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FIELD OF THE INVENTION 
       [0001]    This invention relates to a method of manufacturing structural elements. 
       BACKGROUND OF THE INVENTION 
       [0002]    The superior structural properties of fibre reinforced polymer composites are well recognised. However, to date there have been difficulties with producing viable structural elements of fibre reinforced polymer composites due to cost constraints. 
         [0003]    A popular approach to producing structural elements using fibre reinforced polymers has been through the use of the pultrusion process. However, the dies and machines needed to produce large structural elements with this method are very expensive. Further, many of the structures being produced require “one-off” construction and therefore are not economically produced using the pultrusion process. 
         [0004]    It is well known from basic engineering mechanics that in most structural members under load there are areas in the member that are subjected to much higher internal stresses than other areas in the same member. For example in a beam loaded in uniform bending the material near the top and bottom of the beam are subjected to significantly higher bending stresses than material near the centre of the beam. Hence locating large amounts of expensive fibre composite material near the centre of such a beam is generally uneconomical. However, there is limited flexibility in the pultrusion process to incorporate other materials or to vary the orientation of the fibres. 
         [0005]    In order to incorporate other materials and to optimize the fibre orientation in large structural elements many of them are made using alternative production methods such as hand-lay up or resin infusion methods. However, these methods require large moulds which are generally specific to a particular type of structural member. Hence, if another structural element needs to be produced, another mould is required reducing cost effectiveness. Furthermore, the labour involved in these alternative manufacturing methods is quite significant leading to expensive products. 
       OBJECT OF THE INVENTION 
       [0006]    It is an object of the invention to overcome and/or alleviate one or more of the above disadvantages or provide the consumer with a useful or commercial choice. 
       SUMMARY OF THE INVENTION 
       [0007]    In one form, the invention resides in a structural member comprising:
       a least one syntactic foam sandwich panel; the sandwich panel having a syntactic foam core and at least one skin; and   at least one reinforcement element attached to the sandwich panel.       
 
         [0010]    The syntactic foam core may include microspheres made from polymeric materials such epoxy resin, unsaturated polyester resin, silicone resin, phenolics, polyvinyl alcohol, polyvinyl chloride, polypropylene, and polystyrene or from inorganic materials such as glass, silica-alumina ceramics or Cenospheres (hollow fly ash particles) 
         [0011]    The skins of the syntactic foam sandwich panels may be made from fibre reinforced polymers. The fibres may be made from glass, carbon, Kevlar, thermoplastics or combinations thereof. The polymer may be made of polyester, vinylester, epoxy, polyurethane, thermoplastics or combination thereof. Preferably the polymer used in the skins is the same as that used in the syntactic foam. More preferably the syntactic foam sandwich panel is produced in single manufacturing process, in this way a strong primary bond can be created between the skins and the syntactic foam core. 
         [0012]    The reinforcement elements may be made from steel, concrete, timber, fibre reinforced polymers or any other material. An adhesive is typically used to adhere the syntactic foam sandwich panels to the reinforcement elements. 
         [0013]    If the reinforcement elements are made from fibre reinforced polymers, then the fibres may be made from glass, carbon, Kevlar, thermoplastic or combinations thereof and the polymer may be made of polyester, vinylester, epoxy, polyurethane, thermoplastic resins or combinations thereof. 
         [0014]    One or more tie elements may span across the adhesive in order to avoid delamination of the adhesive and provide the assembly with robustness. The tie elements may be made from steel, concrete, timber, fibre reinforced polymers or any other material. The tie elements might also act as a reinforcement element. 
         [0015]    The structural elements may include bulkheads, diaphragms, strong points and/or internal ties. 
         [0016]    In one form, though not the only or broadest form, the invention resides in a method of producing an improved structural element, said method including the steps of:
       obtaining at least one syntactic foam sandwich panel;   obtaining at least one reinforcement element; and   joining the at least one syntactic foam sandwich panel and reinforcement element to form the improved structural element.       
