GB2396180A

GB2396180A - Column for road sign, street lighting etc.

Info

Publication number: GB2396180A
Application number: GB0328365A
Authority: GB
Inventors: John Thomas Bowden
Original assignee: Mallatite Ltd
Current assignee: Mallatite Ltd
Priority date: 2002-12-10
Filing date: 2003-12-08
Publication date: 2004-06-16
Also published as: GB0228762D0; GB0328365D0

Abstract

The column 10, which is primarily for use with road signs, street lighting, telecommunications antennae etc., is adapted to be partially inserted into the ground and comprises a zone of reduced shear strength spaced from its lower end in the region of the column that is to be disposed at or close to ground level. An in-fill plug 19 is located within the column that includes reinforcements so as to retard the collapse of the column in the event of a failure in the column wall. The in-fill may be formed from an elastomeric material within which strands are embedded to increase the in-fills shear strength. The zone of reduced shear strength in the column may be formed from a circumferential array of apertures 18 in the column wall and an access door 16 may be provided in the column wall along with a region of increased wall thickness 17 associated with the door. The in-fill plug may be formed from a foamed polymeric material and the strands may be formed from polypropylene and have an irregular cross-section. A bore may be centrally disposed in the in-fill plug to provide a passage for cabling to pass through.

Description

PASSIVE SAFETY IN TUBULAR COLUMNS

THIS INVENTION concerns tubular columns such as street lighting columns and the supporting columns of road traffic signs and/ or telecommunications antennae and dishes. Such columns are usually, but not necessarily, of circular cross-section with the lower end region of the column inserted into the ground and extending upwards to a considerable height above the ground.

.e À À À À Such columns, which are often made of steel, present a collision .: hazard to road users inadvertently leaving the carriageway in an accident À À: where the columns may not be protected by safety barriers for economic or À.- À A: aesthetic reasons.

À Àe e. If, to minimise the consequences of the impact in a collision, such columns are made from composite materials such as glass reinforced plastic (GRP), they are liable to shear off at the base if hit by a vehicle and then be propelled through the air and may cause further accidents or injury to other road users or passers by. Moreover columns of this type tend to be costly as they have to be relatively thick to meet the deflection criteria of the relevant design standards. In addition, columns made from

-2 composite materials are vulnerable to vandalism since they may be more readily cut down or melted with heat.

An object of the present invention is to provide a tubular column of the kind referred to, made of a material such as steel but having improved passive safety properties i.e. the column will give on impact, may be less expensive than columns made from composite materials, and has improved safety in so far as it is unlikely to be propelled away from the collision site.

À À. À e À À..Columns of this kind must be of sufficient strength and durability e-.. À Àto withstand wind forces and the like, and the deflection of the column À - Àabout its point of entry into the ground under such loads must not exceed À. À Àe- the relevant design parameters.

In the case of a column supporting a road sign, the maximum stress experienced by the column is at ground level while in a lighting column the maximum stress is normally found immediately beneath any door aperture which is above ground level and provides access to electrical and similar gear within the column. While the thickness of a signpost can be reduced to a minimum at ground level to meet the design criteria, the thickness of a lighting column tends to be greater at ground level than is

-3 required to resist loads imosed on the column owing to the need for greater thickness at the bottom of the door aperture to compensate for the loss of section in this area.

The substantial wall thickness of such columns results in considerable shear strength at ground level such that when a vehicle is in collision with the column the latter is less likely to give and so the accidental damage both to the vehicle and to the occupants it increased accordingly. À À. À À - - À À One way of reducing this shear strength fat ground level is by . À À reinforcing the door aperture effectively compensating for the loss of À. À. section in this area, and reducing the thickness of the entire base.

À À. - However, such thickness must not be less than that required l.o meet the loads imposed on it at ground level.

Another way of reducing the ground level shear strength of a column is to make the column with a circumferential ring of apertures at or near ground level so that if subjected to large side loads such as in a vehicle impact, the- column may shear at these perforations due to the consequently weakened shear strength thcrcabouts. If such apertures are provided then to avoid corrosion due to the ingress of rainwater and de

-4 icing salt solutions, it is preferable to coat the column base with a durable polymer which would block up the apertures and prevent corrosion taking place. It is intended therefore to provide a column with a metal wall which will fail at the base when subjected to a moderate impact speed or force and will not separate immediately upon impact but fall more slowly thus reducing the risk of injury.

