GB2469382A

GB2469382A - Road safety post and fence

Info

Publication number: GB2469382A
Application number: GB201005755A
Authority: GB
Inventors: Richard Mcginnis; Mark Tonks; Matthew Harriman
Original assignee: Hill and Smith PLC
Current assignee: Hill and Smith PLC
Priority date: 2009-04-06
Filing date: 2010-04-06
Publication date: 2010-10-13
Also published as: GB201005755D0; GB2469274A; WO2010116129A1; GB0905939D0

Abstract

A road safety fence post 1 for supporting a longitudinal restraining member, such as a wire rope 10, has a cross-sectional profile in a plane perpendicular to the longitudinal axis that presents at least two points of contact 6, 8 for the longitudinal restraining member 10 on one side of the post 1. The post 1 is formed from a material profiled about the longitudinal axis such that the two points of contact 6, 8 are defined by first and second inflections 3, 5 in the surface of the material that face in one direction. The first and second inflections are joined by a section 7 of the material that defines a third inflection facing in an opposite direction to the first and second inflections 3, 5. A further rope (20, fig. 1b) may be supported on the other side of the post, in contact with the middle section 7 and the free edges of the outer wings 9,11.

Description

Road safety fences and posts therefor This invention relates to road safety fences and to posts therefor, and in particular but not exclusively to road safety fences of the type that employ wire ropes or cables.

Road safety fences that use wire ropes or cables as a vehicle restraining member comprise a series of spaced apart posts that are secured in or on the ground adjacent to the roadway for supporting the wire ropes or cables. The fences typically have one or more wire ropes extending along the fence and may be woven between the posts. Road safety fence posts and fences that are known in the art restrain impacting vehicles with the aim of preventing them from traversing the fence and travelling into oncoming traffic or into the roadside. When the vehicle impacts the fence, the wire ropes or cables break free from the fence in the vicinity of the impact and deflect such as to restrain the vehicle and absorb impact energy.

A road safety fence of this type is described in EP 0 369 659.

A disadvantage with these known road safety fences is that the ropes can deflect to such as extent that an impacting vehicle can still enter or impinge into an adjacent carriageway of oncoming traffic or hit a hazard on the roadside even if it does not traverse the fence. A further disadvantage is that a long length of fence is destroyed or collapses on account of the impact leading to significant reinstatement costs. It is therefore an aim of the present invention to alleviate these disadvantages. 25

: According to the present invention, there is provided a post for a road safety fence for supporting a longitudinal restraining member, the post comprising a U..

longitudinal axis and a cross-sectional profile in a plane perpendicular to the * * longitudinal axis that presents at least two points of contact for the longitudinal * . 30 restraining member on one side of the post, wherein said post is formed from a material profiled about said longitudinal axis such that said at least two points of contact are defined by first and second inflections in the surface of said material that face in one direction, said first and second inflections being joined by a section of said material that defines a third inflection facing in an opposite direction to said first and second inflections.

The first and second inflections may define at least two outwardly facing convex profiles that extend parallel to the longitudinal axis of the post. The join between the first and second inflections with the third inflection is preferably defined by a concave profile that corresponds to a third convex profile that faces in said opposite direction. In this example, the word inflection' means a change from a positive to a negative gradient such as to give rise to the convex or concave (curved) profile, although a more angular profile may be adopted in other embodiments.

In one embodiment of the present invention, said material includes a pair of free edges that extend parallel to said longitudinal axis, the material being profiled 1 5 such that said free edges are directed inwardly towards one another and towards said third convex profile. In this embodiment, each of the free ends may constitute an inflection such that they provide a pair of points of contact on the opposite side of the post from said at least two points of contact for a longitudinal restraining member that passes a side of said post that is opposite said one side thereof. In this case, the post presents four points of contact, two for each longitudinal member that passes on respective sides thereof. Alternatively, the post may be profiled such that said third convex profile has a depth that extends outwardly beyond the outward extent of said free edges such that the post presents one contact point for contacting the longitudinal restraining member passing said opposite side. In this case, the post presents three points of contact, two for the longitudinal restraining member * : passing on one side of the post and one point of contact for the longitudinal restraining member passing the opposite side thereof. In a further alternative, the *.S third convex profile may have a depth that extends substantially to an outward * . * periphery defined by the outward extent of the points of contact defined by the free * . 30 ends, such as to present three points of contact for the longitudinal restraining member passing said opposite side of the post. In this case, the post presents five points of contact, two for the longitudinal restraining member passing on said one side of the post and three points of contact for the longitudinal restraining member passing the opposite side thereof.

