BREAKAWAY POST CONNECTOR

Abstract: A coupling unit for connecting respective segments of a roadside post includes respective end portions (20a, 20b) adapted to engage in or about the segments and an intermediate fracture zone (45) in which the coupling unit divides to cause the post segments to separate when the assembled post is subjected in situ to a vehicle impact greater than a predetermined severity.

Description: BREAKAWAY POST CONNECTOR Field of the Invention This invention relates generally to the provision of roadside structures including posts, vehicle barriers, crash cushions, furniture, sign support systems, and light pole systems, and is concerned in particular with the posts used to support such structures. The invention is described herein with specific reference to roadside vehicle barriers but it will be understood that it has much broader application. Background Art A widely used form of roadside vehicle barrier, commonly known as a crash barrier, consists of one or more, often two, steel rails of generally W cross-section supported by a line of posts and usually tensioned by inclined cables stayed by the end posts. Steel crash barriers have been known in the past to pierce into vehicles impacting the barriers end-on, with potentially horrific consequences for the occupants. To prevent such consequences, it is required by regulatory authorities in Australia that a prescribed initial number of posts at each end must be a specific and exact form of timber designed to snap in two when the barrier is subjected to vehicle impact greater than a predetermined severity. Snapping of the end posts allows the barrier to collapse away from rather than pierce the vehicle, while still absorbing its impact and slowing it down. The remaining intervening posts may be simple steel posts, eg of C-section channel. Summary of the Invention It is an object of this invention to provide a novel coupling unit. In a preferred aspect of the invention, it is an object to provide a post assembly which may be adapted in one application to use as a snap-away end post in roadside vehicle barriers in substitution for the timber post typically now utilised. The invention accordingly provides, in a first aspect, a coupling unit for connecting respective segments of a roadside post, including respective end portions adapted to engage in or about the post segments and an intermediate fracture zone in which the coupling unit divides to cause the post segments to separate when the assembled post is subject in situ to a vehicle impact greater than a predetermined severity. The invention also provides, in a second aspect, a post assembly adapted for installation as a roadside post, including respective post segments adapted to be upper and lower segments in situ and a coupling unit for connecting said segments, which coupling unit includes respective end portions which engage in or about the post segments and an intermediate fracture zone in which the coupling unit divides to cause the upper post segment to separate from the lower post segment when the post is subjected directly or indirectly to an impact greater than a predetermined severity. In a third aspect, the invention further provides a roadside vehicle barrier including one or more impact rails supported by a line of spaced posts supported in the ground, wherein at least a first post in the line is a post assembly according to the second aspect of the invention. The coupling unit is preferably an integrally moulded component. Preferably, the coupling unit is of general H cross-section, including a pair of flanges. These flanges may be joined by a plurality of generally aligned web segments. The web segments are preferably waisted. The coupling unit preferably includes a transverse aperture and advantageously an associated boss, for receiving a cable for tensioning the rail(s) of the vehicle barrier. Preferably, the fracture zone is defined by slot means through the coupling unit. The fracture zone may be further defined by one or more weld or knit lines adjacent the slot means and/or by one or more v-cut grooves in an outer face of the coupling unit. Each of the post segments is preferably a steel segment, more preferably a C- section, with return lips, a closed channel, or a rolled hollow section, dimensioned to snugly receive the respective end portions of the coupling unit. The coupling unit and post segments advantageously include complementary apertures to receive bolts or other fastening means for securing the post segments to the coupling unit. Such bolts may traverse the coupling unit through both flanges and through respective cavities between tiie web segments. In the roadside vehicle barrier of the third aspect of the invention, the lower post segment would typically be largely in the ground so that the fracture zone of the unit is just above ground level. Typically, the first several posts in the line of spaced posts supporting the rails(s) would be post assemblies according to the second aspect of the invention, whereby to allow the end region of the rail(s) to retract aside under a given end-on vehicle impact without piercing the vehicle. In another embodiment, the coupling unit is a fibre filled polyester resin, which may be conveniently derived from recycled materials, for example the recycled polyethylene terephthalate (PET) widely employed for soft drink bottles. The resultant moulded material is amorphous. In this case, the fracture zone may be formed by flowing the material into the mould at a gate at or adjacent said intermediate poition so that the flow lines of the fibres exhibit a sharp turn, eg at the aforesaid flanges. To this end, the fibres of the fibre-filled resin, which are preferably glass fibres, are preferably primarily fibres of at least 5 mm in length. By selecting the parameters of the material of the moulding, eg nature, cross- section, length and density, the yield strength and impact strength of the moulded product, in this case specifically of the fracture zone of the coupling unit, can be varied, and thus can be selected, for example, to match that of traditional support posts for vehicle barriers. Brief Description of the Drawings The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a one-post section of a roadside vehicle barrier incorporating posts with coupling units according to an embodiment of the invention; Figure 2 is a front view of the coupling unit; and Figure 3 is a rear sectioned view of the unit. Description of Preferred Embodiments A typical roadside barrier 8 is illustrated in Figure 1. The barrier has a single impact rail 9 supported