Posts For Road Safety Barrier

Abstract

A road safety barrier having a plurality of ropes supported by posts rigidly mounted on or in the ground is described. Each rope is held in tension against the posts and supported in a notch or groove in a side of the posts. The ropes are released from a post and the post is not pulled from the ground when a vertical force is exerted on the rope. The ropes when weaved are tensioned against the posts and this gives rise to a combined frictional resistance to displacement of the ropes relative to each post along the length of the safety barrier. The structure of at least some of the posts and / or their mounting with respect to the ground defines a minimum bending yield strength in a direction along the length of the barrier. This minimum bending yield strength is greater than the bending moment resulting from the combined frictional resistance forces acting on the post.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of U.S. Ser. No. 10 / 924,240, filed Sep. 15, 2004, which claims priority to United Kingdom Patent Application No. 0321757.7, filed Sep. 17, 2003.FIELD OF THE INVENTION[0002]This invention relates to road safety barriers for use at the sides or central reservations of roads and motorways, and in particular these including a plurality of wire ropes interwoven and maintained under tension between supporting posts.SUMMARY OF THE INVENTION[0003]A known wire rope road safety barrier, described in EP 0 369 659 A1, includes two pairs of wire ropes, one pair of upper ropes supported in slots provided in a number of posts and lying generally parallel to one another, and a lower pair of ropes held in tension against and in contact with opposite side edge surfaces of posts. Each lower cable follows a sinuous path and passes to a different one of the two side surfaces of the same post. Although this safety barrier des...

AI Technical Summary

Benefits of technology

"The present invention provides a road safety barrier that addresses the problems of previous wire rope barriers, such as the lack of connectivity and stiffness between the upper ropes and the possibility of post collapse or damage. The barrier includes four or more ropes held in tension against rigidly mounted posts, each rope being held in tension against the posts and following a sinuous path between the posts. The tensioning of the ropes against the posts gives rise to a combined frictional resistance to displacement of the ropes relative to each post. The structure of each post and its mounting with respect to the ground defines a minimum bending yield strength in a direction along the length of the barrier. The invention also provides an enhanced vehicle restraint capability and a reduced risk of post collapse or damage in the regions of the barrier up and downstream of the impact area."

Problems solved by technology

Although this safety barrier design added substantially to the containment capability over an earlier two wire rope barrier, it is now recognized that there are disadvantages associated with the parallel arrangement of the upper ropes because they have very little connectivity / cohesion with the posts.

Also because of the vertical rigidity of the posts there is a possibility of an errant vehicle straddling the safety barrier and receiving an upward thrust leading to overturning of the vehicle, if the posts fail to collapse in time.

However, a consequence of the pre-tensioning is a tendency for the interwoven ropes to grip the posts so tightly that their combined frictional grip in the direction of the line of the barrier exceeds the elastic bending strength of the posts in that direction.

This can lead to posts located some distance away from the vehicle impact zone being pulled over by the ropes towards the vehicle to the extent that they are permanently deformed.

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