STEPPED WEDGES FOR POST-TENSIONING CONCRETE

Abstract

The present disclosure relates to stepped wedges that used with tendon anchors for maintaining tension on tension in post-tensioned concrete. Exemplary wedges include two halves. Each halve has a first end and a second end. The two halves are assembled to form a wedge having an outer diameter on the first end that is greater than the outer diameter of the second end. Internally, the wedge may have a constant inner diameter to retain a tendon. The inner surface of the wedge has a gripping surface. The wedge may have an external step that is circumferential around the wedge and results in a decrease from the outer diameter between the first and second ends.

Description

FIELD OF THE DISCLOSURE

The present disclosure relates to stepped wedges used with tendon anchors for maintaining tension on tensions in post-tensioned concrete.

BACKGROUND AND SUMMARY

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

Pre-stressed concrete is structural concrete in which internal stresses are introduced to reduce potential tensile stresses in the concrete resulting from applied loads. Pre-stressing may be accomplished by post-tensioned pre-stressing or pre-tensioned prestressing. In post-tensioned pre-stressing, a tension member is tensioned after the concrete has attained a desired strength by use of a post-tensioning tendon. The post-tensioning tendon may include for example and without limitation, anchor assemblies, the tension member, and sheathes.

Traditionally, a tension member is constructed of a material that can be elongated and may be a single or a multi-strand cable. The tension member may be formed from a metal, such as reinforced steel. The post-tensioning tendon traditionally includes an anchor assembly at each end. The tension member is fixedly coupled to a fixed anchor assembly positioned at one end of the post-tensioning tendon, the “fixed end,” and stressed at the stressed anchor assembly positioned at the opposite end of the post-tensioning tendon, the “stressing end” of the post-tensioning tendon.

In a typical tendon tensioning anchor assembly in post-tensioning operations, there are provided anchors for anchoring the ends of the cables suspended therebetween. In the course of installing the cable tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to one of the exposed ends of cable (the stressing end) for applying a predetermined amount of tension to the tendon. When the desired amount of tension is applied to the cable, wedges, threaded nuts, or the like, are used to capture the cable and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.

A prior art anchor system and wedges from GTI is depicted FIG. 1 at 10. The wedges such parts 201115, 201515 and 201518, clamp a tensioning tendon (labelled as 2) on the inner diameter or ID of the wedge (i.e. the barrel portion) while transmitting the tensile force to the anchor (labelled as 1) on the outer diameter or OD of the wedge (i.e. the wedge-shaped portion). While these wedge designs are field tested and represent the industry standard for post-tensioning cable wedges, there are areas for improvement. For example, traditional wedges include an outer diameter (OD) with a single wedge profile comprising a single consistent surface at a single wedge angle. This can be seem in FIG. 1.

After the concrete member is stressed, the tension member extends beyond the edge of the concrete segment. Conventionally, at least a portion of the tension member that extends beyond the edge of the concrete member is removed by cutting.

Traditional methods of cutting the tension member include using an abrasive saw or an arm with a sharp edge that cuts the cable. Both the sharp edge and the saw may leave the cut end of the tension member frayed. Use of the abrasive saw also tends to produce dust. Cutting the tension member using traditional methods may take 20-25 seconds or longer.

Other traditional cutting methods include a conventional acetylene torch or cutting torch. However, use of the open flame of a torch creates some danger of fire or explosion in the surrounding environment. Also, cutting the metal cable with a torch at a point near to the tensioning wedges causes the cable and wedges to become heated and may result in a loss of temper of the metal or loosening of the post-tensioning wedges.

These and other deficiencies exist. Thus, it may be beneficial to provide a wedge with different geometry that improves the overall wedge performance in application.

SUMMARY

Exemplary embodiments include a stepped wedge that includes two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge has a first end having a first outer diameter; a second end having a second outer diameter such that the second outer diameter is smaller than the first outer diameter resulting in a taper from the first end to the second end; and a step located between the first end and the second end, the step being located on an external surface of each of the two circumferential halves and being a sharp inward decrease in an outer diameter.