 
         [0020]    The structural elements produced using this method may be used in conjunction with each other to produce improved structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    Embodiments of the invention will be described with reference to the accompanying drawings in which: 
           [0022]      FIG. 1A  is a side view of a syntactic foam sandwich panel; 
           [0023]      FIG. 1B  is a transverse cross sectional view of the sandwich panel according to  FIG. 1A ; 
           [0024]      FIG. 2  is a transverse cross sectional view of a structural element according to a first embodiment of the invention; 
           [0025]      FIG. 3  is a transverse cross sectional view of a structural element according to a second embodiment of the invention; 
           [0026]      FIG. 4  is a transverse cross sectional view of a structural element according to a fourth embodiment of the invention; 
           [0027]      FIG. 5  is a transverse cross sectional view of a structural element according to a fourth embodiment of the invention; 
           [0028]      FIG. 6  is a transverse cross sectional view of a structural element according to a fifth embodiment of the invention; 
           [0029]      FIG. 7  is a transverse cross sectional view of a structural element according to a sixth embodiment of the invention; 
           [0030]      FIG. 8  is a transverse cross sectional view of a structural element according to a seventh embodiment of the invention; 
           [0031]      FIG. 9  is a transverse cross sectional view of a structural element according to an eighth embodiment of the invention; 
           [0032]      FIG. 10  is a transverse cross sectional view of a structural element according to a ninth embodiment of the invention; 
           [0033]      FIG. 11  is a transverse cross sectional view of a structural element according to a tenth embodiment of the invention; 
           [0034]      FIG. 12  is a side view of a reinforcement system that incorporates a number of bulkheads; 
           [0035]      FIG. 13  shows a perspective view of a structural element according to an eleventh embodiment of the invention; 
           [0036]      FIG. 14  shows a transverse cross sectional view of a structural element according to a twelfth embodiment of the invention; 
           [0037]      FIG. 15A  shows a perspective of a pedestrian bridge which has been produced by combining structural elements according to the invention; 
           [0038]      FIG. 15B  shows an end view of the same pedestrian bridge. 
           [0039]      FIG. 16  shows a transverse cross sectional view of a road bridge which has been produced by combining structural elements according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0040]      FIG. 1A  and  FIG. 1B  shows a sandwich panel  10  used to produce structural elements as shown in  FIGS. 2 to 16 . The sandwich panel has a syntactic foam core  11  and two fibre reinforced polymer skins  12 . The syntactic foam core in this embodiment is made from epoxy resin with Cenospheres and expanded polystyrene bead fillers. It should be appreciated that the materials used to produce the syntactic foam core may be varied to specified need of a structural element. The reinforced polymer skins are made from glass fibre and epoxy resin. It should be appreciated that the syntactic fibre reinforced polymer skins may be also made from other materials depending on the structural requirements of a structural member. 
         [0041]      FIG. 2  shows a cross section of structural member  20  that consists of a syntactic foam panel  10  having two reinforcing elements in the form of two steel reinforcement strips  21 . The two steel reinforcement strips  21  are substantially rectangular in transverse cross section. 
         [0042]    In order to produce the structural member  20 , two grooves are cut in the syntactic foam core  11  of the syntactic panel  10 . Adhesive is then placed on the two steel reinforcement strips  21  and the two steel reinforcement strips  21  are located within the grooves to contact the syntactic foam core. The two steel reinforcement strips  21  increase the strength and stiffness. 
         [0043]      FIG. 3  shows a cross section of a beam  30  having a syntactic foam panel  10  and two reinforcing elements in the form of two fibre reinforced polymer reinforcement strips  31 . The two fibre reinforced polymer reinforcement strips  31  have fibres that are made from carbon and the polymer is epoxy resin. 
         [0044]    The beam shown in  FIG. 3  is produced by applying adhesive on the two fibre reinforced polymer reinforcement strips  31 . The two fibre reinforced polymer reinforcement strips  31  are the placed on respective ends of the sandwich panel to complete the beam  30 . The beam has improved strength and stiffness. 
         [0045]      FIG. 4  shows a cross section of a beam  40  including a sandwich panel  10  and two reinforcement elements in the form of two fibre reinforced polymer U-shape sections  41 . The two fibre reinforced polymer U-shape sections  41  are made from pultruded polyester-glass fibre composites that are relatively inexpensive to manufacture. 
