Patent Publication Number: US-9885180-B2

Title: Load transfer device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Nonprovisional patent application Ser. No. 14/291,651 filed on May 30, 2014, the entire disclosure of which is hereby incorporated by reference. Application Ser. No. 14/291,651 is a continuation of U.S. Nonprovisional patent application Ser. No. 13/468,167, filed on May 10, 2012, which issued as U.S. Pat. No. 8,839,580 on Sep. 23, 2014, the entire disclosures of which are hereby incorporated by reference. U.S. Nonprovisional patent application Ser. No. 13/468,167 claims priority from U.S. Provisional Patent Application Ser. No. 61/484,966, filed May 11, 2011, entitled X-SHAPED LOAD TRANSFER DEVICE, the contents of which is hereby incorporated in its entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     This application relates generally to connectors and load transfer devices for interconnecting components, such as pavement or the structural components of a building, including the concrete wythes and insulation of a concrete sandwich wall panel or double wall panel, roof and floor members, balconies, canopies, and other insulated connections. 
     BACKGROUND 
     Sandwich wall panels, also called integrally insulated concrete panels, are well known in the construction industry. Most sandwich panels are composed of interior and exterior concrete layers, called wythes, and one or more insulation layers between the two concrete layers. The insulation layer is generally rigid insulation, such as expanded or extruded polystyrene or polyisocyanurate. Also included in the sandwich wall panel are connectors that connect the two concrete wythes through the layer(s) of insulation. The connectors hold the components of the sandwich wall panel together and also provide a mechanism whereby loads can be transferred between the components of the wall and the structure&#39;s foundation. Common loads include tension, shear, and moments induced by wind, gravity, and seismic loads, as well as combinations thereof. In composite and partially composite sandwich wall panels, connectors must cause the two concrete wythes to function together as one structure. Depending on the application, load transfer devices may be many different shapes and composed of many different materials. One material in particular, metal, has been used in the past, but metal has undesirable thermal connectivity properties and may suffer corrosion in some situations. These problems can also be present in sandwich panels containing metal trusses or reinforcing. Accordingly, there is a need in the art for a shear connector and load transfer device that reduces the need for metal components to be used as connectors and trusses. 
     Alternatively, non-composite insulated concrete sandwich walls allow the components of the sandwich wall to work independently of each other. Generally, there is a structural concrete wythe, an insulation layer, and an architectural, exterior wythe. The independent behavior eliminates problems associated with large temperature differentials between interior and exterior wythes and the thermal bowing that can be present in some structural composite panels. 
     Sandwich wall panels can be manufactured in a variety of ways known in the art. The entire panel may be manufactured in a plant and transported to a job site, a process known as plant precast. The panel may be constructed on the ground at the job-site and then tilted up and into place, a process known as site-cast tilt-up. Sandwich walls may also be vertically cast in place at the job site, commonly known as cast-in-place construction or vertically cast in a precast factory as part of the individual rooms of a building, this method is commonly known as modular precast construction. Accordingly, the panels may be constructed in both a vertical and horizontal manner. 
     Also known in the industry are double wall panels, which can provide weight and structural connection improvements over traditional sandwich panels. In addition to interior and exterior concrete wythes and an insulation layer, a double wall panel also includes an air void, also called an air gap. Oftentimes, the air void is filled with concrete and/or additional insulation materials or another material upon delivery to the job site. Because double wall panels are typically lighter than sandwich panels, double wall panels may cost less to manufacture and ship. Because of these advantages, double wall panels may be manufactured to a larger size prior to shipment. 
     Sandwich and double wall panels may reduce the energy requirements of buildings and are becoming more popular as energy conservation is a growing concern among building owners and is increasingly present in construction codes. Integration of thicker insulation can provide even higher energy savings. Sustainable building construction is also gaining in popularity. Sandwich panels can provide means for sustainable construction by providing structural composite panels, increasing the thickness of the insulation, and reducing wythe thickness. However, sandwich panels with these features require use of either more or stronger connectors. Accordingly, there is a need in the industry for a connector to provide the strength necessary for these applications. 
     Green roofs are known in the industry and are growing in popularity. In this application, the roof slab should be insulated and provide a watertight surface. Oftentimes, these issues are addressed by including a layer of insulation between two concrete layers. Additionally, floor slabs present many of the same issues. The load transfer devices connecting the components of the roof and floor slabs must transfer the necessary loads and be thermally non-conductive so as to prevent condensation on the roof and floor slabs. 
     In addition, the double wall panels discussed above require devices such as standoff connectors to define the thickness of the double wall panel and/or support the weight of one of the concrete wythes during the manufacturing process. Accordingly, there is a need in the industry for a shear connector that can provide these functions in addition to connecting the components of the double wall panel and transferring loads between same. 
     As is known in the art, sandwich wall panels may be constructed either horizontally or vertically. When constructed horizontally, a first concrete layer is poured, and the insulation layer is placed on top of the wet concrete layer. The insulation layer is designed to receive the connectors or ties that will be used to interconnect the components, usually having precut or pro-machined holes. Oftentimes, these holes are much larger than the connectors themselves. This decreases the thermal efficiency of the panel and may require application of another insulation, such as foam insulation, to fill the remaining volume of the hole not taken up by the connector. Moreover, connectors of the prior art are designed to be placed between side-by-side sections of insulation, leaving behind gaps in the insulation layer that must be filled with another insulation. Accordingly, there is a need in the industry for a shear connector that will eliminate the need to fill the space remaining in the insulation after insertion of the connectors. Sandwich panels that are constructed vertically are often constructed using a method known as “cast-in-place”. In this method, the walls are created at their service location. Vertical forms are erected, and the insulation and connectors are placed into the vertical forms. The vertical forms are open at the top. Both layers of concrete are then poured simultaneously from the top of the forms. Alternatively, the concrete may be pumped into the form from one or more openings near the bottom. Accordingly, the concrete surrounds the insulation as in the horizontal methods of manufacture. 
     Connectors of the prior art are connected to internal reinforcing, which makes installation difficult. Accordingly, there is a need in the art for a connector that is a load transfer device that does not require connection to reinforcing or use of trusses in the wall panel and, therefore, provides ease of assembly and installation. In addition, there is a need in the art for a load transfer device that is composed of discrete load transfer members that can be selectively positioned as the application requires. Moreover, there is a need in the art for a load transfer device which provides for simple and cost-effective handling and transport. 
     Accordingly, a load transfer device is provided that is also a shear connector which can be used in all methods of manufacturing concrete sandwich and double wall panels, including vertical, horizontal, and modular methods. The shear connector of the present invention provides increased strength and load transfer properties over the prior art. Additionally, the present connector eliminates the need to provide foam or other insulation to fill voids left in the insulation layer after insertion of the connector. The connector is thermally nonconductive. Further, the connector can reduce or eliminate the need to include trusses that span the insulation layer. The connector can provide a standoff or spacing function during the manufacture of double wall panels. Further, the connector holds the concrete wythes of the panel from shifting during handling and transport. The connector provides for simple and cost-effective handling and transport. The load transfer device of the present application provides superior shear transfer capacity and can be placed easily in rigid insulation material. 
     SUMMARY 
     Provided is a load transfer device connecting at least first and second concrete elements. The first and second concrete elements each have a first surface closest to the other concrete element. Moreover, the device includes two load transfer members each having a first concrete engaging portion and a second concrete engaging portion, with the load transfer members only in contact with the first and second concrete elements at the first and second concrete engaging portions, respectively. The first and second load transfer members further each include a longitudinal axis which are positioned at an angle to the normal of the first surfaces of the first and second concrete elements. The angle may be between twenty and seventy degrees, such as between forty-five and sixty degrees. Furthermore, the first concrete engaging portions are at least partially embedded in the first concrete element in a spaced relationship with one another and the second concrete engaging portions are at least partially embedded in the second concrete element in a spaced relationship with one another. Moreover, the first and second load transfer members transfer all loads independently of each other. In one embodiment, the first and second concrete elements may be separated by a layer of insulation and the longitudinal axes are positioned at an angle to the normal of the planes at which said first and second concrete elements meet the layer of insulation. The first and second concrete elements may be selected from the group consisting of sandwich wall panel wythes, double wall panel wythes, roof members, floor members, balcony members, canopy members, and sections of pavement. 
