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  
         [0001]    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  
         [0002]    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.  
           [0003]    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  
         [0004]    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.  
           [0005]    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.  
           [0006]    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.  
           [0007]    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  
       [0008]    [0008]FIG. 1 is a perspective view of a reinforcing bar in accordance with one embodiment of the present invention in a structure;  
         [0009]    [0009]FIG. 2 is a perspective view of one end of a core of the bar;  
         [0010]    [0010]FIG. 3 is a perspective view of a side of the core of the bar; and  
         [0011]    [0011]FIG. 4 is a perspective view of the core and a rib layer for the bar. 
     
    
     DETAILED DESCRIPTION  
       [0012]    A 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.  
         [0013]    Referring to FIGS. 2 and 3, the 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.  
         [0014]    Referring to FIGS. 1 and 4, the 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.  
         [0015]    Referring to FIG. 1, the 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.  
         [0016]    When the 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.  
         [0017]    The ductility and the way in which the 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 .  
         [0018]    By way of example only, carbon fibers for use as strands  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.  
         [0019]    Referring to FIGS.  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.  
         [0020]    Next, a strand  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.  
         [0021]    Next, eight strands for 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  
         [0022]    The resulting 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.  
         [0023]    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.