Abstract:
A method for forming a sheathing retaining anchor of a post-tension anchor system includes the steps of: forming an anchor having a bore where the bore has a tapered portion and a constant diameter portion, inserting an end of a tendon through the bore of the anchor so that the end of the tendon extends outwardly of tapered portion of the bore of the anchor, positioning a sheathing lock on the end of the sheathed portion or a tendon, placing a pair of wedges on the unsheathed portion of the tendon, and moving the sheathing lock and the pair of wedges into the bore of the anchor so that the sheathing lock affixes the end of the sheathed portion within the bore and so that the pair of wedges affixes the unsheathed portion within the bore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to post-tension anchor systems. More particularly, the present invention relates to anchors used in such systems. More particularly, the present invention relates to affixing a tendon within an anchor of such systems. Additionally, the present invention relates to affixing a sheathing of a tendon within an anchor of such systems. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     For many years, the design of concrete structures imitated the typical steel design of column, girder and beam. With technological advances in structural concrete, however, concrete design began to evolve. Concrete has the advantages of costing less than steel, of not requiring fireproofing, and of having plasticity, a quality that lends itself to free flowing or boldly massive architectural concepts. On the other hand, structural concrete, though quite capable of carrying almost any compressive load, is weak in carrying significant tensile loads. It becomes necessary, therefore, to add steel bars, called reinforcements, to concrete, thus allowing the concrete to carry the compressive forces and the steel to carry the tensile forces. 
     Structures of reinforced concrete may be constructed with load-bearing walls, but this method does not use the full potentialities of the concrete. The skeleton frame, in which the floors and roofs rest directly on exterior and interior reinforced-concrete columns, has proven to be most economic and popular. Reinforced-concrete framing is seemingly a simple form of construction. First, wood or steel forms are constructed in the sizes, positions, and shapes called for by engineering and design requirements. The steel reinforcing is then placed and held in position by wires at its intersections. Devices known as chairs and spacers are used to keep the reinforcing bars apart and raised off the form work. The size and number of the steel bars depends completely upon the imposed loads and the need to transfer these loads evenly throughout the building and down to the foundation. After the reinforcing is set in place, the concrete, comprising a mixture of water, cement, sand, and stone or aggregate and having proportions calculated to produce the required strength, is set, care being taken to prevent voids or honeycombs. 
     One of the simplest designs in concrete frames is the beam-and-slab. This system follows ordinary steel design that uses concrete beams that are cast integrally with the floor slabs. The beam-and-slab system is often used in apartment buildings and other structures where the beams are not visually objectionable and can be hidden. The reinforcement is simple and the forms for casting can be utilized over and over for the same shape. The system, therefore, produces an economically viable structure. With the development of flat-slab construction, exposed beams can be eliminated. In this system, reinforcing bars are projected at right angles and in two directions from every column supporting flat slabs spanning twelve or fifteen feet in both directions. 
     Reinforced concrete reaches its highest potentialities when it is used in pre-stressed or post-tensioned members. Spans as great as five hundred feet can be attained in members as deep as three feet for roof loads. The basic principle is simple. In pre-stressing, reinforcing rods of high tensile strength wires are stretched to a certain determined limit and then high-strength concrete is placed around them. When the concrete has set, it holds the steel in a tight grip, preventing slippage or sagging. Post-tensioning follows the same principle, but the reinforcing tendon, usually a steel cable, is held loosely in place while the concrete is placed around it. The reinforcing tendon is then stretched by hydraulic jacks and securely anchored into place. Pre-stressing is done with individual members in the shop and post-tensioning as part of the structure on the site. 
     In a typical tendon tensioning anchor assembly used in such post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of tensioning the cable in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of each cable for applying a predetermined amount of tension to the tendon, which extends through the anchor. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable at the anchor plate and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition. 
     In typical post-tension systems, the tendon is received between a pair of anchors. One of the anchors is known as the “live end” anchor, and the opposite end is known as the “dead-end” anchor. The “live end” anchor receives the end of the tendon which is to be tensioned. The “dead-end” anchor holds the tendon in place during the tensioning operation. Under typical operations, a plurality of wedges are inserted into an interior passageway of the anchor and around the exterior surface of the tendon. The tendon is then tensioned so as to draw the wedges inwardly into the interior passageway so as establish compressive and locking contact with an exterior surface of the tendon. This dead-end anchor can then be shipped, along with the tendon, for use at the job site. 