from behind by a line of spaced roadside posts 10. Rail 9 is, as is common, W-section steel. Barriers of this type can have two or more impact rails. Each post 10 includes respective upper and lower post segments 12,14 of C-section steel channel, and a coupling unit 20 for connecting post segments 12,14, integrally injection moulded in a thermoplastic material or formed-up thermosetting compound. As discussed earlier, possible alternatives for post segments 12,14 include closed channels and rolled hollow sections. Post segments 12J4 are formed in a steel channel material already widely employed for support posts of vehicle barriers but such channel is only employed at present for intermediate posts, the end posts being timber for the reasons earlier discussed. With the illustrated construction, however, roadside posts 10 can instead be employed as the end posts. Coupling unit 20 is of general H cross-section, including flanges 22,23 and a web 24 which is divided at its longitudinal centre into two equal segments 24a,24b by a transverse slot 26. Web 24 is waisted in that its cross-section is symmetrically biconically tapered. The respective web segments 24a,24b together with the associated portions of flanges 22,23 form end portions 20a,20b which are a snug fit in post segments 12,14 being transversely retained by the return lips 13 present on the post segments by virtue of their C- section. The coupling unit projects into the post segments until they abut opposite edges of shallow integral spacer ribs 30 centrally located on the outside faces of flanges 22,23. The three components are secured together by respective carriage bolts 32 which traverse central window cavities 27a,27b in the web segments 24a,24b, and pass tlirough pre¬ formed apertures 34,35 in flanges 22,23 and in the post segments. SUBSTITUTE SHEET (RULE 26} Typically, this assembled post 10 is positioned in situ by locating the lower post segment 14 almost wholly in a hole 6 in the ground 5 and the post segment 12 above ground. A boss formation 40 projects integrally from one face of web 24 at slot 26, being defined by two quasi-semitubular segments 40a separated by longitudinal slots 41 of matching width to, and in register with, the web slot 26. Boss 40 defines a central coaxial aperture 42 which extends through both the boss and web 24, and an outer annular face 44 designed to be substantially flush with the outer faces 13a of post segment retum lips 13. In the assembled vehicle barrier, aperture 42 may receive a tensioning cable (not shown) with a washer-type end fitting which abuts faces 13a,44. A remote end of the cable is fastened to a rail of the barrier. Altematively, the coupling unit might be inserted in the post in the opposite orientation to that of Figure 1, so that the boss backs up the main base web 13b of the post. To provide for the upper post segment 14 to break away from the lower post segment 12 in the circumstance of an impact greater than a predetermined severity, slot 26 in web 24 and slots 41 of boss 40 define an intermediate fracture zone 45 in which the coupling unit divides when the post is subjected, directly or indirectly, to such a vehicle impact. A further feature of the fracture zone is the presence of a weld line or knot line across each of the flanges 22,23 at their mid-points 50 adjacent slot 26 and spacer ribs 30. These weld or knit lines are produced by injecting the plastics melt at a central gate of the mould between the flange cavities so that the flow is outwards and upwards to form the web segments and thence into the flanges. The weld or knit lines occur where these fronts of plastic come together at the longitudinal midpoints of the flanges. The fracture zone is still further enhanced by the provision of respective V-notch grooves 52 across the outer faces of flanges 22,23 immediately adjacent spacer ribs 30. A V-notch groove may or may not be necessary depending on the resistance required to the breaking impact forces. A particularly satisfactory material for coupling unit 20 is nylon, including but not limited to types 6,6,6 and 6,6,6,11,12. Other possible thermoplastic materials include polypropylene, including homopolymers, copolymers and their alloys, thermoplastic polyesters including polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), thermoplastic polyurethane and its alloys, polyethylene including but not limited to low, medium and high density, modified forms and alloys. Possible thermosetting compounds include polyesters and epoxies and modifications thereof. The material may or may not be impact modified, or provided with reinforcement, and/or with or without colour or other additives. In an altemative embodiment (not illustrated), the fracture zone is obtained by using a glass fibre-filled polyester resin in which the fibres are primarily of at least 5 mm in length, and by flowing the material into the mould at a centre gate so that the material flows left and right then sharply up and down into the flange. The resultant shaφ changes in orientation of the longer fibres creates the required distinct fracture zone: this change of direction need only occur locally but polyester resin is such that a fracture, once started in a local region, readily extends across the whole object. The fibres should predominantly be greater than 5 mm in length. It has been found that as the fibre length is lowered from this value, the ability to finely control the properties of the fracture zone, especially its location and yield strength, diminish. The glass fibre-filled polyester resin is usefully derived from recycled PET which is widely employed for softdrink containers, and is amoφhous. It will be appreciated that the illustrated configuration provides an assembled post having adequate structural strength for normal use but, when subjected to a prescribed impact, allows the two post segments to part in a controlled manner. Although the invention has been described herein primarily in connection with posts for roadside vehicle barriers, it has much wider application to roadside structures in general, including without limitation crash cushions, roadside furniture, sign support systems and lighting systems. The physical parameters of the mould material may be selected to achieve a required yield strength and impact strength in the fracture zone according to standards determined by the appropriate authorities. For example, they may be chosen to match those of the conventional breakaway timber posts presently used for the end posts of roadside vehicle barriers. Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group integers.

