The present invention relates to road crash barriers comprising at least one horizontal wooden rail.
The main application of the invention lies in making road crash barriers, however the assembly of elements constituting them could be used for other purposes, in particular whenever there is a risk of a wooden element being subjected to a longitudinal traction force and/or an accidental impact that might cause it to break.
Nevertheless, the technical sector that uses all of the characteristics of said assembly and the combination of elements constituting it lies in the field of road crash barriers.
Such crash barriers are well known, placed on the sides of roads and motorways to retain vehicles that accidentally leave the normal traffic paths thereof.
Such crash barriers include one or more horizontal rails, connected to posts that are fixed to the ground, and in the event of an impact from a vehicle they must be capable of withstanding large forces without breaking: various classes or levels of force have been defined by the national authorities in numerous countries, and in France the competent authority is the "Ministere de l'Equipement, du Logement, de l'Amenagement du Territoire et des Transports". That authority has established three classes in particular, with the highest class thereof corresponding to a level 1 that applies to use on motorways and on high-traffic roads.
For this purpose, the rails of crash barriers are generally made up of metal bar elements that are assembled together to ensure continuity, and that make it relatively easy to reach the strength required by the above-mentioned top level.
In addition, and in particular to improve the appearance of such crash barriers, so that they meld better with a rural or an urban environment, and/or so as to integrate them in landscaping development, numerous manufacturers have sought, and are still seeking, to develop crash barriers constituted by wooden rails: nevertheless, the traction strength and the impact strength of this material is naturally much less than that of steel, and at present, few crash barrier implementations that make use of wood can withstand static traction forces exceeding 200 kNewtons, which means they are out of contention for the highest classification mentioned above; and even then such a value can be achieved only when using special coupling and assembly devices for rails made up of wooden elements that are generally identical and need to be held together end to end, like those mentioned below.
In an attempt to improve the strength of such wooden crash barriers, various assemblies and types of crash barriers have been developed, some of which have constituted the subject matter of patent applications, such as:
U.S. Pat. No. 1,824,454, filed Mar. 26, 1931 by William E. White, who, judging that wood is not strong enough on its own, added a strip of iron to the front face of the rail, which strip covered the entire length and area thereof, and thus served, itself to provide the necessary impact and traction strength. Similarly, U.S. Pat. No. 2,085,058 (Wood) filed Mar. 12, 1934 describes a crash barrier including a cable for withstanding forces, with the wood then serving essentially, as in the preceding patent, to improve appearance and visibility, and also because it is relatively inexpensive. By implementing either of those two patents, it is indeed possible to obtain the desired strength, but only at the cost of using large metal elements that are therefore expensive, and even, in the White patent, the metal strip which covers the wooden rail hides it completely and eliminates most of the desired improvement in appearance. Neither of those two relatively old patents has been the subject of development for major application in the field of protecting road traffic.
More recently, for the purpose of retaining the advantages of appearance, the present inventors have developed rails made of wood only, associated with systems for coupling and attaching rail elements to one another in order to improve strength at their ends, e.g. as described in European patent EP 184 525 in the name of Mr. Eynard, dated Nov. 13, 1985, or French patent FR 2 592 974 in the name of Etablissements Galliard, filed Dec. 23, 1985 and relating to metal strap fastenings placed across the ends of the rails in which they are set back, said rails themselves also being constituted by wooden poles: additions to and improvements in the strength of such straps have subsequently constituted the subject matter of certificates of addition, in particular concerning the addition of anchoring spikes to the straps.
Nevertheless, even in the context of developments of the above assembly, the maximum traction strengths that it is has been possible to achieve are 200 kNewtons, which is not sufficient to qualify for level 1 of the classification.