Abstract:
A cable termination and method of terminating a median barrier cable is described. In one form, the cable termination comprises a tubular body with an opening into which an end of the median barrier cable is inserted. A wedge gripper includes three sections for gripping the end of the median barrier cable within the tubular body. The wedge gripper has a tapering outer surface that mates with a tapered inner surface of the tubular body and has a toothed inner diameter. A threaded cap is screwed to an end of the tubular body opposite from the cable opening, such that the threaded cap forces the tapering outer surface of the wedge gripper axially against the tapered inner surface of the tubular body to force the toothed inner diameter of the wedge gripper to contract against three lobes of the median barrier cable to grip the median barrier cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. provisional application No. 61/060,317, filed Jun. 10, 2008, which is hereby incorporated by reference as if fully set forth herein. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to cable terminations particularly adapted to median barrier cables used on highways to enable securing the end of a median barrier cable to a structure so the cable can be tensioned and used as a traffic barrier. 
       BACKGROUND OF THE INVENTION 
       [0004]    High tension cable barriers are used to guard against traffic accidents caused when a vehicle crosses a median on a highway system. These cable systems, made by several different manufacturers, typically use three-quarter-inch (19 mm) diameter, three-by-seven strand cable ropes, that may or may not be pre-stretched depending on the system, and posts to guide the cables through and maintain cable height. If a crash occurs, the posts are designed to break off and the cables redirect or stop vehicles to significantly reduce crash severity. The cable systems usually include three or four cable tiers and each of the cables has two ends that must be terminated and the cables tensioned, for example, to a tension of several thousand pounds (e.g., 5600 pounds). The termination of the cables must be sufficient to withstand the pretension force on the cable, as well as the forces and vibrations that the cable is subjected to when a vehicle hits it. 
         [0005]    Designing these cable terminations has not been without challenges. The cables are a different shape and basic construction than is used in many other cable tensioning applications, such as post-tensioning concrete structures where a standard seven wire post-tension strand is used. Such post-tension strands have a relatively round profile. In high-tension median cable barrier systems, the cable is three twisted strands, each made of seven strands twisted together, and the three, seven strand cables are twisted together to make a cable rope that has a three-lobed profile. 
         [0006]    The three-lobed rope is illustrated in  FIGS. 1 and 2 . It is specified as a 19-3×7 wire rope and conforms to the requirements of AASHTO M30 Type 1 Class A coding 19 mm wire rope. The rope, with connecting hardware attached, is specified to develop 110 kN strength of a single cable. It is particularly specified to be used as the rail element in cable guard rails on highways, particularly in the median, to prevent vehicles from crossing the median into the oncoming lane of traffic. 
         [0007]    A cable wedge fastener is used to terminate the end of the wire rope so that it can be connected to either a turnbuckle for tensioning the wire rope or to another tension-related device to adjust or maintain the tension in the wire rope. Prior wedges for fastening such wire ropes typically had a seven-degree taper on the wedges and the wedges were configured in a manner such that pull-out of the cable ends from the termination was more likely than presently acceptable. The present invention provides an improvement to such prior wedge-style terminations. 
         [0008]    Another type of cable termination is disclosed in U.S. Pat. No. 4,899,499, the disclosure of which is hereby incorporated by reference. The anchor disclosed has a body with a wedge shaped (conical) internal bore surface, a three section cable gripper with a wedge shaped (conical) external surface received in the bore, a cable gripped by the grippers and extending from one end of the body, a threaded cap at the end of the body opposite from the cable, a threaded stem extending from the cap outside of the body at the end opposite from the cable and the stem having a head that is captured against the interior facing surface of the cap. The stem is threaded into an insert that is embedded in a concrete structure or otherwise affixed to a relatively immovable structure. The termination disclosed in the references appears to be particularly adapted to grip post-tensioning strand of the type described above, being made of seven twisted wire bundles, with one of the bundles in the middle and the other six bundles twisted around the middle bundle. 