     One technique for forming such dead-end anchors is to insert the end of a tendon into the cavity of the anchor, inserting wedges into the space between the tendon and the wall of the cavity and then applying a tension force onto another end of the tendon so as to draw the wedges and the end of the tendon into the cavity in interference-fit relationship therewith. This procedure is somewhat difficult since the tendon can have a considerable length and since the use of tension forces can create a somewhat unreliable connection between the wedges and the tendon. Experimentation has found that the application of compressive force onto the end of the tendon creates a better interference-fit relationship between the wedges, the end of the tendon and the wall of the cavity of the anchor. 
     Various patents have addressed the creation of dead-end anchorages. For example, U.S. Pat. No. 6,513,287, issued on Feb. 4, 2003 to the present inventor, discloses a method and apparatus for forming an anchorage of a post-tension system in which a tendon is positioned within a cavity of an anchor such that an end of the tendon extends outwardly of the cavity, a plurality of wedges are mechanically inserted within the cavity between the tendon and a wall of the cavity, and pressure is applied to an end of the tendon such that the tendon and the wedges are in interference-fit relationship with the cavity. A compression mechanism is used having a cylindrical member and a plunger extending in a channel of the cylindrical member. The wedges are attached to the cylindrical member and the cylindrical member is moved toward the cavity such that the wedges enter a space between the tendon and the wall of the cavity. The plunger applies a compressive force to the end of the tendon when the end of the tendon is in the channel of the cylindrical member. 
     U.S. Pat. No. 5,755,065, issued on May 26, 1998 to the present inventor, discloses a post-tension system including an anchor member having a tendon-receiving interior passageway, a tendon extending through the passageway, a pair of wedges interposed between the anchor member and the tendon in the interior passageway, and a spring received by one end of the anchor member so as to be in compressive relationship with the pair of wedges so as to urge the pair of wedges in a direction toward an opposite end of the anchor member. A cap member is affixed to one end of the anchor member and extends over an end of the tendon. The spring is interposed between the cap and the plurality of wedges. The spring is affixed to an interior shoulder on the cap member. A seal is interposed between an exterior surface of a sheathed portion of the tendon and an interior surface of a tubular extension formed in an encapsulation around the anchor. 
     However, these methods do not address the formation of an anchor with a sheathing lock. Sheathing locks were invented so as to retain the sheathing of a tendon within the anchor so as to prevent the shrinkage of the sheathing while post-tensioning. The present inventor has filed various patent applications pertaining to different sheathing locks: U.S. patent application Ser. No. 11/861,185, filed on Sep. 25, 2007, entitled “Apparatus for Preventing Shrinking of a Sheathing Over a Tendon”; U.S. patent application Ser. No. 11/933,029, filed on Oct. 31, 2007, entitled “Shrinkage Preventing Device for the Sheathing if a Tendon”; U.S. patent application Ser. No. 11/933,041, filed on Oct. 31, 2007, entitled “Shrinkage Preventing Apparatus for the Sheathing of a Tendon”; U.S. patent application Ser. No. 11/950,295, filed on Dec. 4, 2007, entitled “Unitary Sheathing Wedge”; U.S. patent application Ser. No. 12/100,066, filed on Apr. 9, 2007, entitled “Sheathing Lock”; U.S. patent application Ser. No. 12/123,432, filed on May 19, 2008, entitled “Sheathing Retaining Clip; and U.S. patent application Ser. No. 12/133,947, filed on Jun. 5, 2008, entitled “Compression Cap Sheathing Lock.” Because current methods for forming dead-end anchors do not address the use of sheathing locks, there is a need for a method for forming a sheathing retaining anchor. 
     It is an object of the present invention to provide a method for forming a sheathing retaining anchor that retains a tendon within an anchor. 
     It is another object of the present invention to provide a method for forming a sheathing retaining anchor that retains a sheathing of a tendon within an anchor. 
     It is another object of the present invention to provide a method for forming a sheathing retaining anchor in which the tendon in installed by compression forces. 
     It is another object of the present invention to provide a method which eliminates the hand positioning of wedges during such compression forming. 
