US20060179742A1

US20060179742A1 - Anchor for concrete post-tension anchoring

Info

Publication number: US20060179742A1
Application number: US11/299,004
Authority: US
Inventors: Thomas Mathews; Stan Landry
Original assignee: Precision Surelock Inc
Current assignee: Precision Surelock Inc
Priority date: 2005-02-14
Filing date: 2005-12-09
Publication date: 2006-08-17

Abstract

An anchor for a concrete post-tension system. The anchor comprises a bearing plate portion, a barrel portion and a plurality of webs. The barrel portion has an upper annular wall extending from the upper surface of the bearing plate and a lower annular wall depending from the lower surface of the bearing plate. The inner surfaces of the upper annular wall and lower annular wall together define an internal wedge-receiving cavity passing through the bearing plate and having a central axis substantially perpendicular to the bearing plane. The wedge-receiving cavity has a fixed angle of taper with respect to the central axis. The cavity has a diameter at the lower end that is at least as great as the diameter of the sheathing on the tendon to be anchored. The cavity has an overall height that is at least as great as the height of the wedges to be used. The outer surface of the upper annular wall is upwardly tapered. The outer surface of the lower annular wall is downwardly tapered. A plurality of webs extend from the outside of the upper annular wall to the upper surface of the bearing plate. The sheathed portion of the tendon may freely pass through the wedge-receiving cavity of the anchor.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Application Ser. No. 60/652,700 titled “ANCHOR FOR CONCRETE POST TENSION ANCHORING,” filed Feb. 14, 2005.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to post-tension anchoring systems, and more particularly, to anchors used in post-tension anchoring systems.