In another embodiment, the post has one, two or more inflections in addition to the first and second inflections, joined by one or more additional sections of material defining one or more further inflections facing in the opposite direction.

According to a second aspect of the present invention, there is provided a road safety fence post having a cross-section defining a pair of parallel channels having a first depth facing in one direction, the pair of parallel channels being joined to define between them an intermediate channel having a depth of substantially the same as said first depth and which faces opposite to said one direction. The road safety fence post may have a substantially "W" or "M" shaped cross-section. In an embodiment, the cross-section defines one or more additional channels with one or more intermediate channels therebetween. For example, the post may have a substantially "WW" or "MM" cross-section.

Embodiments of the present invention may have a cross-section that is substantially symmetrical about a centre line, and the channels or concave/convex profiles may be substantially symmetrical. The post may be formed from an elongate member, optionally in sheet form. The longitudinal free sides of the elongate member may be advantageously directed inwardly towards one another or are directed inwardly towards one another and at least partially inwardly of the channel or third convex profile. The longitudinal member may be fabricated from metal, e.g. steel, although any material may be used. S...

The post may comprise a support for receiving a longitudinal restraining member, that may be in the form of a notch or slot/cut-out that is formed in the post. 30

According to a third aspect of the present invention, there is provided a road safety fence comprising at least one longitudinal restraining member disposed adjacent a road and series of posts that support the longitudinal restraining member, wherein: at least some of the posts have a longitudinal axis and a cross-sectional profile in a plane perpendicular to the longitudinal axis that presents at least two points of contact that support the longitudinal restraining member on one side of the post; and said posts are formed from a material profiled about said longitudinal axis such that said at least two points of contact are defined by first and second inflections in the surface of said material that face in one direction. Said first and second inflections may be joined by a section of said material that defines a third inflection facing in an opposite direction to said first and second inflections.

In one embodiment, said at least one longitudinal restraining member is woven sinusoidally between adjacent posts. The fence may comprise a further longitudinal restraining member that is also woven in a sinusoidal manner between adjacent posts either above or below said at least one longitudinal restraining member or woven so as to pass the opposite side of any given post from said at least one longitudinal restraining member.

In an alternative embodiment, said at least one longitudinal restraining member is disposed parallel (i.e., straight) to the line of the fence so that the member is disposed on the same side of the posts, that is, not woven relative to the posts. One or more further longitudinal restraining members may be disposed above said at least one longitudinal restraining member and/or along the opposite side of the posts. böe*

* *. The posts of the road safety fence may be orientated so that said at least two * : 25 points of contact face in the same direction or alternatively the posts may be orientated so that said at least two points of contact of adjacent posts face in opposite directions with respect to one another. These orientations may be applied to fences in which the longitudinal restraining members are woven or straight.

S S

., 30 Fences embodying the present invention may include posts having profiles that present any one or more of: two; three; four or five contact points for the longitudinal restraining members that pass around them as set out above.

The longitudinal restraining member may be a wire strand or rope, and in some embodiments, the wire strand or rope is woven in a sinusoidal path between the posts as described above, whereas in others, the wire strand or rope extends substantially parallel to the line of the fence.