         [0046]    The beam  40  is manufactured by applying adhesive to the two fibre reinforced polymer U-shape sections  41  and placing the two fibre reinforced polymer U-shape sections  41  over respective ends of the sandwich panel. Due to the shape of the fibre reinforced polymer U-shape sections  41 , the contact area between the reinforcement modules and the syntactic foam panel  10  is significantly increased compared to the fibre reinforced polymer reinforcement strips  31  in  FIG. 3 . This results in significantly increased resistance against delamination of the two fibre reinforced polymer U-shape sections  41  from the sandwich panel  10 . Further, the two fibre reinforced polymer U-shape sections  41  also contact two fibre reinforced polymer skins  12 . The strength of the bond between the fibre reinforced skins  12  and fibre reinforced polymer U-shape sections  41  is high compared to the bond formed between the syntactic foam core  11  and the fibre reinforced polymer U-shape sections  41 . This also assists in reducing the risk of delamination of the syntactic foam sandwich panel  10  U-shape sections  41  from the sandwich panel  10 . 
         [0047]      FIG. 5  shows a beam  50  that is a variation of beam of  FIG. 4 . In this embodiment filler elements  51  in the form of epoxy resin and Cenospheres are located between the two fibre reinforced polymer U-shape sections  41  adjacent the two fibre reinforced polymer skins  12 . 
         [0048]      FIG. 6  shows a beam  60  that is a variation of the beam  50  that is shown in  FIG. 5 . The beam  60  replaced the single syntactic foam sandwich beam  10  with two half-width syntactic foam sandwich panels  15 . 
         [0049]      FIG. 7  shows a beam  70  produced using a syntactic foam sandwich panel  10 , a top reinforcement element in the form of a polymer concrete flange  71  and a bottom reinforcement panel in the form of a pultruded polyester-glass fibre composite U-shape section  72 . Adhesive is again used to adhere the polymer concrete flange and the pultruded polyester-glass fibre composite U-shape section  72  to the syntactic foam sandwich panel  10 . 
         [0050]      FIG. 8  shows a transverse cross section of a hollow beam  80  that is formed from four syntactic foam panels  10  and two reinforcement elements in the form of two pultruded fibre reinforced polymer square sections  81 . 
         [0051]    To produce the hollow beam  80 , the four syntactic foam panels  10  are adhered to the two pultruded fibre reinforced polymer square sections  81 . The two pultruded fibre reinforced polymer square sections  81 . The square reinforcement elements have large planar surfaces which bond strongly to the two fibre reinforced polymer skins  12 . The structural member of  FIG. 8  can be provided with additional bulkheads in the space between the two reinforcement elements as shown in  FIG. 12 . The vertical elements  82  in  FIG. 12  can be made of sections of syntactic foam panels  10  or the sections of the pultruded fibre reinforced polymer square sections  81 . 
         [0052]      FIG. 9  shows a transverse cross section of a hollow beam  90  made from four syntactic foam sandwich panels  10  and reinforcement elements in the form of four angle sections  91 . The angle sections  91  are made of steel. The hollow beam is formed by adhering the four syntactic foam sandwich panels together and adhering the four angle sections in respective corners. The angle sections provide the hollow beam with reinforced corners. The hollow beam may be provided with bulkheads as shown in  FIG. 12 . 
         [0053]      FIG. 10  shows a larger hollow beam  100  that consists of three syntactic foam panels  10  and two different types of reinforcement elements. The first reinforcement element is in the form of two fibre reinforced polymer U-shape sections  101  whilst the second-reinforcement element is in the form of four pultruded fibre reinforced polymer square sections  102 . The two fibre reinforced polymer U-shape sections  101  are made of glass fibre reinforced phenolic resin whilst the four pultruded fibre reinforced polymer square sections  102  are made of carbon fibre reinforced vinyl ester resin. 
         [0054]    The hollow beam  100  is manufactured by using adhering the four pultruded fibre reinforced polymer square sections  102  and the syntactic foam panels  10  are together using an epoxy adhesive. The fibre reinforced polymer U-shape sections  101  are then adhered to the syntactic foam panels  10  using the phenolic resin. The space between the reinforcement modules  92  can be provided with bulkheads as shown in  FIG. 12  as is required. 