BACKGROUND OF THE INVENTION

Structures made from concrete are commonplace. Structural concrete is capable of carrying substantial loads in compression, however is extremely weak in carrying significant tensile loads. To improve its tensile load carrying capacity, steel bars, called reinforcements, are positioned within concrete beams, columns, slabs, etc. to allow the concrete to carry the compressive forces and the steel to carry the tensile forces.
Reinforced concrete reaches its highest potential when used in pre-stressed concrete members. Prestressing is a method of concrete reinforcement that induces forces into the concrete, usually by means of high strength steel bars, wires, or strands, prior to the use of the structure. There are two common methods of prestressing. They are pre-tensioning and post-tensioning. Very long spans and shallow depths can be achieved with prestressed concrete that cannot otherwise be achieved. Basically, in pre-tensioning, reinforcing of high tensile strength steel wires, bars, or strands are stretched to a certain determined limit and then concrete is poured in place around them. When the concrete has set, it holds the pre-tensioned reinforcing in a tight bond, preventing slippage or sagging. Post-tensioning follows the same principal, but the high strength reinforcing is secured in place while the concrete is placed around it. The high strength wires, bars, or strands are prevented from bonding to the concrete so that they can be post-tensioned. The post-tensioned reinforcements are then stretched by hydraulic jacks and securely anchored into place. Post-tensioning tendons may be subsequently grouted to bond to the structure, or they may remain intentionally unbonded. Pre-tensioning is typically done with individual concrete members in the pre-cast fabrication shop and post-tensioning is typically performed on the site. High strength steel strand, known as PC (prestressed concrete) Strand is the most common prestressing reinforcement used in both pre-tensioning and post-tensioning.
In a typical post-tension operation, there is provided a pair of anchors for anchoring the ends of each of the wires, bars, or strands, often referred to as tendons, suspended therebetween. There may also be additional anchorages spaced intermediately along the tendon. The anchors may be bare, or may be encapsulated. The ends of the tendons extend beyond the anchors. In the course of installing the tendon tensioning anchor assembly, a hydraulic jack or the like is releasably attached to one of the exposed ends of the tendons for applying a predetermined amount of tension to the tendon. When the desired amount of tension is applied, wedges, threaded nuts, or the like, are used with the anchor to capture the tendon and prevent its relaxation and hold it in its stressed condition as the jack is removed.
In some instances, the metal components within concrete structures may become exposed to corrosive elements, such as de-icing chemicals, or sea, salt or brackish water. Such exposure can result in corrosion of the anchor, thereby weakening the anchor. The deterioration of the anchor can result in fracturing the anchor or causing the tendons to slip, thereby losing the reinforcement's beneficial effects on the structure. In addition, the large volume of by-products from the corrosive reaction is often sufficient to cause a premature failure of the post-tension anchoring system and a deterioration of the structure.
FIGS. 1 and 2 illustrate various components of a typical post-tension anchoring system in accordance with the prior art, designated generally at 10. FIG. 1 provides an exploded view of the system, i.e., prior to assembly. The 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. The extension tube 16 has a diameter slightly larger than sheath 14 such that one end 16 a of the tube 16 may overlie the sheath. The opposite end 16 b of tube 16 fits over, and communicates with, a rear tubular portion 18 of an anchor 20. Rear tubular portion 18 includes a rear aperture (not shown) which communicates with a frontal aperture 22. The interior walls of the anchor 20 between the frontal aperture 22 and the rear aperture define a cavity 23 for receiving wedges 24 and 26 as shown in FIG. 2.
FIG. 2 illustrates an assembled view (in one-fourth cutaway perspective) of the prior art 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 (not shown).
After tendon 12 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 12, 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 23 defined by aperture 22. Once in place, teeth 24 a and 26 a (see FIG. 1) 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.
Thus, the post-tension anchoring system is vitally important to the integrity of the reinforced concrete structure. Due to the vital importance of the entire anchoring system, the various components must comply with certification and testing requirements. Furthermore, it is important that the anchors, wedges and tendons not fail, be versatile and suited for field installation, and be easy to install.
Over the years, various anchors have been commercialized which use conventional or standard wedges. The standard wedges are typically a pair of semicircular, truncated conical members having an angle of taper of approximately 7° (measured relative to the longitudinal axis of the cylindrical cavity formed between a pair of wedges) and a height (measured along the same longitudinal axis) of approximately 1.25″. The cooperation between the pair of wedges and the tendon and between the cavity walls and the pair of wedges is extremely important to the integrity of the tendon anchoring system. The conventional wedges in widespread use have an established track record in the industry.
In the past, it was common for the anchor cavity to have a constantly diminishing diameter extending from a forward end of the anchor to a rearward end of the anchor. This internal cavity of constantly diminishing diameter was formed during the casting of the anchor. This design was well suited for use as end anchors, but had limitations when used with sheathed tendons at intermediate locations, i.e., at locations between the end anchors. When the anchor is used in the formation of intermediate anchorages of sheathed tendons, it is typically necessary to move the anchor over a very long length of sheathed tendon.
FIG. 3 illustrates another example of a prior art anchor, denoted as 320, intended for use as an intermediate anchorage. The anchor 320 is similar to that shown in U.S. Pat. No. 5,749,185, issued May 12, 1998, to Sorkin. A sheathed tendon 12 is commonly used. Thus, it is to be understood that the smallest diameter of the cavity (shown occupied by wedges 24 and 26) must be large enough to permit the sheathed portion 14 of the tendon 12 to pass through the cavity. If there is insufficient clearance between the narrow diameter end of the cavity and the outer diameter of the sheathed portion of the tendon 12, then nicks, abrasions, and cuts can occur in the corrosion-resistant sheathing 14, thus impairing the integrity of the anchoring system.
Further, the required sheath thickness has increased over time to increase durability, corrosion resistance, and abrasion resistance in response to corrosion problems. Current specifications require a sheath thickness of 0.050″ for all structural slabs and 0.040″ for residential and light commercial ground supported slabs, whereas previously the specification required a thickness of 0.040″ for elevated or structural slabs and allowed variances for ground supported slabs. This old specifications resulted in very thin sheathing in use on ground supported slabs at that time. The problem of increased sheath thickness as it affected intermediate anchors, conventional wedges, and the tolerance between the sheath and the smallest diameter of the wedge cavity was addressed by Sorkin in U.S. Pat. Nos. 6,234,709, 6,027,278 and 6,017,165 filed in 1998. Sorkin, in his patents, stated:

- 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 anchoring 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 sharp, 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. Pat. No. 6,234,709, col. 3, lines 40-64.
FIG. 4 illustrates an example of a prior art cast anchor, denoted as 420, having a cavity with a first portion 27 of constantly diminishing diameter and a second portion 28 of constant diameter. This anchor is similar to that shown in U.S. Pat. No. 6,027,278 to Sorkin. The first and second cavity portions 27, 28 are coaxial and communicate with each other. The first portion 27 extends inwardly from one end of the anchor body while the second portion 28 extends inwardly from the opposite end of the anchor body. However, it was found that the formation of the second portion 28 of constant diameter created problems during the casting process and also had a relative sharp edge at the interface of the cavity and the end of the anchor.
FIGS. 5-7 illustrate further examples of prior art cast anchors, denoted respectively as 520, 620 and 720. Each anchor 520, 620 and 720 defines a cavity with a first portion 27 of constantly diminishing diameter, i.e., a constant angle of taper, denoted a′ (measured relative to the longitudinal axis 25 of the cavity), and a second portion 29 characterized by having an angle of taper, denoted a″, that is less than or negative compared to the angle of taper a′ of the first portion. The first and second cavity portions 27, 29 are coaxial and communicate with each other. These anchors are similar to those shown in Sorkin's U.S. Pat. Nos. 6,017,165 and/or 6,234,709.
In each of Sorkin's '278, '165 and '709 patents, the wedges are described as standard wedges used in conventional prior art anchoring systems and have a length not more than a length of the first portion of the cavity.
It is desirable to provide an improved anchor for a post-tension anchoring system which allows for the use of standard wedges in the wedge cavity and which can be used at the stressing (live) end, fixed (dead) end as well as being used as an intermediate anchor. It is further desirable that the anchor can be used as an intermediate anchor with a sheathed tendon and any anchor location where is desirable for the sheathing to pass through the anchor. It is also desirable that the anchor meets certification and testing requirements. It is also desirable that the anchor eliminate material to reduce weight while maintaining structural integrity. Additionally, it is desirable that the anchor is cost effective, reliable and easy to manufacture and use.

