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RELATED APPLICATION 
       [0001]    This is a continuation-in-part of application Ser. No. 11/485,823, filed on Jul. 13, 2006. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention pertains to a lightweight hollow core structural building element which can be used as a beam or can be joined with other elements to form a floor, deck or wall panel. 
         [0003]    The potential for the use of hollow core elements in the construction of buildings and other structures has been known for many years. Hollow cores of corrugated or honeycomb paper or metal sheet material, enclosed by upper and lower skin panels or sheets, have long been used or proposed for use as floor, wall and roof panels for buildings. However, the use of such hollow core panels has been inhibited because of difficulties in fabricating the panels in an efficient and cost effective manner. 
         [0004]    It is known in the prior art to construct building floors or decks with structures that are reinforced and oriented such that loads are distributed in orthogonal directions (e.g. in the direction of main supporting beams and perpendicular thereto). In one such type of construction, as applied to a flat roof structure, parallel main support beams are tied together with bar joist trusses which help distribute the load in directions perpendicular to the beams. 
         [0005]    In another type of construction, a concrete floor slab has steel reinforcing running in two directions that are perpendicular to one another, again in an attempt to more evenly distribute the load in both directions. Concrete is eliminated in recessed portions bounded by the steel reinforcing in a sort of inverted egg carton construction. 
         [0006]    In both of the foregoing modes of construction, larger spans are attainable by virtue of the orthogonal load distribution. However, both of the foregoing floor plate constructions utilize large amounts of expensive steel and/or relatively massive amounts of concrete. 
         [0007]    In my co-pending patent application Ser. Nos. 11/476,474, entitled “Method and Apparatus for Manufacturing Open Core Elements from Web Material”, filed Jun. 28, 2006, and 11/769,879, entitled “Method and Apparatus for Manufacturing Open Core Elements from Web Material”, filed Jun. 28, 2007, which application are incorporated by reference herein, there is disclosed a system for manufacturing hollow core panels of widely varying dimensions using corrugating techniques and a unique lay-up process. 
       SUMMARY OF THE INVENTION 
       [0008]    In accordance with one embodiment of the present invention, a structural support, such as a floor or bridge deck, is fabricated from open core elements faced with upper and lower steel skins which are welded or otherwise joined together. A layer of concrete may be poured over the upper surface. When applied to a roof panel, the concrete is preferably eliminated. The invention encompasses the modules, the overall structural support, and the method of making the same, and a large span roof made of a plurality of modules. 
         [0009]    In one aspect of the invention, a horizontal structural support includes an open core element that has a plurality of corrugated strips of a web material bonded together and having the flutes oriented vertically. The open core element defines horizontal upper and lower surfaces to which steel skins are attached. A layer of concrete may be placed on the upper steel skin. If a concrete layer is used, the structural support may include a plurality of upstanding steel projections that are attached to the upper steel skin and are embedded in the concrete layer. 
         [0010]    In another embodiment, a plurality of open core elements are provided, each having upper and lower steel skins that are co-extensive with and attached to the core element and shaped to define modules of a generally rectangular shape. The modules are connected edge-to-edge with welded joints or other connectors along abutting edges of the upper and lower skins to form a deck. The deck forms a unitary plate that provides omni-directional stress distribution which, when used as a roof, can be post-stressed to enhance the load carrying capability. When used as a floor deck, a layer of concrete may be placed over the entire deck. Close-out panels may be placed to enclose portions of the assembled core elements that define the outer periphery of the deck. Alternately, the close out panels, which are securely attached to the top and bottom skins, are then glued together at the construction site to bond the modules into a continuous plate structure. In a presently preferred construction, the web material for making the open core elements is paper and, most preferably, resin-impregnated paper to make it waterproof. 
         [0011]    When utilized as a building roof or as a module for a large span roof, the present invention includes a unique post-stressing system and method in which as much as half of the load on the continuous roof plate structure is diverted. A pair of diagonally extending, generally orthogonal tension strips are stressed with a hydraulic force mechanism that pushes the strips away from the underside of the roof plate structure with a counterforce directed upwardly into the roof plate to overcome the dead weight deflection of the panel and, desirably, provide a positive upward deflection to carry the additional load of roofing materials and snow and ice loads. 