According to a fourth aspect of the present invention, there is provided a road safety fence comprising a series of posts adjacent a roadway and a pair of cables held in tension and woven sinusoidally between the posts such that respective cables pass around opposite sides of the posts, wherein each post has a cross-sectional profile that is configured to crush when a compressive force exerted on the 1 5 post between the cables exceeds a predetermined value, said compressive force being established when a vehicle impacts the road safety fence causing the ropes to tighten around fence posts adjacent or near to the vehicle impact area. In an embodiment of this fourth aspect, a road safety fence has a cross-sectional profile that defines a pair of parallel channels facing in one direction, the pair of parallel channels being joined to define between them an intermediate channel that faces in an opposite direction. The pair of parallel channels may each have an outer wing that has a curved profile. In one embodiment, the compressive force compresses the outer wings before the intermediate channel. In an alternative embodiment, the *i..

intermediate channel is compressed before said pair of parallel channels. The post :1. 25 may have a substantially circular or oval cross-section. S..

Embodiments of the present invention are advantageous in that they offer an *..

increased frictional contact between the post and the wire strand or rope as it passes the post. When a road safety fence that is constructed using these posts is impacted 30 by a vehicle, the increased frictional contact is such that the collapse characteristics of the road safety fence posts and consequently, of the fence as a whole is improved. Prior art posts of 1', Z', 0', or S' cross-section have a rigid profile and are intended to be non-deformable so that they yield or collapse at the junction between the post and the ground. Posts embodying the present invention provide for an increased frictional contact between the wire rope or cable and the post so that as the fence is impacted by a vehicle, tension is imparted into the wire rope, strand or cable. In woven embodiments, the strand, rope or cable tighten around the posts outside the vehicle impact are thereby causing the posts to deform, by the free ends being compressed inwardly. This deformation and increased frictional contact serves to absorb more of the impact energy of the vehicle, relative to prior art fences, before the post yields at the junction between the post and the ground, and also before the wire ropes or cables are released from contact with the posts.

As a result, more vehicle impact energy is absorbed on initial impact and so the rope deflection on at least initial vehicle impact is reduced. Furthermore, a shorter length of fence is subject to collapse, reducing reinstatement costs. A yet further advantage arising from this post profile is that no sharp edges are presented to an impacting vehicle or motorcyclist.

The consequent deflection of the rope, as it is released from the posts on vehicle impact, is reduced thereby helping to reduce the ingress of the vehicle into the adjacent carriageway or roadside. This helps to avoid premature collapse of the fence. A still further advantage is that a shorter length of the fence collapses for a given impact event, relative to prior art fences, resulting in reduced reinstatement costs.

The invention will now be described by way of example with reference to the accompanying drawings, in which: 25 Figure Ia is a perspective view of a road safety fence post embodying a first aspect of the present invention; S..

Figure lb is a perspective view (drawn to a different scale) of the post of figure Ia when viewed from the direction of Arrow B; Figures 2a to 2j are plan views of different post profiles embodying the present invention; Figure 3 is a perspective view of a road safety fence according to another aspect of the present invention, the fence having a restraining member disposed on one side thereof; Figure 4 is a perspective view of an alternative embodiment of road safety fence having a pair of restraining members woven between alternate posts; Figure 5 is a further embodiment of a road safety fence embodying the present invention, in which alternate posts face in opposite directions; and Figure 6 shows the road safety fence of figure 5 having a pair of woven restraining members.

Figures 1 a and lb show a road safety fence post I embodying the present invention. The post I has a longitudinal axis X-X with a cross-sectional profile in a plane perpendicular to the axis X-X that follows a generally W' or M' shaped profile. The post I may be formed from sheet steel to have a pair of outer convex 1 5 profiles that are generally U' or V' shaped outer channels 3, 5 connected by an inner concave profile (when viewed from the direction of Arrow A) corresponding to an inner channel 7 of similar profile. The convex profiles define points of contact 6, 8 for a wire rope 10 that lies along the direction Y-Y of the road safety fence. Each one of the outer channels 3, 5 has an outer wing 9, II terminating in a free edge 13, 15 respectively that extends along the length of the post 1. Studs or pegs 17, 18, 19 are provided for holding the wire rope 10 of the road safety fence at its design height. The studs or pegs prevent the rope from moving downwards but allow upward movement in the event of vehicle impact. Figure lb is a view on *. a reduced scale relative to Figure 1 a of the road safety fence post I in the direction :h* 25 of Arrow B. The free edges 13, 15 and the inner channel 7 provide contact points 22, 23 and 24 respectively for a second wire rope 20 that is supported on the opposite side of the post I to the rope 10. The post I therefore provides a total of 5 contact points for the two ropes 10, 20 which results in an increased frictional contact between the wire ropes and the fence posts. This has the advantage that on 30 vehicle impact, the deflection of the ropes is reduced owing to the transfer of impact forces from the ropes to the posts. This also reduces stretching of the ropes. An increased number of contact points between the post and the rope makes it possible to reduce the width of the post and in turn reduce the amount of deflection that occurs as a result of removing posts during vehicle impact.