SUMMARY OF THE INVENTION

The present invention disclosed herein comprises, in one aspect thereof, an anchor for a concrete post-tension system including the anchor, a tendon and a plurality of wedges. The anchor comprises a generally rectangular bearing plate portion having a upper surface and a generally flat lower surface defining a bearing plane. A barrel portion has an upper annular wall extending from the upper surface of the bearing plate and a lower annular wall depending from the lower surface of the bearing plate. The inner surfaces of the upper annular wall and lower annular wall together define an internal wedge-receiving cavity passing through the bearing plate and having a central axis substantially perpendicular to the bearing plane. The wedge-receiving cavity has a fixed angle of taper with respect to the central axis such that the diameter of the cavity is constantly diminishing from the upper end of the barrel to the lower end of the barrel. The cavity has a diameter at the lower end that is at least as great as the diameter of the sheathing on the tendon to be anchored. The cavity has an overall height measured from the upper end of the barrel to the lower end of the barrel that is at least as great as the height of the wedges to be used. The outer surface of the upper annular wall is upwardly tapered such that the outside diameter of the wall increases from the upper end of the barrel to the upper surface of the bearing plate. The outer surface of the lower annular wall is downwardly tapered such that the outside diameter of the wall increases from the lower end of the barrel to the lower surface of the bearing plate. A plurality of webs extend from the outside of the upper annular wall to the upper surface of the bearing plate. The sheathed portion of the tendon may freely pass through the wedge-receiving cavity of the anchor. When an exposed portion of the tendon is positioned within the cavity, wedges may be inserted to produce an interference fit relationship between the inner surfaces of the cavity and the exterior surface of the tendon.
The present invention disclosed herein comprises, in another aspect thereof, an improved anchor for a post-tension anchoring system which includes an anchor having an internal wedge-receiving cavity. The cavity has an angle of taper of constantly diminishing diameter extending inwardly from substantially one end of the anchor to the other. The diameter of the cavity opening at the narrow end is preferably in the range of 0.60″ to 0.75″. Conventional or standard wedges are preferably used with the anchor. The anchor is preferably a cast, unitary piece. The cavity narrow end may include a radiused edge.
Preferably, the cavity is tapered at an approximately 7° angle relative to the centerline of the cavity.
The present invention disclosed herein comprises, in yet another aspect thereof, an intermediate anchor including an anchor and a tendon. A tendon extends through the cavity. A plurality of wedges are arranged in interference fit relationship between the cavity wall and an exterior surface of the tendon. Preferably, each of the plurality of wedges has a length not greater than a length of the cavity. The tendon has a sheathing extending thereover. The narrow end opening 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 art post-tension anchoring system;
FIG. 2 is an assembled view of the prior art post-tension anchoring system of FIG. 1, with a portion cut away for purposes of illustration;
FIG. 3 is a cross-sectional view of a prior art intermediate anchorage system;
FIG. 4 is a cross-sectional view of a prior art anchor having a wedge receiving cavity having a first portion of constantly diminishing diameter and a second portion of uniform diameter;
FIGS. 5-7 are cross-sectional views of prior art anchors, each having a wedge receiving cavity having a first portion of constantly diminishing diameter and a second portion characterized by having an angle of taper less than or negative to the angle of taper of the first portion;
FIG. 8 is a perspective view of an anchor in accordance with a one embodiment of the present invention;
FIG. 9 is an elevation view of the anchor shown in FIG. 8;
FIG. 10 is a view taken along line 10-10 of FIG. 9;
FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 10;
FIG. 12 is a cross-sectional view taken along line 12-12 of FIG. 10; and
FIG. 13 is an assembled view of the post-tension anchoring system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The current invention is described below in greater detail with reference to certain preferred embodiments illustrated in the accompanying drawings.
Referring now to FIG. 8, there is illustrated a perspective view of a post-tension anchor in accordance with one embodiment of the current invention. The anchor 32 includes a bearing plate portion 62, a barrel portion 66 that forms the wedge-receiving cavity 36, and a plurality of bracing rib portions (also known as webs) 64 disposed between the sides of the barrel and the top of the bearing plate. While some prior art anchors have also included a bearing plate, a barrel and a plurality of bracing ribs, the anchor of the present invention has optimally sized and located the various components in an arrangement not previously appreciated by the prior art which not only complies with current requirements, but also can be used as live end, dead end and intermediate anchors for both sheathed and unsheathed tendons. In addition, the unique configuration of the anchor of the current invention allows a reduction in the amount of material required for manufacturing the anchor, thereby allowing reduced weight and manufacturing costs.
In one preferred embodiment, the complete anchor 32, including the bearing plate portion 62, barrel portion 66 with wedge-receiving cavity 36, and rib portions 64, is formed as a one-piece metal casting. Such “bare” anchors may be used “as-is” in environments and/or circumstances where significant corrosion of the anchor is not expected. In an alternative embodiment (having the same external appearance as that shown in FIG. 8), the anchor 32 is fully or partially encased in an outer layer of polymer material, e.g., plastic, elastomer or resin, after casting. Such a polymer encased (i.e., “encapsulated”) anchor may be used in environments and/or circumstances where significant corrosion of the anchor is a possibility, or where increased protection against corrosion of the anchor is desired.