         [0012]    The invention also includes a method for making a load bearing deck or the like comprising the steps of: forming an open core element from a plurality of long and relatively narrow strips of a corrugated web material by bonding the strips together with the flutes extending between and perpendicular to the long edges of the strips, and with the open core element defining parallel rectangular upper and lower surfaces perpendicular to the flutes; bonding rectangular steel skins to the upper and lower surfaces of the core element to form a deck module, the skins each having opposite long edges that correspond to the length of the strips; and, connecting adjacent modules by welding or otherwise securing together the long edges of adjacent upper skins and lower skins. The structure acts as a continuous membrane or plate. The method may further include the step of pouring a layer of concrete over the interconnected upper skins to form the deck. The method preferably includes, prior to the concrete pouring step, the step of attaching a plurality of upstanding steel projections to the exposed surfaces of the upper skins, and the pouring step includes embedding the projections in the concrete. Also prior to the pouring step, the method may include the step of placing utility connections or chases for such connections on the exposed surface of the upper skins and embedding the connections or chases in the concrete during the pouring step. 
         [0013]    In another aspect of the subject invention, a substitute for the steel skins is a metal, such as aluminum, or fiber-reinforced plastics and similar composites. Skin sheets using materials other than steel would similarly be bonded to the upper and lower surfaces of the core element and adjacent deck modules would be joined together along the long edges of adjacent upper and lower skin sheets, using joining techniques appropriate for the skin sheet material being used. 
         [0014]    In accordance with one method of the present invention, the strips of corrugated web material used for forming the open core elements comprise strips of adhesively-joined fluted web and smooth web. The webs are preferably made of paper and the method comprises the additional step of water proofing the paper webs. The water proofing step may comprise applying an A-phase phenolic resin to the paper web and drying it to the B-phase before the forming step, and heating the open core elements after forming to a temperature sufficient to thermoset the resin. 
         [0015]    A structural roof plate or floor plate, made in accordance with the present invention, includes a rectangular open core element that is formed from strips of a web material that are expanded and connected to define open cores and having the open cores oriented to extend vertically. The open core elements have parallel upper and lower surfaces to which skin sheets are attached. A peripheral compression member encloses the core element and a pair of post-stressing tensile members are attached to the core element and the compression member to extend diagonally across the underside of the core element between opposite corners. A tensioning device interconnects the tensile members at their intersection and the underside of the core element. The tensioning device operates to move the tensile members vertically away from the underside of the core element and to impose a desire tensile load in the tensile members and a balancing compression load in the peripheral compression member. 
         [0016]    The web material for the floor plate core element preferably comprises corrugated paper. The web may be made waterproof and open core filled with an insulating foam. The floor or roof plate includes an anchor plate at each corner of the core element to provide an interconnection between the core element, the compression member and the tensile members. The anchor plate also serves as a bearing plate for supporting the roof or floor plate on vertical corner columns. 
         [0017]    The tensioning device for post-stressing the tensile members includes a fluid cylinder that has a cylinder body embedded in the open core element and a rod end connected to the tensile members at their intersection. An operating system applies fluid pressure to the cylinder to extend the rod end. In a presently preferred embodiment, the operating fluid comprises the liquid components of a hardenable epoxy adhesive. The operating system functions to hold the cylinder rod end in a selected extended position until the epoxy adhesive hardens. A load distribution plate is fixed to the cylinder body and bears against the lower skin sheet of the core element to help distribute the load. A connector plate is attached to the rod end of the cylinder and bears against the connected tensile members. 
         [0018]    The peripheral compression member preferably comprises reinforced concrete. There is a peripheral support for the compression member that preferably comprises a rectangular array of angle members, each angle member having a horizontal flange that supports the compression member, the horizontal flange in turn being supported at opposite ends on the anchor plates. 
