US20080296546A1

US20080296546A1 - Cable for use in safety barrier

Info

Publication number: US20080296546A1
Application number: US11/756,730
Authority: US
Inventors: Peter Bergendahl
Original assignee: Trinity Industries Inc
Current assignee: Trinity Industries Inc
Priority date: 2007-06-01
Filing date: 2007-06-01
Publication date: 2008-12-04
Also published as: WO2008150856A1

Abstract

A cable for use in a safety barrier is provided. A cable for use in a safety barrier may include a plastic core wire and a plurality of metal wires disposed adjacent to and longitudinally to the plastic core wire. The cable may be pre-stretched prior to installation in the safety barrier. A method of making cable for use in a safety barrier may include (a)providing a plastic core wire, (b) disposing a plurality of metal wires, each metal wire disposed adjacent to and longitudinally to the plastic core wire, and (c) prestretching the cable prior to installation in the safety barrier.

Description

RELATED APPLICATION

This application is related to co-pending U.S. patent application Ser. No. 11/207,239 entitled “Cable Safety System,” filed Aug. 19, 2005.

TECHNICAL FIELD

The present disclosure is related to highway barriers and safety systems and more particularly to cable safety systems and associated cables.

BACKGROUND OF THE DISCLOSURE

Cable safety systems and cable barriers have been installed along edges of roadways and highways for many years. Cable safety systems and cable barriers have also been installed along medians between roadways and/or highways. Cable safety systems generally include one or more horizontal cables attached to support posts. For some applications cable safety systems and cable barriers may reduce damage to an impacting vehicle and/or injury to occupants of the impacting vehicle as compared with other types of highway safety systems and highway barriers.
Cable safety systems are often designed and installed with at least one cable mounted horizontally on a plurality of generally vertical support posts. Many cable safety systems include three cables spaced vertically from each other on each support post. The number of cables may vary depending on factors such as the type of vehicles using the associated roadway and the hazard which requires installation of the cable safety system. The length of a cable safety system is generally determined based on the adjacent roadside hazard. Each cable is typically installed at a selected height relative to the ground and with selected vertical spacing between adjacent cables.
During the past several years, cable safety systems have been used as an alternative to traditional W-beam or thrie-beam guardrail systems. Cable safety systems are often more aesthetically appealing and minimize potential sight distance problems as compared with W-beam and thrie beam guardrail systems. Cable safety systems generally minimize snow accumulation on adjacent highways and roadways.
As steel prices have increased, there has arisen a need to manufacture cable safety systems with lesser amounts of steel. However, an approach of lowering steel content by merely making steel cables thinner may not be an appropriate solution, as such an approach may lower the effectiveness of cable safety systems in protecting occupants of an impacting vehicle. Accordingly, solutions are needed in which steel content is reduced while at the same time maintaining the effectiveness of the cable safety system in reducing damage to impacting vehicles and/or the occupants thereof.

SUMMARY OF THE DISCLOSURE

In accordance with teachings of the present disclosure, a cable safety system may be provided which overcomes many disadvantages and problems associated with prior cable safety systems and cable barriers.
According to one embodiment of the present disclosure, a safety barrier installed adjacent to a roadway comprising includes a plurality of posts spaced from each other and disposed adjacent to the roadway, and at least one cable releasably engaged with and supported by the posts. The cable may include a plastic core wire and a plurality of metal wires disposed adjacent to and longitudinally to the plastic core wire. The cable may be pre-stretched prior to installation in the safety barrier.
According to another embodiment of the present disclosure, a cable for use in a safety barrier may include a plastic core wire and a plurality of metal wires disposed adjacent to and longitudinally to the plastic core wire. The cable may be pre-stretched prior to installation in the safety barrier.
According to yet another embodiment of the present disclosure, a method of making cable for use in a safety barrier is provided. The method may include providing a plastic core wire. A plurality of metal wires may each be disposed adjacent to and longitudinally to the plastic core wire. The cable may be pre-stretched prior to installation in the safety barrier.
Further technical benefits of the present disclosure may include improved cables for use in safety barriers, wherein the cables may be lighter than similar cables manufactured entirely from metal, while at the same time remaining as effective against impacting vehicles as similar cables manufactured entirely from metal. Other technical advantages and benefits will be apparent to those of ordinary skill in the art in view of the following specification, claims, and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:

