loads of a predetermined magnitude, characterized in that the pipe wall of the pole construction does not comprise local weakenings in the form of grooves, slots or predetermined rupture zones, or internal reinforcements in the form of grids or rods, and that the thickness of the pipe wall remains

in the range of ≤ _j- [formel 1], where the unit for the thickness, t, and

diameter, D, of the hollow pole construction is millimeter and the unit for the yield stress for the material is N/mm², while the diameter, D, to thickness, t, ratio remains in the range

of [formel 2], E being the modulus of elastiticity (Young's modulus)

and having the same unit as the yield stress, σ₀, of the material.

2. Hollow pole construction according to claim 1, characterized in that the pipe wall of the pole construction may have holes or openings to accomodate functions related to, for example, electrical installations, the installation, handling or the operative use, or fastening of equipment, or from asthetical considerations.

3. Hollow pole construction according to claim 1 or 2, characterized in that the pipe wall of the pole construction may have local reinforcements at holes or openings exceeding a certain size, so that the functions of the pole construction related to strength and rigidity are substantially maintained in the sections where the pole construction is weakened due to, for example, holes.

4. Hollow pole construction according to claim 1, characterized in that the pipe wall of the pole construction may have local reinforcements at sections where equipment like plates may be fixed, and at end sections adjacent to foundations or joints of the pole construction.

5. Hollow pole construction according to claim 1, characterized in that the pipe wall of the pole construction may have areas of different thickness (for example ti and ti).

6. Hollow pole construction according to claim 1, characterized in that the pipe wall of the pole construction may have areas of different materials.

7. Hollow pole construction according to claim 1, characterized in that the pole construction may have other sections not designed for flexibility and energy absorption, like, for example, in the upper section of a lamp pole, in the crossbars of sign arrangements, lamp poles and the like.

8. Hollow pole construction according to claim 1, characterized in that the pipe wall of the pole construction may have additional, limiting sections, not in correspondence with claim 1, yet not obstructing the functioning of the invention.

9. Supporting structure or construction for use in connection with arterial traffic characterized in that it comprises one or more pole constructions according to one or more of claims 1-8.