Abstract:
A structural tie  10  is made from at least one layer of composite material  20.  The composite material has a polymer matrix filled with at least one reinforcing material. In one embodiment, the matrix is a thermoplastic and the reinforcing material is fibers encapsulated by the thermoplastic. A structural tie  10  may be selectively formable, in situ, by applying heat to cause the matrix material to soften. Once softened, the structural tie can be conformed to an adjacent surface. The structural tie may include layers  20, 22  of composite material bonded to one another. Optionally, the structural tie is a hybrid of a composite material and a metallic material bonded together. A structural tie may be heat-bondable to a structural member  24.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. provisional application No. 60/898,194, filed Jan. 29, 2007, which is hereby incorporated herein by reference, in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention generally relates to structural ties useful in the construction industry, and more particularly to structural ties useful in joining together and/or supporting structural members such as joists, posts, rafters, and the like. 
       BACKGROUND 
       [0003]    Pre-formed structural ties are widely used in the construction industry to help support and secure structural members together. For example, in the construction of wood-framed buildings, a type of structural tie known as a joist hanger is used to facilitate the placement and mounting of floor or ceiling joists. Generally, these structural ties are made from galvanized metal and are shaped to support the structural members in predetermined orientations. 
         [0004]    Often, the above described structural ties are used and exposed to harsh environments. For example, joist hangers are typically employed to support the joists on outdoor decks. These joist hangers are directly exposed to the prevailing weather conditions of the particular locale in which the deck is situated. This can be particularly detrimental if the locale is a shoreline area where the deck and thereby the joists are exposed to salt-air, salt-vapor or salt spray. In such an area, not only are the joist hangers used on outdoor exposed structural members at risk, structural ties used anywhere on a structure can be exposed to some level of salt air and the corrosive effects attendant therewith. It has been found in areas where exposure to salt water either directly or via vapor, air or spray occurs, galvanized metallic structural ties can be rendered completely ineffective due to the resulting corrosion. 
         [0005]    Another difficulty associated with structural ties is due to the fact that the metal from which the ties are made is homogeneous and exhibits essentially the same mechanical properties throughout the entirety of the tie. While it may be possible to vary the thickness and thereby the mechanical properties within a given tie, the manufacturing costs for such a structural tie would become prohibitive. Accordingly, where a situation warrants that a structural tie exhibit strength in one load direction and ductility in other directions, conventional structural ties cannot address this need. 
         [0006]    In addition to the foregoing, prior art structural ties are available in various different configurations and are selected for use according to the planned orientation between structural members and the type of structural member involved. However, on building sites, the actual orientation needed between particular structural members often differs from what is planned. For example, the structural members may not have the expected configuration for which the structural tie is designed. In particular, a pre-formed structural tie for wooden 2×4s that is suitable in theory may not be suitable on site if the actual 2×4 is warped but is otherwise acceptable for use. A user may attempt to use the structural tie nonetheless, either by attempting to re-shape the tie on-site (e.g., by physically re-bending it), by making ad-hoc variations from the planned structural configuration, or simply by forcing the structural tie to fit the needed orientation. All of these solutions are problematic. Re-bending a structural tie that is not designed to be re-bent, particularly a metal tie, is difficult to do with precision and also weakens the tie, and varying the planned design of a structure can weaken the structure and lead to other construction problems. Forcing the structural tie creates stresses in the tie that can lead to premature failure. 
         [0007]    Yet another problem sometimes encountered with galvanized metal ties occurs as a result of the structural tie being bent or struck with a hammer or other implement during installation. When this happens, the galvanized coating can be cracked or chipped off exposing the underlying metal to the environment. The exposed metal will corrode much more quickly than the galvanized metal resulting in premature failure of the structural tie 
         [0008]    Based on the foregoing, it is the general object of the present invention to improve upon or overcome the problems and drawbacks associated with the prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention resides in one aspect in a structural tie that comprises at least one layer of composite material. The composite material has a polymer matrix filled with at least one reinforcing material. 
