Reusable wedge for post-tensioning concrete

Abstract

The present disclosure provides a wedge assembly for an anchor of a tendon for use in post tensioning concrete. The wedge assembly includes three circumferential wedge segments adapted to be placed on an exterior surface of a tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly. Each wedge segment is threaded on the inside and each wedge segment is tapered from the first end to the second end at a taper angle. Finally, each wedge segment has an exterior surface configured to be inserted into an anchor assembly and has an annular groove around the exterior surface of each wedge segment and located at the first end and being configured to receive a ring.

Description

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application 63 / 698,717, entitled “Reusable Wedge for Post-Tensioning Concrete,” filed on Sep. 25, 2024. The contents of this priority application are incorporated by reference herein in their entirety.FIELD

[0002] The present disclosure relates generally to post-tensioned, pre-stressed concrete construction. The present disclosure relates specifically to wedges for anchors for use therein.BACKGROUND

[0003] Many structures are built using concrete, including, for instance, buildings, parking structures, apartments, condominiums, hotels, mixed-use buildings, casinos, hospitals, medical buildings, government buildings, research / academic institutions, industrial buildings, malls, bridges, pavement, tanks, reservoirs, silos, foundations, sports courts, and other structures.

[0004] Pre-stressed concrete is structural concrete in which internal stresses are introduced to reduce potential tensile stresses in the concrete resulting from applied loads. This can be accomplished by two methods—post-tensioned pre-stressing and pre-tensioned pre-stressing. When post tensioning concrete, the pre-stressing assembly is tensioned after the concrete has attained a specified strength. The pre-stressing assembly, commonly known as a tendon, includes, for example and without limitation, anchorages, one or more strands, and sheathes or ducts. The strand is tensioned between anchors which are embedded in the concrete once the concrete has hardened. The strand is typically formed from a metal or composite or any suitable material exhibiting tensile strength which can be elongated, including, for example and without limitation, reinforcing steel, single wire cable, or multi-wire cable. The strand is typically fixedly coupled to a fixed anchorage positioned at one end of the tendon, the so-called “fixed end”, and is adapted to be stressed at the other anchor, the “stressing end” of the tendon. The strand is generally held to each anchor by one or more wedges. Typically, anchors include a tapered recess, which, when the strand is placed under tension, causes the wedges to further engage the strand. Wedges are typically made of metal. Typically, wedges must be assembled to or threaded onto the end of the strand once the strand is in position in the concrete member. In the case of a bridge or other elevated structure, there is a risk of dropping wedges. Additionally, as strands may extend far from the end of the structure and bend due to gravity, the ability to thread the wedge onto the end of the strand is limited. Furthermore, misalignment between the wedges during installation may damage the strand or result in an insufficient anchor between strand and the anchor.

[0005] Additionally, wedges can crack and chip under stress after a few uses, limiting reusability. Further, wedge design (e.g., counter bore) can cause wedges to shave off coating on strands when being placed. That is, some strands may have a surface coating to improve wear and performance and reduce corrosion. For example, the coating may be an epoxy. Wedge thread hardness depth can be insufficient to allow threads of the wedge to easily penetrate into strand coating. Further, the sharp edges on standard thread minor diameter will chip and crack after only a few uses, and can also deform.

[0006] FIGS. 1A through 1E depict various views and details of a prior art wedge 100 having at least the deficiencies described above. FIG. 1F includes images of prior art wedge interiors following use (that is, the wedge segments have been separated to show the interior threading). Deformation of the threading can be seen in these images.

[0007] These are other deficiencies exist.SUMMARY

[0008] Exemplary embodiments include a wedge assembly for an anchor of a tendon for post tensioning concrete. The wedge assembly may include at least one wedge adapted to fit on an outer surface of a strand of the tendon. The wedge may include an outer surface having a circumferential groove formed thereon positioned in a plane substantially perpendicular with the longitudinal axis of the strand. The wedge assembly may further include a wedge ring adapted to fit into the groove of the wedge and to retain the wedge to the strand.

[0009] Another exemplary embodiment includes a wedge assembly for an anchor of a tendon for use in post tensioning concrete, having: three circumferential wedge segments adapted to be placed on an exterior surface of a tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly; each wedge segment being tapered from the first end to the second end at a taper angle, the taper angle being selected such that compressive force exerted by the wedge assembly against the tendon is substantially evenly longitudinally distributed when the wedge assembly is fully engaged in the receiving bore with the tendon under tension; each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end being configured to receive a ring; and each wedge segment having an interior surface having a threaded segment.