     Also provided is a sandwich wall panel. The sandwich wall panel may have a first and second concrete layers each having a first surface nearest to the other concrete layer. An insulation layer may be located between the first and second concrete layers. Moreover, the sandwich wall panel may include at least one load transfer device connecting the first concrete layer to the second concrete layer and spanning the insulation layer. The load transfer device may include first and second load transfer members having first and second ends. The load transfer members may further each include a longitudinal axis. The longitudinal axes may be positioned an angle to the normal of the first surfaces of the first and second concrete layers. Moreover, the first ends may be at least partially embedded in the first concrete layer in a spaced relationship with one another and the second ends may be at least partially embedded in the second concrete layer in a spaced relationship with one another. The ends of the first and second load transfer members are not in contact with any other load transfer members in the first and second concrete layers. Moreover, the first and second load transfer members are positioned in a plane that is perpendicular to shear force acting on the first and second concrete elements, with the shear force being coplanar to the first and second concrete layers. The load transfer device may further include a retention housing to retain the first and second load transfer members at the angle to normal 
     In another embodiment of the present invention a load transfer device connecting at least first and second concrete elements is provided. The first and second concrete elements may each have a first surface nearest to the other concrete element. Furthermore, the device includes first and second load transfer members each having first and second ends. The load transfer members may further each include a longitudinal axis, and the longitudinal axes may be positioned at an angle to the normal of the first surfaces of the concrete elements. Moreover, the first ends of the load transfer members may be at least partially embedded in the first concrete element in a spaced relationship with one another, while the second ends may be at least partially embedded in the second concrete element in a spaced relationship with one another. The first and second ends of the load transfer members are not in contact with any other load transfer members in the first and second concrete elements. Moreover, the loads transferred by the first and second load transfer members are not transferred to the other load transfer member. 
     In yet another embodiment, a load transfer device connecting first and second concrete elements is provided. The first and second concrete elements may each have a first surface nearest to the other concrete element. Furthermore, the device includes first and second load transfer members each having first and second ends. The load transfer members may further each include a longitudinal axis, and the longitudinal axes may be positioned at an angle to the normal of the first surfaces of the concrete elements. Moreover, the first ends of the load transfer members may be at least partially embedded in the first concrete element in a spaced relationship with one another, while the second ends may be at least partially embedded in the second concrete element in a spaced relationship with one another. The first and second ends of the load transfer members are not in contact with any other load transfer members in the first and second concrete elements. Furthermore, the first and second load transfer members may be positioned in a plane that is perpendicular to shear force acting on the first and second concrete elements wherein the shear force is coplanar with the first and second concrete elements. 
     In still another embodiment of the invention, a load transfer device connecting at least first and second concrete elements is provided. The first and second concrete elements may each have a first surface nearest to the other concrete element. Furthermore, the device includes first and second load transfer members each having first and second concrete engaging portions, with the load transfer members only in contact with the first and second concrete elements at the first and second concrete engaging portions, respectively. The load transfer members may further each include a longitudinal axis, and the longitudinal axes may be positioned at an angle to the normal of the first surfaces of the concrete elements. Moreover, the first concrete engaging portions of the load transfer members may be at least partially embedded in the first concrete element in a spaced relationship with one another, while the second concrete engaging portions may be at least partially embedded in the second concrete element in a spaced relationship with one another. The first and second load transfer members transfer at least one shear load between the first and second concrete elements when the first and second concrete elements are in a service position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view according to one embodiment of a load transfer device of the present invention. 
         FIG. 2  is an exploded view of the load transfer device of  FIG. 1 . 
         FIG. 3  is a perspective view of a second embodiment of a load transfer device of the present invention. 
         FIG. 4  is a perspective view of a third embodiment of a load transfer device of the present invention. 
         FIG. 5  is a perspective view of a fourth embodiment of a load transfer device of the present invention. 
         FIG. 6  is a perspective view of the front face of a load transfer member of the load transfer device of  FIG. 1 . 
         FIG. 7  is a perspective view of the back face of a load transfer member of the load transfer device of  FIG. 1 . 
         FIG. 8  is a perspective view of the anchoring groove of the load transfer device of  FIG. 1 . 
         FIG. 9  is a perspective view of an alternate embodiment of an anchoring means of the load transfer device. 
         FIG. 10  is a perspective view of a second alternate embodiment of an anchoring means of the load transfer device. 
         FIG. 11  is a front elevation view of a retention member of a retention housing of the load transfer device of  FIG. 1 . 
         FIG. 12  is a perspective view of a depth locator of the load transfer device of  FIG. 1 . 
         FIG. 13  is a side elevation view of a section of a sandwich panel according to one embodiment of a sandwich panel of the present invention. 
         FIG. 14  is a flow chart describing a method for manufacturing a sandwich panel in accordance with the present invention. 
         FIG. 15  is an illustration of a form assembly used in the method for manufacturing a sandwich wall panel or a double wall panel in accordance with the present invention. 
         FIG. 16  is an illustration of the form assembly used in the method for manufacturing a sandwich wall panel or a double wall panel further showing reinforcing in accordance with the present invention. 
         FIG. 17  is an illustration of the form assembly used in the method for manufacturing a sandwich wall panel or a double wall panel, wherein a first layer of concrete has been placed in the form assembly in accordance with the present invention. 
         FIG. 18  is an illustration of the form assembly used in the method for manufacturing a sandwich wall panel or a double wall panel, wherein an insulating panel has been added to the first concrete layer in accordance with the present invention. 
         FIG. 19  is an illustration of the load transfer device used in the method for manufacturing a sandwich wall panel or a double wall panel in accordance with the present invention. 
         FIG. 20  is an illustration of the method for manufacturing a sandwich wall panel or a double wall panel, wherein retention housings for the load transfer devices have been inserted into the insulating panel in accordance with the present invention. 
         FIG. 21  is an illustration of the method for manufacturing a sandwich wall panel, wherein load transfer members have been inserted into the retention housings in accordance with the present invention. 
         FIG. 22  is an illustration of the method for manufacturing a sandwich wall panel wherein a second concrete layer has been poured, completely surrounding the load transfer devices in accordance with the present invention. 
         FIG. 23  is a perspective view of a form assembly used in a second method for manufacturing a sandwich wall panel wherein the sandwich wall panel is cast-in-place in accordance with the present invention. 
         FIG. 24  is a side elevation view of a section of a double wall panel including the load transfer device in accordance with the present invention. 
         FIG. 25  is a flow chart describing a method for manufacturing a double wall panel in accordance with the present invention. 
         FIG. 26  is an illustration of a form assembly used in a method for manufacturing a double wall panel, further showing one embodiment of the load transfer device which has been inserted along with standoff devices in accordance with the present invention. 
         FIG. 27  is an illustration of the form assembly used in the method for manufacturing a double wall panel, wherein a second concrete layer has been provided, and the first concrete layer, insulation panel, load transfer devices, and standoff devices are rotated 180° and lowered into the second concrete layer in accordance with the present invention. 
         FIG. 28A  is a front elevation view of a non-composite vertical sandwich panel in accordance with the present invention. 
         FIG. 28B  is a cross-sectional view of the non-composite vertical sandwich panel of  FIG. 28A  taken along lines  28 A- 28 A. 
