Title:
Unbonded Post-Tension Strand Protector
Kind Code:
A1


Abstract:
An unbonded post-tension strand protector (200) and related method of use is provided. The unbonded post-tension strand protector is used to protect one or more unbonded post-tension strands (101) embedded in concrete from damage due to drilling or chipping. Unbonded post-tension strands embedded in poured concrete are tensioned to improve the compressive strength of concrete. The unbonded post-tension strand protector is placed over at least one selected portion of an unbonded post-tension strand (101).



Inventors:
Rizzuto, Anthony (Davie, FL, US)
Rizzuto, Charles (Davie, FL, US)
Application Number:
11/567775
Publication Date:
06/12/2008
Filing Date:
12/07/2006
Primary Class:
International Classes:
E04C5/08
View Patent Images:
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Primary Examiner:
WENDELL, MARK R
Attorney, Agent or Firm:
Fox Rothschild LLP (Princeton, NJ, US)
Claims:
What is claimed is:

1. A method for protecting at least one unbonded post-tension strand in a pre-cast concrete body, comprising the steps of: selecting at least one unbonded post-tension strand; positioning said at least one unbonded post-tension strand in a pre-cast concrete body before concrete is cast in the pre-cast concrete body; determining selected portions of said at least one unbonded post-tension strand to be protected; protecting said selected portions of said at least one unbonded post-tension strand by placing at least a portion of a protective layer adjacent to said selected portions.

2. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, wherein said selecting step includes selecting at least one unbonded post-tension strand having a half inch diameter.

3. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, wherein said selecting step includes selecting at least one unbonded post-tension strand having a three-eighth inch diameter.

4. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, wherein said selecting step includes selecting at least one unbonded post-tension strand having a six-tenth inch diameter.

5. The method for protecting an unbonded post-tension strand in a pre-cast concrete body according to claim 1, wherein further including the step of placing said selected portions in a location wherein said selected portions are protected from damage caused by drilling or chipping.

6. The method for protecting an unbonded post-tension strand in a pre-cast concrete body according to claim 5, further including the step of placing said selected portions under and over doors and windows, adjacent to elevator beams where anchor bolts will be installed, around sleeves for plumbing and electric lines, where column and sheer wall forms are to be installed, on balconies where personnel hoist braces are attached, and portions of a cast concrete body that require drilling or chipping.

7. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, further comprising the step of selecting a first plate that is sized and shaped to be clipped to said at least one unbonded post-tension strand.

8. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 7, further comprising the step of selecting a second plate that is sized and shaped to be clipped to said first plate.

9. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, further comprising the step of selecting a planar shaped plate that attaches to the unbonded post-tension strand using clamps extending from said planar shaped plate.

10. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 1, further comprising the step of selecting at least one recess partially encasing said at least one unbonded post-tension strand.

11. The method for protecting at least one unbonded post-tension strand in a pre-cast concrete body according to claim 10, further comprising the step of joining a plurality of protective layers, uniformly aligning a plurality of equally-spaced unbonded post-tension strands.

12. An unbonded post-tension strand protector, comprising: a first plate having an elongated longitudinal axis; and at least one recess configured for receiving at least one selected portion of an unbonded post-tension strand.

13. The unbonded post-tension strand protector according to claim 12, wherein said at least one selected portion is located under and over doors and windows, adjacent to elevator beams where anchor bolts will be installed, around sleeves for plumbing and electric lines, where column and sheer wall forms are to be installed, on balconies where personnel hoist braces are attached, or at portions of a cast concrete body that require drilling or chipping.

14. The unbonded post-tension strand protector according to claim 12, wherein the first plate is sized and shaped to be removably clipped to at least one unboned post-tension strand.

15. The unbonded post-tension strand protector according to claim 12, wherein the first plate is sized and shaped to be removably clipped to at least one unbonded post-tension strand.

16. The unbonded post-tension strand protector according to claim 15, wherein a second plate is sized and shaped to be removably clipped to said first plate.

17. The unbonded post-tension strand protector according to claim 12, wherein the first plate comprises a planar shape that attaches to said unbonded post-tension strand using clamps extending from said first plate.