     It is still another object of the present invention to provide a method for forming a sheathing retaining anchor which is safe, easy to use, and relatively inexpensive. 
     It is another object of the present invention to provide a method for forming a sheathing retaining anchor which eliminates any buckling of the end of the strand during compression fitting. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a method for forming a sheathing retaining anchor of a post-tension anchor system. The method includes the steps of forming an anchor having a bore where the bore has a tapered portion and a constant diameter portion, removing a portion of a sheathing from an end of a tendon so that the end of the tendon has a sheathed portion and an unsheathed portion, inserting the end of the tendon through the bore of the anchor so that the end of the tendon extends outwardly of the anchor, positioning a sheathing lock on the end of the sheathed portion, placing a pair of wedges on the unsheathed portion, moving the sheathing lock and the pair of wedges into the bore of the anchor so that the sheathing lock affixes the end of the sheathed portion within the bore and so that the pair of wedges affix the unsheathed portion within the bore, removing the anchor from the fixture, forming a compression mechanism that has a cylindrical member and a plunger interior of the cylindrical member, forming the sheathing lock so as to have a tubular body with a collar at one end thereof, and inserting the end of the tendon into the interior of the cylindrical member. 
     The step of positioning the sheathing lock includes placing the sheathing lock onto the sheathed portion such that the collar abuts the end of the sheathed portion. The step of positioning the pair of wedges includes placing the pair of wedges against an end of the cylindrical member such that the pair of wedges overlie the unsheathed portion. The step of moving includes applying pressure against the end of the tendon in axial alignment with the tendon. The step of forming a compression mechanism includes resiliently positioning the cylindrical member over the plunger. The step of forming the sheathing lock includes forming the tubular body of a polymeric material so that the tubular body has a split extending longitudinally along a length of the tubular body. The step of positioning the sheathing lock includes opening the tubular body along the split and urging the tubular body toward the sheathed portion such that the unsheathed portion enters an interior of the tubular body through the opened split. The tubular body has a plurality of ribs formed on an inner wall thereof. The tubular body is interposed between a wall of the bore against the sheathed portion such that the plurality of ribs engage the sheathed portion. 
     The present invention is an apparatus comprising a fixture, a compression mechanism mounted adjacent the fixture, an anchor removably mounted to the fixture, a tendon extending through a cavity of the anchor so as to have an unsheathed portion extending outwardly of an end of the anchor, a sheathing lock positioned over a sheathed portion of the tendon, a pair of wedges positioned over the unsheathed portion of the tendon, and an actuating means cooperative with the compression mechanism. 
     The compression mechanism has a cylindrical member and a plunger interior of the cylindrical member. The cavity is formed in an interior of the anchor. The actuating means urges the plunger toward the cavity of the anchor. The plunger is longitudinally axially aligned with the tendon. The pair of wedges reside against an end of the cylindrical member. The sheathing lock has a generally tubular body with a collar formed at one end thereof. The generally tubular body resides over the sheathed portion. The collar resides against an end of the sheathed portion. The cylindrical member is resiliently mounted over the plunger such that the cylindrical member is resiliently movable relative to the plunger. The cavity has a tapered portion and a constant diameter portion. The tapered portion has a wide end facing the compression mechanism. The tubular body has a plurality of ribs formed on an inner wall thereof. The tubular body has a split extending longitudinally along a length of the tubular body. The sheathing lock is formed entirely of a polymeric material. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  shows a cross-sectional view of the sheathing retaining anchor formed according to the method of the present invention. 
         FIG. 2  shows a cross-sectional view of an anchor fixed in a fixture according to the preferred method of the present invention. 
         FIG. 3  shows a cross-sectional view of the fixed anchor with a tendon inserted therein according to the preferred method of the present invention. 
         FIG. 4  shows a cross-sectional view of the anchor and tendon, with wedges and a sheathing lock placed on the tendon, and a compression mechanism positioned adjacent an end of the tendon according to the method of the present invention. 
         FIG. 5  shows a cross-sectional view of the fixed anchor, with the tendon, sheathing lock, and wedges moved into a bore of the anchor by the compression mechanism according to the method of the present invention. 