         FIG. 29  is a front elevation view of a non-composite horizontal sandwich panel in accordance with the present invention. 
         FIG. 30A  is a front elevation view of a partial composite vertical sandwich panel in accordance with the present invention. 
         FIG. 30B  is a cross-sectional view of the partial composite vertical sandwich panel of  FIG. 30A  taken along lines  30 A- 30 A. 
         FIG. 31A  is a front elevation view of a partial composite vertical sandwich panel in accordance with the present invention. 
         FIG. 31B  is a cross-sectional view of the partial composite vertical sandwich panel of  FIG. 31A  taken along the lines  31 A- 31 A. 
     
    
    
     DETAILED DESCRIPTION 
     The following is a detailed description of an embodiment of a load transfer device  100 , sandwich wall panel  200 , methods for manufacturing a sandwich wall panel, double wall panel  300 , and a method for manufacturing a double wall panel of the present invention. For ease of discussion and understanding, the following detailed description and illustrations refer to the load transfer device  100  for use with wall panels, namely, concrete sandwich wall panels and double wall panels. It should be appreciated that the load transfer device  100  may be used to interconnect components of other structural building components, such as roof, floor, balcony, and canopy members, and in other concrete applications. For example, the load transfer device  100  may also be used to connect and transfer loads in concrete pavement applications. The load transfer device  100  of the present invention is sometimes illustrated and described in an embodiment where two load transfer members  102 ,  104  form an “X” shape. However, it should be appreciated that more than two load transfer members may be employed. Furthermore, the load transfer members  102 ,  104  need not form an “X”. 
     Referring to  FIG. 1 , a load transfer device  100  of the present invention is shown. The load transfer device  100  is primarily a shear connector. The load transfer device  100  includes a first load transfer member  102  and a second load transfer member  104 . In the preferred embodiment and the illustration shown, the load transfer members  102 ,  104  are elongated, flat, linear bars, the ends of which are embedded in and connect first and second concrete elements. As can be seen in  FIG. 1 , the ends extending into the same concrete element are positioned in a spaced relationship with one another. However, one of skill in the art will recognize that the load transfer members  102 ,  104  may be any elongated shape with any shape cross-section as the application may so require without departing from the scope of the present invention. It is contemplated that the load transfer members  102 ,  104  will be made of a material of sufficient strength to hold and transfer the required loads. In the preferred embodiment, the load transfer members  102 ,  104  are made of fiber reinforced polymer material, although one of skill in the art will recognize that the load transfer members  102 ,  104  may be made from any appropriate material. For best results, a thermally nonconductive material should be used. In applications where concrete components are to be interconnected, the preferred fiber reinforced polymer expands and contracts at the same rate as concrete when exposed to differing thermal conditions. In the preferred embodiment, the load transfer members  102 ,  104  are identical and may be interchanged during assembly of the load transfer device  100 , which provides for cost and time savings in the manufacturing process, and ease of assembly in the construction process. One of skill in the art will recognize that the load transfer members  102 ,  104  need not be identical and may differ from each other depending on the application. In its simplest form, the load transfer device  100  includes the load transfer members  102 ,  104  as its only components. Optionally, the load transfer members  102 ,  104  may each include a collar to appropriately position the load transfer members  102 ,  104  in the sandwich panel. However, in the preferred embodiment, the load transfer device  100  includes further components, including a depth locator  120 , which provides means for locating the load transfer members  102 ,  104  at the appropriate depth in the concrete elements they are connecting, and a retention housing  106 , which provides means for retaining the load transfer members  102 ,  104  at their appropriate angle within the concrete elements. In the embodiment illustrated in  FIG. 1 , two load transfer members  102 ,  104  are shown. As will be discussed below, it is contemplated that more than two load transfer members  102 ,  104  may be used. Further, the load transfer members  102 ,  104  may not cross at their centers or at all. 
     As is shown in  FIG. 1 , the load transfer device  100  may include a retention housing  106 . In the preferred embodiment for use with wall panels, the retention housing is made of insulating material. The retention housing  106  is preferably made of the same material as the rigid insulation layer of the wall panel, although it may be made of a different insulating material. In the preferred embodiment, the retention housing  106  is made of a first retention member  108  and a second retention member  110 . One skilled in the art will recognize that the retention housing  106  may be made of any number of insulation pieces. The retention housing  106  has a front surface  101 , back surface  103 , left side  114 , right side  116 , top  142 , and bottom  144 . The two retention members  108 ,  110  may be held in place by adhesive or other connecting means, including mechanical means. In the preferred embodiment, the retention members  108 ,  110  are held together at the left side  114  and right side  116  by a strip of self-adhesive tape  112  that wraps all the way around the perimeter of the left side  114  and right side  116 . When assembled, the load transfer members  102 ,  104  extend outward in opposite directions from said retention housing  106 . The load transfer members  102 ,  104  may include one or more anchoring means  118 . The anchoring means  118  help anchor the load transfer members  102 ,  104  in the concrete or other components to be connected. As is shown in  FIG. 1 , the anchoring means  118  may be a horizontal groove cut in the load transfer members  102 ,  104 , near both the top and bottom ends, such that the grooves will be in communication with the concrete of a sandwich panel. In the preferred embodiment, the anchoring means  118  are located on the exterior surface  134  of the load transfer member  102 ,  104 , although they may be located on the interior surface. As will be discussed in more detail, other anchoring means  118  may also be employed. 
       FIG. 2  provides an exploded view of components of the load transfer device  100 . Specifically,  FIG. 2  shows the first and second retention members  108 ,  110 , the first and second load transfer members  102 ,  104 , and the depth locator  120 . The retention members  108 ,  110  each have a left side  114 , right side  116 , top  142 , and bottom  144 , corresponding to the same sides on the assembled retention housing  106  of  FIG. 1 . Referring again to  FIG. 2 , the retention members  108 ,  110  may optionally include a recessed portion  122 ,  124  to accept the load transfer members  102 ,  104 . Recessed portion  124  is shown in  FIG. 2 . Recessed portion  122  is blocked from view as it is located directly behind load transfer member  102 . The retention members  108 ,  110  and the recessed portions  122 ,  124  may be formed by any method, now known in the art or later developed, such as but not limited to pre-machining or molding. Further, the load transfer device  100  may include a depth locator  120 . The depth locator  120  is held in place by a channel  126  in the first retention member  108  and a channel  126  in the second retention member  110 . The channel  126  can be seen in the first retention member  108  in  FIG. 2 . The channel  126  in the second retention member  110  is identical to the channel  126  in the first retention member  108 , but is not shown in  FIG. 2  due to the angle. The depth locator  120  is designed to accept the first and second load transfer members  102 ,  104  and lock same in place using a pair of slightly flexible tabs  128 ,  130 . The load transfer members  102 ,  104  each include a first  132  and second indentation  133 , which can be seen in  FIG. 6 . Referring again to  FIG. 2 , the load transfer members  102 ,  104  are each inserted from the top  142  of the retention housing  106 . The load transfer members are inserted until the tab  128  or  130  snaps into the first indentation  132  and locks into place. When the load transfer members  102 ,  104  have reached their appropriate depth, the tab  128  or  130  and its corresponding indentation  132  create an audible noise, letting the user know that the load transfer member  102  or  104  has been inserted to the appropriate depth. As one skilled in the art will appreciate, the appropriate depth is important for proper anchorage in the concrete wythes and is determined depending on the application. Accordingly, the position of the indentations  132 ,  133  will vary with the application. 