FIG. 1 a is a schematic drawing in elevation with portions broken away of a cable safety system, in accordance with the present disclosure;

FIG. 1 b is a schematic drawing showing a plan view with portions broken away of the cable safety system of FIG. 1 a;

FIG. 1 c is a schematic drawing in elevation with portions broken away of another cable safety system incorporating teachings of the present disclosure;

FIG. 1 d is a schematic drawing in section and in elevation with portions broken away of a below ground cable anchor assembly satisfactory for use with the cable safety system of FIG. 1 c;

FIG. 2 is a schematic drawing showing an isometric view with portions broken away of a post and cables, in accordance with the present disclosure;

FIG. 3 a is a schematic drawing in section showing one example of a cable formed using a seven strand metal wire rope, in accordance with the present disclosure;

FIG. 3 b is a schematic drawing in section depicting the forces that may be applied during an impact to individual wires of the wire rope of FIG. 3 a;

FIG. 4 a is a schematic drawing in section showing one example of a cable formed using a plastic core wire surrounded by a plurality of metal wires adjacent to and disposed longitudinally to the plastic core wire, in accordance with the present disclosure;

FIG. 4 b is a schematic drawing in section depicting the forces that may be applied during an impact to the individual wires of the wire rope of FIG. 4 a;

FIG. 5 a is a schematic drawing in section showing one example of a cable formed from three groups of seven strand metal wire rope, in according with the present disclosure;

FIG. 5 b is a schematic drawing in section showing one example of a cable formed from three groups of wire rope, each of the three groups formed using a plastic core wire surrounded by a plurality of metal wires adjacent to and disposed longitudinally to the plastic core wire, in accordance with the present disclosure; and