         [0019]    The roof plate just described can be used in a multiple array for a large span roof for a building. The large span roof includes a plurality of rectangular open core roof modules positioned side-to-side and end-to-end to define the roof. Each module is formed from strips of a web material expanded and connected to define open cores. The open cores are oriented to extend vertically and define horizontal upper and lower surfaces. Skin sheets are attached to the upper and lower surfaces of the roof modules. A major peripheral compression member encloses the large span roof and minor peripheral compression members enclose each module. A pair of post-stressing tensile members are attached to each roof module and extend diagonally across the underside of the module between opposite corners. A tensioning device interconnects the tensile members at their intersection with the underside of the module. The tensioning device operates to move the tensile members at their intersection vertically away from the underside of the core element to impose a desired tensile load in the tensile members and to impose a balancing compression load in the major and minor compression members. 
         [0020]    The junctions of the ends of the tensile members of adjacent modules, and the junctions of the ends of the tensile members with the ends of minor peripheral compression members and with the major peripheral compression member are connected. The corners of the modules are supported on vertical columns. The major peripheral compression member is made of reinforced concrete and rests on a horizontal flange of a peripheral angle member, the angle member being attached to and supported by the columns. The peripheral edge of the roof rests on the horizontal flange and is tied to the concrete compression member. The minor peripheral compression members are preferably made of steel, but hollowcore beams made in the manner of the basic hollowcore module may also be used. 
         [0021]    In order to provide means for attaching equipment, equipment hangers and the like to the underside of an open core module, connector supports, preferably made of wood, are embedded in the open core element and have surface portions that are in contact with a skin sheet, such as the lower skin of the module. The supports are parallel and uniformly spaced across the width of the element and extend the full length thereof. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a perspective view of a structural deck or floor assembled from modules according to the present invention. 
           [0023]      FIG. 2  is a perspective view, similar to  FIG. 1 , showing a single open core module used in fabricating the deck of  FIG. 1 . 
           [0024]      FIG. 3  is a bottom plan view of the  FIG. 1  deck, showing reinforcing strips used in long-span construction. 
           [0025]      FIG. 4  is a bottom plan view of the deck module of  FIG. 2  with a portion of the lower skin sheet broken away to show the interior construction. 
           [0026]      FIG. 5  is an enlarged detail of a portion of  FIG. 4 . 
           [0027]      FIG. 6  is a section taken on line  6 - 6  of  FIG. 5 . 
           [0028]      FIG. 7  is a perspective view of a two-story building with the roof and second floor are constructed of modules similar to those used to form the deck of  FIG. 1 . 
           [0029]      FIG. 8  is an enlarged detail taken on line  8 - 8  of  FIG. 7 . 
           [0030]      FIG. 9  is an enlarged detail taken on line  9 - 9  of  FIG. 7 . 
           [0031]      FIG. 10  is an enlarged detail taken on line  10 - 10  of  FIG. 7 . 
           [0032]      FIG. 11  is an enlarged detail taken on line  11 - 11  of  FIG. 7 . 
           [0033]      FIG. 12  is an enlarged detail taken on line  12 - 12 - of  FIG. 7 . 
           [0034]      FIGS. 13 and 14  are enlarged vertical sections showing the construction and operation of the post-stressing system according to the present invention. 
           [0035]      FIG. 15  is a perspective view of a large building that uses a plurality of small roof decks of the  FIG. 7  building. 
           [0036]      FIG. 16  is a perspective view similar to  FIG. 2  showing a single open core module incorporating a connector support system. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Referring first to  FIG. 1 , there is shown a portion of a deck  10  or floor useful, for example, in the construction of a bridge or a building, in which a series of long and relatively narrow modules  11  are joined together and, optionally, covered with a poured concrete slab  12 . Each of the modules  11  (shown in  FIG. 2 ) could be made of any desired dimensions, but for use in a floor deck, for example, module  11  could have a depth or thickness of 24 in., a width of 10 ft. and a length of 50 ft. To fabricate a deck  10  50 ft. long and 50 ft. wide, five modules  11  would be joined along their long edges, as partly shown in  FIG. 1 . 