Another exemplary embodiment includes a stepped wedge that includes two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge includes: a first end having a first outer diameter; a first length extending therefrom towards a second end, the first length tapering inward towards the second end; a step located at an end of the first length, the step being located on an external surface of each of the two circumferential halves; a second length extending from the step towards the second end and tapering inward; the second end having a second outer diameter that is less than the first outer diameter.

Another exemplary embodiment includes a stepped wedge including two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge includes: a first end having a first outer diameter; a first length extending therefrom towards a second end, the first length tapering inward towards the second end; a step located at an end of the first length, the step being located on an external surface of each of the two circumferential halves; a second length extending from the step towards the second end and tapering inward; the second end having a second outer diameter that is less than the first outer diameter; an internal channel having an inner diameter that is constant from the first end to the second end; and a gripping surface located on an interior surface of the internal channel and extending from the first end to a location proximate the second end.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure, together with further objects and advantages, may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

FIG. 1 depicts an example of a prior art anchor and wedge system.

FIGS. 2A and 2B are drawings of pressure distribution on a prior art wedge (FIG. 2A) and a stepped wedge (FIG. 2B) according to exemplary embodiments.

FIG. 3 depicts a wedge according to exemplary embodiments.

FIG. 4A depicts a side view of a wedge according to exemplary embodiments.

FIG. 4B depicts a top of the wedge according to exemplary embodiments.

FIG. 4C depicts a section view along the line 4C-4C of the wedge according to exemplary embodiments.

FIG. 4D depicts a partial view of the wedge according to exemplary embodiments.

FIGS. 5A and 5B are images of wedges according to exemplary embodiments.

These and other objects, features and advantages of the exemplary embodiments of the present disclosure will become apparent upon reading the following detailed description of the exemplary embodiments of the present disclosure, when taken in conjunction with the appended paragraphs.

DETAILED DESCRIPTION

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

FIGS. 2A and 2B (collectively, FIG. 2) illustrate the benefit of a stepped wedge geometry according to exemplary embodiments. In application, a wedge clamps a tensioning tendon as the tendon attempts to relax from the tension applied by a stressing jack. As the wedge clamps the tensioning tendon, the tendon pulls the wedge inward toward the concrete structure that is being post-tensioned. The outer diameter (OD) of the wedge transmits this force to an anchor designed to receive the wedge. The wedge has a tapered outer surface that enables it to seat into the cooperating tapered inner wedge receiving bore in the anchor. Doing so serves to laterally compress the wedge against the tendon as axial tension (tension along the longitudinal axis of the tendon is applied to the tendon. In this manner, the circumferential segments of the wedge (in exemplary embodiments, two) are compressed to cause the wedge to grip the tendon and restrain the tendon from axial movement when the wedge is fully seat (engaged) in the anchor.

Due to the geometry, as illustrated in FIG. 2A, this force is initially concentrated on the smallest portion of the wedge (i.e. the smaller OD at the bottom of the wedge—the small end). Thus, when a wedge fails, it generally fails at this location. However, (as depicted in FIG. 2B), when a stepped wedge according to exemplary embodiments is used in the same anchor, the pressure is initially applied to a portion of the wedge with a larger OD. Therefore, the pressure is concentrated on a portion of the wedge greater equipped to bear the load. The step may be designed such that as the load on the wedge increases, eventually the second wedge surface also bears some of the load, but the load is not maximized on this smaller portion of the wedge profile. With this stepped geometry, exemplary wedges may be capable of carrying higher loads before failure as compared to traditional designs of the same general size and shape. Moreover, the stepped wedge geometry disclosed herein may allow for a smaller overall wedge given a specified load capacity. That is, increasing the strength of a wedge may allow for greater tension in a given tendon and/or a smaller wedge and smaller overall tension retaining system.