18. The unbonded post-tension strand protector according to claim 12, wherein each unbonded post-tension strand is partially encased by said at least one recess formed in said first plate.

19. The unbonded post-tension strand protector according to claim 18, wherein each of said at least one recess is located adjacent one another.

20. A protector for protecting one or more unbonded post-tension strands, comprising: at least one plate having an elongated length and a predetermined width, and a portion of said at least one plate located in proximity to one or more unbonded post-tension stands for protecting said one or more unbonded post-tension strands along said elongated length of said at least one plate.

21. The protector according to claim 20, wherein said plate is adapted to be removably clipped to said one or more unbonded post-tension strands.

22. The protector according to claim 20, wherein the plate consists of a planar shape that attaches to said one or more unbonded post-tension strands using clamps extending from said at least one plate.

23. The protector according to claim 20, wherein each unbonded post-tension strand is partially encased by a recess formed in said at least one plate.

Description:

STATEMENT OF THE TECHNICAL FIELD

The present invention relates to a device and method for protecting strands used in pre-stressed concrete. More particularly, the invention relates to a protector and method for protecting unbonded post-tension strands.

DESCRIPTION OF THE RELATED ART

Concrete has long been used in the construction industry for its great compressive strength. However, concrete is inherently weak when placed under tension. For general strengthening, concrete has been reinforced by the use of steel reinforcement bars, called rebar, inside poured concrete. The high tensile strength of steel, combined with concrete's great compressive strength provides improved results under both tension and compression when the structure is cast.

To further overcome concrete's natural weakness in tension, methods of pre-stressing concrete with the use of steel have been developed. The principle behind pre-stressed concrete is that compressive stresses induced by high-strength “tendons” in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service. Pre-stressing removes a number of design limitations conventional reinforced concrete places on span and load. Pre-stressed concrete methods are used to produce beams and floors with longer unsupported spans than is practical with ordinary reinforced concrete. This allows architects and engineers to design and build lighter and shallower concrete structures without sacrificing strength.

When referring to a “tendon,” it is a term that encompasses several components. This includes a strand, which is a cable that is conventionally manufactured in ½ inch, or 6/10 inch diameter sizes. This strand is made from very high-tensile-strength steel wire, usually seven wires twisted together. In addition, the term also includes an anchorage having a cast-iron bearing plate and special wedges to secure the strand inside an anchor housing.

There are two main methods for inducing compressive strength in pre-stressed concrete: pre-tensioning and post-tensioning the steel reinforcement. In pre-tensioning, the steel is stretched before the concrete is poured. High-strength tendons are placed between two abutments is poured into molds around the tendons and allowed to cure. Once the concrete reaches the required strength, the stretching forces are released. As the steel of the tendons reacts to return to its original length, the tensile stresses are transferred into a compressive stress in the concrete.

In contrast, post-tensioning stretches the steel after the concrete hardens. Notably, the concrete is cast around but does not contact the unstretched steel. There are two types of post-tension systems: bonded and unbonded. With a bonded system, steel, aluminum, or plastic ducts are positioned in the formed area where tension would otherwise occur in the concrete element. The ducts are then attached to anchorages at either end. Once the poured concrete has hardened to the required strength, the strands are threaded through the ducts and tensioned. The tendons are tensioned by hydraulic jacks that urge against the concrete member itself. When the tendons have been stretched to design specifications, they are locked in position to maintain tension after the jacks have been removed. Thus, the locking action imparts a tensile force to the concrete. The ducts are then filled with a special grout designed to protect the tendons from corrosion.

Unbonded systems do not employ a duct system like the bonded systems described above. Instead, unbonded systems use stands surrounded with special corrosion-inhibiting grease and encased in waterproof plastic sheaths. This assembly is positioned within a mold and then has concrete poured around it, similar to standard reinforced concrete. Unbonded systems are conventionally used for building and floor slab construction, while bonded systems are used mostly for bridge construction.