         FIG. 6  shows a cross-sectional view of the anchor with wedges and sheathing lock affixed to the tendon and sheathing, respectively, therein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is shown a cross-sectional view of the sheathing retaining anchor  100  formed according to the preferred method of the present invention. The sheathing retaining anchor  100  has an anchor  10 . The anchor  10  has a bore  26 . The bore  26  has a tapered portion  40  and a constant diameter portion  42 . A pair of wedges  32  affix the tendon  22  within the bore  26  of the anchor  10 . The wedges  32  are positioned between a tapered portion  40  of the bore  26  and the tendon  22 . A sheathing lock  30  affixes the sheathing  14  of the tendon  22  within the bore  26  of the anchor  10 . The sheathing lock  30  is positioned between a constant diameter portion  42  of the bore  26  and the sheathing  14 . An end  24  of the tendon  22  extends outwardly of the tapered portion  40  of the bore  26  at the end  28  of the anchor  10 . The wedges  32  affix the tendon  22  within the bore  26  of the anchor  10 . The sheathing lock  30  affixes the sheathing  14  of the tendon  22  within the bore  26  of the anchor  10 . The sheathing lock  30  holds the sheathing  14  within the anchor  10  and resists shrinkage of the sheathing  14  away from the anchor  10  that typically occurs during installation of post-tensioning systems utilizing tendons and anchors. The method of the present invention affixes the tendon  22  and sheathing  14  within the anchor  10 . 
     Referring to  FIG. 2 , there is shown a cross-sectional view of an anchor  10  fixed in a fixture  12  according to the preferred method of the present invention. The anchor  10  has a tapered bore  26  that has a tapered portion  40  and a constant diameter portion  42 . The end  28  of the anchor  10  is located at the wide end of the bore  26 . The fixture  12  is an apparatus that holds the anchor  10  in a stationary position. The bore  26  is made of a size suitable for placing a tendon having a sheathing therein. 
     Referring to  FIG. 3 , there is shown a cross-sectional view of the fixed anchor  10  with a tendon  22  inserted therein according to the preferred method of the present invention. The tendon  22  has a sheathing  14  extending therearound. The sheathing  14  and the tendon  22  extend freely through the bore  26  of the anchor  10 . The tendon  22  is inserted through the constant diameter portion  42  before being inserted through the tapered portion  40  of the bore  26  of the anchor  10 . As can be seen in  FIG. 3 , a portion  16  of the sheathing  14  has been removed from the end  24  of the tendon  22  so as to create an unsheathed portion  20  and a sheathed portion  18  of the tendon  22 . The portion  16  is discarded and no longer used in the method of the present invention. Thus, a sheathed portion  18  and an unsheathed portion  20  extend outwardly of the end  28  of the anchor  10 . 
     Referring to  FIG. 4 , there is shown a cross-sectional view of the anchor  10  and tendon  22 , with wedges  32  and a sheathing lock  30  placed on the tendon  22 , and a compression mechanism  34  positioned adjacent an end  24  of the tendon  22  according to the method of the present invention. The compression mechanism  34  has a cylindrical member  36  and a plunger  38  interior of the cylindrical member  36 . The cylindrical member  36  is resiliently mounted over the plunger  38  such that the plunger  38  moves relative to the cylindrical member  36 . The interior  37  of the compression mechanism  34  is placed over the end  24  of the tendon  22 , which is also the end  21  of the unsheathed portion  20 . The wedges  32  are placed around the end  21  of the unsheathed portion  20 . The cylindrical member  36  of the compression mechanism  34  abuts the wedges  32 . In the preferred embodiment of the present invention, the wedges  32  and the cylindrical member  36  are made of a magnetic metallic material, and the wedges  32  are held around the unsheathed portion  20  of the tendon  22  by a magnetic force provided by the cylindrical member  36  of the compression mechanism  34 . 
     The sheathing lock  30  is placed around the end  19  of the sheathed portion  18  of the tendon  22 . The sheathing lock  30  has a tubular body  33 . The sheathing lock  30  has a collar  31  formed on an end thereof. When the sheathing lock  30  is placed on the sheathed portion  18 , the collar  31  abuts the end  19  of the sheathed portion  18  and helps hold the sheathing lock  30  on the sheathing  14  of the sheathing portion  18 . The collar  31  abuts the wedges  32 . The collar  31  also serves to hold the sheathing lock  30  and wedges  32  in place around the sheathed portion  18  and unsheathed portion  20 , respectively, while the compression mechanism  34  is actuated. The tubular body  33  has ribs  35  formed on an inner wall  39  thereof. The tubular body  33  is interposed between a wall of the bore  26  and the sheathed portion  18  so that the ribs  35  engage the sheathed portion  18 . The tubular body  33  is formed of a polymeric material. The tubular body  33  has a split extending longitudinally along a length of the tubular body  33 . The tubular body  33  is opened along the split so that the unsheathed portion  20  enters an interior of the tubular body  33  as the tubular body  33  is urged towards the sheathed portion  18 . 