FIG. 3 at 100 depicts a post-tensioning wedge design that departs significantly from traditional geometry. Traditional wedges include an outer diameter (OD) with a single wedge profile comprising a single consistent surface at a single wedge angle. Exemplary wedges, such as wedge 100 (which represents one circumferential half of a full wedge, with the second circumferential half being a mirror image), having an overall length L 102, including a first end with an OD 104 with a first wedge surface (having length L1, 106) at a first wedge angle 116 (α) measured from a vertical line downward from the larger end with OD 104, and a second wedge surface (having length L2, 108) at a second wedge angle 118 (β) measured from the same vertical line as angle 116 and terminating in second end with an OD2120. It should be appreciated that the first and second wedge angles shown in FIG. 3 are exemplary and represent angles taken at approximately the same point relative to the lengths L1 and L2. The angle could be measured at other points along the length of each section. According to exemplary embodiments the second wedge angle 118 is larger than the first wedge angle 116. Stated differently, due to the step 110 (as described below), the angle from the first surface 106 increases to the second wedge surface 108 in a manner that is greater than if a constant surface taper existed externally on the wedge. In some embodiments, the first and second wedge angles may be equal. In exemplary embodiments, the length L2 (108) may be less than the length L1 (108). In some embodiments, L1 and L2 may be equal.

There may be a step 110 on the external surface of the wedge (i.e., on each wedge half). The step may be a ridge or other structure. The step may run circumferentially around the exterior of each wedge half. The step may be a point or location that results in an inward decrease in the outer diameter of the wedge such that the step results in a smaller OD (OD2120) (in the L2 section, at or below the step portion) than what would result from a single consistent wedge surface at a given wedge angle. Thus, there is a marked inward taper of the wedge 100 from OD 104 to OD2120, as can be seen in FIG. 3, for example. That is, the outer diameter “steps” inward from the first end to the second end at that point along the length L where the step is located. The step 110 extends circumferentially around the wedge 100 when the two halves are assembled. In various embodiments, the step 110 may be a sharp inward decrease in the outer diameter (inward from OD to OD2).

Internally, there is a gripping surface 114. This surface may consist of teeth or threads. There is a portion I 112 where gripping surface 114 ramps up to full depth. This portion may lack a gripping surface or may have a gradual increase in the gripping surface from smooth to rough.

FIGS. 4A, 4B, 4C, and 4D (collectively, FIG. 4) depicts a wedge 200 according to exemplary embodiments in various views. The wedge 200 includes the structure depicted in FIG. 3 for the wedge 100. The wedge 200, according to exemplary embodiments, is constructed of steel or alloy steel. Other suitable materials may be used.

The wedge has a first wedge surface 202 at a first wedge angle, and a second wedge surface 204 at a second wedge angle (see FIG. 3 for exemplary wedge angle measurements that can be applied here in a similar manner). There may be a step 210 located on the external surface. The step 210 may run circumferentially around the exterior of the wedge (i.e., each wedge half) and represent an inward decrease in the outer diameter (as described above for FIG. 3 in exemplary embodiments). The step results in a smaller OD (in the L2 section) than what would result from a single consistent wedge surface at a given wedge angle. In some embodiments, the first and second wedge angles may be equal. There is a larger first end (larger OD) 206 and a smaller second end (smaller OD) 208. As can be seen in the Figures, such as FIG. 4A, the wedge 200 has a taper from the larger end to the smaller end.

The wedge 200 has two circumferential halves 212 and 214. The two halves, when placed together (or assembled) as shown in FIGS. 4A and 4B, for example, create a circular inner hole 216 or channel (the inner diameter or ID). The ID may be constant from the larger end to the smaller end. This channel is where the tendon runs through when the wedge is in use.

Internally, the wedge 200 may have a gripping surface 218. It can be seem, such as in FIG. 4C, this gripping surface 218 is present on both halves for the majority of the length of the wedge 200 (from the larger end 206 to or near the smaller end 208). There is a section 220 proximate the smaller end 208 that lacks this gripping surface profile (e.g., it is smooth) and/or provides a transition zone from a smooth surface to the gripping surface 218. This can be best seen, for example, in FIG. 4D.

The gripping surface 218 may be a series of ridges or threads. For example, the threads known for use on anchor wedges may be so-called “buttress” threads, or may be other industry standard thread types known by designations “UNC” (unified coarse thread) or “UNF” (unified fine thread, also known as Society of Automotive Engineers—SAE thread). The threads are dimensionally defined by pitch P (number of threads per unit length along the longitudinal axis of the threaded element) and a difference, denoted at D between the thread major diameter and thread a minor diameter. Major diameter is the maximum diameter defined at the root (base or bottom of each thread) of the thread and the minor diameter is the minimum diameter defined at the crest of the thread (point or tip of each thread).