[0010] Another exemplary embodiment includes a wedge assembly for an anchor of a tendon for use in post tensioning concrete, having: three circumferential wedge segments adapted to be placed on an exterior surface of an epoxy coated tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly and this is configured to be reusable, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly, the first end having a first end angle of 10 degrees around a first end perimeter and the second end having a second end angle of 6 degrees around the second end perimeter; each wedge segment being tapered from the first end to the second end at a taper angle of 7.5 degrees; each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end and being configured to receive a ring; and each wedge segment having an interior surface having a threaded segment running from proximate the first end to proximate the second end and having buttress type threads, wherein further the wedge assembly is configured to be reusable.

[0011] Another exemplary embodiment includes a wedge assembly for an anchor of a tendon for use in post tensioning concrete, having: three circumferential wedge segments adapted to be placed on an exterior surface of an epoxy coated tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly and this is configured to be reusable, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly, the first end having a first end angle of 10 degrees around a first end perimeter and the second end having a second end angle of 6 degrees around the second end perimeter; each wedge segment being tapered from the first end to the second end at a taper angle of 7.5 degrees; each wedge segment is heat treated to a case depth of 0.025 to 0.035 inches and to a case hardness of 79-84 Rockwell Hardness A (HRA) and a core hardness of 36-46 Rockwell Hardness C (HRC); each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end and being configured to receive a ring; and each wedge segment having an interior surface having a threaded segment running from proximate the first end to proximate the second end and having buttress type threads, wherein further the wedge assembly is configured to be reusable.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to facilitate a fuller understanding of the various embodiments, reference is now made to the attached drawings. The drawings should not be construed as limiting any embodiments, but are intended only to illustrate different aspects and embodiments of the various embodiments.

[0013] FIGS. 1A, 1B, 1C, 1D, and 1E depict various views of a prior art wedge.

[0014] FIG. 1F depicts an image of sections of the prior art wedge showing the interior thereof.

[0015] FIG. 2A is a front perspective view of a wedge according to exemplary embodiments.

[0016] FIG. 2B is a front view of the wedge according to exemplary embodiments.

[0017] FIG. 2C is a rear view of the wedge according to exemplary embodiments.

[0018] FIG. 2D is a rear perspective view of the wedge according to exemplary embodiments.

[0019] FIG. 2E is a rear view of the wedge according to exemplary embodiments with the section 2F-2F labeled.

[0020] FIG. 2F is a cross-section view of the wedge according to exemplary embodiments along the line 2F-2F.

[0021] FIGS. 2G and 2H are magnified view of the wedge of FIG. 2F.

[0022] FIG. 2I is a close-up view of the internal teeth of the wedge according to exemplary embodiments.

[0023] FIGS. 3A, 3B, 3C, 3D, 3E, and 3F are images of the wedge according to exemplary embodiments being used in a post-tensioning system.

[0024] FIG. 4 is a side by side image of a prior art wedge and the wedge according to exemplary embodiments.DETAILED DESCRIPTION

[0025] Exemplary embodiments will now be described in order to illustrate various features of the invention. The embodiments described herein are not intended to be limiting in scope, but rather are intended to provide examples of the components, use, and operation of the various embodiments.

[0026] Wedges according to exemplary embodiments may have the following improvements over prior wedges.

[0027] The wedges may be used with various configurations of tendons, including, but not limited to, mono-strand and multi-strand. Tendons may include a coating, such as, but not limited to, an epoxy coating.

[0028] Thread configuration has been changed. A buttress type thread replaced the standard 118° / 12 pitch screw thread used in previous wedges. The problem with the standard screw thread is that the minor diameter may be too sharp and steep. When the wedge is stressed and penetrating the coating to bite into the steel strand, the sharp edges on standard thread minor diameter will chip and crack after only a few uses. The buttress type thread is a stronger thread and may not have the same chipping and cracking issues that the standard thread has.

[0029] Wedge body blank changed to a more durable larger version with a thicker cross sections and longer overall length. A thicker wedge section can add strength to each wedge section and eliminate cracking at the sections small end of the wedge. A longer overall length has a longer gripping surface and allows for more efficient stressing. For example, the length of a prior art wedge may be 2.06 inches (end to end). The wedge according to exemplary embodiments may be 2.375 inches (end to end).

[0030] A 10° taper at the large end of the wedge replaces a counter bore on the prior wedge design. The 10° angle allows the wedge, when assembled, to slide more easily along a coated strand. The counter bore used on the previous design can shave off some of the coating and was harder to slide on the strand.

[0031] An overall taper angle of 7.5° of the wedge from the large end to small end is selected such that compressive force exerted by the wedge assembly against the tendon is substantially evenly longitudinally distributed when the wedge assembly is fully engaged in the receiving bore with the tendon under tension.