         [0038]    Each deck module  11  includes a hollow core element  13  of the type described and manufactured in accordance with the method disclosed in my above identified patent application. The hollow core element  13  includes a stack of long, narrow corrugated paperboard strips  14 , each of which in the embodiment shown comprises a fluted web  15  and a smooth web  16  joined with a suitable adhesive. The webs  15  and  16  may be made of many suitable materials, but resin-impregnated paper is presently preferred. 
         [0039]    In accordance with the hollow core lay-up method of my above-identified application, flutes are formed in the fluted web  15  of a substantially larger size than typically used for corrugated paperboard. The flutes may have a height of about ½ in. and, in order to provide a stack of strips  14  to make a module  11  with a 10 ft. width, approximately 240 strips would be required. The strips are 24 in. wide and 50 ft. long. The method and apparatus of my above-identified application are capable of forming up hollow core elements of the required size. 
         [0040]    Each of the rectangular hollow core elements  13  has plan dimensions of 10 ft. by 50 ft. Steel sheets comprising an upper skin  17  and a lower skin  18  are attached to the respective upper and lower surfaces  20  and  21  of the hollow core element  13 . The upper skin  17  may be, for example, 0.062 in. or less in thickness (for example as thin as 0.020 in.) and the lower skin  18  may be 0.125 in. in thickness and possibly as thin as 0.020 in. In such arrangements, the depth of core could be reduced down to 18 in. Although high modulus steel is preferred, other materials may be utilized, particularly for the upper skin where tensile strength and high modulus of elasticity are not major concerns. The skins  17  and  18  may be secured to the hollow core element  13  with any of a number of suitable adhesives, including epoxies. The resulting deck module  11  of  FIG. 2  is attached to like modules to fabricate the deck  10  shown in  FIG. 1 . Modules  11  are positioned side-by-side, preferably in their final positions in the structure in which they are used, with the long edges  22  of the steel skins  17  and  18  abutting. In this position, each abutting pair of upper skins  17  and lower skins  18  are connected with welds  23 . 
         [0041]    The upper surface of the upper skins  17  may be provided with an array of upstanding projections  24 , preferably short steel posts  25  which are welded to the skin  17 . The height of the posts  25  depends on the thickness of the concrete slab  12 , but for a 2 in. slab, posts having a height of about 1.5 in. are satisfactory. Once the modules  11  are welded together, concrete is poured onto the upper skin surfaces to form a slab  12  of a desired thickness. Any necessary utility connections, such as electric power conduits, piping and the like are placed on the upper skin surface and embedded in the subsequently poured concrete. 
         [0042]    The exposed core elements  13 , along the outer periphery of the fabricated deck  10 , are closed with suitable close-out panels  26 . The panels  26  may be made of any suitable material and glued, welded or otherwise secured to the exposed core elements  13  or the edges of the skins  17  and  18 . 
         [0043]    Although the composite structural support of the present invention has been described with respect to the fabrication of a floor for a building or a deck for a bridge, the present invention lends itself well to the fabrication of structural supports of a wide variety of shapes and sizes. For example, a much narrower module, namely one using a much smaller number of strips  14  (say 16 strips stacked to form a hollow core element about 8 in. wide) can function as a beam. 
         [0044]    A floor, deck or beam member made in accordance with the present invention could be provided with a camber as is sometimes done in long span beams. The inherent flexibility of the fluted paper core element  13  will permit the necessary flexure to be imparted to provide a camber. For example, one of the skins  17  or  18  is applied to the core element, the element then flexed to the desired camber and the other skin attached to the core in the bowed orientation. 
         [0045]    The stresses in the lower skin  18  of a deck  10  made in accordance with the present invention are very low and are uniformly distributed omni directionally throughout the lower skin. As a result, materials other than steel may be used for the lower skin, including aluminum, fiberglass and other fiber-reinforced plastic composites. 
         [0046]    The narrow strips  14  of corrugated web material preferably comprise paper and, as indicated above, include a fluted web  15  and a smooth web  16 . As also indicated previously, resin-impregnated paper is preferred. The resin impregnation provides a water proofing that protects the paper cores in the presence of moisture. One effective way of providing the water proofing is to apply an A-phase phenolic resin to the paper web and drying it to the B-phase before forming the open core elements  13 . Then, after formation, core elements are heated to a curing temperature sufficient to cause thermal setting of the phenolic resin. 
