GB2268774A

GB2268774A - Energy absorbing pole

Info

Publication number: GB2268774A
Application number: GB9314144A
Authority: GB
Inventors: Mackenzie Richard Dowling
Original assignee: DOWLING MACKENZIE R
Current assignee: DOWLING MACKENZIE R
Priority date: 1992-07-17
Filing date: 1993-07-08
Publication date: 1994-01-19
Anticipated expiration: 2013-07-08
Also published as: CN1050875C; GB9314144D0; HK69996A; AU2038792A; NZ247817A; AU631104B3; MY115283A; CN1086283A; GB2268774B

Abstract

An energy absorbing pole (10) comprises an elongate tube having a series of elongate slits or slots in the wall of the tube, the slits or slots being arranged in first and second pairs of lines extending substantially longitudinally along the wall of the tube, wherein the first pairs of lines alternate with the second pairs of lines and wherein the second pairs of lines extend to a greater distance along the wall of the tube than the first pairs of lines. <IMAGE>

Description

Title: "EasKGY ABSORBING POLE" FIELD OF THE THIS INVENTION relates to poles and, in particular, energy absorbing poles such a street side light poles designed to crumple upon impact by a motor vehicle.

BACKGROUND TO THE INVENIIAN Prior Australian Patent Specification 546648 (77732/81) describes an impact absorbing pole which comprises an octagonal tapered. tube with a pattern of slots therein to weaken the pole so that it absorbs impact energy within itself. The more of the impact energy which is absorbed within the pole, the better if fatalities are to be avoided.

Prior Australian Petty Patent describes an impact absorbing pole which achieves a better performance than the pole of Patent No. 546648.

Poles of the above type are in common use and road authorities and manufacturers are constantly seeking improved performance in meeting the dual requirements of rigidity sufficient to withstand loads.

such as experienced in high winds, particularly during cyclones, and to collapse. in an impact with a vehicle in a manner calculated to reduce the likelihool of loss of life. It is desired that the pole deforms in impact to absorb energy over time to effect as slow a deceleratio of the vehicle as possible~ These dual requirements are not such as to enable developments of improvements through theoretical modelling. Improved designs are the result of testing and more particularly full scale testing of actual poles.

In production of poles of the above type, when aiming for smaller deceleration, stresses at the base of the pole can result in the pole shearing, particularly at the base, at which time impact energy absorption ceases and the pole fall is uncontrolled; OBJECT OF THE It is an object of the present invention to provide a pole of the above type with improved energy absorbing characteristics NATURE OF TEEK K INVENTION The invention achieves its object in an energy absorbing pole comprising a tube which, in use, is stood projected from a base at ground level and which is provided with a pattern of slits in its wall, the pattern being extended upwardly from or near ground level, the slits comprising elongate slits in the wall of the tube, the slits arrayed with their elongate length oriented in lines along the tube wall, the lines of slits extended axially of the pole, the pattern of slits comprising a plurality of alternating first and second pairs of slits in the wall, the first pairs of lines of slits being angularly spaced about the wall having their slit lengths in each line of each pair substantially equal to slit spacing and the slits in the two lines of each pair being staggered, the second pairs of lines of slits in the wall being each interposed between angularly spaced first pairs of lines of slits each having slit spacing therein substantilly equal to slit length and likewise staggered, every second pair of the pairs of lines of slits of the plurality of alternating first and second extending to a greater distance above ground level than does the first pairs To achieve the best possible results with a pole of the above defined character, it is best to have the rows of slots commence as close to the base as possible.

In this specification reference is made to slits or slots. These are cuts extend through the material of the, pole to sever the material through its thickness over a length. Slits or slots. are to be read interchangeably and to include anything of the above character. In practice, the slits or slots will be filled out by galvanising material but the weakening effect of the slit or slot is not lost by this.