         [0055]      FIG. 11  shows a hollow beam  110  that is a variation of beam  100  shown in  FIG. 10 . The hollow beam  110  has a top first reinforcement member in the form of a polymer concrete member  111  that replaces the top fibre reinforced polymer U-shape sections  101 . The polymer concrete member  111  combines good compression capacity with excellent durability. 
         [0056]      FIG. 13  shows a solid beam  120  having a syntactic foam sandwich panel  10  and a reinforcement element in the form of a layer of polymer concrete  121 . The polymer concrete layer  121  provides the sandwich panel with improved wear resistance and compression capacity. 
         [0057]      FIG. 14  shows a solid beam  130  consisting of two syntactic foam sandwich panels  10  and a reinforcement element in the form of a layer of standard concrete  131 . 
         [0058]    The solid beam  130  is formed by adhering the two syntactic foam sandwich panels  10  together using an epoxy adhesive. The top of the double syntactic foam sandwich panel is provided with an aggregate interface  132 . The aggregate interface  133  is made of aggregate having an average size of 10 mm and is adhered to a top fibre reinforced polymer skin  12  of the syntactic foam sandwich panel  10  with epoxy adhesive. The layer of standard concrete  131  is then laid directly onto the aggregate interface. The concrete layer is approximately 150 mm thick. During the casting of the standard concrete, the syntactic foam panels act as formwork and support the wet concrete. Once the concrete has cured the syntactic foam sandwich panels act as external fibre composite reinforcement for the concrete. This aggregate interface  133  provides an excellent bonding surface for the layer of polymer concrete  132  to prevent delamination of the layer of standard concrete  132  from the top of the syntactic foam sandwich panel  10 . 
         [0059]      FIG. 15A  and  FIG. 15B  show an example of a pedestrian bridge consisting of structural elements produced using the current method, which have been used in conjunction with each other to produce improved structures. The bridge has multiple deck planks  135  which are made of the structural element shown in  FIG. 13 . The longitudinal bridge beams  140  are made of the structural element shown in  FIG. 10 . The posts  150  are made from the structural element shown in  FIG. 9 . The rails of the hand rails  160  are made from the structural element shown in  FIG. 6 . 
         [0060]      FIG. 16  shows an example of a road bridge consisting of structural elements produced using the current method, which have been used in conjunction with each other to produce improved structures. The bridge beams  170  are made using the principles of the structural element shown in  FIG. 11 . The concrete deck  180  is reinforced using the principle of the structural element shown in  FIG. 14 . The bottom flange of the bridge beams are tied together using a syntactic foam sandwich panel  190  which is adhered to the beams. 
         [0061]      FIG. 17  shows another embodiment of a road bridge  200  that consists of five syntactic foam panel beams  210  interlinked by a syntactic foam sandwich panel deck  220 . The five syntactic foam panel beams  210  are adhered to the syntactic foam sandwich panel deck  220 . Each syntactic foam panel beam  210  includes six syntactic foam panels  211  with adhered reinforcement in the form of nineteen pultruded fibre reinforced polymer square sections  212 . Each of the reinforcement sections are made of glass fibre reinforced epoxy resin. Most of the pultruded fibre reinforced polymer square sections  212 A are filed with polymer concrete. Some of the pultruded fibre reinforced polymer square sections  212 B are filled with a steel reinforcement bar and polymer concrete. The syntactic foam sandwich panel deck  220  is made from six syntactic foam panels  221  adhered together. 
         [0062]    The properties of these structural elements such as stiffness, strength and mass can be tailored to specific applications by selection of the materials and dimensions of the syntactic foam sandwich panels and reinforcement elements. 
         [0063]    It should be appreciated that various other changes and modifications may be made to the embodiments described without departing from the spirit or scope of the invention.

Summary:
A structural member comprising at least one syntactic foam sandwich panel; the sandwich panel having a syntactic foam core and at least one skin; and at least one reinforcement element attached to the sandwich panel.