         [0047]    It may be desirable to construct a deck module  11  of the present invention to prevent the ingress and accumulation of water in the flute spaces defined by the hollowcore element  13 . One particularly suitable filler would be ultra-expanded closed cell foam. One method of filling the flute spaces is to first apply one of the skin sheets  17  or  18  to the hollowcore  13  and then fill the flute spaces with the liquid components necessary to generate the foam. After the foaming chemicals are in place, the opposite panel face is closed and the entire element is inverted so that the foam that is generated reaches the entire open flute space. It may be desirable to provide relief through one of the skins to permit expanding gases to exhaust. 
         [0048]    In the example discussed above, 50 ft. modules  11  having a length of 50 ft. and a width of 10 ft. are joined to fabricate a 50 ft.×50 ft. deck. In certain applications, in order to retain the long span and eliminate additional supporting columns and beams, supplemental reinforcing skin strips may be added as shown in  FIG. 3 . A series of long and narrow reinforcing strips  27  are attached to the lower skin  18  in a built-up diagonal orientation. In the arrangement shown, the first and second strips  28  and  29  are the narrowest and extend generally perpendicular to one another and nearly the entire diagonal distance across the lower skin  18 . These and the subsequently applied strips are preferably made of fiberglass with the glass fiber orientation being primarily in the long direction, for example, 90% of the fibers. The strips are applied with a resin adhesive and, in a preferred embodiment, the strips are laid in tension and held until the resin cures to provide a slight camber to the deck module  11 . The camber is subsequently eliminated when the concrete layer  12  is laid on the upper surface. The second strip  29 , identical in size and shape to the first strip  28 , is laid diagonally and perpendicular to the first strip. 
         [0049]    Third and fourth strips  30  and  31 , which are wider and shorter than the first and second strips  28  and  29 , are added. Fifth and sixth strips  32  and  33 , again shorter and wider than the third and fourth strips  30  and  31 , complete the reinforcing strip arrangement shown in  FIG. 3 . Obviously, more or less strips of different dimensions could be used, as required. This arrangement can also be utilized to permit the use of a thinner lower skin  18 , possibly as thin as 11 gauge (about ⅛ inch or 3 mm), possibly as thin as 0.015 in. This built-up strip arrangement concentrates the reinforcing at the center of the deck where the stresses are greatest. 
         [0050]    Any suitable skin material may be used for the reinforcing strips and the material may be the same as or different than the material used for the lower skin  18 . The upper skin layer  17  is not as critical from a strength standpoint and, as indicated above, the upper skin  17  may be much thinner (e.g. half the thickness) than the lower skin  18 . Thus, any suitable material may be used and, preferably, to which concrete will bond. 
         [0051]    In the process of attaching the upper and lower skins  17  and  18  to the hollow core element  13 , it is important to assure that an adequate amount of adhesive reaches the interface between the edges of the open core webs  15  and  16  and the respective skin sheet  17  or  18 . 
         [0052]    One method for maximizing the amount of adhesive at the interface is shown in  FIGS. 4-6 . A liquid adhesive layer  34  is applied to the inside surface of the skin sheet  18 . The hollow core element is placed on the glued face of the skin sheet. The skin and core element are held together and supported on a rotating structure that rotates the entire structure in a gyratory motion on a small radius (e.g. ¼ inch or 6 mm) at approximately 300 rpm or more. This causes an accelerative force to be imposed on the adhesive that causes the adhesive to be pulled from the center of each flute space to the edges of the flute/skin interface where the adhesive will slightly climb the core element edges and assure an adequate adhesive fillet. The semi-completed deck module  11  is inverted and the process is applied to glue the other skin sheet to the hollow core element. Most conveniently, the process of filling the flute spaces with a closed cell foam may be carried out simultaneously by adding the liquid components of the foam after the first skin sheet is applied and then inverting the module. 