     The embodiment shown in  FIGS. 1 and 2  includes two load transfer members  102 ,  104  which cross each other at their center. Depending on the application, the load transfer device  100  may include more than two load transfer members  102 ,  104 . In addition, the load transfer members  102 ,  104  need not cross each other. Because the load transfer members  102 ,  104  are independent, discrete components, the user may construct the load transfer device  100  of the present invention to provide greater load transfer capacity in necessary areas of the application. Illustrated in  FIG. 3  is a load transfer device  100  of the present invention wherein the retention housing  106  is long enough to accommodate three load transfer members  102 ,  104 , and  105 . Also shown in  FIG. 3 , the anchoring means  118  may be positioned to face inward, outward, or a combination of the two.  FIG. 4  provides an illustration of an embodiment wherein two load transfer members  102 ,  104  are provided that do not cross each other.  FIG. 5  illustrates an embodiment wherein two retention housings  106 ,  107  and four load transfer members  102 ,  104  are used. The second retention housing  107  is located in-line with the first retention housing  106 . In the illustrated embodiment, the two retention housings  106 ,  107  are located parallel to each other. However, the retention housings  106 ,  107  may be located at angle with respect to each other. As can be seen in the  FIG. 5 , the load transfer members  102 ,  104  need not be positioned at the same angle. The retention housings  106 ,  107  may include any number of load transfer members  102 ,  104  located at any position. Furthermore, the user need not use two separate retention housings  106 ,  107  to create the load transfer device illustrated in  FIG. 5 . Rather, one retention housing  106  that can receive numerous load transfer devices may be used. 
       FIGS. 6-7  provide further illustrations of the load transfer members  102 ,  104 . In the preferred embodiment, the load transfer members  102 ,  104  are identical. Accordingly in  FIGS. 6-7 , one load transfer member is shown to represent all. However, one skilled in the art will recognize that the load transfer members  102 ,  104  need not be identical, which may be advantageous depending on the application.  FIG. 6  shows the exterior face  134  of a load transfer member  102 ,  104 . In the illustrated embodiment, the exterior face  134  of the load transfer member includes two anchoring means  118 . As is shown in  FIG. 1 , the exterior face  134  of the load transfer member  102 ,  104  faces outward when inserted into the retention housing  106  and depth locator  120 . Referring again to  FIG. 6 , the load transfer members  102 ,  104  each include two indentations  132 ,  133 . The first indentation  132  communicates with and accepts the appropriate tab  128 ,  130  of the depth locator  120 . The second indentation  133  is provided for versatility, allowing the load transfer member  102 ,  104  to be used interchangeably. The load transfer members  102 ,  104  each include a top edge  136  and a bottom edge  138 . In the exemplary load transfer members  102 ,  104  shown in  FIGS. 6-7 , the top edge  136  and bottom edge  138  are each finished at an angle, such that when the load transfer members  102 ,  104  are inserted into the retention housing  106  and depth locator  120 , the top edge  136  and bottom edge  138  are generally parallel to the planar surface of the concrete wythes of a sandwich panel. Accordingly, the shape and angle of the top edge  136  and bottom edge  138  will vary depending on the angle at which the load transfer members  102 ,  104  are positioned. Further, the top edge  136  and bottom edge  138  need not be parallel to the planar surface of the connected components, which may be particularly desirable in an embodiment wherein the components of a double wall panel are connected, or in a pavement application. 
       FIG. 7  shows the back face  140  of a load transfer member  102  or  104 . As is shown in the drawing, the back does not include anchoring means  118  in this embodiment. However, one skilled in the art will appreciate that anchoring means  118  may also be included on the back of the load transfer member  102 ,  104 . As can be seen in  FIG. 7 , the first indentation  132  and second indentation  133  extend all the way through and also cut out the back face  140  of the load transfer member  102 ,  104 . 
       FIG. 8  shows one example of an anchoring means  118  on a load transfer member  102  or  104 . The anchoring means  118  is a depression located near the bottom edge  138  (or identically, on the top edge  136 ) of the load transfer member  102  or  104 . The depression extends about one third of the depth of the load transfer member  102  or  104 . The component to be connected, such as the concrete wythes of a sandwich panel or double wall panel, form around the depression, thereby anchoring the load transfer member  102 ,  104  in the concrete or other component to be connected. One skilled in the art will appreciate that the depression may be any shape or depth necessary for the application and may be moved to a different location on the load transfer member  102  or  104  as the application may require. In addition, other anchoring means  118  known now or in the future may be employed, such as a hole drilled in the load transfer member  102  or  104 , as illustrated in  FIG. 9 . In another embodiment of the anchoring means  118 , a short piece of reinforcing bar is placed through a hole drilled in the load transfer member  102  or  104 , as shown in  FIG. 10 . The reinforcing bar is not part of the optional reinforcing network generally found in the concrete layers of sandwich panels, but is rather a short piece that allows concrete to cure around it, thus anchoring the load transfer member  102  or  104  in the concrete or other component to be connected. 
       FIG. 11  shows a retention member  108  or  110 . The retention housing  106 , and accordingly the retention members  108 ,  110  are designed to retain the load transfer members  102 ,  104  at their proper angles. The retention housing  106 , including the retention members  108 ,  110 , is generally made of a rigid insulation material, including, but not limited to, expanded or extruded polystyrene, polyisocyanurate, and high density rockwool. One skilled in the art will appreciate that the retention housing  106  may be made of any material, particularly any type of insulating material. Further, the retention housing  106  may be manufactured in any number of pieces, including one complete retention housing or two or more retention members. The retention members  108 ,  110  shown in  FIGS. 1-2  are identical. However, when the load transfer device  100  is assembled, the two identical retention members  108 ,  110  face each other such that the recessed portions  122 ,  124  to accept the load transfer members  102 ,  104  and channels  126  to accept the depth locator  120  face each other. Accordingly, when assembled, the two recessed portions  122 ,  124  are X-shaped and cross each other rather than being parallel to each other. However, depending on the application, the configuration of the recessed portions  122 ,  124  may differ from the described embodiment. The channels  126  are identical and directly across from each other such that they may accept the same depth locator  120 . The retention member  108 ,  110  includes a top  142 , bottom  144 , left side  114 , and right side  116 . As is shown in  FIG. 11 , the channel  126  to accept the depth locator  120  includes two vertical portions  146 ,  148  at the ends of a single, horizontal portion  150 . The vertical portions  146 ,  148  extend downward from the horizontal portion  150  toward the bottom  144  of the retention member  108 ,  110 . Optionally, the retention housing  106  and accordingly the one or more retention members  108 ,  110  may be tapered to prevent the retention housing from slipping through the insulation layer of a sandwich or double wall panel during construction. 
     Illustrated in  FIG. 12  is an embodiment of the depth locator  120 . The depth locator acts as a retention device to retain the load transfer members at their appropriate depth in the concrete layers. As one skilled in the art will recognize, the appropriate depth may vary depending on the application. The depth locator  120  includes a planar member having a top surface  152  and bottom surface  154 . Further a left leg  156  and a right leg  158  are present and extend downward from the bottom surface  154  of the depth locator  120 . In the preferred embodiment, the depth locator  120  is symmetrical such that it is identical when rotated 180° in the horizontal plane. However, one of skill in the art will recognize that the depth locator  120  may not be symmetrical in certain applications. The depth locator  120  includes a cutout portion  164 , through which the two load transfer members  102 ,  104  can be inserted. The depth locator  120  includes two tabs  128 ,  130  protruding from the perimeter of the cutout portion  164 . As is shown in  FIGS. 6-7 , the load transfer members  102 ,  104  include indentations  132 ,  133 . When the first indentation  132  meets the appropriate tab  128  or  130  the parts click into place. The user will hear an audible noise signaling that the load transfer members  102 ,  104  have reached their appropriate depth. In the preferred embodiment, the load transfer members  102 ,  104  may only move downward through the depth locator  120 . Once the load transfer members  102 ,  104  are inserted, upward movement of the load transfer members  102 ,  104  will cause the tabs  128 ,  130  to snap and break. As is shown in  FIG. 12 , the tabs  128 ,  130  may taper slightly to accommodate movement of the load transfer members  102 ,  104  through the depth locator  120 . Optionally, as shown by tab  130 , the tabs may include a hinge joint  131  to accommodate movement of the load transfer members  102 ,  104  through the depth locator and into place. Accordingly, the depth locator  120  provides a means to assist the user in correctly assembling the load transfer device  100  and also to retain the load transfer members  102 ,  104  at the appropriate depth. 