[0032] The cut edges of each wedge section on the threaded inner diameter (I.D.) is sanded to keep the sharp cut edges from chipping during stressing.

[0033] Heat Treatment of the wedge has changed from 0.016-0.023 case depth to 0.025-0.035 case depth. This increases the thread hardness depth allowing the threads of the wedge to penetrate easily into the strand coating and bite into the steel strand without collapsing into the softer wedge core. The wedge has a Rockwell A (HRA) case hardness of 79-83 and a Rockwell C (HRC) core hardness of 38-46.

[0034] The “flared” I.D. angle and diameter of the wedge small end has changed in order to allow for smoother transition from flat threads to sharp threads. There is a 6 degree angle at the opening, as opposed to 15 degrees in the prior art wedge.

[0035] The opening of the small end of the wedge has a diameter of 0.660 inches and the opening at the large end flares to 0.730 to 0.750 inches.

[0036] FIGS. 2A-2I consists of various view of a wedge, or wedge assembly, 200 according to exemplary embodiments is depicted. FIG. 2A is a front perspective view, FIG. 2B is front view, FIG. 2C is a rear review, FIG. 2D is a rear perspective view, and FIGS. 2E and 2F show the wedge 200 in cross-section, with a centerline CL, a length (end to end) L, an inner diameter at the small end ID, and an inner diameter at the large end ID2. ID2 is greater than ID according to exemplary embodiments as described above. FIGS. 2G-2I show magnified views of parts of the wedge 200.

[0037] According to exemplary embodiments, the wedge 200 may be reusable multiple times for post-tensioning activities. The wedge 200 may include the various improvements described above over the prior art wedge. For example, the wedge 200 may include the improvements described above. In various embodiments, the wedge 200 may have other improvements over the prior art wedge.

[0038] For the purposes of this disclosure, the perpendicular axis to the page in FIGS. 2C and 2D is an axis that is parallel with the length of a strand or tendon when the wedge 200 is in use. This axis will be referred to as the longitudinal axis of the strand and the wedge. The wedge 200 may be substantially wedge shaped, as can be seen in FIGS. 2A and 2D and adapted to fit into a tapered recess formed in anchor body when in use. The wedge 200 has a front portion 212 and a rear portion 214. The front portion 212 is the portion inserted into the anchor. Tension on a strand to which the wedge is affixed causes the wedge to move into this tapered recess, applying a gripping force on strand.

[0039] The wedge 200 may have three segments for its body: 202, 204, and 206. The segments are held together by a ring 208. The each body segment may encompass an arc of 120 degrees as shown by the arc 218 in FIG. 2C. The ring 208 may be recessed into an annular groove 216 located circumferentially around the end of the wedge segments (that is, in a plane located perpendicular to the longitudinal axis of the strand and running circumferentially around the exterior surface of each wedge segment as shown in the Figures). The annular groove 216 can be seen in FIG. 2F, with detail shown in FIG. 2H. Internal to the wedge 200 along each segment are threads 210. The threads 210 can be seen in FIG. 2F, with details of the threads 210 shown in FIG. 2I. The threads 210 may extend from one end of the wedge assembly to the other. In exemplary embodiments, the threads 210 may extend from a location proximate each end through the length of the wedge assembly (that is, terminating between each end). That is, there may be a transition area at each end of the wedge assembly wherein there is a transition from a flat surface to a threaded surface. In various embodiments, the transition may be longer at the rear portion (214) as can be seen in FIG. 2F, for example. This transition area may be the 10 degree taper region described below (at 220) and can be seen in FIGS. 2F and 2H. The front portion (212) may have a smaller transition area with a taper of 6 degrees (224) as also can be seen in FIGS. 2F and 2G

[0040] As described above and shown in FIG. 2F, there is a 10 degree taper at the large end of the wedge (220), that is a transition area before the threaded portion starts. There is a 7.5 degree taper angle from the large end to the small end as shown (222). According to exemplary embodiments, this taper may start at a 0.5 inches from the large end (that is, a section of the wedge may be not tapered moving from the large end to the small end). As depicted in FIG. 2G, there may be a 6 degree taper or entrance ramp at the front end of the wedge (224).

[0041] The wedge segments can be positioned onto a strand (i.e., the wedge may be assembled around the strand). The wedge segments can then be coupled together using the ring and form the wedge. The ring (such as ring 208) may include a gap to allow the ring to be positioned around the segments and slipped into place. To accomplish this, the ring may be constructed of an elastically deformable material.