Once the pre-stressed concrete members have been incorporated into the overall design of a structure, other features of the structure can be installed. Such features can include, but are not limited to: the installation of doors and windows, installing anchor bolts into elevator beams, laying plumbing and electric piping, installation of column and sheer walls, and attaching anchor supports on balconies where personnel hoist braces are attached. These features typically require drilling and/or chipping of the pre-stressed concrete which is tensioned using unbonded post-tension stands. Aside from the plastic sheath, the unbonded strands are relatively unprotected from drilling or chipping when installing the other features of the structure.

Sometimes in the process of drilling and/or chipping, a construction worker will accidentally damage the highly tensioned strands that are hidden within the concrete. Given the extremely high tension force of these strands (typically 30,000 pounds of force), the slightest nick, cut, or impact to these strands can result in the strand popping out of the concrete structure with extreme force. It is akin to a stretched rubber band that snaps. This is a potential safety hazard that has resulted in a great number of construction injuries (i.e. impalements, lacerations, amputations) and deaths.

In addition to the problem of construction worker safety, a cut strand compromises the strength and stability of the concrete structure itself. This could lead to immediate or gradual structural failure as greater stress and strain is applied to the remainder of the structure. When there are apparent indications of strand damage (i.e. the strand popping out of the concrete body), there may be a chance to repair the concrete structure before any additional or irreversible damage is incurred. However, repairing these unbonded post-tension systems is quite expensive and dangerous.

There are also instances where there could be no immediate indication that the strands and the pre-stressed concrete have been compromised. Unfortunately, in the absence of external indicators there is no non-invasive way, such as X-ray analysis, of detecting whether a pre-stressed concrete form has in fact been compromised. Considering that a typical concrete floor slab can have between 100-300 hidden strands, the task of inspecting each strand can be daunting.

To date, the problem of protecting unbonded post-tension strands from drilling and chipping has gone unsolved. Therefore, what is need in the art is a device and method that can protect unbonded post-tension strands from drilling or chipping. At the same time, the device should be adapted such that it can be strategically and removably placed in a location where selected portions of the unbonded post-tension strands(s) are protected from damage. Such a device and method would minimize both weight and construction cost, while reducing the risk of potentially life-threatening injures.

SUMMARY OF THE INVENTION

The invention is an unbonded post-tension strand protector. The protector includes a plate that is sized and shaped to be place over at least one selected portion of the unbonded post-tension strand. The one or more selected portions are protected from damage caused by drilling or chipping. Moreover, the one or more selected portions are located in several locations. These locations include under and over doors and windows, adjacent to elevator beams where anchor bolts will be installed, around sleeves for plumbing and electric lines, where column and sheer wall forms are to be installed, on balconies where personnel hoist braces are attached, or at portions of a cast concrete body that require drilling or chipping.

In another aspect of the invention, the invention relates to a protector for protecting one or more unbonded post-tension strands. The protector includes one or more plates having an elongated length and a predetermined width. Moreover, a portion of the plate(s) are located in proximity to one or more unbonded post-tension strands for protecting the unbonded post-tension strand(s) along the elongated length of the plate(s).

In one embodiment of the invention, the plate is formed of steel. In addition, there are several embodiments of the plate's size and shape. According to one embodiment of the invention, the plate is sized and shaped to be removably clipped to at least one unbonded post-tension strand. In another embodiment, the plate includes a planar shape. The planar shape attaches to the unbonded post-tension strand using clamps extending from the plate. Another embodiment, the plate is comprised of at least one recess. The recess partially encases each unbonded post-tension strand. As an alternative, each recess is located adjacent to one another. As another separate embodiment, a first plate is sized and shaped to be removable clipped to at least one unbonded post-tension strand. Moreover, a second plate is shaped and sized to be removably clipped to the first plate.

In another aspect of the invention, the invention relates to a method for protecting one or more unbonded post-tension strands in a pre-cast concrete body. The method includes selecting one or more unbonded post-tension strand having either a half inch, three-eight inch, or six-tenth inch diameter. At least one unbonded post-tension strand is positioned in a pre-cast concrete body before the concrete is cast in the pre-cast concrete body. Selected portions of one or more unbonded post-tension strands to be protected are determined.