         [0053]    Referring to  FIG. 7 , there is shown a two story building  35  in which the second floor  36  and the roof  37  are constructed using modules similar to those shown in  FIG. 2  to form the deck  10 . In the  FIG. 7  example, the roof  37  has six modules, each 10 ft.×50 ft., resulting in a building having plan dimensions of 50 ft.×60 ft. The second floor  36  has only five modules, leaving a high ceiling foyer space at the front of the building, as will be discussed in more detail below. 
         [0054]    The roof deck  38  is constructed in the manner described above, however, only two deck modules  11  are shown so other elements of the construction are more clearly visible. In the embodiment shown, the roof deck  38  is supported along the joined upper edges of building wall panels  40 . An angle member  41  is attached to and extends along the upper inner face of the wall panels  40  which define the rectangular shape and size of the roof deck  38 . At the corners of the wall panels, the ends of the angle members  41  are supported on a vertical column  42  which may be separate from the wall panels  40 , as shown, or be formed integrally with the vertical edges of the wall panels. The horizontal flanges  43  of the rectangular array of angle members  41  also support a peripheral compression member  44  that surrounds and encloses the roof deck  38 . The compression member  44  preferably comprises reinforced concrete having, for example, a cross section that is 3 in. wide and 24 in. deep, the depth being approximately equal to the depth of the hollow core modules  11 . 
         [0055]    A pair of post-stressing tensile members  45  extend diagonally across the underside of the roof deck  38  and are attached at opposite ends to the deck and the compression member  44 . To facilitate interconnection of the members, an anchor plate  46 , preferably made of steel, is attached near the upper end of each column  42  and to underside of the horizontal flanges  43  of the angle members  41 . The tensile members  45 , which may comprise steel strips ⅝ in. thick and 18 in. wide, may be welded or bolted to the anchor plates  46  and are also rigidly connected at their center crossing points. A tensioning device  47  provides a vertical connection between the tensile members  45  where they intersect and the underside of the deck  38 . The tensioning device  47  operates to move the tensile members  45  vertically away from the underside of the deck and to impose a desired tensile load in the tensile members. 
         [0056]    Referring also to  FIGS. 11 ,  13  and  14 , the tensioning device  47  includes a fluid cylinder  48  which is embedded in the hollow core  13  of the deck  38 . The lower skin  18  of the deck is sandwiched between a cylinder end plate  50  and a load distribution plate  51  that bears against the underside of the skin. The load distribution plate  51  may, for example, be about 10 ft. in diameter. The rod end  52  of the cylinder is attached to the tensile members  45  at their intersection with a connector plate  53  somewhat smaller n diameter than the load distribution plate  51 , for example, 18 in. By applying fluid pressure to the piston  54  of the cylinder  48 , the rod end  52  is extended and the tensile members are pushed away from the underside of the deck. By extending the cylinder rod and pushing the intersection of the tensile members  45  away from the underside of the deck by distance of, for example, 1½-2 ft. a high tensile load to approximately 60,000 psi may be imposed in the tensile members. The concrete peripheral compression member balances the tensile load. 
         [0057]    A presently preferred means of pressurizing the cylinder  48  and imposing and holding the desired tensile load in the tensile members  45  is to inject a mixed liquid epoxy directly into the cylinder under pressure. When the cylinder is extended to the end of its stroke (sized to match the distance by which the tensile members are moved away from the underside of the deck) pressure in the cylinder would be held until the epoxy hardens. When the epoxy is cured, position of the tensile members is fixed and there is no possibility of loss of pressure and/or leakage. In other words, the tensioning system is rigidly fixed. 
         [0058]    The roof deck  38  and tensioning device  47 , in effect, act like a virtual column that would otherwise be placed in the center of the building at the point of intersection of the tensile members  45 . The tensioning device  47  removes a substantial amount of the dead load and any additional live load on the roof deck without adding a center column support. Thus, in the present example, the building  35  provides a 50 ft.×60 ft. clear span with no interrupting columns. The operation of the tensioning device  47  results in upward force being imposed on the roof deck  38  sufficient to overcome the downward deflection of the roof deck under dead load and, in addition, to provide a positive upward deflection or camber of the roof deck to handle snow and ice loads. The tensioning device  47  also provides the opportunity to reduce the thickness of both the upper and lower steel skins  17  and  18  to, for example, 0.015 in. or less. 