         [0010]    In the preferred embodiment of the present invention the polymeric matrix is a thermoplastic and the reinforcing material is in the form of a plurality of fibers encapsulated by the thermoplastic polymeric matrix. The fibers can be formed from virtually any fibrous reinforcing material known to those skilled in manufacturing composite materials, such as, but not limited to boron, carbon, Kevlar, E-Glass and S-Glass. The fibers can be continuous or chopped or a combination of continuous and chopped fibers. In addition, the fibers can be oriented, e.g. parallel to one another, or the fibers can be randomly oriented. The structural tie can also include a combination of parallel and randomly oriented fibers depending on the desired mechanical properties of the structural ties. While the polymeric matrix has been described as being formed from a thermoplastic material, the present invention is not limited in this regard as a thermosetting material can also be employed. 
         [0011]    In another aspect, the present invention is directed to a structural tie that is selectively formable, in situ, by selectively applying heat to the structural tie thereby causing the matrix material to soften. Once softened, the structural tie can be moved to conform to a shape defined by an adjacent surface upon cooling of said structural tie. 
         [0012]    In an embodiment of the present invention, the structural tie includes a plurality of layers of composite material bonded to one another. Each layer of composite material will include the polymeric matrix as well as the reinforcing material. In a preferred embodiment of the present invention, the reinforcing material in each of the layers is in the form of a plurality of elongated continuous fibers arranged in a substantially parallel relationship relative to one another. The laminated composite material can be arranged so that the fibers in successive layers are oriented parallel or at an angle relative to one another. 
         [0013]    In still another embodiment of the present invention, the composite material includes at least one first composite material having a first polymeric matrix material and a first reinforcing material and at least one second layer of composite material having a second polymeric matrix material and a second reinforcing material. At least a portion of the first and second layers of composite material are bonded to one another. Preferably, the first and second layers of composite material are different from one another. This difference can manifest itself in the first and second matrix materials being different. For example, one matrix material can be a thermoplastic and the other matrix material can be a thermosetting polymer. The first and second materials can also both be thermoplastic or thermosetting polymers with the polymers themselves being different. Similarly, the first and second reinforcing materials may be different materials, such as but not limited to E and S glass. In addition, the reinforcing materials may be chopped, continuous or combinations thereof. 
         [0014]    The present invention also resides in a structural tie that is heat bondable to a structural member. In such an embodiment the polymeric matrix is of such a type that can be heat bonded to the material forming the structural member. Alternatively, a layer of heat bondable polymer can be provided on the structural tie in an area of the tie that will abut the structural member. 
         [0015]    In another embodiment of the present invention, the structural tie is a hybrid consisting of a composite material and at least one layer of metallic material bonded to said composite material. The metallic layer of material can be made from any suitable material, such as, but not limited to steel, aluminum, stainless steel, metal matrix, composites, sintered metals and the like. The metallic layer can be encapsulated in a polymer which can then be bonded to the structural tie. The metallic layer can also be encapsulated by an elastomer or a composite material that is the same as, or different from a composite material used to form the remainder of the structural tie. The layer of metallic material can be embedded in the structural tie, or the metallic layer can be positioned adjacent to, or form an interior or outer layer of the structural tie. 
         [0016]    The metallic layers can be formed to follow the contours of the entire structural tie, or the metallic layer can be formed and sized so that it is selectively positionable in areas where the mechanical properties of the metallic layer will be beneficial to the overall integrity of the structural tie. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an exemplary structural tie of the present invention, shown in the illustrated embodiment as a joist hanger. 
           [0018]      FIG. 2  is a perspective view of the structural tie of  FIG. 1  shown attached to a structural member. 
           [0019]      FIG. 3  is a perspective view of the structural tie of  FIG. 1  attached to a structural member. 
           [0020]      FIG. 4  is a partial cross-sectional view of an embodiment of the material from which the structural ties of the present invention are made. 