A typical tendon is a steel cable or wire, and may include multiple wires, such as six wires generally wound in a helical pattern around a centrally positioned wire. Typically, the steel from which the wires are made has a surface hardness in a range of about 40-54 Rockwell “C.” This is a non-limiting example for exemplary purposes only. Accordingly, as used in this description, the term “tendon” is intended to include any element that is placed under tensile stress under ordinary operation. The tensile stress is communicated, through the wedges, to a load transfer device, such as an anchor (anchor base). Any tendon structure and/or material known in the art for use in such reinforcing systems may also be used in different embodiments, including, without limitation, single-strand tendons, steel bars, wire rope, composite (e.g. fiber reinforced plastic) tendons, guide wire and the like.

FIGS. 5A and 5B (collectively, FIG. 5) depicts wedges 500 and 502, respectively. The two wedges are of differently lengths as labelled in FIGS. 5A and 5B. These wedges may include the features described herein. For example, the wedges 500 and 502 each have the step configuration according to exemplary embodiments.

Although embodiments of the present invention 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 of the present invention can be beneficially implemented in other related environments for similar purposes. The invention should therefore not be limited by the above described embodiments, method, and examples, but by all embodiments within the scope and spirit of the invention as claimed.

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.

In the invention, 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 invention as set forth in the claims that follow. The invention and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.

Claims

1. A stepped wedge, comprising: two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge comprises:a first end having a first outer diameter;a second end having a second outer diameter such that the second outer diameter is smaller than the first outer diameter resulting in a taper from the first end to the second end;a step located between the first end and the second end, the step being located on an external surface of each of the two circumferential halves; andan internal channel extending from the first end to the second end,wherein a gripping surface is located on an interior surface of each circumferential half and extending in the internal channel from the first end to a location proximate the second end such that a smooth portion exists on the interior surface between the second end and a start of the gripping surface.

2. (canceled)

3. (canceled)

4. The stepped wedge of claim 4, wherein the gripping surface comprises a threaded surface.

5. The stepped wedge of claim 1, wherein the step is a decrease in outer diameter that increases the inward taper at a location between the first end and the second end.

6. A stepped wedge, comprising: two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge comprises:a first end having a first outer diameter;a first length extending therefrom towards a second end, the first length tapering inward towards the second end;a step located at an end of the first length, the step being located on an external surface of each of the two circumferential halves;a second length extending from the step towards the second end and tapering inward;the second end having a second outer diameter that is less than the first outer diameter; andan internal channel extending from the first end to the second end,wherein a gripping surface is located on an interior surface of each circumferential half and extending in the internal channel from the first end to a location proximate the second end such that a smooth portion exists on the interior surface between the second end and a start of the gripping surface.

7. (canceled)

8. (canceled)

9. The stepped wedge of claim 6, wherein the gripping surface comprises a threaded surface.

10. The stepped wedge of claim 6, wherein the second length is less than the first length.

11. The stepped wedge of claim 6, wherein: the first length is at a first angle relative to the first outer diameter and the second length is at a second angle relative to the first outer diameter such that the first angle is less than the second angle.

12. A stepped wedge, comprising: two circumferential halves, such that when the two circumferential halves are assembled, the stepped wedge comprises:a first end having a first outer diameter;a first length extending therefrom towards a second end, the first length tapering inward towards the second end;a step located at an end of the first length, the step being located on an external surface of each of the two circumferential halves;a second length extending from the step towards the second end and tapering inward;the second end having a second outer diameter that is less than the first outer diameter;an internal channel extending from the first end to the second end; anda gripping surface located on an interior surface of the internal channel and extending from the first end to a location proximate the second end such that a smooth portion exists on the interior surface between the second end and a start of the gripping surface and the gripping surface comprises a threaded surface.

13. (canceled)

14. The stepped wedge of claim 12 wherein the second length is less than the first length.

15. The stepped wedge of claim 12, wherein: the first length is at a first angle relative to the first outer diameter and the second length is at a second angle relative to the first outer diameter such that the first angle is less than the second angle.