Àe.e À À À À.- À. Thus, according to the present invention, there is provided, a À À.. tubular column adapted for partial insertion into the ground; a zone of I À À reduced shear strength spaced from a lower end thereof in a region of the Àe- À. column to be disposed at or close to ground level; an in-fill plug within the A.- À À.- column in said zone; and said in- fill plug having reinforcement such as to retard the collapse of the column in the event of failure of the column wall in said zone.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 illustrates, in elevation, a lighting column made in accordance with the invention;

Fig. 2 is an enlarged cross-section of a part of the column at ground level; and Figs. 3a to 3c illustrate the effect of failure of the column at ground level. Referring now to the drawings, a lighting column generally indicated at 10 comprises an upper part 11 and a lower part 12 of :increased cross-section. Preferably, but not necessarily, the column is À À. À. circular in cross-section.

À. À À À À: À A lower end region 13 of the column is disposed below ground level À. À. 14 and comprises an aperture 15 through which cabling may pass to be.. À Àe.e provide electrical power for a lamp (not shown) to be mounted on the column, and a door 16 is provided for access to the cabling and electrical gear disposed within the column.

By the use of suitable reinforcement the wall thickness of the column in a region at, above and below the door 16 may be effectively increased as illustrated at 17 to provide additional strength in the region of the door.

Alternatively, or in addition, at or slightly above ground level 14 a circumferential array of slots or holes 18 may be provided in the column wall to reduce its shear strength at ground level.

To reduce the possibility of a thin walled column suffering from damage during handling a combination of a reinforced door and a thinned wall may be used.

: Within the column, above and below ground level is a plug l9 of À À..À. foamed polymeric material which may be introduced as a pre-formed plug À. À.. into the column during manufacture or, alternatively, it may be injected as Àe a gettable expanding foamed material which thus expands and sets to À. À À À form the plug. Centrally- within the plug is a bore 20 through which . À... cabling for the lamp may pass.

In accordance with the invention there may be provided, within the plug 19, reinforcing means, in this example, strands 21 of polypropylene, (Al) nylon, polyester, Kevlarior the like. Such strands serve to absorb some of the energy of impact thereby slowing down the speed of collapse and reducing the likelihood of the top section of the column becoming completely detached from the base section.

-7 Referring now to Figs. 3a to 3c it will be seen that when a transverse impact is imposed upon the column in its lower region as shown by arrow 22, the column wall will fail, usually at or close to ground level as illustrated in Fig. 3b. However, the plug 19 having enhanced energy absorption characteristics by virtue of the strands 21, remains effectively intact and serves as a hinge to ensure that the column falls immediately adjacent its base and is not propelled away (Fig. 3c). Thus, the foam plug 19 has a degree of flexibility and thus tensile strength by À À virtue of the strands 21. The column shearing at its base, together with the A. À À. work done in deforming the plug, will result in a considerable amount of À- À À. the energy imposed by the impacting vehicle being absorbed thus I À minimising injury to the occupants.

À. À À À À.e À À... As illustrated in Fig. 2, the reinforcing strands may be of irregular cross-section in the manner of strands of barbed wire, whereby they are not readily pulled through the material of the plug thus increasing its ability to absorb impact forces.

The plug 19 may be of a material such as a foamed polymer, a metal foam or so-called foamed concrete, or a lightweight concrete mix.

The overall length of the plug 19 may be in the region of 600mm.

Claims

-8 CL,AIMS

1. A tubular column adapted for partial insertion into the ground; a zone of reduced shear strength spaced from a lower end thereof in a region of the column to be disposed at or close to ground level; an in-fill plug within the column in said zone; and said in-fill plug having rcinforcetnent such as to retard the collapse of the column in the event of failure of the column wall in said À À. À zone. À À

2. A tubular column according to Claim 1, wherein the in-fill

e À À plug is of a material having elastomeric properties.

À. À.

3. A tubular column according to Claim 1 or Claim 2, wherein Àe À I the reinforcement is provided by strands embedded within the in fill plug, which serve to increase the shear strength thereof substantially throughout its length.

4. A tubular column according to any preceding claim, wherein the zone of reduced shear strength is provided by a circumferential array of apertures in the column wall in said region to be disposed at or close to ground level.

5. A tubular column according to any preceding claim, including an access door in the wall of the column, and a zone of increased wall thickness in the region of said access door.

6. A tubular column according to any preceding claim, wherein the in-fill plug is of foamed polymeric material.

7. A tubular column according to Claim 3, wherein the strands are of polypropylene.

8. A tubular column according to Claim 3, wherein the strands are of irregular cross-section.

À À e

9. A tubular column according to any preceding claim, se À. À. including a bore centrally disposed within said in-fill plug to provide a passage for cabling to pass through the plug.

À À. À. À Àe he