FIG. 5 c is a schematic drawing in section showing one example of a cable formed from three groups of wire rope, wherein one of the three groups is formed using a plastic core wire surrounded by a plurality of metal wires adjacent to and disposed longitudinally to the plastic core wire, in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention and its advantages are best understood by reference to FIGS. 1 a-11 wherein like reference numbers indicate like features.
The terms “safety system” or “safety systems”, “safety barrier” or “safety barriers,” and “barrier” or “barriers” may be used throughout this application to include any type of safety system and/or barrier which may be formed at least in part using cables and support posts incorporating teachings of the present disclosure. The term “roadway” may be used throughout this application to include any highway, roadway or path satisfactory for vehicle traffic. Safety systems and barriers incorporating teachings of the present disclosure may be installed in median strips or along shoulders of highways, roadways or any other path which is likely to encounter vehicular traffic.
Various aspects of the present disclosure will be described with respect to cable safety systems 20 and 20 a. However, teachings of the present disclosure may be used to form a wide variety of safety systems and barriers. Cable safety systems 20 and 20 a may have similar design features and characteristics except cable safety system 20 includes above ground anchors 24 and 26. Cable safety system 20 a includes below ground anchors 24 a and 26a. The present disclosure is not limited to cable safety systems 20 and 20 a as shown in FIGS. 1 a-1 d.
Cable safety systems 20 and 20 a may be installed adjacent to a roadway (not expressly shown) to prevent motor vehicles (not expressly shown) from leaving the roadway and to redirect vehicles away from hazardous areas without causing serious injuries to the vehicle's occupants or other motorists. The general direction of traffic flow along the roadway is illustrated by directional arrow 22.
Cable safety systems 20 and 20 a may be satisfactorily used as a median, a single barrier installation along the edge of a roadway and at merge applications between adjacent roadways. For some applications, cable safety systems 20 and 20 a may satisfactorily withstand a second impact before repairs have been made after a first impact. For many applications, cable safety systems 20 and 20 a may be described as generally maintenance free except for repairs required after a vehicle impact.
Cable safety systems 20 and 20 a preferably include a plurality of support posts 30 anchored adjacent to the roadway. Posts 30 may be anchored with the ground using various techniques. For some applications a concrete foundation (not expressly shown) may be provided with holes to allow relatively quick and easy insertion and removal of parts. The number, size, shape and configuration of posts 30 may vary significantly among various applications and installations. Optimum spacing between posts 30 may also vary among various applications and installations. See, for example, U.S. Pat. No. 6,962,328, granted Nov. 8, 2005 and entitled “Cable Safety Systems,” which is incorporated by reference herein for all purposes.
Various types of cables and/or wire ropes may be satisfactorily used to form a cable safety system in accordance with teachings of the present disclosure. Cables 160 a, 160 b and 160 c may be substantially identical. However, for some applications each cable of a cable safety system formed in accordance with teachings of the present disclosure may have different characteristics. Cable safety systems 20 and 20 a may be generally described as flexible, substantially maintenance free systems with designed low deflection of cables 160 a, 160 b, and 160 c during a vehicle impact. Forming cable safety systems 20 and 20 a in accordance with teachings of the present disclosure minimizes damage during a vehicle impact with posts 30 and/or cables 160 a, 160 b and 160 c. For some applications cables 160 a, 160 b and 160 c may be formed from seven strand wire rope, e.g. cable 170 as depicted in FIG. 3 a. Other types of wire ropes and cables may also be used, e.g., cable 175 as depicted in FIG. 4 a, cable 180 depicted in FIG. 5 a, cable 190 depicted in FIG. 5 b, and/or cable 195 as depicted in FIG. 5 c.
A plurality of cables 160 a, 160 b and 160 c may be attached to support posts 30 in accordance with teachings of the present disclosure. Support posts 30 generally maintain associated cables 160 a, 160 b and 160 c in substantially horizontal positions extending along an edge of the roadway. Support posts 30 often allow relative quick and easy repair of cable safety systems 20 and 20 a after a vehicle impact.