         [0009]    Another problem with cable terminations of this type is corrosion inside the anchor. For example, corrosion can occur between the grippers in the body, between the cable and the grippers, and between the cap and the stem, which can ultimately reduce the tension in the cable and the grip of the termination on the cable. 
       SUMMARY OF THE INVENTION 
       [0010]    In one aspect, a cable termination is described for use with a median barrier cable made of three bundles of twisted wires, the three bundles being twisted together to form a wire rope having three lobes, each lobe being formed by one of the bundles. The cable termination comprises a tubular body with a cable opening in at least one end into which an end of the median barrier cable can be inserted. A wedge gripper has three sections for gripping the end of the median barrier cable within the tubular body. The wedge gripper further has a tapering outer surface that mates with a tapered inner surface of the tubular body, and has a toothed inner diameter. A threaded cap is screwed to an end of the tubular body opposite from the cable opening. Screwing the threaded cap into the body forces the tapering outer surface of the wedge gripper axially against the tapered inner surface of the tubular body to force the toothed inner diameter of the wedge gripper to contract against the three lobes of the median barrier cable so as to grip the median barrier cable in the body. 
         [0011]    In another aspect, a method of terminating a median barrier cable made of three bundles of twisted wires, the three bundles being twisted together to form a wire rope having three lobes is described. The method comprises providing a tubular body with a cable opening in at least one end and a tapered inner surface, a wedge gripper having a plurality of sections, a tapering outer surface, and a toothed inner diameter, and a threaded cap; inserting the median barrier cable into the cable opening in the body; mating the tapering outer surface of the wedge gripper with the tapered inner surface of the tubular body; and screwing the threaded cap to an end of the tubular body opposite from the cable opening to force the tapering outer surface of the wedge gripper against the tapered inner surface of the tubular body to force the toothed inner diameter of the wedge gripper to contract against the median barrier cable so as to grip the median barrier cable in the body. 
         [0012]    In a further aspect, a cable termination is described comprising a tubular body having a tapered inner surface and an opening at one end into which an end of a cable can be inserted, a wedge gripper having at least two sections positioned within the tubular body, each of the at least two sections includes a tapering outer surface that mates with the tapered inner surface of the tubular body and a toothed inner diameter, and a threaded cap screwed to an end of the tubular body opposite from the opening and engaged with the wedge gripper to retain the wedge gripper within the tubular body and maintain engagement of the toothed inner diameter of the wedge gripper with the cable. 
         [0013]    These and still other aspects will be apparent from the description that follows. In the detailed description, a preferred example embodiment of the invention will be described with reference to the accompanying drawings. This embodiment does not represent the full scope of the invention; rather the invention may be employed in other embodiments. Reference should therefore be made to the claims herein for interpreting the breadth of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a simplified side plan view of typical median barrier cable; 
           [0015]      FIG. 2  is an end plan view of the median barrier cable of  FIG. 1 ; 
           [0016]      FIG. 3  is a cross-sectional assembly view in schematic form of a termination of the invention; 
           [0017]      FIG. 4  is a side plan view of the wedge in  FIG. 3  prior to longitudinal separation into three sections; 
           [0018]      FIG. 5  is a simplified end plan view of the wedge of  FIG. 4  after separation and with a cable contained in it; 
           [0019]      FIG. 6  is a detail view of the angle on the wedge and showing the angles of the teeth on the inside of the wedge; 
           [0020]      FIG. 7  is a side plan view of the body of the termination of  FIG. 3 , it being understood that the teeth on the inner surface continue for substantially the whole length of the gripper; 
           [0021]      FIG. 8  is an end plan view of the body; 
           [0022]      FIG. 9  is a side plan view of the stem in  FIG. 3 ; 
           [0023]      FIG. 10  is a side plan view of the washer used in  FIG. 3 ; 
           [0024]      FIG. 11  is a side plan view of the cap used in  FIG. 3 ; and 
           [0025]      FIG. 12  is an end plan view of the cap. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    Referring to  FIG. 3 , a termination  8  of the invention has a body  10  containing a wedge gripper  12  having a larger diameter end  34  abutting a washer  13  that is pressed against the wedge gripper  12  by a threaded cap  14  that is screwed into the body  10 . A stem  15  extends through a hole  64  in the cap  14  and is trapped inside the body  10  and a median barrier cable  16  is trapped by jaw sections  18  of the wedge gripper  12 . 