[0042] FIG. 4 depicts a prior art wedge 402 (on the left side) compared to a wedge assembly 404 (on the right side) according to exemplary embodiments. The prior art wedge 402 may represent a typical, conventional wedge design that is similar to the wedge 100 of FIG. 1. The wedge assembly 404 represents an embodiment of the wedge 200, described above, according to exemplary embodiments. The side-by-side positioning allows for visual assessment of the relative sizes, structural characteristics, and design features that distinguish the wedge assembly 404 from the wedge 402.

[0043] The structural differences visible in FIG. 4 may demonstrate how the wedge assembly 404 incorporates improved specifications compared conventional wedges. For example, as described herein, the wedge assembly 404 may exhibit a thicker cross-sectional configuration that provides increased material strength throughout the length of each wedge segment, addressing the structural weaknesses that may cause cracking and failure in conventional wedge designs. In some cases, the thicker cross-section visible in the wedge assembly 404 may provide the material strength needed to withstand repeated loading cycles without experiencing the threading deformation and structural degradation that may limit the reusability of conventional wedges, like wedge 402. The dimensional enhancements may also contribute to improved load distribution characteristics that reduce localized stress concentrations during tensioning operations.

[0044] The wedge assembly 404 may demonstrate a longer overall length compared to the wedge 402, providing extended gripping surface area that enhances the effectiveness of tensioning operations. The increased length of the wedge assembly 404 may allow for more efficient stress distribution along the tendon surface, creating more uniform gripping forces that reduce the likelihood of localized damage to tendon coatings or strand materials. The extended length configuration may also provide enhanced threading engagement area that distributes the gripping forces over a larger contact surface, reducing the stress per unit area and contributing to the enhanced durability characteristics of the wedge assembly 404. In some cases, the longer overall length may facilitate more gradual engagement with anchor assemblies during tensioning operations, allowing for progressive load transfer that reduces shock loading and stress concentrations that may cause threading damage in conventional wedge designs. The length enhancement may also provide improved alignment characteristics that reduce the likelihood of misalignment during installation and tensioning operations.

[0045] FIGS. 3A through 3F consist of various images of the wedge according to exemplary embodiments in use. As would be understood by one of ordinary skill in the art, an a post-tensioned concrete slab, a tendon's live end is where a hydraulic jack is used to apply tension after the concrete is poured and cured. The dead end is the opposite, fixed end of the tendon that is anchored in place before the concrete is even poured and is not involved in the tensioning process.

[0046] FIG. 3A provides a view of a dead end prior to stressing. Here, the wedge assemblies (300, which are exemplary wedges as described herein (e.g., the wedge 200)) are not seated in the anchors (302). In the pre-stressing state shown in FIG. 3A, the wedge assemblies 300 are in an initial positioning before tensioning is applied to the tendons. The anchor 302 may provide a structural housing that receives the wedge assemblies 300 during tensioning operations. As shown, the configuration may include multiple tendons with wedge assemblies positioned in parallel arrangement.

[0047] FIG. 3B provides a view of the live end prior to stressing. Here, the wedge assemblies (304, which are exemplary wedges as described herein (e.g., the wedge 200)) are not seated in the anchors (306). The live end configuration prior to stressing may illustrate the opposite end of the post-tensioning system where tensioning forces may be applied during post-tensioning operations. As shown, the configuration may include multiple tendons and wedge assemblies positioned in parallel arrangement.

[0048] In FIGS. 3C and 3D, the dead end and the live end, respectively, can be seen following stressing with the wedges fully seated in the anchors. As shown in FIG. 3C, the dead end configuration following stressing operations may illustrate the engaged state where each of the wedges assemblies (300) may be fully seated within its respective anchor (302). Similarly, as shown in FIG. 3D, the live end configuration following stressing operations may show the final engaged state where each wedge assemblies (304) may be fully seated within its respective anchor (306), after the post-tensioning process has been completed.

[0049] FIG. 3E shows an image of a cable (308), which is epoxy coated, following use with a wedge according to exemplary embodiments (i.e., the wedge 200 or the wedge 300 / 304). The section 310 indicates where a wedge assembly was positioned. The teeth marks from the wedge can be seen in this section. As also can be seen, the coating is not damaged.

[0050] FIG. 3F shows parts of a wedge (300 or 304), following use and disassembled (i.e., after stressing in a post tensioning system as depicted in FIG. 3A-D, for example). It can be seen there is little to no observable deformation in the threads (312). This is different from what was seen in prior art wedges following a single pull (i.e., deformation was observed) such as shown in FIG. 1F, for example.