BRIEF DESCRIPTION OF TEE DRAWINGS The invention will now be described with reference to preferred embodiments which are illustrated in the accompanying drawings, in which: FIG. 1 is a view of an octagonal sectioned energy absorbing pole in accordance with the present invention; FIG. 2 shows the pattern of slits which are applied to a blank from which the pole of FIG. 1 might be produced; FIG. 3 is a view of a circular sectioned energy absorbing pole in accordance with the present invention; and FIG. 4 shows the pattern of .slits which are applied to a blank fron which. the. pole of FIG. 3 might be produced, PREFERRED EMBODIWELS: In FIG. 1 is seen a pole 10 in accordance with the invention which is stood above a base plate 11 as is usual with street lighting poles, etc.. The pole 10 of the drawing has a octagonal cross section and is. hollow being formed from sheet, steel stock. The usual form of door can be fitted to a door cut out 12 which may be provided to give access to the inside of the pole. The pole 10 may be tapered. towards its top as is shown.

FIG. 2 shows in greater detail, a pattern of slits or slots which may be applied to a pole of the type which is shown in FIG. 1. The object of the slits or slots is to establish an energy absorbing character for the pole. The slits or slots exist to weaken the steel of the pole. In practice, the pole is galvanised or otherwise coated to avoid corrosion such that the slits or slots may not be evident in the finished pole.

Galvanising, for example, may fill out the slits or slots.

In FIG. 2, two forms of slotting exist being in first and second pairs of lines of slits characterized by the different height the lines of slits extend up the pole in each of the first and second pairs of lines of slits. The pole is produced from a blank 14 which is bent along lines a to g to produce an octagonal tapered pole. The pole may be welded at the edge h to complete the pole. The octagonal pole then has eight flat faces 15 to 22. The first form of slotting, in this embodiment, is along ever second edge or bend line between the faces including the welded joint line. The other form of slotting exists along the edges of the remaining faces. In each form of slotting, slits or slots are in pairs of lines on either side of and near to the bend and they are oriented along the length of the pole. Typically, the slits or slots may be 50 mm long and separated by 50 mm in the usual street lighting pole. The two forms of slotting are distinguished by the height to which the slits or slots are taken. In each form of slotting the lines of a pair may be 8 mm apart in the blank from which the pole is made.. Clearly the same technique can be applied to the other polygonal sectioned poles and to round poles wherein the two types of lines are likewise angularly spaced around the pole as will become more clear below.

The slits or slots along and near to the corners between faces are typically at spacings which equal the slit or slot length and they are staggered Thus, the pole blank might be cut for 50 mm with 50 mm missed before the next 50 mm cut with the cut in one line of a pair of lines at the space between slots in the other. Slotting at this separation may contimia up the pole along and: adjacent to the bend lines:. The two forms of pairs of lines of slotting altFrnobe about th.

pole with each flat face of a polygonal pole preferably slotted at both edges The patterns of slots in each line of slots need only be differentiated in each form of slotting with every other pair of slots being carried: to a different height up the pole.

The slits or slots near the lines a to h preferably start on one side at 50 mm from ground level and carry on up to typically either a height of 3000 mm or 4000 mm typically in a usual sized street lighting pole and depending on the dimensions. such: as diameter, height, desired load capabilities, etc. The slits or slots on the other side of the lines a to h start at ground level and carry on up to their respective heights of 3000 mm or 4000 mm. This starts the pairs of lines at ground level and sets the desired staggering in the adjoining lines of slots.

The blank 14 is provided with a cut out 23 to define the opening for the door.

FIGS. 3 and 4 show a round pole of the above character. Pole 24 has a door cut out 25 above a base 26 as before. The pole is provided with a pattern of slits or slots wherein one first pattern of a pair of lines such as a 28 with typically 50 mm slots spaced by 50 mm with the two lines at an 8 mm separation alternates with a second pattern of the same type such as 28 with the first pattern extended to 3000 mm above ground level and the second to 4000 mm. In each pair, the slits or slots of one line start at ground level.

In the other line the first slit or slot is at 50 mm.

In crash tests of poles of the above kind, energy is absorbed in crushing of the pole and in tearing or shearing os the material of the pole aleaq the lines of slots. The pole is reduced to a plurality of strips of material with energy absorbed in tearing along the lines of slits. Shear across the face of the pole, if it commences, is caught by a pair of slit lines and redirected therealong to reduce the likelihood of the pole shearing off. The spacing of the lines of a single pair of lines is reduced relative to the spacing between pairs with the above in mind.