     The angle at which the load transfer members  102 ,  104  are each positioned is precise, but adjustable. Generally, angles of 20° to 70° from normal may be used, with 30° to 60° angles from normal providing optimal load transfer properties, as the force resisted at those angles is mostly tension. In a sandwich wall or double wall panel, the load transfer members  102 ,  104  are each positioned at an angle to the normal of the plane at which the layers meet. In addition, the load transfer members are each positioned at an angle to the planar surface of the concrete layers. However, one of skill in the art will recognize that load transfer members  102 ,  104  may be positioned at any angle. In addition, one of skill in the art will recognize that the angle will vary depending on the application and other factors, such as the loads to be transferred and, in a wall panel application, the thickness of the various layers. In the provided illustrations, oftentimes the load transfer members  102 ,  104  cross each other at their center. One of skill in the art will recognize that the load transfer members  102 ,  104  need not cross at their center, which may be advantageous in some applications, such as a double wall panel. In addition, the load transfer members  102 ,  104  need not cross at all. 
     In its simplest form, the load transfer device  100  consists of the two load transfer members  102 ,  104 . The load transfer members  102 ,  104  can be inserted into components to be connected, such as the sections of pavement or the concrete of a wall panel. If the user desires, the retention housing  106  and/or depth locator  120  may also be employed. The retention housing, as will be discussed below, is particularly useful in applications involving wall panels that include a layer of insulation. The device  100 , when using the depth locator  120  and retention housing  106  is assembled by sliding the depth locator  120  into the channel  126  of the first retention member  108  and then the channel  126  of the second retention member  110 . The vertical portions or legs  156 ,  158  of the depth locator  120  should extend toward the bottom  144  of the first retention member  108 . The second retention member  110  should then be inserted around the depth locator  120  such that the depth locator  120  is inserted into the channel  126  of the second retention member  110 . Accordingly, the retention housing  106  and depth locator  120  may work in cooperation with each other to retain the load transfer members  102 ,  104  at their proper angle and depth. One of skill in the art will recognize that the retention housing may be constructed of any number of retention members or as a single structure. In addition, the depth locator  120  may be included in the retention housing  106  during the molding process, such that the retention housing  106  forms around it. Each retention member  108 ,  110  includes a recessed portion  122 ,  124  designed to accept and guide the load transfer members  102 ,  104 . The depth locator  120  and retention members  108 ,  110  should be designed such that the cutout portion  164  of the depth locator  120  is located at the intersection of the recessed portions  122 ,  124  of the retention members  108 ,  110 . As one skilled in the art will appreciate, the exact design of the recessed portions  122 ,  124  and cutout portion  164  will vary depending on the application, by taking into consideration such factors as the size and shape of the load transfer members  102 ,  104  and the angle at which the load transfer members  102 ,  104  will be positioned. Once the depth locator  120  and two retention members  108 ,  110  are assembled, the two retention members  108 ,  110  may optionally be connected by a connecting means. In the preferred embodiment, a strip of self-adhesive tape  112  may be applied to the perimeter of the left end  114  and right end  116  of the assembled retention housing  106 , as is shown in  FIG. 1 . However, other connecting means may be used, such as other mechanical connection or chemical bonding. 
     Next, the load transfer members  102 ,  104  should be inserted. When constructing a sandwich or double wall panel, it is generally desirable to insert the retention housing  106  with the depth locator  120  inside into the insulation layer of the panel prior to inserting the load transfer members  102 ,  104 . In the preferred embodiment, the anchoring means  118  face outward from the device  100 . Referring to  FIG. 1 , the retention member  110  that is associated with the front surface  101  of the device  100  accepts a load transfer member  104  whose anchoring means  118  faces in the same direction as the front surface  101 . The retention member  108  that is associated with the back surface  103  of the device  100  accepts a load transfer member  102  whose anchoring means  118  face in the same direction as the back surface  103 . The load transfer members  102 ,  104  are inserted through the top end  142  of the retention members  108 ,  110  until the indentations  132  click into place with the appropriate tabs  128  or  130  of the depth locator  120 . It is contemplated that the load transfer members  102 ,  104  may be used alone, with the depth locator  120 , with the retention housing  106 , or with both the depth locator  120  and retention housing  106 . It will be appreciated by one skilled in the art that the length of the load transfer members  102 ,  104 , the angle at which the two load transfer members  102 ,  104  are positioned, and the configuration of the components of the device  100  are adjustable and can be varied to fit the selected application. Further, the load transfer device  100  of the present invention may be used alone or in combination with other known connectors and load transfer devices. It will be appreciated that the load transfer device  100  may be shipped to a job site either assembled, partially assembled, or unassembled as the situation requires. Additionally, it is contemplated that the components of the load transfer device  100  may be ordered separately or as a set. When all components of the load transfer device  100  are shipped together, the unassembled components can be stacked neatly and compactly in a box, thus reducing shipping costs. 
     Flexural loads applied to a wall panel are internally resisted by shear in the connector. Similarly, the self-weight of the exterior layer is resisted by shear in the connector. The present invention has a greater shear capacity than connectors of the prior art. Fiber reinforced polymer is stronger in tension than shear. In addition, by placing the load transfer members at an angle, the load transfer device of the present invention resists force due to flexural load and self-weight in tension and thus has a larger capacity. In addition to the increased shear capacity, the load transfer device of the present invention provides many other advantages over the prior art. First, no large voids are left in the insulation layer for placement of the connector that need to be filled by spray foam or another insulation. Because the present connector includes discrete load transfer members, the load transfer members can be strategically placed where the most resistance is required. Further, by using the depth locator, embedment is more accurate during construction. There is no need to tie the load transfer device to the longitudinal steel as required in the prior art. Moreover, the load transfer device can be placed anywhere in the panel as compared to prior art connectors, which must be placed between two insulating sheets. 