Figures 2a to 2j show alternative examples of post profiles that may be adopted instead of the profile shown in Figures Ia and lb. These profiles all present 3 contact points to one rope and 2 contact points to the other except for Figure 2c which presents I contact point instead of 3 as the depth of the inner channel is greater than the depths of the outer convex profiles. Alternatively, the relative depths of the outer convex profiles to the inner channel may be reversed so that there are 2 contact points on each side of the post. In figure 2a, the free edges of the outer convex profiles are directed inwardly which increases the strength of the post against collapse and also has the advantage that there are no sharp edges facing a possible impacting vehicle, which may be a motorcyclist. Instead of curved profiles, more angular profiles may be adopted as in Figures 2b, 2e, 2g and 2h. In Figure 2i, the profile has inwardly directed free edges 13, 15. In Figure 2i, the profile has inwardly directed free edges 13, 15. In Figure 2j, the profile has outwardly directed free edges 13, 15. Either could be combined with any embodiment of Figures 2a to 2h.

Figures 3 to 6 show four alternative road safety fence configurations using the post I of Figures la and lb although any of the posts of figures 2a to 2j could be used instead. Figure 3 shows a road safety fence 30 having posts 31a to 31e supported in the ground 32. The posts support a wire rope 33 along one side *..* thereof, the posts all facing in the same direction so that there are two contact points * : 25 at each post. More ropes may optionally be provided on the same side as the rope 33 or on the opposite side. Figure 4 shows a similar road safety fence 40 as in Figure 3 having posts 31a to 31e supported in the ground 32, again having posts *.S profiled as shown in Figures Ia and lb. This fence 40 has a pair of ropes 43, 44 * a woven between the posts so that there are five contact points on each post. The ** 30 weaving between the posts provides for increased frictional contact between the ropes and the posts. Figure 5 shows a road safety fence 50 in which a single woven rope 51 is employed and alternate posts 52a to 52d face in opposite directions. The consequence of this is that the rope 51 has three contact points at each post 52a to 52d. Figure 6 shows a further road safety fence 60 in which alternate posts 52a to 52d face in opposite directions as in Figure 5 except that a pair of ropes 61 and 62 are woven between the posts. The consequence of this is that the rope 61 has two contact points at each one of the posts 52a to 52d while the other rope 62 has three contact points at each post. The wire ropes are supported on pegs or studs (not shown in Figures 3 to 6) similar to those described and illustrated with reference to Figures Ia and lb. A technical advantage arising from the use of the posts 1 in the road safety fences of Figures 4 to 6 is that on vehicle impact a two stage energy absorption process commences. First, the wire ropes or cables tighten around the posts adjacent to or near the vehicle impact area and absorb impact energy by virtue of the increased friction contact between the ropes and the posts. The tightening of the cables around a given post progressively increases as the vehicle approaches said given post as it runs along the fence on impact. Second, on increased tightening of the ropes, the posts are deformed or compressed between the pair of ropes 43, 44 or 61, 62 passing either side, this serving to absorb more vehicle impact energy. The pair of outer channels may be compressed first followed by the inner channel.

Fences embodying posts according to this second aspect of the present invention absorb more vehicle impact energy before the ropes are released from the posts and the posts reach their collapse yield point at the post/ground interface. As a consequence, a shorter length of fence is disturbed or collapsed for a given vehicle impact relative to fences using prior art fence post profiles. * I

* : : 25 The posts and safety fences described herein may be utilised in median (central reserve) barriers, or in shoulder (verge) applications. I...

