US20040018351A1

US20040018351A1 - Device for reinforcing a structure and a method for making thereof

Info

Publication number: US20040018351A1
Application number: US10/208,273
Authority: US
Inventors: Petru Petrina
Original assignee: Cornell Research Foundation Inc
Current assignee: Cornell Research Foundation Inc
Priority date: 2002-07-29
Filing date: 2002-07-29
Publication date: 2004-01-29

Abstract

Rebar for reinforcing a concrete includes a core, a rib layer, and a cover layer. The rib layer is placed over at least a portion of the core and the cover layer is placed over at least a portion of the rib layer. A method for making the rebar for reinforcing a concrete includes providing a core, placing a rib layer over at least a portion of the core, and placing a cover layer over at least a portion of the rib layer.

Description

FIELD OF THE INVENTION

This invention relates generally to reinforcing devices and methods for making the devices and, more particularly, to a bar for reinforcing a structure, such as hardened concrete, and a method for making the bar.

BACKGROUND OF THE INVENTION

Typically, fiber reinforced polymer (“FRP”) bars are made of continuous fibers which are embedded in polymeric matrix. The FRP bars are used to reinforce structures, such as hardened concrete.

Unfortunately, there are some major problems with these prior FRP bars. One problem is that these bars do not adequately bond to concrete. Another problem with these bars is that they are susceptible to sudden brittle fracture. This problem of avoiding sudden brittle fracture has not been efficiently resolved by currently available rebars.

SUMMARY OF THE INVENTION

A device for reinforcing a structure in accordance with embodiments of the present invention includes a core, a rib layer, and a cover layer. The rib layer is placed over at least a portion of the core and the cover layer is placed over at least a portion of the rib layer.

A method for making a device for reinforcing a structure in accordance with embodiments of the present invention includes providing a core, placing a rib layer over at least a portion of the core, and placing a cover layer over at least a portion of the rib layer.

Rebar for reinforcing a structure, such as concrete, in accordance with embodiments of the present invention includes a number os strands or rods packed together in a circular configuration. The strands or rods are made of fiber reinforce polymer and the diameter and shape of the strands or rods can be adjusted to permit better packing configurations. The strands or rods could have different tensile modulus of elasticity to provide a bar which will fail sequentially while subjected to tension.

The present invention provides a device for reinforcing a material, such as hardened concrete. The present invention bonds better with materials, than prior reinforcing bars. Additionally, the present invention is less susceptible to sudden brittle fracture than prior reinforcing bars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a reinforcing bar in accordance with one embodiment of the present invention in a structure; [0008]
FIG. 2 is a perspective view of one end of a core of the bar; [0009]
FIG. 3 is a perspective view of a side of the core of the bar; and [0010]
FIG. 4 is a perspective view of the core and a rib layer for the bar.[0011]

