Abstract:
An improved anchor for a post-tension system having an anchor body with an internal wedge-receiving cavity. The cavity has a first portion of constantly diminishing diameter extending inwardly from one end of the anchor body. The first portion has an angle of taper with respect to a center line of the cavity. The cavity has a second portion extending inwardly from an opposite end of the anchor body. The first portion and the second portion are coaxial and communicate with each other. The second portion has an angle of taper which is less than the first portion. The first and second portions are cast with the anchor body. The angle of taper of the second portion is less than seven degrees or a negative angle with respect to the center line. The second portion of the cavity has a radiused edge curving outwardly from the cavity to the opposite end of the anchor body. The radiused edge is flush with the second portion of the cavity.

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/157,800, filed on Sep. 21, 1998 and entitled “Improved Wedge-Receiving Cavity for an Anchor Body of a Post-Tension Anchor System ”,now U.S. Pat. No. 6,017,165. U.S. patent application Ser. No. 09/157,800 is a continuation-in-part of U.S. patent application Ser. No. 09/007,608, filed on Jan. 15, 1998 and entitled “Wedge-Receiving Cavity for an Anchor Body of a Post-Tension Anchor System”, now U.S. Pat. No. 6,027,278. 
    
    
     TECHNICAL FIELD 
     The present invention relates to post-tension anchor systems, in general. More particularly, the present invention relates to the structure of an anchor body for such post-tension systems. Furthermore, the present invention more specifically relates to the formation of the cavity within the interior of the anchor body. The present invention also relates to wedge-receiving cavities having radiused edges. 
     BACKGROUND ART 
     For many years, the design of concrete structures imitated typical steel design of column, girder and beam. With technological advances in structural concrete, however, its own form began to evolve. Concrete has the advantages of lower cost than steel, of not requiring fireproofing, and of its 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 (vertical) load, is extremely 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 (horizontal) 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 quite 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, a mixture of water, cement, sand, and stone or aggregate, of proportions calculated to produce the required strength, is placed, 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 100 feet can be attained in members as deep as three feet for roof loads. The basic principal 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 principal, but the reinforcing is held loosely in place while the concrete is placed around it. The reinforcing is then stretched by hydraulic jacks and securely anchored into place. Prestressing 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 in such post-tensioning operations, there is provided a pair of anchors for anchoring the ends of the tendons suspended therebetween. In the course of installing the tendon tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of the tendon for applying a predetermined amount of tension to the tendon. When the desired amount of tension is applied to the tendon, wedges, threaded nuts, or the like, are used to capture the tendon and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition. 
     Metallic components within concrete structures may be come exposed to many corrosive elements, such as de-icing chemicals, sea water, brackish water, or spray from these sources, as well as salt water. If this occurs, and the exposed portions of the anchor suffer corrosion, then the anchor may become weakened due to this corrosion. The deterioration of the anchor can cause the tendons to slip, thereby losing the compressive effects on the structure, or the anchor can fracture. In addition, the large volume of by-products from the corrosive reaction is often sufficient to fracture the surrounding structure. These elements and problems can be sufficient so as to cause a premature failure of the post-tensioning system and a deterioration of the structure. 
     FIGS. 1 and 2 illustrate various components of a typical post-tension assembly designated generally at  10 . System  10  includes a tendon  12  having an exposed end protruding from a sheath  14 . The end of the tendon  12  is typically fitted through an extension tube  16 . Extension tube  16  has a diameter slightly larger than sheath  14  such that one end  16   a  of tube  16  may overlie sheath  14 . The opposite end  16   b  of tube  16  fits over, and communicates with, a rear tubular portion  18  of an anchor  20 . Rear tubular member  18  includes an aperture (not shown) which communicates with a frontal aperture  22 . Frontal aperture  22  defines a cavity in which wedges  24  and  26  are received as shown in FIG. 2, below. 
     FIG. 2 illustrates an assembled view (in one-fourth cutaway perspective) of system  10  shown in FIG.  1 . As known in the art, tendon  12  is disposed through extension tube  16  and through anchor  20 . In one known embodiment, end  16   b  of extension tube  16  is force-fitted over rear tubular member  18 . The other end  16   a  of extension tube  16  is sealed to sheath  14 , by use of tape or other means. 
     After tendon  18  extends through frontal aperture  22  (see FIG.  1 ), and assuming the far end of the tendon (not shown) is fixed in place, tension is applied to tendon  16 , typically by use of a hydraulic jack. While applying this tension, wedges  24  and  26  are forced in place on both sides of tendon  12  within the wedge cavity defined by aperture  22 . Once in place, teeth  24   a  and  26   a  of wedges  24  and  26  operate to lock tendon  12  in a fixed position with respect to anchor  20 . Thereafter, the tension supplied by the hydraulic device is released and the excess tendon extending outward from anchor  20  is cut by a torch or other known device. Wedges  24  and  26  thereafter prevent tendon  12  from releasing its tension and retracting inward with respect to anchor  20 . Moreover, this tension provides additional tensile strength across the concrete structure. 
     After years of work with the anchor body of the prior art, it was found that the cavity used in the anchor body created many problems. The cavity in the anchor body is of a constantly diminishing diameter extending from a forward end of the anchor body to a rearward end of the anchor body. This internal cavity of constantly diminishing diameter is formed during the casting of the anchor body. Unfortunately, the narrow diameter end of the cavity creates problems with the installation of tendons in a corrosion-resistant environment. 
     When the anchor body is used in the formation of intermediate anchorages, it is often necessary to move the anchor body over a very long length of sheathed tendon. If there is insufficient clearance between the narrow diameter end of the cavity and the outer diameter of the sheathed portion of the tendon, nicks, abrasions, and cuts can occur in the corrosion-resistant sheathing. As such, the integrity of the anchorage system is impaired. Furthermore, there are circumstances where the sheathing may exceed expected tolerances and will prevent the anchor body from easily sliding along the length of the tendon so as to assume its position as an intermediate anchorage. Additionally, in recent years, there has been a tendency to increase the thickness of the sheathing so as to facilitate greater protection of the tendon from corrosive elements. 
     An easy solution to this problem would be to expand the diameter of the cavity so as to avoid the aforementioned problems. Unfortunately, if the diameter of the cavity is expanded, then conventional wedges cannot be used. Problems would further occur because of the use of larger wedges or of irregular wedges. If the cavity were enlarged, then the wedge components would have to be replaced in all such post-tension anchor systems. Furthermore, the use of variant sized wedges could create new problems associated with the tensioning of the anchor system. 
     It is also possible to drill out the narrow diameter end of the cavity so as to produce a portion of generally constant diameter. However, any past attempts at drilling have been unsuccessful for a number of reasons. First, the drilling is a very expensive process in comparison with the casting of the anchors. Furthermore, the drilling of a constant diameter portion in the anchor body can create burrs and deformations which could potentially cut the sheathing of the tendon and cause adverse corrosion-protection results. Finally, the drilling of the hole can intrude into the wedge-receiving area so as to create an uneven and irregular contact area between the wedges and the wall of the cavity. The drilling of a hole will create a share, potentially damaging edge at the end of the anchor into which the hole is drilled. This sharp edge can cut into, snag, or otherwise injure the sheathing of the tendon. 
     U.S. patent application Ser. No. 09/007,608, filed on Jan. 15, 1998, by the present inventor, describes an improved anchor for a post-tension system which has a cavity with a first portion of constantly diminishing diameter and a second portion of constant diameter. The first and second portions are coaxial and communicate with each other. The first portion extends inwardly from one end of the anchor body while the second portion extends inwardly from the opposite end of the anchor body. This improved anchor is a cast anchor. However, it was found that the formation of the second portion of “constant diameter ” created problems during the casting process. It is known that for making cast objects, it is often difficult to cast or form cavities of constant diameter. Constant diameter cavities in objects often require complex forms and molds in order to create such constant diameter cavities. As such, the constant diameter second portion created certain manufacturing problems. Also, the second portion had a relative sharp edge at the interface of the cavity and the end of the anchor. 
     It is an object of the present invention to provide an improved anchor for a post-tension anchor system which allows for the use of existing wedges in the wedge cavity while enlarging the narrow end of the cavity. 
     It is a further object of the present invention to provide an improved anchor body with a cavity with a wide end which requires no machining. 
     It is a further object of the present invention to provide an anchor body that avoids sharp edges and irregular contact surfaces. 
     It is a further object of the present invention to provide an anchor body that has a smooth curving edge at the interface of the cavity and the end of the anchor. 
     It is still another object of the present invention to provide an anchor body which enhances the corrosion resistance of the post-tension anchor system. 
     It is still a further object of the present invention to provide an improved anchor body which is relatively inexpensive, easy to manufacture, and easy to use. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     SUMMARY OF THE INVENTION 
     The present invention is an improved anchor for a post-tension system which includes an anchor body having an internal wedge-receiving cavity. The cavity has a first portion having an angle of taper of constantly diminishing diameter extending inwardly from one end of the anchor body. The cavity has a second portion extending inwardly from an opposite end of the anchor body. The first portion and the second portion are coaxial and communicate with each other. The first and second portions are cast with the anchor body. The second portion has an angle of taper less than or negative to the angle of taper of the first portion. The second portion of the cavity has a radiused edge at the interface of the opposite end of the anchor and the cavity. 
     The first portion has a wide end opening at the one end of the body. The first portion has a narrow end of a diameter no less than the constant diameter of the second portion. The first portion is tapered at an approximately 7° angle relative to the centerline of the cavity. In one form of the present invention, the second portion has a larger diameter at the opposite end of the anchor body than the diameter at the narrow end of the first portion. The radiused edge should have a radius of between 0.05 and 0.07 of an inch. 
     In the present invention, a tendon extends through the cavity. A plurality of wedges are arranged in interference fit relationship between a wall of the first portion and an exterior surface of the tendon. Each of the plurality of wedges has a length not more than a length of the first portion. The tendon has a sheathing extending thereover. The second portion has a diameter greater than the diameter of the sheathing on the tendon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective exploded view of a prior post-tension anchor system. 
     FIG. 2 is an assembled view of the prior art post-tension anchor system of FIG.  1 . 
     FIG. 3 is a cross-sectional view showing the post-tension system of the present invention. 
     FIG. 4 is a cross-sectional view showing the anchor body in accordance with the teachings of the present invention. 
     FIG. 5 is a greatly enlarged and exaggerated view of the cavity of the anchor body in accordance with the preferred embodiment of the present invention. 
     FIG. 6 is a greatly enlarged and exaggerated view of the cavity of the anchor body in accordance with a first alternative embodiment of the present invention. 
     FIG. 7 is a greatly enlarged view of circled area A of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 3, there is shown at  30  the improved post-tension anchor system in accordance with the teachings of the present invention. The post-tension anchor system  30  includes an anchor body  32 , a tendon  34  extending through a cavity  36  in the anchor body  32 , and a corrosion-protection tube  38  extending around an exterior of the tendon  34 . The tendon  34  is retained in proper position within the anchor body  32  through the use of wedges  40  and  42 . Wedges  40  and  42  are arranged in interference fit relationship between the wall of the cavity  36  and the exterior surface of the tendon  34 . The tendon  36  has one end  44  extending outwardly of a forward end  46  of the anchor body  32 . A tubular portion  48  is formed in encapsulation material  50  so as to extend outwardly from an opposite end of the anchor body  32 . The encapsulation material  50  is a polymeric encapsulation that surrounds the steel anchor  52 . 
     In the present invention, the cavity  36  has a first portion  54  of constantly diminishing diameter extending inwardly from end  56  of the steel anchor  52 . The internal cavity  36  also includes a second portion  58  extending extending inwardly from an opposite end  60  of the steel anchor  52 . The first portion  54  communicates with the second portion  58 . The first portion is coaxial with the second portion  58 . The second portion  58  has an angle of taper which is less than the angle of taper of the first portion  54 . Alternatively, as will be described hereinafter, the angle of taper of the second portion can actually be a negative angle relative to the angle of taper of the first portion. As used herein, the term “angle of taper” refers to the angle of the wall of the cavity  36  in relation to the center line  45  of the anchor body  32 . A radiused edge  47  is formed at the end of the second portion  58  at the end  60  of the anchor body  32 . 
     As can be seen in FIG. 3, the wedges  40  and  42  are fit within the first portion of the cavity  36 . Wedges  40  and  42  are standard wedges used in conventional prior art anchor systems. The first portion  54  of cavity  56  will have a diameter similar to the diameter of existing cavities. The taper of the first portion  54  is approximately a 7° angle relative to the longitudinal axis of cavity  36 . 
     Unlike prior art systems, the second portion  58  has an angle of taper which is less than the angle of taper of the first portion  54 . The second portion  58  extends from an end of the first portion  54  to the end  60  of the steel anchor  52 . Prior art anchor systems had a constant taper extending from end  56  to end  60  of the steel anchor  52 . As can be seen, a significant clearance  64  is formed between the wall of the second portion  58  of cavity  36  and the exterior surface of tendon  34 . As such, the steel anchor  52  can slide easily along the length of the tendon  34  without causing damage to the sheathing on the tendon. Furthermore, since the first portion  54  is formed by casting with the second portion  58 , no machining is required. As such, the expense of the production of the anchor body  32  is reduced. There will be no sharp burrs or snarled edges which could compromise the integrity of the sheathing of the tendon  34 . The radiused edge  47  further assures that the anchor body  32  will slide smoothly along the tendon  34 . The radiused edge  47  assures that snags and cuttings of the sheathing of the tendon  34  are avoided. The radiused edge  47  also facilitates the installation of the anchor body  32  onto the tendon  34  by “funneling” the tendon through the cavity  36  in the anchor body  34 . 
     In FIG. 3, it can be seen that the corrosion-protection tube  38  includes a forward end  66  having a spearhead-shaped configuration. The wide end of the spearhead-shaped configuration is in snap-fit engagement with a shoulder  70  formed on the interior of the tubular portion  48 . The end  72  of the tubular portion  48  will abut a shoulder  74  formed on the exterior surface of the corrosion-protection tube  38 . A sealing member  76  is formed on the opposite end of the corrosion-protection tube  38  so as to establish a liquid-tight seal with the exterior surface of the tendon  34 . In order to install the corrosion-protection tube  38 , it is only necessary to insert the spearhead-shaped end  66  into the opening at end  72  of the tubular portion  48 . The corrosion-protection tube  38  can then be pushed inwardly of the tubular portion  48  until the end  66  snap-fits over the shoulder  70 . 
     FIG. 4 is an isolated view showing the anchor body  32 . In FIG. 4, it can be seen that the first portion  54  is illustrated as tapering from end  56 . The narrow end  80  of the first portion  54  connects with the second portion  58 . The second portion  58  extends from the end  80  of the first portion  54  to the end  60  of the steel anchor  52 . The second portion  58  has an angle of taper less than or negative to the first portion  54 . Within the concept of the present invention, it is possible that the second portion  80  could have a slightly increasing diameter extending from the end  80  of the first portion  54  toward the end  60  of the steel anchor  52 . The second portion  58  will have a diameter of between 0.6 and 0.7 inches. In the preferred embodiment of the present invention, the second portion  58  will extend inwardly from the end  60  for more than 0.20 of an inch. The radiused edge  47  is formed at the interface of the end  60  with the opening to the cavity  36 . The first portion  54 , as can be seen, has a length which is greater than the length of the second portion  58 . 
     Referring to FIG. 4, it can be seen that the steel anchor  52  of anchor body  32  has a cavity  36  with a first portion  54  that extends inwardly from the end  56 . It can be seen in FIG. 5 that the first portion  54  has a constant diameter extending from the end  56  to the end  80 . The first portion  54  transitions to the second portion  58  at end  80 . 
     FIG. 5 illustrates how the present invention differs from the prior art. As can be seen by the broken line  82 , the constantly decreasing diameter of the first portion  54  would normally continue from end  56  to end  60 . However, since the second portion  58  has a taper which is less than the angle of taper of the first portion  54 , the second portion  58  will emerge on end  68  with a greater diameter than which would occur by the continuously tapering first portion  54 . As shown in FIG. 5, the angle of taper of the first portion  54  is shown by α. The angle of taper of the second portion  58  is shown by β. In accordance with the present invention, angle β is less than angle α. 
     In the present invention, a radiused edge  47  is formed between the second portion  58  and the end  60  of anchor body  32 . This radiused edge  47  is formed so as to curve outwardly from the cavity  36  toward the end  60 . This creates a smooth flush relationship with the second portion  58  of cavity  36 . This avoids any sharp edges that would otherwise occur at the end of the cavity  36 . This radiused edge  47  can be formed during the casting of the anchor body  32 . No machining is required to create the radiused edge  47 . Preferably, the radiused edge  47  will have a radius of between 0.05 and 0.07 of an inch. 
     FIG. 6 shows an alternative embodiment of the present invention. In FIG. 6, the anchor body  90  has a first portion  92  and a second portion  94 . The first portion  92  opens at end  96  of the anchor body  90 . The second portion  94  opens at the opposite end  98  of the anchor body  90 . Radiused edge  105  is formed at the interface between the opposite end  98  and the second portion  94  of cavity  100 . The first portion  92  of cavity  100  connects with the second portion  94  at end  102 . 
     It can be seen in FIG. 6 that the first portion  92  has a constantly narrowing diameter extending from end  96  to the end  102 . The second portion  94  has a constantly expanding diameter as extending from the end  102  to the end  98 . Alternatively stated, the second portion  94  constantly tapers so as to narrow in diameter from the end  98  of anchor body  90  to the end  102  of the first portion  92  of cavity  100 . 
     As can be seen in FIG. 6, the first portion  92  has an angle α relative to the center line  104 . The second portion  94  forms an angle β with respect to the center line  104 . The angle β is negative to angle α. As such, angle β is also less than angle α relative to the center line  104 . 
     The embodiment shown in FIG. 6 offers certain advantages. For example, the constantly widening diameter of the second portion  94  (as extending from end  102  to the end  98 ), along with the radiused edge  105 , will serve to “funnel” the tendon through the cavity  100  of the anchor body  90 . This outward taper can, under certain circumstances, facilitate the manufacture and casting of the anchor body  90 . Since the second portion  94  has a greater diameter at end  98  than the diameter of the first portion  92  at end  102 , the second portion  94  will suitably accommodate the sheathing on a tendon extending therethrough. 
     FIG. 7 is a detailed view of the circled area “A” of FIG.  5 . FIG. 7 specifically shows the radiused edge  47  formed between the second portion  58  of cavity  36  and the end  60  of anchor body  32 . The radiused edge  47  will curve outwardly toward the end  60  of the anchor body  32 . This radiused edge will have a radius of between 0.05 and 0.07 of an inch. As such, the diameter of the opening to the cavity  36  at end  60  is slightly larger than the diameter of the second portion  58  just before the end  36 . As can be seen, there are no sharp edges at the end  60  of anchor body  32 . 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction may 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.