GB2023695A

GB2023695A - Crash barriers

Info

Publication number: GB2023695A
Application number: GB7913368A
Authority: GB
Original assignee: TRANSPORT SECRETARY OF STATE F
Current assignee: TRANSPORT SECRETARY OF STATE F
Priority date: 1978-04-28
Filing date: 1979-04-17
Publication date: 1980-01-03

Abstract

A roadside barrier rail is carried on metal posts 6 each of which is supported on a base comprising two parallel vertical metal plates 2 set into concrete or attached e.g. integrally to a ground-anchored base plate 1 and arranged to be connected to the post by bolts or pins 9 passing through holes in the plates, the bolts being such that they will fracture under loadings sufficient to bend the post. The posts may be of Z-section steel squared off at their lower ends by steel straps 7 which include bosses 8 to receive the bolts. <IMAGE>

Description

SPECIFICATION Improvements in or relating to safety barriers The invention relates to safety barriers such as the fences bounding the carriageways of major highways and at the parapets of road bridges.

Hitherto, safety barriers of this nature have generally comprised a wide metal guard-rail extending along the side of a road and mounted about 2 feet above ground level on a succession of metal posts set into the ground or carried in sockets or brackets set into concrete 'plugs' let into the ground.

In one construction offset brackets are interposed between the post and guard-rail; in another, the guard-rail is connected to the posts by bolts designed to fracture when posts are bent over when struck by a vehicle. In both cases the guard-rail remains at about its initial height in order to redirect the errant vehicle back to the roadway. Both types of construction cope satisfactorily with collisions by cars but tend to fail under the heavier impacts experienced with large vehicles, the one with offset brackets causing a large vehicle to roll over: the one with fracture bolts militates against roll over of the vehicle buttends to be over-run by wheels of a large vehicle because of the comparatively weak posts necessarily employed.

These disadvantages can be substantially reduced by the provision of a safety barrier supported on more substantial posts provided with a 'weak-link' at or near ground level.

Accordingly, the present invention provides a safety barrier comprising a guard-rail carried by posts secured to the ground through the agency of fastenings arranged to fracture under the efect of bending moments acting at or near the foot of the posts in a direction perpendicular to the guard-rail when such bending moments correspond to a force sufficient to cause bending of the posts.

In one embodiment of the invention, posts are carried in pairs of brackets intended to be secured to the ground, the posts being con nected to the brackets by bolts or pins of mild steel and of such a size that they fracture at a bending moment commensurate with that at which the post starts to bend.

The bending moment is chosen in relation to the post spacing along the guard-rail to be of an order sufficient to prevent wheels of heavy vehicles over-running the barrier.

An embodiment of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, of which: Figures 1, 2 and 3 are respectively an end elevation, plan view and side elevation of a bracket carrying a metal post, and Figures 4 and 5 are respectively a section view and a plan view of part of a safety barrier.

Referring to Figs. 1, 2 and 3, an attachment member comprises a rectangular steel plate 1 having cuts made in its longer sides, the central portions of which are then bent upwardly to form a pair of parallel vertical brackets 2, typically about 50 mm in height.

Holes 3 are drilled near the extremity of the unbent portion of the plate 1 whereby the attachment member may be bolted to a base such as a 'plug' of concrete set into the ground and indicated at 4 in Figs. 4 and 5. A hole 5 (Fig. 3) is drilled substantially centrally through each of the brackets 2.

A post 6 comprises a length of Z-section steel with one end squared off by steel straps welded across the open sides, each strap incorporating a steel boss 8 with a hole at its centre, the hole extending also through the strap. The hole in each of the bosses 8 is aligned with the other.

The post 6 is assembled into a support member as previously described with the holes in the bosses 8 and straps 7 aligned with the holes 5 in the brackets 2. Metal guard-rails 10 (see Figs. 4 and 5) are bolted to a series of posts 6 towards the free ends of the latter and with the support units firmly attached to the ground a safety fence is thus formed. The guard-rails 10 are attached to one of the parallel flanges of each Z-section post which consequently has its strong axis perpendicular to the line of the fence.

In an alternative construction the brackets 2 may be formed from separate parallel metal plates either set directly into concrete or through the medium of a cage-like structure by which the plates are attached to each other. The remaining sides of the cage consist of reinforcing steel rods and the whole is set into a concrete base to the depth required for the plates to protrude about 50 mm above the flat surface of the concrete. The pins 9 may also be replaced by bolts of a similar size.

When a heavy vehicle collides with the barrier, the bending moment at the foot of each post in advance of the vehicle as it moves along the fence in the direction of the arrow in Fig. 5 will build up in a direction perpendicular to the guard-rail until the pins 9 fracture allowing the post and the guard-rail together to deflect laterally relative to the line of the barrier until such time as the vehicle stops or is redirected back to the roadway.

Where the fracture point is substantially at ground level rather than at guard-rail height, the containment capability of a safety barrier can be increased in two ways: i the posts can be made stronger than hitherto since they will move with the guardrail and will not run over by a vehicle; ii guard-rails can now be attached to the post at more than one height since the whole assembly moves laterally in one piece rather than separately. This can be most advantageous in providing protection where the barrier forms a metal-bridge parapet.

The pins or bolts which connect a post to a support assembly are of such a material, usually mild steel, and of such a size that they will fracture at a bending moment comparable with that at which the post starts to bend.

A barrier according to the invention is equally effective in either direction and so can be used along both sides of a carriageway and along the central reserve.

A Z-section post as described is preferable in that it provides high stiffness across a barrier at minimum cost but other structural materials such as rectangular and circular hollow sections and rolled steel joists can also be used for posts in conjunction with generally similar frangible base constructions to those described.

Claims

1. A safety barrier comprising a guard-rail carried by metal posts secured to the ground through the agency of fastenings arranged to fracture under the effect of bending moments acting at or near the foot of the posts in a direction substantially perpendicular to the guard-rail when such bending moments correspond to a force sufficient to cause bending of the posts.

2. A safety barrier according to Claim 1 in which the lower end of each post is carried in a pair of brackets secured to the ground, the posts being secured to the brackets by bolts or pins of such a size that they will fracture at a bending moment commensurate with that at which a post will start to bend.

3. A safety barrier according to Claims 2 in which the bolts or pins are of mild steel.

4. A safety barrier according to Claim 2 or Claim 3 in which each pair of brackets is formed integrally with a plate having holes for the receipt of ground holding means.

5. A safety barrier according to any of Claims 1-4 in which the bolts or pins extend substantially parallel to the line of the guardrail.

6. A safety barrier according to any previous claim in which guard-rails are attached to the posts adjacent the free ends thereof at more than one height above the ground.

7. A safety barrier according to any previous claim in which the posts are constructed from Z-section material and the or each guardrail is attached to one of the parallel flanges of each post.

8. A safety barrier substantially as herein described with reference to the accompanying drawings.