         [0059]    One arrangement for effecting the corner connection of the various elements in the roof deck  38  of  FIG. 7  is also shown in the  FIG. 10  detail. Each of the four corner columns  42  comprises a vertical angle member  55  that extends from the building foundation to the top of the roof deck  38 . The vertical angle member  55  has, for example, 8 in. flanges and a length of about 28 ft. for the two story building shown. In the seam where the flanges join, the upper end of the angle member  55  is cut to provide a vertical slot  56  about ½ in. to ⅝ in. wide and 2½-3 ft. long. A triangular gusset plate  57  is welded in the slot  56  and to the top face of the anchor plate  46 . The anchor plate, in turn, provides for connection to the tensile members  45  and also for attachment of the horizontal angle members  41 , the peripheral concrete compression member  44 , and the corner of the roof deck  38 . A tight and rigid connection is thus provided for each corner of the roof deck. 
         [0060]    Referring to  FIG. 8 , the second floor  36  of the building is preferably constructed in a manner described for the structural deck  10  of  FIG. 1 . Thus, the second floor deck  36  is made of modules  11  having hollowcore elements  13  enclosed with upper and lower skin sheets  17  and  18 . The floor deck is also covered with a layer of concrete  12  of a suitable thickness, for example, 2 in.-4 in. Because the floor deck  36  does not include a tensioning device  47  as does the roof deck, the skin sheets  17  and  18  must be of somewhat greater thickness, for example, 0.020 in. 
         [0061]    The roof is supported along its peripheral edges on horizontal angle members  58  which are connected by welding or other rigid connections to the inside faces of the vertical column  42 . As may be seen in  FIGS. 7 and 9 , the floor deck  36  is made with one less hollowcore module  11  than the roof deck  38 . The free front edge  60  of the floor deck  36  is reinforced to form a beam-like structure  61  along the front edge  60 . The beam structure is conveniently formed of long, narrow hollowcore beam elements  62  having their own narrow enclosing skins  63  and attached to the upper and lower skins  17  and  18 , respectively, along the free front edge  60 . The beam-like structure provides support for the edge in lieu of a horizontal angle member  58  used to support the other three edges of the floor  36 . As shown, the lower beam element is somewhat deeper than the upper beam element. 
         [0062]    While the plate structure reduces the tension and compression in the skins, it also reduces the shear stress in the core by a factor of two because there is support on all four sides as opposed to just two opposite walls. This means that for normal roof loadings and floor loadings, the arrangement brings the normal shear stress requirements down to the range that can be accommodated with the low density paper core material, as described herein. 
         [0063]    As indicated above, the wall panels  40  are also preferably constructed using hollowcore elements similar to the elements  13  used in the  FIG. 1  building. As shown in  FIGS. 9 and 12 , the wall panels  40  are tied together by wooden closeouts  64  extending vertically along adjacent panel edges. The closeouts  64  are glued or otherwise fastened together to form a rigid continuous wall. The wall panels are 28 ft. long for the two story building shown in  FIG. 7  and may typically be 10 ft. in width to match the modularity of the elements used for the roof and second floor. 
         [0064]    Preferably, however, the wall panels  40  are also faced with outer skins  68  and inner skins  70  of thin steel or similar construction, the abutting edges with the columns of which are connected by gluing or other suitable connections, as described above with respect to the modules  11  forming the roof and second floor. Thus, the wall panels would also act as a continuous plate member, just as the roof and second floor decks. This rigid construction, coupled with the continuous roof and floor decks, post-stressing of the roof deck, and the rigid corner connections together provide tremendous load transferring capability and an extremely rigid structure. For example, a wind load perpendicularly against one of the walls will be transferred throughout and resisted by the entire structure. 
         [0065]    Referring now to  FIG. 15 , there is shown a large building  71  that is constructed of a plurality of roof decks  38  of small building  35  using the same principles of post-stressing and stress distribution described above with respect to the small building  35 . A large building  71  of virtually any size could be constructed. In the  FIG. 15  building  71 , the roof  73  is made of large building modules  72 , each of which is, in effect, a roof deck  38  of the small building  35  of  FIG. 7 . 
