Source: https://patents.google.com/patent/US8985891B1/en
Timestamp: 2018-12-16 18:47:51
Document Index: 344075805

Matched Legal Cases: ['Application No 0321757', 'art.\n14', 'application No. 2004212563', 'application No. 2009201382', 'application no. 2009201382', 'application No. 2009201382']

US8985891B1 - Posts for road safety barrier - Google Patents
Posts for road safety barrier Download PDF
US8985891B1
US8985891B1 US14282172 US201414282172A US8985891B1 US 8985891 B1 US8985891 B1 US 8985891B1 US 14282172 US14282172 US 14282172 US 201414282172 A US201414282172 A US 201414282172A US 8985891 B1 US8985891 B1 US 8985891B1
US14282172
This application is a continuation of U.S. Ser. No. 14/262,501, filed Apr. 25, 2014, which is a continuation of U.S. Ser. No. 12/371,735, filed Feb. 16, 2009, which is a continuation of U.S. Ser. No. 10/924,240, filed Sep. 15, 2004, now U.S. Pat. No. 7,497,640, which claims priority to United Kingdom Patent Application No 0321757.7, filed Sep. 17, 2003.
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 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. Consequently the upper ropes behave less stiffly and have less energy absorption capability than the (interwoven) lower ropes. 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.
In the arrangement shown in FIG. 1, posts 1, 2 and 3 are inserted into the ground (not shown) and support two pairs of wire ropes 4,5 and 6,7. The posts may be inserted into the ground either into recesses in pre-cast footings or by any other suitable means. The posts may be made from steel pressings having, for example, an “S” or “Z” cross-section such that a rounded corner of the line of the bend is offered to the direction of the traffic instead of a sharp edge. In addition the post shape will preferably present a smooth conforming surface to the ropes, and a smooth radiussed surface to any other impacting bodies so as to minimize the damage thereto under collision conditions.
In the first embodiment of the present invention, as illustrated in FIG. 2, the ropes of both pairs 4, 5 and 6, 7 are interwoven about the posts 1, 2 and 3 instead of only the lower pair 6, 7. Each of the ropes is supported in a vertical direction on the side of the posts by way of supports 11, 12 and 13. The ropes of the first pair 4, 5 are at substantially the same height above the ground as one another and the ropes of the second pair 6, 7 are also at substantially the same height above the ground as one another but lower than the first pair. In the second embodiment, illustrated in FIG. 3, all of the ropes 4 to 7 are interwoven but instead of being arranged in two pairs vertically spaced apart from one another, all of the ropes are vertically spaced apart with respect to one another at different heights above the round. The first and second embodiments have the advantage, relative to the prior art arrangement illustrated in FIG. 1, that the containment capability of the barrier is improved and the risk of an impacting vehicle overturning is reduced for a wider range of vehicle weights and sizes. It is noted that FIGS. 2 and 3 illustrate a preferred method of interweaving in that each of the ropes passes from one side of the first post to the alternate side of the next one and so on progressively along the length of the barrier. It is preferred for the interweaving of half of the ropes to be arranged out of phase with the other half and in a manner which balances the potential bending moments on the respective posts, to ensure a consistent resistance to penetration (by vehicles) along the length of the barrier.
FIGS. 4 a to 4 c show rope supports which may be advantageously adopted in the posts of the embodiments of FIGS. 2 and 3. FIG. 4 a shows a keyhole slot 15 formed in the wall of the post 1. A support roller 16 is mounted within the keyhole slot 15 and held therein by spigot 17. The roller 16 supports the wire rope 4 so that it is free to slide in the longitudinal direction of the safety barrier and free to move upwardly in the event of a vehicle impact. The roller supports are preferably frangible so that, in the event of a vehicle impact in which the posts fail to collapse towards the ground, the ropes are able to become detached from the posts more easily. Instead of supporting the ropes by way of the support roller 16 illustrated in FIGS. 4 a to 4 c, the ropes could be supported by a simple protuberance formed in the surface of the post.
The post cross-section may be of any size and shape which satisfies the above criteria, and may vary in dimensions along the length of the barrier to reflect differing requirements, e.g. curves in the highway and/or changing post spacing.
Superficial 2nd Moment of Inertia mm4
dimensions of post cross-section mm In plane of
Depth Width Thickness barrier Normal to barrier
The constructional design detail of the rope tendons is believed non-critical to the initial functionality of the barrier so long as the ultimate strength and axial stiffness of the ropes are correctly specified, in keeping with the expected (crash) performance of the barrier. However the 19 mm diameter 3×7(6/1) rope is commonly used at present in this application and is a suitable rope for use in barriers embodying the present invention. This type of rope is favored both for ease of manufacture/handling, and for its structural integrity when subjected to mechanical abrasion/abuse. In addition it is substantially torque balanced under load which facilitates pre-tensioning and avoids undesirable rotational displacements in service.