Referring now to FIG. 9, there is illustrated a side view of the anchor 32. It can be seen that the bearing plate portion 62 has an upper surface 62 b and a generally flat lower surface 62 a defining a bearing plane 63. It can further be seen that the barrel portion 66 includes an upper annular wall 66 b extending upward from the upper surface 62 b of the bearing plate 62 to the upper end 56 of the barrel, and a lower annular wall 66 a depending downward from the lower surface 62 a of the bearing plate to the lower end 60 of the barrel. As further described herein, the outer surface of the upper annular wall 66 b is upwardly tapered such that the outside diameter of the wall decreases from the upper surface 62 b of the bearing plate 62 to the upper end 56 of the barrel. Similarly, the outer surface of the lower annular wall 66 a is downwardly tapered such that the outside diameter of the wall decreases from the lower surface 62 a of the bearing plate 62 to the lower end 60 of the barrel. This bi-tapered configuration of the barrel portion 66 provides benefits in manufacturing ease as well as reducing the amount of materials needed for manufacture of the anchor.
Referring still to FIG. 9, it will be appreciated that the anchor 32 is configured such that the bearing plate portion 62 is disposed near the midpoint of the barrel portion 66. This provides advantages. in manufacturing, strength, and material usage. In preferred embodiments, the distance from the upper end 56 of the barrel to the upper surface 62 b of the bearing plate, denoted L′, is within the range from about 46% to about 54% of the distance from the upper end of the barrel to the lower end 60 of the barrel, denoted L″.
Referring now to FIG. 10, there is illustrated a top view of the anchor 32. The generally rectangular configuration of the bearing plate portion 62 is clearly shown, as is the wedge-receiving cavity 36 passing through the center of the barrel portion 66.
Referring now to FIGS. 11 and 12, cross-sectional views of the anchor 32 are provided to further illustrate aspects of the invention. The annular nature of the barrel's upper annular wall 66 b and lower annular wall 66 a can be seen, centered around the centerline 45 of the barrel. It will be appreciated that the centerline 45 of the barrel portion 66 is substantially perpendicular to the bearing plane 63 formed by the bearing plate 62. The inner surfaces of the annular walls 66 a and 66 b define the wedge-receiving cavity 36 of the anchor 32. The cavity 36 has a portion 54 of constantly diminishing diameter extending substantially from the first (i.e., upper) end 56 to the second (i.e., lower) end 60 of the barrel 66. Preferably, the first end 56 of the barrel 66 includes an angled or rounded face 58 surrounding the upper cavity aperture, the purposes of which will be further explained herein. The edge 47 of the lower aperture formed at the second end 60 of the cavity 36 may be un-radiused as shown, or optionally, radiused. In a preferred embodiment, the angle of taper of the cavity portion 54 is approximately a 7° angle relative to the longitudinal axis (i.e., centerline) 45 of cavity 36. 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 cavity 36.
Referring now to FIG. 13, there is shown a post-tension anchoring system in accordance with another embodiment of the invention. The post-tension anchoring system, generally designated as reference numeral 30, includes an anchor 32, a tendon 34 extending through a cavity 36 (see FIGS. 11 and 12) in the anchor, and a plurality of wedges 40 and 42 received within the cavity. In use, the anchor 32 is fixed in place against, or embedded within, hardened concrete 38. After tensioning, the tendon 34 is retained in the proper position within the anchor 32 by the wedges 40 and 42, which have an interference fit relationship between the wall of the cavity 36 and the exterior surface of the tendon. The anchoring system of the current invention may be used in a live end, dead end or intermediate anchor configuration, and for both sheathed and unsheathed tendons. FIG. 13 illustrates the intermediate anchor configuration, i.e., the tendon 34 is encased in a sheathing 14 on either side of the cavity 36, but is unsheathed within the cavity, and the cavity has a diameter D′ at the lower end 60 of the barrel 66 that is at least as great as the diameter D_sof the sheathing on said tendon. This allows the anchor 32 to be moved along the sheathed tendon 34 without damaging the sheathing 14.
The wedges 40 and 42 are fit within, or substantially entirely within, the cavity 36. Preferably, the wedges 40 and 42 are standard wedges used in conventional prior art anchoring systems. In the preferred embodiment, the wedges 40, 42 have a constant outer angle of taper of approximately 7°, corresponding with the taper of the cavity 36. The wedges 40, 42 have a substantially semi-circular inner surface adapted to engage the tendon 34.
Further aspects of the current invention are now described and compared to the prior art. As discussed above, prior art anchors having a constant taper extending from first end to second end (see FIG. 3) did not have a large enough opening at the second end to accommodate a sheathed tendon as requirements for sheath thickness increased. As further indicated above, current specifications require a sheath thickness of 0.050″ for all structural slabs. In order to accommodate the increased sheath thickness, various prior art anchor designs such as shown in FIGS. 4-7 resulted.