     The compression mechanism  34  is actuated against the end  21  of the unsheathed portion  20  so as to push the sheathing lock  30  placed around the sheathed portion  18  and the pair of wedges  32  placed around the unsheathed portion  20  into the bore  26  of the anchor  10 . During actuation, the end  21  of the unsheathed portion  20  resides in the interior  37  of the cylindrical member  36 . The cylindrical member  36  moves toward the anchor  10  until the cylindrical member  36  is adjacent the end  28  end of the anchor  10  (as is shown in  FIG. 5 ). If needed, the plunger  38  of the compression mechanism  34  can move so as to push the end  21  of the unsheathed portion  20  toward the bore  26  of the anchor  10 . 
     Referring to  FIG. 5 , there is shown a cross-sectional view of the fixed anchor  10 , with the tendon  22 , sheathing lock  30 , and wedges  32  moved into the bore  26  of the anchor  10  by the compression mechanism  34 . As can be seen, the cylindrical member  36  and plunger  38  of the compression mechanism  34  are adjacent the end  28  of the anchor  10 . The end  21  of the unsheathed portion  20  still resides  37  within the interior  37  of the cylindrical member  36 , but the plunger  38  can be activated, if needed, to move the end  21  of the unsheathed portion  20  toward the tapered portion  40  of the bore  26  of the anchor  10 . The wedges  32  affix the tendon  22  within the tapered portion  40  of the bore  26  of the anchor  10 . The sheathing lock  30  affixes the sheathing  14  of the end  19  of the sheathed portion  18  in the constant diameter portion  42  of the bore  26  of the anchor  10 . The collar  31  of the sheathing lock  30  is adjacent the wedges  32  within the bore  26  of the anchor  10 . 
     Referring to  FIG. 6 , there is shown a cross-sectional view of the anchor  10  with the wedges  32  and sheathing lock  30  affixed to the tendon  22  and sheathing  14 , respectively, therein. The cylindrical member  36  and plunger  38  of the compression mechanism  34  have been retracted from the end  21  of the unsheathed portion  20  of the tendon  22 . The plunger  38  retracts into the interior  37  of the cylindrical member  36 . The wedges  32  reside between the tapered portion  40  of the bore  26  of the anchor  10 . The sheathing lock  30  resides between the constant diameter portion  42  of the bore  26  of the anchor  10 . 
     In  FIGS. 4-6 , it can be seen that the compression mechanism  34  is guided along the longitudinal axis of the bore  26  of the anchor  10  by the fixture  12 . This prevents any multi-directional movement of the compression mechanism  34  and the anchor  10  while executing the method of the present invention. 
     After affixing the tendon  22  and sheathing  14  within the bore  26  of the anchor  10 , the anchor  10  is removed from the fixture  12  so as to produce a sheathing retaining anchor  100  as shown in  FIG. 1 . Using a sheathing lock  30  with an anchor  10  is the simplest way yet to seal an end of the anchor  10  from moisture and other environmental contaminants that could cause corrosion in the bore  26  of the anchor  10  and to the tendon  22 . The sheathing lock  30  effectively retains the sheathing  14  of the tendon  22  within the bore  26  of the anchor. This retention prevents the sheathing  14  from shrinking away from the anchor  10  so as to expose the tendon  22  to moisture and other corrosion-causing contaminants. Moreover, when the sheathing  14  shrinks away from the anchor  10 , the bore  26  of the anchor  10  is susceptible to corrosion. The sheathing lock  30  seals the sheathing  14  in the bore  26  of the anchor  10  and avoids the use of corrosion-protection tubes placed on the end of the anchor  10 , thus lowering the cost of manufacturing and installing of such anchors  10 . 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction can be made within the scope of the appended claims without departing from the true spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.