The selected portions are placed in a location where said selected portions are protected from damage caused by drilling or chipping. According to one aspect of the method, the selected portions are placed under and over windows, adjacent to elevator beams where anchor bolts are to be installed, around sleeves for plumbing and electric lines, where column and sheer wall forms are to be installed, on balconies where personnel hoist braces are attached, and portions of a cast concrete body that require drilling or chipping.

The selected portions of the one or more unbonded post-tension strands are protected by placing a least a portion of a protective layer, adjacent to the selected portion. According to one embodiment, the protective layer of the protecting step includes a first plate that is sized and shaped to be clipped to one or more unbonded post-tension strands. As an alternate embodiment, a second plate is sized and shaped to be clipped to the first plate. According to another embodiment, the protective layer of the protecting step includes a planar shaped plate that attaches to the unbonded post-tension strand using clamps extending from the planar shaped plate. According to yet, another embodiment, the protective layer of the protecting step is selected to have one or more recesses configured to partially encase one or more unbonded post-tension strands. A plurality of equally-spaced unbonded post-tension strands is uniformly aligned by joining a plurality of protective layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of segments of a plurality of strand(s) are arranged in a concrete body that is useful for understanding the invention;

FIG. 2 is a perspective view of a first embodiment of the unbonded post-tension strand protector that is useful for understanding the invention;

FIG. 3 is a cross-sectional view of the first embodiment of the unbonded post-tension strand protector shown in FIG. 2 along the line 3-3 that is useful for understanding the invention;

FIG. 4 is a perspective view of a second embodiment of the unbonded post-tension strand protector that is useful for understanding the invention;

FIG. 5 is a cross-sectional view of the second embodiment of the unbonded post-tension strand protector shown in FIG. 4 along the line 5-5 that is useful for understanding the invention;

FIG. 6 is a perspective view of a third embodiment of the unbonded post-tension strand protector shown that is useful for understanding the invention;

FIG. 7 is a cross-sectional view of the third embodiment of the unbonded post-tension strand protector shown in FIG. 8 along the line 7-7 that is useful for understanding the invention;

FIG. 8 is a perspective view of a first embodiment of the unbonded post-tension strand protector that is useful for understanding the invention;

FIG. 9 is a cross-sectional view of the first embodiment of the unbonded post-tension strand protector shown in FIG. 8 along the line 9-9 that is useful for understanding the invention; and

FIG. 10 is a flow diagram of a method for protecting unbonded post-tension strands that is useful for understanding the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of segments of a plurality of conventional unbonded post-tension strands 101 disposed within a cutaway portion of a hardened concrete body 105. Each unbonded post-tension strand 101 is usually manufactures in standard ½ inch, ⅜ inch, or 6/10 inch diameter sizes. However, the diameter of the unbonded post-tension strand 101 is not intended to be limiting, as other diameters can also be used. The unbonded post-tension strand 101 is typically formed using very high-tensile-strength wire, usually seven wires 102 twisted together. Each wire 102 is typically made of steel, although other materials having similar tensile strengths can be used. Moreover, it should be understood that the number of wires 102 used to form the strand 101 is not intended to be limiting. The wires 102 are encapsulated by a sheath 103. The sheath 103 can be preferably made from plastic or other moisture-resistant material. A corrosion-inhibiting grease (not shown) is disposed between the sheath 103 and the wires 102. Before concrete is poured, the plurality of unbonded post-tension strands 101 are positioned within a concrete mold, similar to standard reinforced concrete. Once the concrete has been poured over the unbonded post-tension strands 101, the unbonded post-tension strands 101 become hidden from view.

At least one region 100 outlines selected portions of the plurality of unbonded post-tension strands 101 that are to be protected from potential damage caused by drilling and/or chipping through the concrete body 105 to the point the it impacts the underlying unbonded post-tension strands 101. Typically locations where region 100 can be found include where drilling and/or chipping occurs. These locations include, but are not limited to, under and over doors and windows, adjacent to elevator beams where anchor bolts are to be installed, around sleeves for plumbing and electric lines, where column and sheer wall forms are to be installed, and on balconies where personnel hoist braces are attached.

To protect the selected portions of the plurality of unbonded post-tension strands 101, an unbonded post-tension strand protector 200 (FIG. 2) is placed over the selected portions of the unbonded post-tension strands 101 desired to be protected from drilling and chipping generally underlying the region 100.

Referring now to FIG. 2, shown is a perspective view of one embodiment of an unbonded post-tension strand protector 200 located on selected portions of the unbonded post-tension strands 101. The unbonded post-tension strand protector 200 is designed to protect the adjacent unbonded post-tension strand 101 generally underlying the region 100 (FIG. 1). The unbonded post-tension strand protector 200 comprises a U-shaped plate 201. The U-shaped plate 201 is further comprised of a first planar portion 202, a second planar portion 204 that is spaced apart from and parallel to the first planar portion 202, an arcuate portion 203 that is connected to the first and second planar portions 202, 204, and an open side portion 205 located opposite the arcuate portion 203.

Referring now to FIG. 3, shown is a cross-section of the unbonded post-tension strand protector 200 taken along the line 3-3 of FIG. 2 that is useful for understanding the invention. Distal ends 302 of the U-shaped plate 201 are each formed with an undulation 303. The undulations 303 are intended to securely fasten the unbonded post-tension strand 200 over the selected region 100 of the unbonded post-tension strand 101. Each undulation 303 is curved away from the other such that each of their respective convex portions 304 are spaced from and facing each other. The closet distance between convex portions 304 is less than the diameter of the unbonded post-tension strand 101.

The U-shaped plate 201 is sized and shaped to be clipped to one or more unbonded post-tension strands 101. In this regard, the word “clipped” means that the unbonded post-tension strand 101 is inserted through the opens side portion of the U-shaped plate 201 and is secured within the U-shaped plate 201. The unbonded post-tension strand(s) 101, when clipped, would be bounded by the first planar portion 202, the second planar portion 204, the arcuate portion 203, the convex portions 304. The U-shaped plate 201 is designed to protect the top side, bottom side and a single side of the unbonded post-tension strand 101 from any drilling or chipping that would otherwise damage the unbonded post-tension strand 101. According to a preferred embodiment, the U-shaped plate 201 is formed of a hard material, such a steel. However, the invention in not limited in this regard and other materials can be used so long as the U-shaped plate 201 can resist penetration by a drill bit 210 or a tip of a chipping hammer (not shown).

The unbonded post-tension strand protector 200 is advantageous in that it permits the construction worker to adjust the position of the unbonded post-tension strand protector 200 relative to the unbonded post-tension strand 101. In addition, it is advantageous to place the U-shaped plate 201 on selected portions of the elongated length of the unbonded post-tension strand 101 as compared to placing the U-shaped plate 201 along the entire length of the unbonded post-tension strand 101. The advantage is that the above arrangement minimizes the additional weight and cost of the overall structure by using the minimum amount of material forming the unbonded post-tension strand protector 200.

Referring now to FIG. 4, shown is a perspective view of another embodiment of an unbonded post-tension strand protector 400. Similar to the previous embodiment of the unbonded post-tension strand protector 200, the unbonded post-tension strand protector 400 is designed to protect at least a portion of the unbonded post-tension strand 101 delineated by region 100, shown in FIG. 1. The unbonded post-tension strand protector 400 comprises a planar-shaped plate 401. Although, the planar-shaped plate is preferably rectangular, the invention should not be limited in this regard. Other plate shapes are possible so long as the plate is dimensioned such that the surface of the plate provides a barrier of protection of at least one unbonded post-tension strand 101 from drilling or chipping in the selected region. The planar-shaped plate 401 attaches to one or more unbonded post-tension strands 101 using at least one clamp 402 (best seen in FIG. 5). The clamp 402 is preferably C-shaped, such that the clamp 402 has an improved grasp of each unbonded post-tension strand 101. However, this is in no way meant to be limiting as there could be other clamp shapes that can effectively grasp the unbonded post-tension strand 101. The claim 402 can be made from a resilient material. If the resilient material is a metal, the clamp 402 can be attached to the planar-shaped plate 401 by welding the clamp to the planar-shaped plate 401. If the resilient material is a non-metal such as plastic, the clamp 402 can be attached to the planar-shaped plate 401 using screws (not shown). However, the invention should not be limited in this regard.

Referring now to FIG. 5, shown is a cross-section of the unboned post-tension strand protector 400 taken along line 5-5 of FIG. 4. The planar-shaped plate 401 is designed to protect the top or bottom sides of the unbonded post-tension strand 101 from any drilling or chipping that would otherwise damage the unbonded post-tension strand 101. According to a preferred embodiment, the planar-shaped plate 401 is formed of a hard material, such as steel. However, the invention is not limited in this regard and other materials can be used so long as the planar-shaped plate 401 can resist penetration by a drill bit 210 or a tip of a chipping hammer (not shown). The planar-shaped plate 401 can be configured to protect one or more unbonded post-tension strands 101. Another advantage of this configuration is that the clamps 402, and hence the planar-shaped plate 401 can slidably adjust depending on the region that is to be protected. This is accomplished by sliding the planar-shaped plate 401 and its attached clamps 402 along the elongated length of the unbonded post-tension strand(s) 101. Alternatively, if there is one clamp 402 attached to the planar-shaped plate 401, it is possible to also slidably adjust the planar-shaped plate 401 by rotating the clamp 404 around the periphery of the unbonded post-tension strand 101. This enables the planar-shaped plate 401 to protect side and angled regions of the unbonded post-tension strand 101 in additional to the top or bottom sides.

Referring now to FIG. 6, shown is a perspective view of another embodiment of an unbonded post-tension strand protector 600. Similar to the previous two embodiments 200, 400, the unbonded post-tension strand protector 600 is designed to protect at least a portion of the region of the unbonded post-tension strand 101 delineated by region 100, shown in FIG. 1. The unbonded post-tension strand protector 600 comprises a barrel-vaulted pate 601. The barrel-vaulted plate 601 is formed by at least one recess 602. Each recess 602 partially encases a respective unbonded post-tension strand 101. If a plurality of recesses 602 are employed to protect adjacent unbonded post-tension strands 101, each recess 602 is positioned adjacent one another by welding abutting side portions 603 of each barrel vaulted pate 601. This allows for improved alignment of the unbonded post-tension strands 101 before setting them in concrete. The barrel-vaulted plate 601 should be dimensioned such that the surface of the plate provides a barrier of protection for a portion of at least one unbonded post-tension strand 101 from drilling or chipping in the selected region.

Referring now to FIG. 7, shown is a cross-section of the unbonded post-tension strand protector 600 taken along line 7-7 of FIG. 6. The barrel-shaped plate 601 is designed to protect the top side of the unbonded post-tension strand 101 from any drilling or chipping that would otherwise damage the unbonded post-tension strand 101. Alternatively, the barrel-shaped plate 601 can be positioned underneath the unbonded post-tension strand 101 such that portions of the unbonded post-tension strand 101 is protected from any drilling or chipping that can damage the underside portions of the unbonded post-tension strand 101. The barrel-shaped plate can be secured to the unbonded post-tension strand 101 using tie wraps (not shown). The barrel-shaped plate 601 is preferably formed of a hard material, such as steel. However, the invention is not limited in this regard and other materials can be used so long as the barrel-shaped plate 601 can resist penetration by a drill bit 210 or a tip of a chipping hammer (not shown). The barrel-shaped plate 601 can be configured to protect one or unbonded post-tension strands 101. Another advantage of this configuration is that the barrel-shaped plate 601 can slidably adjust depending on the region that is to be protected.

Referring now to FIG. 8, shown is a perspective view of an embodiment of an unbonded post-tension strand protector 800 located on selected portions of the unbonded post-tension strands 101. The unbonded post-tension strand protector 800 is designed to protect the adjacent unbonded post-tension strand 101 generally underlying the region 100 (FIG. 1.) The unbonded post-tension strand plate 802. The first U-shaped plate 801 is identical in shape as compared to the U-shaped plate 201, described earlier. Structurally, the first U-shaped plate 801 comprises a first planar portion 803, a second planar portion (shown in FIG. 9 as 804) that is spaced apart from and parallel to the first planar portion 803, a first arcuate portion 805 that is connected to the first and second planar portions 803, 804, and a first open side portion 806 located opposite the first arcuate portion 805.

The second U-shaped plate 802 is identically shaped as the first U-shaped plate 801, yet different in size. The second U-shaped plate 802 is comprised of a third planar portion 807, a fourth planar portion 808 that is spaced apart from and parallel to the third planar portion 807, a second arcuate portion 809 that is connected to the third and fourth planar portions 807, 808, and a second open side portion 809 located opposite the second arcuate portion 809. The principal difference between the first and second U-shaped plates is that the second arcuate portion 809 is larger than the first arcuate portion 805. As a result, the distance separating the third and fourth planar portions 807, 808 is larger than the distance separating the first and second planar portions 803, 804. This allows the second U-shaped plate 802 to fit over the first U-shaped plate 801.

Referring now to FIG. 9, shown is a cross-section of the unbonded post-tension strand protector 800 taken along the line 9-9 of FIG. 8 that is useful for understanding the invention. First distal ends 902 of the first U-shaped plate 801 are each formed with a first undulation 903. The first undulations 903 are intended to securely fasten the first U-shaped plate 801 over the selected region 100 (shown in FIG. 1) of the unbonded post-tension strand 101. Each first undulation 903 is curved away from the other such that each of their respective first convex portions 904 are spaced from and facing each other. The closest distance between first convex portions 904 is less than the diameter of the unbonded post-tension strand 101.

In addition, second distal ends 905 of the second U-shaped plate 802 are each formed with a second undulation 906. Each second undulation 906 is curved away from the other such that each of their respective second convex portions 907 are spaced from and facing each other. Since the second undulations 906 are intended to securely fasten the second U-shaped plate 802 to the first U-shaped plate 801, the closest distance between second convex portions 907 is less than the closest distance between first and second planar portions 803, 804.

The first U-shaped plate 801 is sized and shaped to be clipped to one or more unbonded post-tensions strands 101. A second U-shaped plate 802 is sized and shaped to be clipped over the first U-shaped plate 801. In this regard, the word “clipped” means that the first U-shaped plate 801, which is already secured to a portion of the unbonded post-tension strand 101, is in turn inserted through the second open side portion of the second U-shaped plate 802. The first and second U-shaped plates 801, 802 are clipped to one another such that they are arranged in opposite orientations relative to each other. The first U-shaped plate 801 is secured within the second U-shaped plate 802. The first U-shaped plate 801, when clipped, would be bounded by the third planar portion, the fourth planar portion, the second arcuate portion, and the second convex portions. In effect, the portion of the unbonded post-tension strand 101 secured by the unbonded post-tension strand protector 800 would now be protected on all sides from any drilling or chipping that would otherwise damage the unbonded post-tension strand discussed in embodiment 200 of the unbonded post-tension strand protector, shown in FIGS. 2 and 3.

According to a preferred embodiment, the first and second U-shaped plates 801, 802 are formed of a hard material, such as steel. However, the invention is not limited in this regard and other materials can be used so long as the first U-shaped plate 801 and the second U-shaped plate 802 can resist penetration by a drill bit 210 or a tip of a chipping hammer (not shown).

Referring now to FIG. 10, shown is a process flow diagram illustrating a method for protecting at least one unbonded post-tension strand in a pre-cast concrete body using the apparatus illustrated in FIGS. 2-9. Method 1000 begins with step 1002 and continues with step 1004. In step 1004, at least one unbonded post-tension strand is selected. After selecting the unbonded post-tension strand, method 1000 continues with step 1006 where at least one unbonded post-tension strand is positioned in a pre-cast concrete body before the concrete is cast in the concrete body. In step 1008, selected portion(s) of at least one unbonded post-tension strand to be protected is/are identified. In step 1010, the selected portion(s) of one or more unbonded post-tension strands is/are protected by placing at least a portion of a protective layer adjacent to the selected portions. The method ends with step 1012.

All of the apparatus and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the invention has been described in terms of preferred embodiments, it will be appreciated by those skilled in the art that variations may be applied to the apparatus, methods and sequence of steps of the method without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain components may be added to, combined with, or substituted for the components described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined. Accordingly, the particular arrangements disclosed are meant to be illustrative only an not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.