Referring again to FIG. 11, in a preferred embodiment of the current invention, the diameter of the cavity 36 at the second end 60, referred to as the minor diameter D′, is in the range of 0.60″ to 0.75″, more preferably 0.67″ to 0.70″, and most preferably 0.68″ to 0.69″. Preferably, the diameter of the cavity 36 at the first end 56, referred to as the major diameter D″, is fixed by the minor diameter D′, the constant taper and the overall height of the cavity. Typically, the major diameter D″ is in the range of 0.96″ to 1.00″, more preferably 0.97″ to 0.99″, and most preferably 0.98″. The overall height of the barrel 66, denoted L′ (FIG. 9), including the cavity height and the angled or rounded face 58, is preferably approximately the length of the wedges 40, 42, and more preferably the wedge length plus 0.05″ or greater. Thus, if the wedge length is 1.25″, the overall height L′ of the anchor 32 is preferably 1.25″ to 1.30″ or greater. This allows the entire outer surface or substantially the entire outer surface of the wedges 40 and 42 to be in interference contact with the wall of the cavity 36 when pressed into the cavity 36. Also, since the cavity 36 has a constant taper along its length, there is even bearing along the cavity wall, reducing the risk of a point-load failure.
A typical tendon 34 having a minimum sheath thickness of 0.050″ has an approximate overall thickness in the range of 0.62″ to 0.67″. In the preferred embodiment, the minor diameter D′ is at least the diameter of the sheathed tendon or greater. As such, the anchor 32 can slide easily along the length of the tendon 34 without causing damage to the sheathing 14 on the tendon.
The anchor 32 of the preferred embodiment is further optimized to eliminate unnecessary cast material from areas where it is not needed while complying with specification and code requirements.
As stated above, the anchor 32 of the present invention sizes the minor diameter D′ to accommodate a sheathed tendon while still being able to use standard wedges. The preferred embodiment of the present invention retains a 7° tapered cavity compatible with the wedges but made it uniformly tapered substantially the height of the barrel 66 with the barrel height approximately the length of the wedges. It is to be understood that the present invention is not restricted to a 7° tapered cavity used with 7° wedges but that the tapered cavity angle is substantially the same as the angle of the wedges, preferably within 0.5° of each other. Additionally, it is to be understood that the present invention is not restricted to a 7° tapered cavity but includes a range of other angles for the tapered cavity, as for example angles ranging from approximately 4° to 10° with compatible wedges. Thus, the present invention contemplates a 4° tapered cavity used with wedges having an angle of approximately 4°.
In a preferred embodiment, the bearing plate 62 has dimensions of approximately 2.25″×5.0″ with a bearing plate thickness of approximately 0.23″. The barrel 66 has outer diameters of approximately 1.20″ at the lower end 60 and approximately 1.68″ at the upper end 56. Referring again to FIGS. 9, 11 and 12, the bearing plate lower surface 62 a is preferably approximately 0.40″ above the lower end 60 of the barrel 66. As shown in FIGS. 11 and 12, the lower barrel portion 66 a below the bearing plate lower surface 62 a has a thinner wall thickness than the remainder of the barrel 66. The wall thickness at the lower end 60 is 0.26″ in a preferred embodiment. The wall thickness of the lower barrel portion 66 a is generally uniform and preferably has a 0.25″ radius at the intersection with the lower surface 62 a of the bearing plate 62. In the preferred embodiment, the upper portion 66 b of the barrel above the upper surface 62 b of the bearing plate 62 increases in thickness as it approaches the upper surface 62 b. Preferably, the outer surface of the upper portion 66 b of the barrel 66 has an outward angle of approximately 7° (relative to the cavity centerline 45 but opposite to the 7° angle of the cavity 36).
The plurality of bracing ribs 64 have also been optimally designed to provide strength where needed and eliminate the material where not needed. Preferably, each bracing rib 64 of the two pair of ribs has a maximum height above the bearing plate, denoted HR (FIG. 9), of approximately 0.36″ and a width at the upper surface 62 b of the bearing plate, denoted WR (FIG. 11), of approximately 0.39″.
The advantages of the anchor of the present invention are numerous. The anchor 32 can be used at live end, dead end and intermediate anchor locations with sheathed or unsheathed tendons. As previously indicated, conventional wedges are used. The entire or substantially entire outer surface of the wedges are in frictional engagement with the cavity wall, thus transferring load along the entire length of the wedges and avoiding any concentrated load points. By optimizing the size and shape of the anchor components, Applicant has been able to reduce the overall weight of preferred embodiments of the anchor of the current invention by approximately 13.5% (compared to prior versions) while still complying with codes and regulations. The anchor 32 can be cast and no machining is required. As such, the expense of the production of the anchor 32 is reduced. There will be no sharp burrs or snarled edges which could compromise the integrity of the sheathing of the tendon 34. When present, the optional radiused edge 47 further assures that the anchor 32 will slide smoothly along the tendon 34. The radiused edge 47 assures that snags and cuttings of the sheathing 14 (if present) of the tendon 34 are avoided. The radiused edge 47 also facilitates the installation of the anchor 32 onto the tendon 34 by “funneling” the tendon through the cavity 36 in the anchor body 34.
It is to be understood that while the preferred embodiment of the present invention has been described as having a 7° tapered cavity with compatible wedges, the invention is not so limited in scope. The present invention also includes a constant tapered cavity of angles other than 7°, as for example angles ranging from approximately 4° to 10° with compatible wedges, and is relevant to both bare and encapsulated (e.g., with polymer) anchors.
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.