         [0027]    Referring to  FIGS. 4 ,  5 , and  6 , the wedge gripper  12  has an outer surface  20  that tapers and, in the example embodiment, is formed by machining a piece of suitable metal, for example tool steel or other steel, to that shape and then drilling a hole in it and tapping the hole so that the hole has teeth, as shown in  FIG. 6 , that serve to grip the cable  16 . The cable  16  has a nominal effective diameter of 19 mm (¾ inches), even though the cross-sectional profile of it as shown in  FIG. 2  is not round. However, the circle defined by the outer points of the lobes  22  of the cable  16  define a circle that would be approximately three-quarter inch or 19 mm in diameter. Preferably, the major diameter of the teeth formed on the inside diameter of the wedge gripper  12  is less than the nominal effective diameter of the cable. For example, for the median barrier cable that is ¾ inches nominal effective diameter, the hole in the wedge gripper  12  is preferably smaller than the effective diameter of three-quarters of an inch. In particular, the major diameter, i.e. to the bottoms of the valleys between the teeth, is less than three-quarter inch (19 mm). For example, for a three-quarter inch wire rope, the major diameter could be 0.716 inches. This would be the result of using a tap of 0.716-26 to form the teeth, which means 0.716 inches major diameter and 26 threads, or teeth, per inch. 
         [0028]    In addition, when assembling the cable  16  to the termination  8 , the lobes  22  should be oriented relative to the sections  18  as shown in  FIG. 5 , with each lobe roughly centered on each section  18  at the larger diameter end  34  of the wedge gripper  12 . Since the lobes  22  are twisted along their length, the position of the lobes relative to the sections  18  will change along the length of the wedge gripper  12 , but at the large diameter end they should be centered relative to the sections  18  as shown in  FIG. 5 . 
         [0029]    In addition, as shown in  FIGS. 4 and 6 , the taper angle X° of the wedge gripper  12  is preferably four degrees. This differs from typical taper angles for the wedges in common post-tension terminations. In addition, the tooth angles of the teeth on the inner diameter of the wedge sections  18 , that is, angles Y° and Z°, may be 60 and 20 degrees, respectively, as shown in  FIG. 6 , with the 20-degree angle resisting pull-out of the cable, to try to maximize the pull-out forces necessary to dislodge the cable from the termination  8 . 
         [0030]    The body  10  has a mating frusto-conical surface  30  of the same angle as the frusto-conical outer surface  20  of the wedge gripper  12 , in the preferred embodiment, four degrees. Thus, as the wedge gripper  12  is moved leftwardly as viewed in  FIG. 3 , in other words toward the cable opening  32  or smaller diameter end of the surface  30 , the wedge sections  18  collapse inwardly on the cable  16  to bite the teeth of the wedge gripper  12  into the outer surface of the cable  16  and thereby hold the cable  16  firmly to the termination  8 . 
         [0031]    The seating force to bite the teeth of the wedge gripper  12  into the cable  16  can be very large, often requiring that the wedges be “seated” by applying a hydraulic load to the cable to apply the seating force. This operation is most commonly done with a post-tensioning jack system, which includes a jack, hose, gauge, and pump. 
         [0032]    In the present invention, to minimize or avoid the use of such hydraulic equipment, the wedge gripper  12  may be at least partially seated using a threaded connection. The washer  13  (shown in  FIGS. 3 and 10 ) resides generally between the larger diameter end  34  of the wedge gripper  12  and the end  72  of the cap  14 . The washer  13  has an enlarged head  38  that resides in this position, and a reduced diameter shank  40  that extends into a bore  42  in the cap  14 . An O-ring  17  in a groove  70  (best shown in  FIGS. 3 and 10 ) of the shank  40  loosely secures the washer  13  inside the bore  42 . The washer  13  can rotate relative to the cap  14  to reduce the transmission of rotary force from the cap  14  to the wedge gripper  12  as the cap  14  is rotated. 