Cable safety systems 20 and 20 a are generally relatively narrow as compared to conventional W-beam and thrie beam guardrail systems. The length of cables 160 a, 160 b and 160 c may be up to 3,000 meters between anchors 24 and 26 or anchors 24 a and 26 a. For other applications the length of cable 160 a, 160 b and 160 c may exceed 3,000 meters without an intermediate anchorage. Support posts 30 maintain desired vertical spacing between cables 160 a, 160 b and 160 c and desired vertical spacing of each cable relative to the ground. Cable safety system 20 and 20 a including support posts 30 formed in accordance with teachings of the present disclosure may be designed in accordance with teachings of the present disclosure to meet or exceed the criteria of NCHRP Report 350 Level 3 requirements.
Cable safety systems 20 and 20 a preferably include cables 160 a, 160 b and 160 c disposed in slot 40 of each post 30. Cable 160 a, 160 b and 160 c are preferably disposed at different heights relative to the ground and relative to each other. Varying the vertical spacing between cables 160 a, 160 b and 160 c often provides a much wider lateral catch area for vehicles impacting with cable safety systems 20 and 20 a. The vertical spacing between cables 160 a, 160 b and 160 c may be selected to satisfactorily contain both pickups and, to some extent, even larger vehicles with a relatively high center of gravity, as well as vehicles with a low front profile and low center of gravity.
Cables 160 a, 160 b and 160 c may be prefabricated in approximately three hundred (300) meter lengths with desired fittings attached with opposite ends of each cables 160 a, 160 b and 160 c. Tailor made cables 160 a, 160 b and 160 c may then be delivered to a desired location for installation adjacent to a roadway.
Alternatively, cables 160 a, 160 b, and 160 c may be formed from a single cable stored on a large drum (not expressly shown). Cables stored on drums may often exceed three thousand (3,000) meters in length. Cables 160 a, 160 b, and 160 c may be cut in desired lengths from the cable stored on the drum. Appropriate fittings (not expressly shown) may be swaged or otherwise attached with opposite ends of the respective cable 160 a, 160 b and 160 c at an onsite location. Cables 160 a, 160 b and 160 c may be installed between anchors 24 and 26 or anchor 24 a and 26 a with approximately twenty thousand Newtons of tension over a length of approximately three thousand (3,000) meters.
FIG. 1 d shows one example of a below ground anchor which may be satisfactorily used with a cable safety system incorporating teachings of the present disclosure. Respective holes 27 may be formed in the ground at desired locations for anchors 24 a and 26 a. A portion of each hole 27 may be filled with concrete foundation 28. Anchor plate 29 may be securely engaged with concrete foundation 28 using various types of mechanical fasteners, including, but not limited to, a plurality of bolts 23 and nuts 24. Anchor plate 29 may be formed at an appropriate angle to accommodate the design of cable safety system 20 a. Also multiple slots and/or openings (not expressly shown) may be formed in anchor plate 29 to receive respective end fittings 64.
For the embodiment of the present disclosure as shown in FIG. 1 d, end fitting 64 a of cable 160 a is shown engaged with anchor plate 29. Various types of anchor assemblies and cable end fittings may be satisfactorily used with a cable safety system incorporating teachings of the present disclosure. The present disclosure is not limited to anchor 24 a or end fittings 64 a as shown in FIG. 1 d.
One example of support posts 30 and cables 160 a, 160 b and 160 c which may be satisfactorily used to form cable safety system 20 in accordance with teachings of the present disclosure is shown in FIG. 2. Post 30 includes first end 31 and second end 32. For this embodiment of the present disclosure, post 30 includes a generally C-shaped cross section defined in part by web 34 with respective legs 35 and 36 extending therefrom. As shown in FIG. 2, the extreme edge of each leg 35 and 36 opposite from web 34 may be rounded or bent inward to eliminate any sharp edges. Support post 30 may also have a generally “rounded” or “soft” profile. For some applications post 30 may be formed using roll forming techniques.
Slot 40 is preferably formed in web 34 extending from first end 31 towards second end 32. The length of slot 40 may be selected in part based on desired vertical spacing of cable 160 c relative to the adjacent roadway. The length of slot 40 may also be selected to accommodate the number of cables which will be installed therein and desired vertical spacing between each cable. Slot 40 may have a generally elongated U-shaped configuration defined in part by first edge 41, second edge 42 and bottom (not expressly shown). For the embodiment of the present disclosure as shown in FIG. 2, first edge 41 and second edge 42 may have a generally smooth profile and extend generally parallel with each other. Forming slot 40 within web 34 of post 30 eliminates requirements for bolts, hooks or other mechanical attachments to releasably secure cables 160 a, 160 b and 160 c with post 30. Further examples of support posts 30 and cables 160 a, 160 b, and 160 c that may be used to form cable safety system in accordance with the present disclosure may be set forth U.S. Pat. No. 6,962,328, discussed above.