Claims

1. An anchor for a concrete post-tension system including the anchor, a tendon having a longitudinal axis and a first diameter with at least one portion of the tendon being exposed and at least another portion of the tendon being encased in sheathing having a second diameter, and a plurality of wedges, each wedge having a height, a substantially semi-circular inner surface adapted to engage the exposed portion of the tendon and an outer surface with constant outer angle of taper with respect to the longitudinal axis, the anchor comprising:

a generally rectangular bearing plate portion having a upper surface and a generally flat lower surface defining a bearing plane;

a barrel portion having an upper annular wall extending from the upper surface of the bearing plate and a lower annular wall depending from the lower surface of the bearing plate, the inner surfaces of the upper annular wall and lower annular wall together defining an internal wedge-receiving cavity passing through the bearing plate and having a central axis substantially perpendicular to the bearing plane;

the wedge-receiving cavity having a fixed angle of taper with respect to the central axis such that the diameter of the cavity is constantly diminishing from the upper end of the barrel to the lower end of the barrel, the cavity having a diameter at the lower end that is at least as great as the diameter of the sheathing on the tendon to be anchored, and the cavity having an overall height measured from the upper end of the barrel to the lower end of the barrel that is at least as great as the height of the wedges to be used;

the outer surface of the upper annular wall being upwardly tapered such that the outside diameter of the wall decreases from the upper surface of the bearing plate to the upper end of the barrel;

the outer surface of the lower annular wall being downwardly tapered such that the outside diameter of the wall decreases from the lower surface of the bearing plate to the lower end of the barrel; and

a plurality of webs extending from the outside of the upper annular wall to the upper surface of the bearing plate;

whereby the sheathed portion of the tendon may freely pass through the wedge-receiving cavity of the anchor, and when an exposed portion of the tendon is positioned within the cavity, the wedges may be inserted to produce an interference fit relationship between the inner surfaces of the cavity and the exterior surface of the tendon.

2. A post-tension anchor in accordance with claim 1, wherein the anchor is a one-piece metal casting.

3. A post-tension anchor in accordance with claim 1, wherein the anchor is a metal casting encapsulated in a polymer material.

4. A post-tension anchor in accordance with claim 1, wherein the upper surface of the bearing plate is disposed near the midpoint of the barrel, the distance from the upper end of the barrel to the upper surface of the bearing plate being within the range from about 46% to about 54% of the distance from the upper end of the barrel to the lower end of the barrel.