         [0033]    The cap  14  is threaded into the end of the body  10  to bear against the washer  13  and the washer  13  to bear against the larger diameter end  34  of the wedge gripper  12  to force the wedge gripper  12  axially against the tapered surface  30 . In addition, the cap  14  mechanically retains the wedge gripper  12  and the washer  13  within the body  10 , thereby inhibiting vibrations of the cable  16 , such as those encountered during a collision, from substantially loosening the engagement of the wedge gripper  12  with the cable  16 . The cap  14  (also shown in  FIGS. 11 and 12 ) has a hex  48  in conventional fashion, and the body  10  (also shown in  FIGS. 7 and 8 ) is also formed with a hex  50  at its cable end that can be gripped by a wrench or other tool. Thus, a significant torque can be placed on the cap  14  while holding the body  10  with a wrench to force the wedge gripper  12  against the surface  30  and collapse the inside diameter of the wedge gripper  12  against the cable  16 . 
         [0034]    A threaded stem  15  (shown in  FIGS. 3 and 9 ) extends through a hole  64  in the cap  14  and has an enlarged head  66  trapped in the body  10  by the cap  14 . The head  66  may be flat as shown, or may have a ball surface that mates against a similar socket-shaped surface of the cap  14  so that the stem  15  can be articulated relative to the cap  14 . The stem  15  has threads  68  to attach the termination  8  to a suitable foundation, turnbuckle, or other structure so that a high tension can be induced in the cable  16 . 
         [0035]    The wedge gripper  12  is initially made in one piece, by forming the tapered outer side and drilling and tapping the inside diameter, and then it is cut into the three sections  18 . There must be enough space between the sections  18  so that the wedge gripper  12  can collapse to the full extent onto the cable  16 . Also, when fully compressed against the cable  16 , the wedge gripper  12  preferably does not extend beyond the left end of the body  10 , as viewed in  FIG. 3 . A groove  19  is formed in the outer surface  20  so an o-ring (not shown) can be used to hold the wedge sections  18  together when the wedge is placed around a cable, prior to inserting the wedge into the body. 
         [0036]    As best shown in  FIG. 3 , the wedge gripper  12  is preferably of sufficient length such that the teeth of the each of the three sections  18  each grip at least two of the lobes  22  of the cable  16  when the cap  14  is tightened to the body  10 . For example, a wedge gripper  12  having a length of approximately two and one-half inches is sufficient to engage multiple lobes  22  of cable  16  having a nominal effective diameter of approximately ¾ inches. 
         [0037]    In addition, an opening  60  can be formed in the side of the body  10 , and if desired, the opening  60  can be tapped and a zerc fitting  62  installed. The opening  60  and if a zerc fitting  62  is used, are used for introducing a potting compound into the interior of the body  10 , and particularly into the interior of the wedge gripper  12  to fill the spaces between the lobes  22  of the cable  16  and the inside diameter of the wedge gripper  12 . It would also fill all void spaces inside the body  10 , including any spaces between the lobes  22  and spaces between the individual wires of the lobes  22  to fix the connection between the cable  16  and the body  10 . The potting compound may be, for example, an epoxy resin that bonds well to metal surfaces and hardens solid. The potting compound would help hold the barrier cable  16  inside the body  10 , help prevent it from flattening into the voids which would otherwise be there, and also reduce corrosion inside the body  10 . It could be introduced either directly through the opening  60 , or through a zerc or other suitable fitting screwed into the opening  60 . 
         [0038]    Preferred embodiments of the invention have been described in considerable detail. Many modifications and variations to the preferred embodiments described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiments described but by the claims which follow.