     The present invention may be used to connect and transfer loads between a variety of components. In one embodiment, the load transfer device  100  may be used with a sandwich wall panel  200 , also called an integrally insulated concrete panel. An exemplary sandwich wall panel is shown in  FIG. 13 . Generally, three layers are present, a first concrete layer  202 , a second concrete layer  204 , and an insulation layer  206 . The first concrete layer  202  includes a first surface  201  that is closest to the second concrete layer  204 . In addition, the second concrete layer  204  also includes a first surface  203  that is closest to the first concrete layer  202 . Although not shown, the sandwich wall panel  200  may further include an exterior façade attached to the exterior layer of concrete. The sandwich panel  200  includes at least one load transfer device  100  to connect the first concrete layer  202 , second concrete layer  204 , and insulation layer  206 , as is illustrated in  FIG. 13 . Furthermore,  FIG. 13  includes two arrows, A and B, which represent the shear force in the wall panel while in its service position. Generally, the load transfer device  100  of the illustrated embodiment is placed in the wall vertically. At minimum, the load transfer device  100  includes two load transfer members  102 ,  104 . Although one skilled in the art will recognize that any material may be used, in the preferred embodiment the load transfer members  102 ,  104  are made of fiber reinforced polymer material, which advantageously expands and contracts at the same rate as concrete when exposed to different temperatures and is not as thermally conductive as other materials, such as metal. In the preferred embodiment, the load transfer device  100  further includes a retention housing  106  made of rigid insulation material. Although not shown in the view of  FIG. 13 , in the preferred embodiment, the retention housing  106  is made of two retention members. The retention members may optionally include recessed portions  122 ,  124  disposed to accept and guide the load transfer members  102 ,  104  into place during assembly. The load transfer members  102 ,  104  may optionally include one or more anchoring means  118 . The length of the load transfer members  102 ,  104  and the angle at which they are positioned are precise, but adjustable and depend on the application and other factors, including but not limited to the thicknesses of the first concrete layer  202 , the second concrete layer  204 , and the insulation layer  206 . The insulation layer  206  may be made of any insulation, as the application requires, but is most often a rigid insulation. Preferred embodiments include expanded or extruded polystyrene or polyisocyanurate, although many types of insulation are known in the art. The insulation layer is disposed to receive at least one load transfer device  100 . The present sandwich panel does not depend on insulation bonding with the concrete wythes for strength and load transferring. Rather, the load transfer device  100  is able to transfer the entire loads associated with the sandwich panel  200 . Further shown are a first load transfer member longitudinal axis  160  and a second load transfer member longitudinal axis  161 . The longitudinal axes  160 ,  161  are positioned at an angle to the normal of concrete layers  202 ,  204 , and insulation  206 . In addition, each load transfer member  102 ,  104  further includes first  162 ,  163  and second  164 ,  165  concrete engaging portions. The first concrete engaging portions  162 ,  163  are at least partially embedded in the first concrete layer  202  in spaced relationship with one another, while the second concrete engaging portions  164 ,  165  are at least partially embedded in the second concrete layer  204  in a spaced relationship with one another. 
     The present invention includes methods for manufacturing a sandwich wall panel  200  employing a load transfer device  100 , which is described in the flow chart of  FIG. 14 . The methods can be used with a variety of construction techniques known now or in the future, including but not limited to site-cast tilt-up, plant precast, cast-in-place, and modular precast. As is known in the art, site-cast tilt-up panels are produced horizontally at the job-site, usually using the building floor slab as the primary casting surface. Once the panels are assembled and have cured, the panels are lifted into place to form the building envelope. Precast concrete panels are cast horizontally into shape at a location other than the job-site. Once the panels are assembled and have cured, the panels are transported to the job-site for construction. The precast concrete panels of the present invention may be prestressed. Similar to the site-cast tilt-up method, cast-in-place sandwich panels are manufactured at the job site. Cast-in-place wall panels are manufactured vertically and in place at their final location. 
     Referring to  FIG. 14 , a method for manufacturing a sandwich wall panel generally begins by providing a first concrete layer, as is shown by block  208 . As illustrated in  FIG. 15 , the concrete may be poured into a mold or form  226  for plant precast methods to make sections of sandwich panel  200  which will then be shipped to a job site. Alternatively, the first concrete layer  202  may be poured into a large mold as part of a site-cast tilt-up method with cutouts such as windows and doors included in the mold. As shown in  FIG. 16 , the form  226  may include reinforcing  229  placed into the mold before the concrete is poured into the form  226 . Alternatively, the reinforcing may be pushed into the wet concrete after it has been poured into the form  226 . As discussed above, the reinforcing is optional. The form  226  is then filled with wet concrete, as shown in  FIG. 17 . 
     Next, as provided in  FIG. 14  block  210  and illustrated in  FIG. 18 , an insulation panel  228  is placed on top of the first concrete layer while the concrete is still wet or plastic. Optionally, this is accomplished by providing small sections of insulation in a predetermined pattern. One of skill in the art will recognize that more than one piece and/or layer of insulation may be provided. The insulation panel  228  is disposed to receive at least one load transfer device  100 . In the preferred embodiment, this means that the insulation panel  228  is disposed to receive at least one retention housing  106  of the load transfer device, generally by having cavities  230  at predetermined locations. In addition, the insulation panel  228  may be disposed to receive one or more connectors of a different type. 
     Next, referring to block  212  of  FIG. 14 , at least one load transfer device  100  is inserted into the insulation panel  228  such that the load transfer members  102 ,  104  are positioned at an angle to the normal of the planes at which the first concrete layer  202  and the insulation panel  228  meet and the second concrete layer  204  and the insulation layer meet. As previously discussed, the load transfer device  100  may be composed solely of the two load transfer members  102 ,  104 . Optionally, the load transfer device  100  may include a depth locator  120 , a retention housing  106 , or, as in the preferred embodiment, both. When using only the two load transfer members  102 ,  104 , they are inserted through the insulation panel  228  and into the wet concrete. In the preferred embodiment, as illustrated in  FIG. 19 , the depth locator  120  is inserted into the channel  126  to accept the depth locator  120  of the first insulating retention member  108 . The second insulating retention member  110  is then added, such that the channel  126  of the second insulating retention member  110  receives the depth locator  120 . Optionally, an adhesive or other connecting means may be used to hold the retention members  108 ,  110  in place. In the preferred embodiment, a piece of self-adhesive tape  112  is wrapped around the perimeter of the left end  114  and right end  116  of the retention housing, which is illustrated in  FIG. 13 . 
     The assembled depth locator  120  and retention housing  106  are then inserted into the cavities  230  of the insulation panel  228 , as is illustrated by  FIG. 20 . Generally the depth of the retention housing  106  is the same distance as the depth of the insulation layer  206 , which for purposes of this illustration is one insulation panel  228 . Therefore, the retention housing is flush with the insulation layer  206  where the insulation layer  206  meets the first concrete layer  202  and second concrete layer  204 . Accordingly, once the one or more retention housings  106  are inserted into the insulation panel  228 , the only voids in the insulation are the recessed portions  122 ,  124  in the one or more retention housings  106  to accept and guide the load transfer members  102 ,  104 , as is shown in  FIG. 20 . The ends of the retention housing  106  may taper downward and correspond to a tapering in the cavities  230  of the insulation panel to hold the retention housing  106  in the insulation panel  228 . Alternatively, the retention housings  106  may already be inserted into the insulation panel  228  when it is placed on top of the wet concrete. 
     Next, the load transfer members  102 ,  104  are inserted, as is shown in  FIG. 21 . The load transfer members  102 ,  104  are inserted through the top of the retention housing  106  until the indentation  132  of each load transfer member  102 ,  104  reaches the appropriate tab  128  or  130  of the depth locator  120 , as shown in  FIG. 2 . This creates an audible clicking noise. When the indentation  132  snaps into place with the appropriate tab  128  or  130 , it also becomes significantly harder to continue to insert the load transfer member  102 ,  104 , thus creating another way for the user to determine that the load transfer member  102 ,  104  has reached the appropriate depth. As is shown in  FIG. 13 , the bottom portion  166  of the load transfer member  102 , including the optional anchoring means  118 , extends into the first concrete layer  202 . The second load transfer member  104  is then inserted through the retention housing  106  and into the first concrete layer  202 . As is shown in  FIGS. 13 and 21 , the top portion  168  of both load transfer members  102 ,  104  extend beyond the insulation panel  228 . 
     Referring to block  214  of  FIG. 14 , the second concrete layer  204  is then poured atop the insulation layer, such that it completely surrounds and encloses all parts of the load transfer device  100 , as is shown in  FIG. 22 . The method eliminates any remaining spaces or voids, which decrease thermal efficiency, in the insulation layer  206 . Oftentimes, these spaces or voids are present in the sandwich panels of the prior art and require a second application of insulation, such as foam insulation, in the spaces or voids to increase the thermal efficiency of the panel. The present sandwich panel eliminates the need to apply a second form of insulation, thus providing time and cost savings. Once the concrete cures, the sandwich wall panel is complete. It may be removed from the form and used to construct a building or other structure. 