5. A post-tension anchor in accordance with claim 4, wherein when the tendon to be anchored is encased in sheathing having a diameter within the range from about 0.62″ to about 0.67″, then the wedge-receiving cavity has an angle of taper that is within the range from about 0.67″ to about 0.75″.

6. A post-tension anchor in accordance with claim 5, wherein when the wedges to be used have a height of about 1.25″ and an outside taper of about 7°, then the wedge-receiving cavity has a height from the upper end of the barrel to the lower end of the barrel that is within the range from about 1.25″ to about 1.30″, and the wedge-receiving cavity has an angle of taper that is within the range from about 6.5° to about 7.5°.

7. A multi-purpose anchor for a post-tension anchoring system comprising an anchor body having an internal wedge-receiving cavity defined by a wall, said cavity has a constantly diminishing diameter extending from a first end of said anchor body to a second end of said anchor body, said cavity having an angel of taper with respect a centerline of said cavity, said cavity having a diameter at said second end.

8. An anchor in accordance with claim 7, wherein said anchor body is a cast member.

9. An anchor in accordance with claim 7, wherein said angle of taper is approximately 7° relative to the center line of said cavity.

10. An anchor in accordance with claim 7, further comprising:

a tendon extending through said cavity; and

at least two wedges in interference fit relationship between said wall and an exterior surface of said tendon.

11. An anchor in accordance with 10, wherein each of said wedges has a length not greater than a length of said cavity.

12. An anchor in accordance with 10, wherein said tendon has a sheathing extending therearound, said diameter of said cavity at said second end being greater than a diameter of said sheathing on said tendon.

13. An anchor in accordance with claim 10, wherein each of said wedges has a length approximately the same as the length of said cavity.

14. An anchor in accordance with claim 13, wherein the length of said cavity is approximately 0.05″ greater than the length of each of said wedges.

15. An anchor in accordance with claim 14, wherein said cavity has a length of 1.30″.

16. An anchor in accordance with claim 14, wherein each of said wedges is in interference fit relationship with said cavity wall along the entire length of said cavity.

17. An intermediate anchor for a post-tension system, comprising:

an anchor having a bearing plate portion and a barrel portion;

the bearing plate portion having a upper surface and a generally flat lower surface defining a bearing plane;

the a barrel portion having an upper annular wall extending from the upper surface of the bearing plate and a lower annular wall depending from the lower surface of the bearing plate, the inner surfaces of the upper annular wall and lower annular wall together defining an internal wedge-receiving cavity passing through the bearing plate and having a central axis substantially perpendicular to the bearing plane;

the wedge-receiving cavity having a fixed angle of taper with respect to the central axis such that the diameter of the cavity is constantly diminishing from the upper end of the barrel to the lower end of the barrel,

the outer surface of the upper annular wall being upwardly tapered such that the outside diameter of the wall increases from the upper end of the barrel to the upper surface of the bearing plate;

the outer surface of the lower annular wall being downwardly tapered such that the outside diameter of the wall increases from the lower end of the barrel to the lower surface of the bearing plate; and

a tendon extending through the wedge-receiving cavity, the tendon being encased in a sheathing on either side of the cavity, the cavity having a diameter at the lower end of the barrel that is at least as great as the diameter of the sheathing on said tendon.

18. An intermediate anchor in accordance with claim 17, further comprising:

at least two wedges in interference fit relationship between the interior wall of the wedge-receiving cavity and an exterior surface of an unsheathed portion of the tendon.

19. An intermediate anchor in accordance with claim 18, wherein when the wedges have a height of about 1.25″ and an outside taper of about 7°, then the wedge-receiving cavity has a height from the upper end of the barrel to the lower end of the barrel that is within the range from about 1.25″ to about 1.30″, and the wedge-receiving cavity has an angle of taper that is within the range from about 6.5° to about 7.5°.

20. An intermediate anchor in accordance with claim 17, wherein the upper surface of the bearing plate is disposed near the midpoint of the barrel, the distance from the upper end of the barrel to the upper surface of the bearing plate being within the range from about 46% to about 54% of the distance from the upper end of the barrel to the lower end of the barrel.