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Claims

Claims: 1. A road safety fence post for supporting a longitudinal restraining member, the post comprising a longitudinal axis and a cross-sectional profile in a plane perpendicular to the longitudinal axis that presents at least two points of contact for the longitudinal restraining member on one side of the post, wherein said post is formed from a material profiled about said longitudinal axis such that said at least two points of contact are defined by first and second inflections in the surface of said material that face in one direction, said first and second inflections being joined by a section of said material that defines a third inflection facing in an opposite direction to said first and second inflections.

2. A road safety fence post according to claim 1, wherein the first and second inflections define at least two outwardly facing convex profiles that extend parallel to the longitudinal axis of the post.

3. A road safety fence post according to claim 1 or claim 2, wherein the third inflection is defined by a concave profile that corresponds to a third convex profile that faces in said opposite direction.

4. A road safety fence post according to any one of claims 1 to 3, wherein said material includes a pair of free edges that extend parallel to said longitudinal axis, the material being profiled such that said free edges are directed inwardly towards one another and towards said third convex profile.S.....S S

5. A road safety fence post according to claim 4, wherein each of the free ends constitutes an inflection such as to provide a pair of points of contact on S..the opposite side of the post from said at least two points of contact for said longitudinal restraining member that passes a side of said post that is opposite said 30 one side thereof.

6. A road safety fence post according to claim 4, wherein the post is profiled such that said third inflection has a depth that extends outwardly beyond the outward extent of said free edges such that the post presents one contact point for contacting the longitudinal restraining member passing said opposite side.

7. A road safety fence post according to claim 4, wherein the post is profiled such that said third inflection has a depth that does not extend as far as the outward extent of said free edges such that the post presents two contact points for contacting the longitudinal restraining member passing said opposite side.

8. A road safety fence post according to claim 4, wherein the third inflection has a depth that extends substantially to an outward periphery defined by the outward extent of the points of contact defined by the free ends, such as to present three points of contact for the longitudinal restraining member passing said opposite side of the post.

9. A road safety fence post according to any one of the preceding claims wherein said cross-sectional profile that said first and second inflections define a pair of parallel channels respectively having a first depth facing in said one direction, the pair of parallel channels being joined to define between them an intermediate channel that corresponds to said third inflection and having a depth substantially the same as said first depth and which faces in said opposite direction such that the post presents five contact points for longitudinal restraining members passing the post.

* :: ::* fence post according to any one of the preceding claims : 25 corn iving said longitudinal restraining member. ***

II. A road safety fence comprising at least one longitudinal restraining ** member disposed adjacent a road and series of posts that support the longitudinal *:** restraining member, wherein: at least some of the posts have a longitudinal axis and * . 30 a cross-sectional profile in a plane perpendicular to the longitudinal axis that presents at least two points of contact that support the longitudinal restraining member on one side of the post; and said posts are formed from a material profiled about said longitudinal axis such that said at least two points of contact are defined by first and second inflections in the surface of said material that face in one direction.

12. A road safety fence comprising a post according to any one of claims itolO.

13. A road safety fence according to claim 11 or claim 12, wherein at least one longitudinal restraining member is woven sinusoidally between adjacent posts.

14. A road safety fence according to claim 13, comprising a further longitudinal restraining member that is also woven in a sinusoidal manner between adjacent posts either above or below said at least one longitudinal restraining member or woven so as to pass the opposite side of any given post from said at least one longitudinal restraining member.

15. A road safety fence according to claim 11 or 12, wherein said at least one longitudinal restraining member is disposed parallel to the line of the fence so that the member is disposed on the same side of the posts.

16. A road safety fence according to claim 15, wherein one or more further longitudinal restraining members are disposed above or below said at least one longitudinal restraining member and/or along the opposite side of the posts. *.. * *

:hh 25 17. A road safety fence according to any one of claims 11 to 16, wherein * the posts are orientated so that said at least two points of contact face in the same S... . direction. a a

18. A road safety fence according to any one of claims 11 to 16, wherein * ., 30 the posts are orientated so that said at least two points of contact of adjacent posts face in opposite directions with respect to one another.