           [0021]      FIG. 5  is a partial cross-sectional view of an embodiment of a structural tie showing the material configuration of the structural tie. 
           [0022]      FIG. 6  is a partial cross-sectional view of an embodiment of a structural tie showing the material configuration of the structural tie. 
           [0023]      FIG. 7  is a partial cross-sectional view of an embodiment of a structural tie showing the material configuration of the structural tie. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    As shown in  FIG. 1  a structural tie in the form of a joist hanger is generally designated by the reference number  10 . As used herein, the term “Structural Tie” should be broadly construed to mean components employed to aid in the positioning and retention of at least one structural member relative to an adjacent structural member or surface. The structural tie  10  is comprised of at least one layer of composite material. The composite material includes a polymeric matrix filled with at least one reinforcing material. The joist hanger  10  is symmetric about the longitudinally extending centerline  12  and includes an interior area  14  defined by generally opposite side walls  16  and bottom surface  18 . While a joist hanger  10  has been shown and described, the present invention is not limited in this regard as other structural ties known to those skilled in the pertinent art to which the present invention pertains are also considered to form part of the present invention. A representative sampling of the type and shape of structural ties encompassed by the present invention are manufactured by Simpson Strong-Tie of 5956 W. Las Positas Blvd. Pleasanton, Calif. 94588. 
         [0025]    In an embodiment of the present invention the polymeric matrix material is a thermoplastic, such as, but not limited to polypropylene, polyethylene, nylon, PEI and copolymers and the like. Because, the structural tie  10  can potentially be exposed to extremes in temperature depending on where it is used, the softening temperature of the thermoplastic matrix should in general be greater than any environmentally induced temperature to which the structural tie may be exposed in service. For example, the thermoplastic may be selected to have a softening temperature greater than about 50 to about 65° C. (about 120 to about 150° F.). Conversely, where the structural tie will be exposed to cold temperatures it may be necessary to employ a thermoplastic matrix material having a glass transition temperature, e.g. the temperature where the thermoplastic becomes brittle, that is lower than the exposure temperature. Accordingly, it may prove necessary to use structural ties formed of different thermoplastics depending on the environment where the structural tie will be used. While a thermoplastic has been shown and described, the present invention is not limited in this regard as other polymeric materials such as, elastomers or thermosetting polymers can be employed without departing from the broader aspects of the present invention 
         [0026]    The reinforcing material forming part of the above-described composite material used in the structural tie  10  of the present invention can be in particulate, flake or fiber form. If in fiber form, the fibers can be chopped or continuous and can also be aligned or randomly oriented relative to one another. Fibers found to be useful as reinforcing materials include, but are not limited to, E-glass, S-glass, aramid fibers such as, inter alia, those marketed under the tradenames Kevlar, Twaron and Technora, fibers made from basalt, glass (ECR, A and C), ultra-high molecular weight polyethylene, carbon (such as, but not limited to, fiber marketed under the names Toray, Fortafil, and Zoltek), boron, silica carbide, liquid chrystal polymer (such as, but not limited to, Vectran, metallic fibers, etc. The choice of the material to use as a reinforcing material will depend on several factors including the desired mechanical properties of the structural tie, and the cost of manufacturing the structural tie. 
         [0027]    In a preferred embodiment of the present invention, the composite material includes fibers embedded in a polymeric matrix (either thermoplastic or thermoset) that are continuous and aligned relative to one another. The composite material of the present invention can consist of a single layer of material, or it can comprise multiple layers stacked one-on-top-of-the-other and bonded together to form a laminate. The layers of the laminate can be bonded to one another via an adhesive, or the polymeric matrix material can function as the adhesive so that via the application of pressure and/or heat the layers are bonded to one another. 