DETAILED DESCRIPTION

A [0012] bar 10 for reinforcing a structure 12, such as hardened concrete, in accordance with one embodiment of the present invention is illustrated in FIGS. 1-4. The bar 10 includes a core 16, a rib layer 18, and a cover layer 20. The present invention provides a bar 10 which bonds better with structures, such as hardened concrete, and is less susceptible to sudden brittle fracture than prior reinforcing bars.
Referring to FIGS. 2 and 3, the [0013] core 16 comprises a center strand 16(1) which is surrounded by eight, equally spaced strands 16(2)-16(9), which are surrounded by another eight, equally spaced strands 16(10)-16(17) which are surrounded by another eight, equally spaced strands 16(18)-16(25) to form a 1+8+8+8 hierarchy configuration, although the core 16 could comprise other numbers of strands, such as just one strand or multiple strands, and could be packed in other configurations and with other spacing arrangements. Each of the strands 16(1)-16(25) extends along and is substantially parallel with a first axis AA, although some or all of the strands 16(1)-16(25) could be oriented in other directions, such as in an overlapping pattern. The center strand 16(1) has circular cross-sectional shape and a diameter of about {fraction (1/16)}″ to ⅛′″, strands 16(2)-16(9) have circular cross-sectional shape and each have a diameter of about {fraction (1/32)}″ to {fraction (1/16)}″, strands 16(10)-16(17) have a circular cross-sectional shape and each have a diameter of about {fraction (1/16)}″, and strands 16(18)-16(25) have a circular cross-sectional shape and each have a diameter of about ⅛″, although the diameter of and cross-sectional shape of each of the strands 16(1)-16(25) can vary. The required diameter of the finished bar 10 dictates the number of and the diameter of each of the strands 16(1)-16(25). The strands 16(1)-16(25) are each made of carbon, although some or all of the strands 16(1)-16(25) could be made of other materials, such as glass fiber reinforcing polymers. If the strands 16(1)-16(25) have substantially the same diameter, then the practical packing configuration of the strands 16(1)-16(25) is 1+8+16. If additional strands of substantially the same diameter were added, then packing configuration would continue along in this progression. If one or more of the strands had a different diameter or shape, then other packing configurations would be used.
Referring to FIGS. 1 and 4, the [0014] rib layer 18 comprises a strand 18(1) which is wound in a double helical configuration around the strands of the core 16 at angles of about +45° and −45° with respect to the first axis A-A, although the rib layer 18 can comprise other numbers of strands and can be wound or wrapped around the core 16 in other configurations and at other angles, such as a single helical configuration. The strand 18(1) crisscrosses the strands 16(1)-16(25) of the core 16 to create deformations on the surface of the bar 10. The crisscross configuration of the rib layer 18 provides deformations on the bar 10 which helps the bar 10 bond to the concrete. The strand 18(1) has a circular cross-section, although the strand 18(1) can have other shapes, such as a flat shape to form a tape. The strand 18(1) is an uncured polymer impregnated yarn from a prepreg tow and has a diameter of about {fraction (1/32)} to {fraction (1/16)} inch, although strand 18(1) can be made of other materials and can have other diameters. During the curing process, the rib layer 18 bends to the core 16 at contact points.
Referring to FIG. 1, the [0015] cover layer 20 comprises eight, equally spaced strands 20(1)-20(4) (four of the strands of cover layer 20 are not shown) which are located over and around the rib layer 18 and the core 16 and each of the strands for cover layer 20 extend substantially along the first axis A-A, although the number of strands for cover layer 20, their spacing, and their orientation with respect to the first axis A-A can vary depending on the diameter of the bar. The desired size and shape for the bar 10 dictates the number of, shape and size of the strands used for the cover layer 20. The strands for cover layer 20 are uncured pre-impregnated fiber rods, although the strands for cover layer 20 can be made of other materials, such as glass fiber.
When the [0016] bar 10 is subjected to tension, the cover layer 20, which is bent over the rib layer 18, tends to straighten giving a localized expansion between the rib layer 18 which is wrapped around the bar 10. This lateral expansion is inducing normal stresses on the interface between the bar 10 and the structure in which the bar 10 is being used, such as hardened concrete, which increases the mechanical bond to the structure. The cover layer 20 also protects the rib layer 18 to resist longitudinal stripping when the bar 10 is under tension.
The ductility and the way in which the [0017] bar 10 sequentially fails can be controlled by using strands 16(1)-16(25) and strands for cover layer 20 of different stiffness for the core 16 and the cover layer 20. In this particular embodiment, the core 16 has a stiffness which is twice as much as the stiffness of the cover layer 20, although the stiffness of the core 16 and cover layer 20 can vary, for example, they could be the same. Typically, since the core 16 is stiffer than the cover layer 20, the core 16 is going to fail first followed by the failure of the cover layer 20.
By way of example only, carbon fibers for use as strands [0018] 16(1)-16(25) and strands for cover layer 20 are available with a standard modulus, an intermediate modulus, and a high modulus. As a result, depending on the particular type of carbon fibers selected for each of the strands 16(1)-16(25) for the core 16 and strands for cover layer 20, a different stiffness for the core 16 and cover layer 20 can be obtained. In another example, the modulus of the glass fibers can be altered by twisting the glass fiber. The more a glass fiber is twisted, the lower the modulus of the glass fiber is. This is the same for other types of fibers as well, such as carbon fiber. Accordingly, depending on the amount each of the glass fibers selected for use as strands 16(1)-16(25) and for cover layer 20 is twisted, a different stiffness for the core 16 and cover layer 20 can be obtained. Thus, by modifying the strands 16(1)-16(25) for core 16 and strands for cover layer 20 a desired ductility for the bar 10 can be obtained and also the manner and sequence in which the core 16 and cover layer 20 fail can be controlled. Accordingly, a reinforcing bar can be customized for the particular application or job.
Referring to FIGS. [0019] 1-4, a method for making the bar 10 in accordance with one embodiment will be described, although other methods for making the bar 10 can be used. First, eight strands 16(2)-16(9) are spaced equally around a center strand 16(1), then another eight strands 16(10)-16(17) are spaced equally around to the eight strands 16(2)-16(9), and then another eight strands 16(18)-16(25) are spaced equally around to the eight strands 16(10)-16(17) and these strands will stay put against each other, although devices and/or techniques for holding the strands 16(1)-16(25) together can be used, such as using epoxy to hold some or all of the strands 16(1)-16(25) together. This forms a 1+8+8+8 hierarchy configuration for the core 16, although again the core 16 could comprise other numbers of strands, such as just one strand or multiple strands, and could be packed in other configurations and with other spacing arrangements.
Next, a strand [0020] 18(1) which comprises the rib layer 18 is wound in a double helical configuration around the strands 16(1)-16(25) of the core 16 at angles of about +45° and −45° with respect to the first axis A-A, although the rib layer 18 can comprise other numbers of strands and can be wound or wrapped around the core 16 in other configurations and at other angles, such as a single helical configuration. The rib layer 18 is secured to the strands 16(1)-16(25) of the core 16 by the helical configuration.
Next, eight strands for [0021] cover layer 20 are spaced equally around and are secured to the rib layer 18 and portions of the core 16 and each of the strands for cover layer 20 extends substantially along the first axis A-A, although the number of strands for cover layer 20, their spacing, and their orientation with respect to the first axis A-A can vary. The strands of the cover layer 20 are secured to the rib layer 18 and portions of the core 16 by epoxy, although other devices and/or techniques for securing could be used
The resulting [0022] bar 10 bonds better with structures, such as hardened concrete, and is less susceptible to sudden brittle fracture than prior reinforcing bars. Additionally, as illustrated above the bar 10 is easy to manufacture. As a result, the bar 10 can be constructed at the construction site, eliminating the complications associated with transporting long pre-made bars. Further, because the bar 10 is easier to make and to transport it is less expensive than prior reinforcing bars.
Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefor, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto. [0023]