         [0066]    In the large building  71 , a plurality of rectangular large building modules  72  are positioned side-to-side and end-to-end to define the roof  73 . Each large building module  72 , like the roof deck  38 , is in turn made of plurality of modules  11  as previously described. 
         [0067]    The entire outer edge of the large roof  73  is enclosed by a major peripheral compression member  74 . As in the small building  35 , the major compression member  74  is made of reinforced concrete and is supported along its lower edge on the horizontal flange  75  of a peripheral angle member  76 . The peripheral edges of each large building module  72  not supported along an outer wall  77  are enclosed by minor peripheral compression members  78 . Thus, building modules  72  in the corner of the building  71  will have two edges supported on a peripheral angle member  76  and two edges closed and supported by a minor peripheral compression member  78 . Large building modules  72  along one building wall  77  will have one edge supported on a peripheral angle member  76  and the other three edges closed and supported by a minor peripheral compression member  78 . In the interior of the building  71 , all modules  72  not supported along an outer wall  77  will be closed on all four sides and supported by a minor peripheral compression member  78 . The minor compression members  78  comprise beams which are, in effect, dispersed in a checkerboard pattern in a manner allowing them to carry approximately the same loads in both directions as a result of the diaphragm construction of the roof module  72 . The beams, of course, also support vertical loads from the roof modules as well. 
         [0068]    Each large building module has a tensioning arrangement  80  that includes diagonal tensile members  81  and a tensioning device  82  which may be identical, respectively, to the tensile members  45  and tensioning device  47  used to post-stressed the roof deck  38  of  FIG. 7 . Hydraulic cylinders  83  for the respective tensioning devices  82  are tied together with a common hydraulic pressure system so that all tensile members  81  are deflected and stressed equally and simultaneously. As with the small building  35  previously described, the tensile load imposed in the tensile members  81  is balanced by the compression load in the compression members  74  and/or  78 , depending on the location of the module  72 . To tie the structure of the large roof  73  and the co-acting tensioning arrangements  80 , the junctions of the ends of tensile members  81  of adjacent modules  72 , and the junctions of the ends of tensile members  81  with the ends of minor peripheral compression members  78  and with the major peripheral compression member  74  are connected. The corners of each of the large building modules  72  are supported at their corners on vertical columns  84 . The columns at the corners of the large building may be angle members as described with respect to the columns  42  of the  FIG. 1  small building. The columns  86  located along a wall and the interior columns  87  may be of any suitable construction depending on the anticipated roof load. The minor peripheral compression members  78  may conveniently comprise inverted T-sections  88  made of steel. These sections could be adapted to be attached to and support the edges of adjacent roof decks  38  which comprise the large building modules  72  forming the roof  73 . Of course, as explained above, the skin sheets along the edges of adjoining large building modules  72  are also welded or otherwise securely connected. 
         [0069]    Referring now to  FIG. 16 , in order to provide convenient and easily accessible areas to attach equipment, hangers, wiring and the like to the underside of a module  11 , portions of the hollowcore element  13  may be routed or cut out before the lower skin  18  is attached and suitable wooden connector supports  89  inserted into the cut out portions. The connector supports  90  preferably comprise wooden members, such as 2 in.×4 in. pieces that extend the full length (e.g. 50 ft.) of the module  11 . The connector supports  90  may be spaced at 16 in. intervals or any other convenient spacing. Connections to the underside of the module are made by drilling through the lower skin sheet  18  and into the wooden support  90 . The outer surfaces  91  of the supports are in contact with and secured in the gluing operation to the lower skin sheet  18 . Similar connector supports could also be embedded in the core material at the upper surface of the module and flush with the upper skin sheet  17 .

Summary:
A stress-optimized structural support which may be utilized as a beam or assembled with similar supports to form a building floor or roof panel or a bridge deck utilizes an open core element, made preferably of suitably treated fluted paper, upper and lower thin skin sheets, preferably steel skins, and a layer of concrete poured over the top skin. