Abstract:
A protective tendon tensioning anchor assembly comprising an anchor plate, a sealing cup and a resilient sealing ring for providing corrosion protection for exposed portions of a tendon secured in the tendon tensioning anchor assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to tendon tensioning anchor assemblies, and more particularly to improvements in sealing post-tension anchor assemblies to protect the exposed portions of a tendon from corrosion. 
     2. Description of the Prior Art 
     Conventional concrete reinforcing using tendons for stressing typically includes a pair of anchor assemblies mounted in spaced apart relation with an elongated reinforcing tendon extending therebetween. The tendon is placed under an axial load, either by pretensioning or post-tensioning, and connected to the concrete in the tensioned condition by the anchor assemblies. Tensioning of the tendon after the formation and setting of the concrete structure is known as post-tensioning and is widely used in the construction of prestressed concrete structures. 
     In the course of installing a tendon tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to an exposed extending end of the tendon to apply a predetermined amount of tension to the tendon. The sheath, within which the remainder of the tendon is enclosed, protects against moisture and isolates the tendon from the surrounding concrete to facilitate the movement of the tendon relative to the surrounding concrete. When the desired amount of tension is applied to the tendon, wedges, threaded nuts or the like are used to connect the tendon to the anchor to hold the tendon in a stressed condition. After tensioning, the recessed ends of the tendon are cut off at the anchor by use of a cutting torch or the like. 
     Moisture travels through concrete. Concrete structures are frequently exposed to corrosive elements, such as de-icing chemicals, sea water, salt air or brackish water. In some environments, ground, water, run-off, snow and the like can immerse portions of the slab for substantial periods of time. The exposed ends of tendons from which the waterproof sheath has been stripped for tensioning can represent a substantial potential corrosion problem. Unless sealed against moisture, the exposed portions of the tendon are likely to suffer corrosion. This not only weakening the tendon, but the by-products of the corrosive reaction can fracture the surrounding structure. 
     One method of protecting tendons is disclosed in U.S. Pat. No. 4,348,844 issued to Schupack et al on Sept. 14, 1982. According to the teachings of this patent, the entire anchor assembly is enclosed in a housing or envelope. The use of a housing enclosing the entire anchor assembly is unduly expensive and is subject to damage during the cutting of the exposed recessed tendon end by use of a cutting torch. Installation of the housing as a separate unit apart from the anchor plate assembly, is time consuming and costly. This increased cost is unnecessary because there is no need to protect the entire anchor plate assembly from corrosion so long as the tendon itself is protected. Further, this assembly relies on plastic threads to form the seal. The manufacturing tolerances, dirty environment, distortion from heat and potential for stress deformation can result in a less than a reliable seal arrangement. Other examples of anchor assemblies using unreliable pleastic thread seals and/or multiple parts are shown in U.S. Pat. Nos. 4,616,458, 4,343,122, 3,956,797 and 3,820,832 and the U.S. and foreign patents cited in these U.S. patents. 
     The U.S. Pat. No. 3,596,330, to Scott, discloses another method which uses a deformable plug pushed into place to form a seal. However, no means are provided for positively locking the seal in position to prevent it from being dislodged during grouting. 
     SUMMARY OF THE INVENTION 
     The present invention provides a reliable sealed anchor assembly which is simple and inexpensive to manufacture and install. 
     In accordance with the invention, an anchor body is provided for anchoring a tendon in a concrete slab. The anchor body cooperates with and engages a removable seal carrying cap to provide a positive seal therebetween to prevent the entrance of moisture into the interior of the anchor body. The cap locks in place to compress a trapezoidal cross-section shaped seal ring between two nonparallel seal surfaces on the body and cap to ensure a positive seal. At least one surface of the seal ring is provided with a protrusion to improve sealing against the anchor body. 
     The anchor body has a base plate for fixing the anchor body in place. A tubular portion for receiving the tendon therein extends from the base plate. Locking means cooperate with the anchor body for releasably connecting the tendon to the body after the tendon has been tensioned. A locking recess is formed on the interior of the tubular portion for engaging locking fingers on the cap to positively attach the cap to the anchor body. A seal ring carrying portion is formed on the cap to position the seal ring to engage a first seal surface on the cap and second seal engaging surface on the end of the tubular portion whereby the seal can be compressed therebetween. 
     This assembly utilizes a minimum of parts and provides a positive seal for use in a dirty environment whose integrity is independent of stress distortion, the destructive presence of heat in cutting off the exposed tendon ends and manufacturing tolerances. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the present invention will become apparent from the following detailed description of the invention and accompanying drawings in which: 
     FIG. 1 is an exploded sectional view of the anchor assembly according to the present invention; 
     FIG. 2 is a sectional view of the anchor assembly of FIG. 1; 
     FIG. 3 is a perspective view of the anchor body and cap of the present invention; 
     FIG. 4 is an enlarged cross-sectional view of a resilient seal ring; and 
     FIG. 5 is an enlarged cross-sectional view of the cap and resilient seal installed on an anchor body. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings where like reference characters designate like or corresponding parts throughout the various figures, there is shown the improved anchor assembly of the the present invention which, for purposes of description, is designated by reference numeral 30. The anchor assembly 30 includes an anchor body 10, a sealing cap 11, a resilient annular seal 12, and a tubular trumpet member 13. Anchor body 10 can be formed from metallic material in a casting process. As a consequence of this manufacturing process, the surfaces of the body 10 can be rough and irregular. The body 10 has a tubular portion 21 with an external wall 32, a tendon receiving aperture 22 and a substantially larger diameter rear aperture 24 connected by a tapered central bore 26. Tapered central bore 26 is provided with a countersink 33 adjacent to the receiving aperture 22 for facilitating insertion of a tendon &#34;T&#34;. 
     As shown in detail in FIG. 1 within the central bore 26 is formed an annular recess 27 located adjacent the aperture 24. Recess 27 forms a locking shoulder whose function will be hereinafter described in detail. Defining aperture 24 and extending radially to the external wall 32 of the tubular member 21 is a compound surface rim 20. Rim 20 comprises an annular seal engaging surface 28, and a cap mating shoulder 29. Surface 28 surrounds the rear aperture 24 and is aligned transverse to length of tubular portion 21. The cap mating shoulder 29 extends between surface 28 and the external wall of the tubular member 21. Shoulder 29 is outwardly inclined relative to the annular seal engaging surface 28. 
     As shown in FIGS. 1 and 3, extending outwardly from the external wall 32 of the tubular member 21 is a mounting flange 23 which is substantially planer and is aligned transverse to the length of member 21. Flange 23 is provided with a plurality of holes 36 and 37 for permitting the temporary attachment of the anchor body 10 to form members while pouring and hardening of the surrounding concrete. Extending outwardly from the external wall 32 of the tubular member 22 and connected to the mounting flange 23 are reinforcing ribs 34 and 35. 
     As shown in FIGS. 3 and 5, sealing cap 11 has a central cavity 17. A receiving collar 19 provides a close telescoping fit over and around the tubular member 21 such that in the assembled condition, the inside wall 16 of the receiving collar 19, engages the external wall 32 of the tubular member 21 to help properly align the cap 11 in position. Within cavity 17, is provided an annular frusto-conical sealing surface 18 correspondingly inclined to mate with shoulder 29 when the cap 11 is position as shown in FIG. 5. 
     A plurality of circumferentially spaced resilient locking fingers 15 provide a means for securing the sealing cap 11 to the tubular member 21. The locking fingers 15 being engagable with the shoulder in annular recess 27. 
     In the preferred embodiment, a plurality of guide fingers (not shown) are positioned between the locking fingers 15. Guide fingers are adapted to telescope in a close fitting arrangement into bore 26. Within the cylindrical space defined by the locking fingers 15 and the guide fingers, there is defined a chamber for the severed end of a tendon &#34;T&#34;. 
     In the preferred embodiment, seal 12, is positioned within the central cavity 17 of the sealing cup 11, contacting the annular frusto-conical sealing surface 18 and closely fitted around the circular formation of locking fingers 15 and the guide fingers. The resilient annular seal 12, best illustrated in FIG. 4, has a trapezoidal cross-section shape. Seal ring 12 has generally cylindrical inner and outer surfaces 12a and 12b which intersect non-parallel faces 12c and 12d. Face 12c is preferably inclined at an angle &#34;A&#34; of, for example, twenty degrees relative to face 12d. To facilitate forming a seal against annular seal engaging surface 28, an annular projection or bead 12e is formed to extend from face 12d intermediate inner and outer surfaces 12a and 12b. Bead 12e has a small radius, for example, 3/64th inch if face 12d is 0.40 inch, to provide a ring of increased bearing pressure to facilitate deformation of bead 12e such that resilient material flows and deforms to seal against roughened portions of surface 28. 
     The shape of seal ring 12 permits a frusto-conical mating between seal and the frusto-conical sealing surface 18 when the cap 11 is in place. The trapezoidal configuration of the resilient annular seal 12 permits a watertight seal having a range of sealing integrity substantially greater than that of a conventional O-ring seal. This range responds to potential variations in axial distance between the annular frusto-conical sealing surface 18 of the sealing cap 11 and the annular seal engaging surface 28. These variations in axial distance being frequently encountered in the process of mass production of mating components. 
     Trumpet member 13 has a central bore corresponding to the tendon axis, enshrouds the receiving aperture 22 of the tubular member 21 and can be conventionally sealed to the tendon &#34;T&#34;. 
     In use, once the anchor body 10 has been set in concrete &#34;C&#34; in a recessed position as shown in FIG. 2, the tendon &#34;T&#34; can be engaged and tensioned in a conventional manner. Tensioned locks or wedges &#34;W&#34; are used to lock the tendon to the anchor. The extending end of the tendon can be cut off using a cutting torch or the like. Use of a cutting torch allows the tendon to be quickly cut off in the recess so that the end is flush with the upper surface of the anchor body 10. During this cutting process, any exposed plastic parts of the anchor sealing assembly would be exposed to destructive heat. As can be seen in the present invention, no plastic parts or threads are exposed to the intense heat of the cable cutting process. Once the cable is cut, the sealing cap 11 is pushed into the locked sealing position shown in FIG. 5. 
     the embodiment shown and described in this application is but one embodiment for accomplishing applicant&#39;s invention. It is to be understood that the present invention shall include all embodiments of the invention as defined in the accompanying claims.