FIG. 3 a is a schematic drawing in section showing one example of a cable 170 for use in cable barrier system 20. Cable 170, as depicted, may comprise a metal core wire 71, and a plurality of metal wires 72 disposed adjacent to and longitudinally to metal core wire 71. In some embodiments, cable 170 may comprise a seven strand wire rope. In the same or alternative embodiments, metal core wire 71 and/or metal wires 72 may comprise steel. FIG. 3 b depicts the forces that may be applied during an impact to individual wires 71, 72 of cable 170 during a vehicle impact to cable safety system 20 comprising cable 170. As shown, a vehicle impact to cable safety system 20 may cause metal wires 72 to be forced towards metal core wire 71, thus decreasing the flexibility of cable 170.
In order to increase the flexibility of cable 170 depicted in FIG. 3 a, a plastic core wire 73 may be substituted in place of metal core wire 71, as depicted in FIG. 4 a, forming cable 175. As shown in FIG. 4 a, cable 175 may include a plastic core wire 73 and a plurality of metal wires 72 disposed adjacent to and longitudinally to plastic core wire 73. In certain embodiments, plastic core wire 73 may comprise polypropylene. In the same or alternative embodiments, cable 175 may comprise six metal wires 72. In addition, cable 175 may be manufactured or formed by methods similar to that of cable 170.
FIG. 4 b depicts the forces that may be applied during an impact to individual wires 72, 73 of cable 175 during a vehicle impact to cable safety system 20 comprising 175. As shown, a vehicle impact to cable safety system 20 may cause some of metal wires 72 ( e.g. metal wires 72 d, 72 e and 72 f) to be forced towards plastic core wire 73, while other metal wires ( e.g. metal wires 72 a, 72 b, and 72 c) may be forced away from plastic core wire 73, due to the flexible nature of plastic core wire 73. Accordingly, cable 175 may remain more flexible during a vehicle impact with cable safety system 20, and thus may be more resistant to breaking than a similarly-sized metal-wire-only cable 170.
In certain embodiments, cables comprising three groups of seven-strand wire, for example, cables 180, 190 and 195 depicted in FIGS. 5 a, 5 b and 5 c, respectively, may be used to form cable safety system 20. FIG. 5 a depicts a cable 180 formed from three groups of seven strand metal wire rope, as is often used in conventional cable safety systems. During a vehicle impact to cable safety system 20 comprising cable 180, the metal wires 72 comprising each wire rope of cable 180 may be forced towards the metal core wire 71 of their respective wire rope, as depicted in FIG. 3 b, which may result in decreased flexibility.
To increase the flexibility of a cable formed from three groups of seven strand wire rope, a plastic core wire 73 may be substituted in place each wire rope's metal core wire 71, as depicted in FIG. 5 b, forming cable 190. As shown in FIG. 5 b, cable 190 may include three wire ropes, each including a plastic core wire 73 and a plurality of metal wires 72 disposed adjacent to and longitudinally to the respective plastic core wires 73. In a vehicle impact to a cable safety system 20 comprising cable 190, some of the metal wires 72 of each wire rope comprising cable 190 may be forced towards their respective plastic core wires 73, while other metal wires 72 may be forced away from their respective plastic cores wires, as depicted in FIG. 4 b. Accordingly, cable 190 may remain more flexible during a vehicle impact with cable safety system 20, and thus may be more resistant to breaking than a similarly-sized metal-wire-only cable 180.
In addition to the embodiments depicted in FIGS. 5 a and 5 b, cable safety system 20 may comprise three groups of seven strand wire ropes, wherein some of the groups may include a plastic core wire 73, while others may not, such as cable 195 depicted in FIG. 5 c.
In conventional cable safety systems, cables are often pre-stretched to about 50% of designed or rated breaking strength in order to obtain a desired modulus of elasticity for the cable. However, in accordance with the present disclosure, cables 170, 175, 180, 190 and 195 may be pre-stretched to between approximately 60% and approximately 70% of designed or rated breaking strength. Such increased pre-stretching may reduce elasticity of the cable, thus decreasing the amount of deflection of the cable during a vehicle impact, as compared to a cable pre-stretched to 50% of its breaking strength. In certain embodiments, increased prestretching to between 60% and approximately 70% of designed or rated breaking strength may permit use of smaller-diameter cables as compared to that of conventional cable safety systems, thus potentially reducing raw materials cost.
Some of the advantages of the various alternatives discussed above may be illustrated in TABLE 1.