Claims: Claims 1. A coupling unit for connecting respective segments of a roadside post, including respective end portions adapted to engage in or about the segments and an intermediate fracture zone in which the coupling unit divides to cause the post segments to separate when the assembled post is subjected in situ to a vehicle impact greater than a predetermined severity. 2. A coupling unit according to claim 1, being of general H cross section including a pair of flanges. 3. A coupling unit according to claim 2 wherein said flanges are joined by a plurality of generally aligned web segments. 4. A coupling unit according to claim 3 wherein said segments are waisted. 5. A coupling unit according to any preceding claim wherein said fracture zone is defined by slot means through the coupling unit. 6. A coupling unit according to claim 5 wherein the fracture zone is further defined by one or more weld or knit lines adjacent said slot means. 7. A coupling unit according to claim 5 or 6 wherein the fracture zone is further defined by one or more V-cut grooves in an outer face of the coupling unit. 8. A coupling unit according to any preceding claim, being an integrally moulded component. 9. A coupling unit according to claim 8 wherein the material of said component is selected from nylon, polypropylene, thermoplastic polyester including polyethylene terephthalate and polybutylene terephthalate, thermoplastic polyurethane and its alloys, polyethylene, and thermosetting compounds including polyesters, epoxies and modifications thereof. 10. A coupling unit according to any preceding claim further including a transverse aperture, and preferably an associated boss, for receiving a cable for tensioning the rail(s) of a vehicle barrier. 11. A coupling unit according to any preceding claim further including apertures to receive bolts or other fastening means for securing the post segments to the coupling unit. 12. A coupling unit according to any one of claims 1 to 11 wherein said fracture zone is formed by flowing the material into a mould at a gate at or adjacent to said intermediate portion so that the flow lines of the fibres exhibit a shaφ turn, eg at the aforesaid flanges. 13. A post assembly adapted for installation as a roadside post, including respective post segments which are upper and lower segments in situ and a coupling unit for connecting said segments, which coupling unit includes respective end portions which engage in or about the post segments and an intermediate fracture zone in which the coupling unit divides to cause the upper post segment to separate from the lower post segment when the post is subjected directly or indirectly to an impact greater than a predetermined severity. 14. A post assembly according to claim 13 wherein each of the post segments is a steel segment, being one of a channel with retum lips, a closed channel and a rolled hollow section, dimensioned to snugly receive the respective end portions of the coupling unit. 15. A post assembly according to claim 14 wherein the steel channels are generally of c-section. 16. A post assembly according to claim 13, 14 or 15, wherein said coupling unit is of generally H cross-section, including a pair or flanges. 17. A post assembly according to claim 16 wherein said flanges are joined by a plurality of generally aligned web segments. 18. A post assembly according to claim 17 wherein said web segments are waisted. 19. A post assembly according to any one of claims 13 to 18 wherein said fracture zone is defined by slot means through the coupling unit. 20. A post assembly according to claim 19 wherein the fracture zone is further defined by one or more weld or knit lines adjacent to said slot means. 21. A post assembly according to claim 19 or 20 wherein the fracture zone is further defined by one or more V-cut grooves in an outer face of the coupling unit. 22. A post assembly according to any one of claims 13 to 21, wherein the coupling unit is an integrally moulded component. 23. A post assembly according to claim 21 wherein the material of said component is selected from nylon, polypropylene, thermoplastic polyester including polyethylene terephthalate and polybutylene terephthalate, thermoplastic polyurethane and its alloys, polyethylene, and thermosetting compounds including polyesters, epoxies and modifications thereof. 24. A post assembly according to any one of claims 13 to 23, wherein the coupling unit further includes a transverse aperture, and preferably an associated boss, for receiving a cable for tensioning the rail(s) of a vehicle barrier. 25. A post assembly according to any one of claims 13 to 24 further including complementary apertures in the coupling unit and post segments to receive bolts or other fastening means for securing the post segments to the coupling unit. S 26. A roadside vehicle barrier including one or more impact rails supported by a line of spaced posts supported in the ground, wherein at least a first post in the line is a post assembly according to any one of claims 13 to 25. 27. A roadside vehicle barrier according to claim 26 wherein the lower post segment is in the ground so that the fracture zone of the coupling unit is just above ground level. 28. A roadside vehicle barrier according to claim 26 or 27 wherein a first plurality of posts in the line of spaced posts supporting the rail(s) are post assemblies according to any one of claims 13 to 25, whereby to allow the end region of the rail(s) to retract aside under a given end-on vehicle impact without piercing the vehicle.

Inventors: MELROSE GARY JAMES, WASSON LANCE DAVID, MELROSE, GARY, JAMES, WASSON, LANCE, DAVID
Applicants: BHP STEEL JLA PTY LTD, MELROSE GARY JAMES, WASSON LANCE DAVID, BHP STEEL (JLA) PTY. LTD., MELROSE, GARY, JAMES, WASSON, LANCE, DAVID
Application year: 1996
Main classification: E01F9
IPC codes: E01F9, E01F15