     Alternatively, the sandwich panel  200  may be constructed vertically using a cast-in-place method. To do so, a cast-in-place form  232  is used, as shown in  FIG. 23 . The cast-in-place form  232  includes an interior form wall  234  and exterior form wall  236 , which are erected at the wall&#39;s service position. A piece of insulation  238  is then placed between the interior form  234  and exterior form  236 . Before the insulation  238  is set into place, one or more load transfer devices  100  are inserted into the insulation  238  at predetermined locations in the manner described above. Concrete is then introduced into the cast-in-place form  232  on both sides of the insulation  238  to create interior and exterior concrete wythes. 
     The present invention also includes a double wall panel  300  engaging the disclosed load transfer device  100 . Referring to  FIG. 24 , the double wall panel  300  includes a first concrete layer  302 , a second concrete layer  304 , an insulation layer  306 , and an air void  308 . The first concrete layer  302  includes a first surface  301  which is closest to the second concrete layer  304 . In addition, the second concrete layer  304  includes a first surface  303 , which is closest to the first concrete layer  301 . The double wall panel  300  further includes at least one load transfer device  100 . In its simplest form, the load transfer device includes two load transfer members  102 ,  104 . Optionally, the load transfer device  100  may further include a depth locator  120  (not shown in  FIG. 24 ), a retention housing  106 , or, as in the preferred embodiment, both. The load transfer members  102 ,  104  may include anchoring means  118 . As is shown in  FIG. 24 , in the preferred embodiment of the double wall configuration, the load transfer member  104  includes three anchoring means  118 . The load transfer member  102  also includes three anchoring means  118 , which are not shown in this view. If desired, the air void  308  may be filled with another material, such as concrete and/or additional insulation materials, once the double wall panel has been set into place at the construction site. Accordingly, the anchoring means  118  located in the air void  308  provides anchoring with the optional air void material. As can be seen in  FIG. 24 , the top edges  136  and bottom edges  138  of the two load transfer members  102 ,  104  are not parallel with the planar surface of the concrete layers  302 ,  304  or insulation layer  306 , as is the case with the preferred embodiment of the sandwich wall panel  200 . Rather, the top edges  136  and bottom edges  138  are at an angle to the planar surface of the concrete layers  302 ,  304  and insulation layer  306 . Further, the load transfer device  100  can be a standoff connector, with the lower tip  332  extending to the outside surface of the second concrete layer  304 . The load transfer members further include a portion  324  that spans the first concrete layer  302 , a portion  326  that spans the insulation layer  306  through the retention housing  106 , a portion  328  that spans the air void  308 , and a portion  330  that spans the second concrete layer  304 . 
     Also provided in the present invention is a method for manufacturing a double wall panel  300  employing the disclosed load transfer device  100 . Referring to  FIG. 25 , as shown in block  310 , the first step in the method for manufacturing a double wall panel is to provide a first concrete layer  302 . In horizontal applications, such as the plant precast and site-cast tilt-up methods discussed above, the first concrete layer  302  is generally poured into a form  226 , such as a steel pallet in the plant. An exemplary form  226  is provided in  FIG. 15 . Optionally, reinforcing  229  may be provided in the first concrete layer. The reinforcing  229  may be placed in the form before the wet concrete is added, as shown in  FIG. 16 , or, alternatively, the reinforcing  229  may be placed in the wet concrete after it is poured. As illustrated in  FIG. 17 , wet concrete is then poured into the form  226 . Next, referring to block  312 , an insulation panel  228  is provided on top of the wet concrete in the form  226 , as is shown in  FIG. 18 . One of skill in the art will recognize that the insulation layer may be provided in multiple panels with one or more pieces and/or layers of insulation provided. Generally, the insulation panel  228  is added while the concrete is still wet or plastic. The insulation panel  228  is disposed to receive at least one load transfer device  100 . In the preferred embodiment, this means that the insulation panel  228  is designed with rectangular-shaped cavities  230  to receive at least one retention housing  106 , as shown in  FIG. 18 . 
     Next, referring to block  314  of  FIG. 25 , while the concrete is still wet, at least one load transfer device  100  is inserted into the insulation panel  228  and wet concrete, such that the load transfer members  102 ,  104  are positioned at an angle to the normal of the plane at which the wet concrete and insulation panel  228  meet, as well as the planes at which the insulation panel  228  and air gap  308  will meet and the air gap  308  and second concrete layer will meet. In its simplest form, the load transfer device  100  of the present invention includes two load transfer members  102 ,  104 . The load transfer members  102 ,  104  are inserted through the rigid insulation, which is designed to accept the load transfer members  102 ,  104 . Generally, the cavities are just large enough to accept and guide the load transfer device  100 , whether it is the load transfer members  102 ,  104  only or the retention housing  106  which will in turn accept the load transfer members  102 ,  104  and the depth locator  120 . In the preferred embodiment, the cavities accept the retention housing  106  of the load transfer device  100 . 
     Optionally, the load transfer device  100  may include a depth locator  120  also. The retention housing  106  and depth locator  120  are assembled prior to insertion into the insulation panel  228 . As is shown in  FIG. 19 , the depth locator  120  is inserted into the channel  126  designed to accept the depth locator  120  of the first retention member  108 . The second retention member  110  is then added, such that the depth locator is inserted into its channel  126  to accept the depth locator  120 . Optionally, as in the preferred embodiment, the retention members  108 ,  110  may be held together with an adhesive, or other connecting means. In the preferred embodiment, the retention members  108 ,  110  are held together by a strip of self-adhesive tape  112  at the left end  114  and right end  116  of the retention housing  106 , as illustrated in  FIG. 1 . The retention housing  106 , with the depth locator  120  inside, is then inserted into a cavity  230  of the insulation panel  228 . In the preferred embodiment, the retention members  108 ,  110  include two recessed portions  122 ,  124  to accept and guide the load transfer members  102 ,  104 , which become the only voids present in the insulation panel  228 , as shown in  FIG. 20 . The first load transfer member  102  is inserted into the retention housing  106  and through the depth locator  120 . As discussed above and shown in  FIGS. 2 and 12 , the depth locator  120  includes a set of slightly flexible tabs  128 ,  130 . The load transfer members  102 ,  104  each include an indentation  132 . The indentation  132  accepts the appropriate tab  128  or  130  of the depth locator. The first load transfer member  102  is inserted until the indentation  132  accepts the appropriate tab  128  or  130 . At that point, an audible clicking sound is created. In addition, it becomes more difficult to continue pushing the load transfer member  102  through the depth locator. Accordingly, the user can be sure that the load transfer member  102  is inserted to the appropriate depth for the application. The same process is repeated for the second load transfer member  104  which also includes an indentation  132  that corresponds to a tab  128  or  130 . 
       FIG. 26  provides an illustration of the double wall panel  300  at this point. The wet concrete has been poured, and the insulation panel  228  has been provided on top of the wet concrete. The retention housing  106  of the load transfer device  100  has been inserted into the cavities  230  of the insulation panel  228 . Further, the load transfer members  102 ,  104  have been inserted into the retention housing  106 , clicking into place with the depth locator  120  (not shown), and with portions  324  extending into the wet concrete. The load transfer members  102 ,  104  also extend above the retention housing  106  into the air above the wet concrete and insulation panel  228 . The anchoring means  118  of load transfer member  104  can be seen. 