Claims

1. An energy absorbing pole compris; ng a tube which, in use, is stood projected from a haste. at ground level and which is provided with a pattern of slits in its wall, the pattern being extend upwardly from or near ground level, the slits comprising elongate slits in the wall of the tube, the slits arrayed with their elongate length oriented in lines along the tube wall, the lines of slits extended axially of the pole, the pattern of slits comprising a plurality of alternating first and second pairs of slits in the wall, the first pairs of lines of slits being angularly spaced about the wall having their slit lengths in each line of each pair substantially equal to slit spacing and the slits in the two lines of each pair being staggered, the second pairs of lines of slits in the wall being each interposed between angularly spaced first pairs of lines of slits each having slit spacing therein substantially equal to slit length and likewise staggered, every second pair of the pairs of lines of slits of the plurality of alternating first and second. extending to a greater distance above ground level than does the first pairs.

2. An energy absorbing pole as claimed in Clan 1 wherein: lines of slits in one line of each pair of lines start at ground level and at the. height of the spacing between slits in the other line of each pair of lines

3. An energy absorbing pole as claimed in Claim 1 wherein: the slits are 50 mm long, their spacing is 50 mm and one pair of lines goes to a height of 3000 mm and the other pair to 4000 mm.

4. An energy absorbing pole as clnimPf in any one of Claims 1 to 3 wherein: the pole is polygonal in cross section and each pair of lines of slits lie on either side of an edge between two adjoining flat faces of the pole.

5. An energy absorbing pole as claimed in any one of Claims 1 to 3 wherein: the pole is circular and the number of first pairs of lines equal the number of second pairs and the pairs are equally angularly spaced around the pole.

6. An energy absorbing pole as claimed in any one of Claims 1 to 5 wherein: the pole is tapered from its base.

7. An energy absorbing pole as claimed in any one of Claims 1 to 3 wherein: the pole is formed from a sheet steel blank wherein the slits are first formed and the blank is bent or rolled to form a polygonal or round pole.

8. An energy absorbing pole which comprises an elongate tube having a series of elongate slits or slots in the wall of the tube, the slits or slots being arranged in first and second pairs of lines extending substantially longitudinally along the wall of the tube, wherein the first pairs of lines alternate with the second pairs of lines and wherein the second pairs of lines extend to a greater distance along the wall of the tube than the first pairs of lines.

9. An energy absorbing pole according to Claim 8, wherein the lengths of the slits or slots in a line of a pair of lines are substantially the same as the lengths of the spaces therebetween.

10. An energy absorbing pole according to Claim 8 or 9, wherein the slits or slots in one line of the pair of lines are staggered with respect to the slits or slots in the other line of the pair of lines.

11. An energy absorbing pole according to Claim 10, wherein the slits or slots in one line of a pair of lines are positioned opposite the spacings between the slits or slots in the other line of the pair of lines.

12. An energy absorbing pole according to any one of Claims 8 to 11, wherein the spacings between the lines in a single pair of lines are smaller than the spacings between the pairs of lines.

13. An energy absorbing pole according to any one of Claims 8 to 12, wherein the pairs of lines are equidistantly spaced around the wall of the tube.

14. An energy absorbing pole according to any one of Claims 8 to 12, wherein the tube has a frusto-conical shape.

15. An energy absorbing pole according to Claim 14, wherein the pairs of lines are spaced at equal angles around the wall of the tube.

16. A method of forming an energy absorbing pole according to any one of Claims 1 to 15, which method comprises forming the slits or slots in a sheet steel blank and then bending or rolling the blank to form a polygonal or round tube or pole.

17. An energy absorbing pole substantially as hereinbefore described, with reference to and as shown in Figures 1 and 2 or 3 and 4 of the accompanying drawings.

18. A method of forming an energy absorbing pole substantially as hereinbefore described with reference to Figures 1 and 2 or 3 and 4 of the accompanying drawings.

19. Any novel feature or combination of features described herein.