TABLE 1

		20 steel	18 steel
		wires, 1	wires, 3
		plastic	plastic
	21 steel	core	core
	wires;	wire;	wires;
21 steel	60%-70%	60%-70%	60%-70%
wires; 50%	pre-	pre-	pre-
pre-stretch	stretch	stretch	stretch
force	force	force	force
(conventional)	(FIG. 5a)	(FIG. 5c)	(FIG. 5b)

Wire	3.00	mm	2.81	mm	2.88	mm	3.06	mm
diameter
Cable	19.00	mm	18.12	mm	18.58	mm	18.12	mm
diameter
Tensile	1370	N/mm²	1570	N/mm²	1570	N/mm²	1570	N/mm²
strength
Minimum	183.00	KN	184.00	KN	183.16	KN	183.69	KN
breaking
load
Weight	1.18	Kg/m	1.04	Kg/m	1.04	Kg/m	1.06	Kg/m
of metal

The second column of TABLE 1 depicts the wire diameter, cable diameter, tensile strength, minimum breaking load, and weight of metal for an example conventional cable 180 comprising three groups of seven-strand steel wire rope. The third, fourth, and fifth each depict the same parameters for alternatively constructed cables having a similar minimum breaking load. Specifically, the third, fourth, and fifth columns respectively depict these same parameters for each of: (a) a 21 steel wire strand cable 180 similar to that depicted in FIG. 5 a pre-stretched to 60% to 70%, (b) a 20 steel wire, 1 plastic core wire cable 195 similar to that depicted in FIG. 5 c pre-stretched to 60% to 70%, and (c) a 18 steel wire, 3 plastic core wire cable 190 similar to that depicted in FIG. 5 b pre-stretched to 60% to 70%. From TABLE 1, it can be seen that by using pre-stretched cables, lighter steel strands, and plastic core wire strands, cables of similar minimum breaking load to that of conventional cables may be constructed using less metal, and therefore, may be less expensive to manufacture.
Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.

Claims

1. A safety barrier installed adjacent to a roadway comprising:

a plurality of posts spaced from each other and disposed adjacent to the roadway; and

at least one pre-stretched cable releasably engaged with and supported by the posts; and

the cable having a first plastic core wire, a first plurality of metal wires disposed adjacent to and extending longitudinally along the first plastic core wire.

2. The safety barrier of claim 1, further comprising the cable pre-stretched using a force equal to between approximately 60% to approximately 70% of the force required to break the cable.

3. The safety barrier of claim 1, wherein the first plastic core wire comprises a polypropylene thread.

4. The safety barrier of claim 1, wherein the first plurality of metal wires comprises six metal wires.

5. The safety barrier of claim 1, further comprising:

a first wire rope having the first plastic core and the first plurality of metal wires; and

a second wire rope and a third wire rope disposed adjacent to and extending longitudinally along the first wire rope.

6. The safety barrier of claim 5, wherein at least one of the second wire rope and third wire rope comprises:

a plastic core wire; and

a plurality of metal wires disposed adjacent to and extending longitudinally along the plastic core wire.

7. The safety barrier of claim 5, wherein at least one of the second wire rope and third wire rope comprises:

a metal core wire; and

a plurality of metal wires disposed adjacent to and extending longitudinally along the metal core wire.

8. A cable for use in a safety barrier comprising:

a first plastic core wire;

a first plurality of metal wires disposed adjacent to and longitudinally to the first plastic core wire; and

the cable pre-stretched prior to installation in the safety barrier.

9. The cable of claim 8, comprising the cable pre-stretched using a force equal to between approximately 60% to approximately 70% of the force required to break the cable.

10. The cable of claim 8, wherein the first plastic core wire comprises a polypropylene thread.

11. The cable of claim 8, wherein the first plurality of metal wires comprises six metal wires.

12. The cable of claim 8, further comprising:

13. The cable of claim 12, wherein at least one of the second wire rope and third wire rope comprises:

a plastic core wire; and

14. The cable of claim 12, wherein at least one of the second wire rope and third wire rope comprises:

a metal core wire; and

15. A method of making cable for use in a safety barrier comprising:

providing a first plastic core wire; and

disposing a first plurality of metal wires adjacent to and extending longitudinally along the first plastic core wire; and

prestretching the cable prior to installation in the safety barrier.

16. The method of claim 15, further comprising prestretching the cable using a force equal to between approximately 60% to approximately 70% of the force required to break the cable.

17. The method of claim 15, further comprising forming the first plastic core wire from a polypropylene thread.

18. The method of claim 15, further comprising wrapping six metal wires adjacent to and extending along the first plastic core wire.

19. The method of claim 15, further comprising forming a first wire rope with the first plastic core and the first plurality of metal wires, and

disposing a second wire rope and a third wire rope adjacent to and extending longitudinally relative to the first wire rope.

20. The method of claim 19, further comprising:

forming at least one of the second wire rope and third wire rope using a second plastic core wire; and

disposing a plurality of metal wires adjacent to and extending longitudinally relative to the second plastic core wire.