     In addition to the load transfer device  100 , other connectors known now or in the future, may also be used to connect the layers of the double wall panel  300  without departing from the scope of the present invention. Referring again to  FIG. 26 , standoff connectors  334  may be used. The standoff connectors  334  span the entire double wall panel and define its thickness. The standoff connectors  334  are inserted at the same time as the load transfer device  100  and extend all the way to the bottom of the form and accordingly through the entire first concrete layer  302 . The standoff connectors  334  further span the insulation layer and extend into the air above the insulation layer. When the second layer of concrete  304  is added, the standoff connector  334  further spans it and hits the bottom of the form, thus defining the thickness of the double wall panel, while leaving a space for the air gap. As will be described below, in the preferred embodiment, the first concrete layer  302 , insulation layer  306 , load transfer device  100 , and any other connectors are lifted, rotated 180° and lowered into the second concrete layer. In this embodiment the standoff connectors  334  hit the bottom of the form and may help support those layers that are suspended above the second concrete layer  304 . Alternatively, the second concrete layer  304  may be added above the other layers. Optionally, means may be added to transport the first concrete layer  302 , insulation layer  306 , load transfer device  100 , and optional standoff connector  334 . The standoff connector  334  may further include the means for transporting the first concrete layer  302 , insulation layer  306 , and load transfer device  100 . 
     After the first concrete layer  302 , insulation layer  306 , at least one load transfer device  100 , and any other connectors, including standoff connectors  334 , and transporting means are added, the concrete of the first concrete layer  302  is allowed to cure, as shown by block  316  of  FIG. 25 . In the preferred embodiment, the panel thus far is moved to an oven or steam chamber for curing. Alternatively, the panel may be left at room temperature for a prescribed period of time, such as twenty four (24) hours. Once the first concrete layer  302  has cured, the first concrete layer  302 , insulation layer  306 , load transfer device  100 , and any other connectors such as standoff connectors  334  are one unit and may be moved or transported as such. Accordingly, the double wall panel  300  in progress may be transported, and the panel need not be finished in the same location as where it was started. For example, the double wall panel  300  in progress may be transported to the job-site for the remaining steps. In the alternative, the remaining steps may take place in a plant. 
     The next step is providing a second layer of concrete  304 , as shown by block  318  of  FIG. 25 . In methods where the double wall panel is manufactured horizontally, the second concrete layer  304  may be added on top of the existing panel. Alternatively, referring to block  320  of  FIG. 25 , as in the preferred embodiment, the double wall panel in progress, including the first concrete layer  302 , insulation layer  306 , at least one load transfer device  100 , and any other connectors, including standoff connectors  334 , and transporting means, are lifted, rotated 180°, and lowered into the second concrete layer  304 , which is still wet or plastic concrete that has been poured into a form  226 , as shown by  FIG. 27 . In this embodiment, the second concrete layer  304  may be provided with optional reinforcing. The reinforcing may be present in the form when the concrete is poured, or may be lowered into the concrete after it has been poured. At this point, the top layers, the first concrete layer  302 , insulation layer  306 , at least one load transfer device  100 , and any other connectors, including standoff connectors  334 , and transporting means, may be mechanically held in place, such as by a steel suspension apparatus. Alternatively, the load transfer device(s)  100  in combination with one or more standoff connectors  334  may provide means for supporting the top layers above the air void  308 . Finally, the load transfer device  100  may support the layers above the air void  308  without assistance from other means. The second concrete layer  304  is then allowed to cure, either in a steam chamber or oven, or at room temperature for a prescribed period of time. 
     At this point, the double wall panel is complete. It may be removed from the form and used to construct a building or other structure. If the double wall panel  300  was manufactured, in whole or in part, horizontally at the job-site, the double wall panel  300  will then be tilt-up into the appropriate position. If the double wall panel  300  was wholly manufactured by plant precast methods, the double wall panel will then be shipped to a job-site. Oftentimes, double wall panels  300  are lighter than sandwich panels of the same area. Accordingly, double wall panels  300  manufactured using the plant precast method may be shipped in larger sections than sandwich panels  200 . Once in place at the job site, the double wall panel  300  air void  308  may be filled with another material, such as concrete and/or additional insulation materials. 
     Generally, the sandwich panel  200  and double wall panel  300  will include more than one load transfer device  100  and other connectors known now or in the future. The number of load transfer devices  100  and other connectors will vary depending on the application, and can be designed using methods known now or later developed.  FIGS. 28A-31B  provide examples of embodiments of panels of the present invention engaging at least one load transfer device  100 . Although  FIGS. 28A-31B  are directed to sandwich panels  200  of the present invention, one skilled in the art will recognize that the configurations may be used to manufacture double wall panels  300  of the present invention. 
       FIG. 28A  provides an embodiment of a non-composite vertical sandwich panel  218 , while  FIG. 28B  provides a cross-sectional view of the panel illustrated in  FIG. 28A . As is known in the art, in a non-composite sandwich panel, the layers of the panel, although connected, work independently of each other. The non-composite vertical sandwich panel  218  is connected using ten load transfer devices  100  and one hundred thirty other connectors  220 . The load transfer devices  100  are represented by dashes (-), and the other connectors  220  are represented by dots (•). It can be desirable to employ the load transfer device  100  and other connectors  220  in combination, because the practice can provide cost savings. The load transfer device  100  provides significantly higher load transfer properties than other connectors  220 ; however, the other connectors  220  are smaller, and therefore provide cost savings in manufacturing and shipping compared to the load transfer device  100 . Accordingly, one skilled in the art will be able to design panels using both types of connectors by considering the loads required for the application and the cost of each type of connector. In the illustrated embodiment, there are two rows of five load transfer devices  100  in the middle of the panel  218 . The remaining area of the panel is connected using other connectors  220 . The other connectors  220  are used around the entire perimeter of the panel  218 . 
       FIG. 29  provides an embodiment of a non-composite horizontal panel  222 . The load transfer devices  100  are provided in one horizontal row. The other connectors  220  are provided at regular intervals in the remaining area of the panel, including around the entire perimeter. 
       FIG. 30A  provides an embodiment of a partially composite vertical panel  224  while  FIG. 30B  provides a cross-sectional view of the panel illustrated in  FIG. 30A . As is known in the art, a partially composite sandwich panel combines the properties of a non-composite panel, wherein the layers of the panel work independently of each other, and a composite sandwich panel, wherein the layers work in unison. The illustrated partially composite vertical panel  224  includes ten load transfer devices  100  and one hundred thirty other connectors  220 . In  FIG. 30A , the load transfer devices  100  are represented by long horizontal lines, and the other connectors  220  are represented by shorter horizontal lines. In this illustration, the load transfer devices  100  are present in two rows of five. One row is at the top of the panel  224 , and the second row is at the bottom of the panel  224 . The other connectors  220  are present in the middle of the panel  224  and in the corners of the panel  224 . 
       FIG. 31A  provides a second embodiment of a partially composite vertical panel  224 , while  FIG. 31B  provides a cross-sectional view of the panel illustrated in  FIG. 31A . In this embodiment, only load transfer devices  100  are employed. Because the load transfer device  100  has a higher capacity to transfer loads than other connectors, this embodiment is advantageous in applications where more shear transfer is needed due to prominent vertical loading and excessive wind or seismic loads, such as in the case of a tornado shelter. The partially composite vertical panel  224  of  FIG. 31A  includes eighty load transfer devices  100 , arranged in four vertical rows of twenty. 
     Although various representative embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of the inventive subject matter set forth in the specification and claims. Joinder references (e.g. attached, adhered) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. In some instances, in methodologies directly or indirectly set forth herein, various steps and operations are described in one possible order of operation, but those skilled in the art will recognize that steps and operations may be rearranged, replaced, or eliminated without necessarily departing from the spirit and scope of the present invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims. 
     Although the present invention has been described with reference to the embodiments outlined above, various alternatives, modifications, variations, improvements and/or substantial equivalents, whether known or that are or may be presently foreseen, may become apparent to those having at least ordinary skill in the art. Listing the steps of a method in a certain order does not constitute any limitation on the order of the steps of the method. Accordingly, the embodiments of the invention set forth above are intended to be illustrative, not limiting. Persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Therefore, the invention is intended to embrace all known or earlier developed alternatives, modifications, variations, improvements, and/or substantial equivalents.