[0051] Although embodiments have been described herein in the context of a particular implementation in a particular environment for a particular purpose, those skilled in the art will recognize that its usefulness is not limited thereto and that the embodiments can be beneficially implemented in other related environments for similar purposes. The embodiments should therefore not be limited by the above described embodiments, method, and examples, but by all embodiments within the scope and spirit of the various embodiments as claimed.

[0052] Further, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The terms “a” or “an” as used herein, are defined as one or more than one.

[0053] Various embodiments have been described with references to the accompanying drawings. It may, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the claims that follow. The description and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.

Claims

1. A wedge assembly for an anchor of a tendon for use in post tensioning concrete, comprising:three circumferential wedge segments adapted to be placed on an exterior surface of a tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly;each wedge segment being tapered from the first end to the second end at a taper angle, the taper angle being selected such that compressive force exerted by the wedge assembly against the tendon is substantially evenly longitudinally distributed when the wedge assembly is fully engaged in the receiving bore with the tendon under tension;each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end being configured to receive a ring; andeach wedge segment having an interior surface comprising a threaded segment.

2. The wedge assembly of claim 1, wherein the threaded segment of each wedge segment comprises a buttress type thread.

3. The wedge assembly of claim 1, wherein the wedge has a 10 degree taper at the first end.

4. The wedge assembly of claim 1, wherein cut edges of each wedge segment are sanded.

5. The wedge assembly of claim 1, wherein each wedge segment is heat treated to a case depth of 0.025 to 0.035 inches.

6. The wedge assembly of claim 5, wherein each wedge segment is heat treated to a case hardness of 79-84 Rockwell Hardness A (HRA) and a core hardness of 36-46 Rockwell Hardness C (HRC).

7. The wedge assembly of claim 1, wherein an angle at an edge of the circular opening at the second end of each wedge segment is 6 degrees.

8. The wedge assembly of claim 1, wherein the wedge assembly is reusable.

9. The wedge assembly of claim 1, wherein the tendon is epoxy coated.

10. The wedge assembly of claim 1, wherein the tendon is mono-strand.

11. The wedge assembly of claim 1, wherein the tendon is multi-strand.

12. A wedge assembly for an anchor of a tendon for use in post tensioning concrete, comprising:three circumferential wedge segments adapted to be placed on an exterior surface of an epoxy coated tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly and this is configured to be reusable, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly, the first end having a first end angle of 10 degrees around a first end perimeter and the second end having a second end angle of 6 degrees around the second end perimeter;each wedge segment being tapered from the first end to the second end at a taper angle of 7.5 degrees;each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end and being configured to receive a ring; andeach wedge segment having an interior surface comprising a threaded segment running from proximate the first end to proximate the second end and comprising buttress type threads;wherein further the wedge assembly is configured to be reusable.

13. The wedge assembly of claim 12, wherein cut edges of each wedge segment are sanded.

14. The wedge assembly of claim 12, wherein each wedge segment is heat treated to a case depth of 0.025 to 0.035 inches.

15. The wedge assembly of claim 14, wherein each wedge segment is heat treated to a case hardness of 79-84 Rockwell Hardness A (HRA) and a core hardness of 36-46 Rockwell Hardness C (HRC).

16. The wedge assembly of claim 12, wherein the tendon is mono-strand.

17. The wedge assembly of claim 12, wherein the tendon is multi-strand.

18. A wedge assembly for an anchor of a tendon for use in post tensioning concrete, comprising:three circumferential wedge segments adapted to be placed on an exterior surface of an epoxy coated tendon and form a wedge assembly to be inserted into a receiving bore of an anchor assembly and this is configured to be reusable, the wedge assembly having a first end and a second with each of the first end and the second end having a circular opening therein such that the tendon is surrounded by the wedge assembly and runs through the wedge assembly on a longitudinal axis of the wedge assembly, the first end having a first end angle of 10 degrees around a first end perimeter and the second end having a second end angle of 6 degrees around the second end perimeter;each wedge segment being tapered from the first end to the second end at a taper angle of 7.5 degrees;each wedge segment is heat treated to a case depth of 0.025 to 0.035 inches and to a case hardness of 79-84 Rockwell Hardness A (HRA) and a core hardness of 36-46 Rockwell Hardness C (HRC);each wedge segment having an exterior surface configured to be inserted into an anchor assembly and having an annular groove, running circumferentially around the exterior surface of each wedge segment and located at the first end and being configured to receive a ring; andeach wedge segment having an interior surface comprising a threaded segment running from proximate the first end to proximate the second end and comprising buttress type threads;wherein further the wedge assembly is configured to be reusable.

19. The wedge assembly of claim 18, wherein the epoxy coated tendon is mono-strand.

20. The wedge assembly of claim 18, wherein the epoxy coated tendon is multi-strand.

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