Claims

What is claimed is:

1. A device for reinforcing a structure, the device comprising:

a core;

a rib layer over at least a portion of the core; and

a cover layer is placed over at least a portion of the rib layer.

2. The device as set forth in claim 1 wherein the core comprises a plurality of core strands which extend substantially along a first axis.

3. The device as set forth in claim 2 wherein one of the core strands is surrounded by the remaining core strands.

4. The device as set forth in claim 1 wherein the rib layer comprises at least one rib strand.

5. The device as set forth in claim 1 wherein the rib layer comprises at least one rib tape.

6. The device as set forth in claim 1 wherein the rib layer is wrapped around the core in a crisscrossed configuration.

7. The device as set forth in claim 6 wherein the rib layer in the crisscrossed configuration intersects itself at an angle of about forty-five degrees with respect to a first axis which is substantially parallel with the core.

8. The device as set forth in claim 1 wherein the cover layer comprises cover strands which surround the at least a portion of the rib layer and extend along in substantially the same direction as the core.

9. The device as set forth in claim 1 wherein the core, the rib layer and the cover layer each has a different modulus of elasticity.

10. The device as set forth in claim 1 wherein at least one of the core, the rib layer, and the cover layer is twisted to provide a different modulus of elasticity.

11. A method for making a device for reinforcing a structure, the method comprising:

providing a core;

placing a rib layer over at least a portion of the core; and

placing a cover layer over at least a portion of the rib layer.

12. The method as set forth in claim 11 wherein providing the core further comprises providing a plurality of core strands which are adjacent each other and extend substantially along a first axis.

13. The method as set forth in claim 12 further comprising surround one of the plurality of core strands with the remaining plurality of core strands.

14. The method as set forth in claim 11 wherein the rib layer comprises at least one rib strand.

15. The method as set forth in claim 11 wherein the rib layer comprises at least one rib tape.

16. The method as set forth in claim 111 wherein placing the rib layer further comprises wrapping the rib layer around the core in a crisscrossed configuration.

17. The method as set forth in claim 16 wherein the rib layer in the crisscrossed configuration intersects itself at an angle of about forty-five degrees with respect to a first axis which is substantially parallel with the core.

18. The method as set forth in claim 11 wherein placing the cover layer further comprises placing cover strands around at least a portion of the rib layer, each of the cover strands extending along in substantially the same direction as the core.

19. The method as set forth in claim 11 wherein the core, the rib layer and the cover layer each has a different modulus.

20. The method as set forth in claim 11 wherein at least one strand of the core, the rib layer, or the cover layer is twisted to provide a different modulus for the core, the rib layer, or the cover layer.