However to optimize the functionality of the barrier in the immediate post-crash period steps should be taken to minimize the loss in rope tension when the barrier is impacted by a vehicle. In addition to ensuring that the barrier is uniformly pre-tensioned along its length, the ropes should be pre-stretched at a tension equivalent to 50% of their breaking strength, to remove initial stretch and elevate the elastic limit of the wire rope. Typically such ropes will have a minimum breaking strength of 174 kN and an axial stiffness of at least 23 MN.
This is admittedly a worst case scenario and in practice a considerable amount of these tension losses will be taken up by the undisturbed rope in the adjoining fence bays. Nevertheless the residual tension in the ropes will be significantly less than if they had not been interwoven. This emphasizes the need for effective pre-tensioning of the ropes to the recommended level, if a degree of barrier integrity is to be maintained in the immediate post-crash period.
Comparison of Maximum Bending Stresses in Z-Posts at 2.4 m centres:
In-line Combined
Post dimensions mm moment of bending Maximum bending
D × W × Thickness inertial mm4 moment Nm stress N/mm2
With the Standard (100×32×6 mm) post it was found that the maximum bending stress greatly exceeded the yield strength of the post, which is 275 MPa [for Fe430A grade material]. The use of a larger (100×40×6.0 mm) post was therefore considered but the maximum bending stress still marginally exceeded the Fe430A yield strength. In this instance the problem could be solved by using a higher grade of steel post, e.g. Grade Fe510A which offers a yield strength of 355 MPa. A possible alternative solution would be to use a yet larger post such as the 120×50×6 mm section. Whilst this increases the angular deviation of the ropes and the bending moment slightly, the maximum bending stress falls to 224 MPa, well below the normal yield strength of 275 MPa.
1. A safety barrier post secured on or in the ground, the post comprising:
wherein the first side defines an indentation formed on a surface of the first side to receive and support a first wire rope and wherein a depth of the indentation from the surface is less than a diameter of the first wire rope;
wherein the first wire rope is held in tension against the indentation to withstand an impact from a vehicle; and
such that the first wire rope is released from the indentation in an upwards or downwards direction when a vertical force is exerted on the first wire rope.
2. The post of claim 1 wherein the second side defines at least one indentation formed on a surface of the second side to receive and support a second wire rope and wherein a depth of the indentation from the surface is less than a diameter of the first wire rope such that the second wire rope is released from the indentation in an upwards or downwards direction when a vertical force is exerted on the second wire rope.
3. The post of claim 2 wherein the indentation on the first side is at substantially the same height as the indentation on the second side.
4. The post of claim 1 wherein the first side defines a second indentation to receive and support a second wire rope and wherein a depth of the second indentation from the surface is less than a diameter of the first wire rope, the second indentation vertically displaced from the first indentation such that the second wire rope is released from the second indentation in an upwards or downwards direction when a vertical force is exerted on the first wire rope.
5. The post of claim 1 wherein the indentation is vertically symmetrical.
6. A safety barrier post comprising:
an elongate member having a first side and a second side, and a first end secured in the ground;
wherein the first side defines at least one indentation formed on a surface of the elongate member to receive and support a first wire rope and wherein a depth of the indentation from the surface is less than a diameter of the first wire rope;
such that the elongate member is not pulled from the ground when a vertical force is exerted on the first wire rope.
7. The post of claim 6 wherein the second side defines at least one indentation formed on the second side to receive and support a second wire rope such that the elongate member is not pulled from the ground when a vertical force is exerted on the second wire rope.
8. The post of claim 6 wherein the first side defines a second indentation formed on the surface of the first side to receive and support a second wire rope such that the elongate member is not pulled from the ground when a vertical force is exerted on the second wire rope.
9. A road safety barrier comprising:
a plurality of wire ropes supported by the posts, the ropes held in tension along a length of the barrier;
wherein each of the posts comprises a first indentation and a second indentation, each of the first indentation and second indentation formed on a surface of the posts and wherein a depth of the first indentation and second indentation from the surface is less than a diameter of the first wire rope; and
such the plurality of wire ropes is released from the first indentation and the second indentation in an upwards or downwards direction when a vertical force is exerted on the plurality of wire ropes.
10. The road safety barrier of claim 9 wherein the first indentation is arranged such that the post is not pulled from the ground when a vertical force is exerted on one of the wire ropes.
11. The road safety barrier of claim 9 wherein the first and second indentations are on opposite sides of each of the plurality of posts.
12. The road safety barrier of claim 9 wherein the first indentation is disposed at a first height on the post and the second indentation is disposed at a second height on the post.
13. The road safety barrier of claim 12 wherein the first indentation and the second indentation are on a first side of the post, such that the first height and the second height are vertically spaced apart.
14. The road safety barrier of claim 12 wherein the first indentation and the second indentation are on opposite sides of the post.
15. The road safety barrier of claim 14 wherein the first height and the second height are substantially the same.
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