         [0028]    Where a laminated structure incorporating continuous aligned fibers is employed, the individual layers of composite material can be positioned relative to one another so that the fibers of one layer are oriented at an angle relative to the fibers of adjacent layers. The number of layers of composite material and the fiber angles are all dependant upon the configuration of the structural tie and the desired mechanical properties. For example, it may be necessary for a structural tie to have strength and rigidity with respect to forces applied in one direction and flexibility with respect to forces applied in another direction. 
         [0029]    The present invention also contemplates the use of more than one type of fiber in the same structural tie. For example, two or more fiber materials can be employed. Where the composite material is a laminate, the different types of fiber can be present in individual layers, or different layers can employ different fibers. The phrase “more than one type of fiber” is also to be construed herein to mean that the fiber configuration can be different. For example, chopped and continuous fibers may be used in the same composite material. Moreover, randomly oriented and aligned fibers may be used in the same composite material. 
         [0030]    As shown in  FIG. 4 , the composite material of the present invention can also include laminated materials having different polymeric matrices for different layers  20  and  22 . The reinforcing material, as described above, can be the same from layer to layer, or different. The layers of composite material  20  and  22  each employ a different thermoplastic or thermosetting material as the polymeric matrix. In addition, one of the layers of composite material  20  and  22  can employ a thermoplastic polymeric matrix material while the other of the layers  20  and  22  employs a thermosetting polymer as the matrix material. 
         [0031]    Referring to  FIGS. 2 and 3 , in an embodiment of the present invention, the structural tie  10  can be bonded to a structural member  24  by heating a surface of the structural tie to a point where polymeric material on that surface softens to the point where an adhesive bond can be made between the structural tie and the structural member. Where a thermoplastic polymeric matrix is employed, the matrix material may be used to form the adhesive bond. Where a thermosetting polymer is employed to form the polymeric matrix, a layer of heat-meltable polymer that can function as an adhesive between the structural tie and the structural member  24  can be coated onto the thermosetting polymer matrix material. This layer of heat-meltable polymer can be applied at the time the structural tie  10  is made, or subsequent to manufacture but prior to use. 
         [0032]    Where a combination of thermoplastic and thermosetting polymers are employed as the matrix materials in the structural tie  10 , depending on what surface of the structural tie  10  will be heat-bonded to the structural member  24 , a layer of heat-meltable polymer can be applied to the structural tie. If an exposed surface of the thermoplastic matrix material coincides with the surface of the structural member  24  to be heat bonded to the structural tie, the thermoplastic matrix material can be used to operate as the adhesive material. While the heat bondable material has been described as a thermoplastic, the present is not limited in this regard. A thermoplastic elastomer, or an elastomeric material can also be applied to the structural tie  10  for use in heat-bonding the structural tie to the structural member  24 . 
         [0033]    Turning to  FIGS. 5-7 , the structural tie  10  can also include a layer of metallic material to enhance the mechanical properties of the structural tie. The metallic material can be made from any suitable material, such as, but not limited to steel, stainless steel, aluminum, copper, nickel, alloys and metal matrix composites. As shown in  FIG. 5 , the layer of metallic material  26  can be positioned adjacent the composite material  28  on the structural tie  10  so that an outwardly facing surface of the metallic layer  26  is exposed. Where the portions of the metallic layer  26  are exposed to the environment in which the structural tie  10  is used, the exposed surface, or the entire metallic layer can be coated with a polymeric material to prevent degradation of the metallic layer due to environmental exposure. In the embodiments shown in  FIGS. 6 and 7 , the layers of composite material  28  can be laminated as described above. In addition, the layers of composite material  28  can be different from one another as described above. 
         [0034]    Referring to  FIG. 6 , the layer of metallic material  26  can be sandwiched between and encapsulated by layers of composite material  28 . In addition, and as shown in  FIG. 7 , the structural tie  10  can also have multiple layers of composite material  28  with the layer of metallic material  26  located on an outer surface of the structural tie. The layer of metallic material  26  can be coated with a layer of polymeric material (not shown) to prevent degradation due to exposure to the environment. 
         [0035]    Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements and steps thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the above description.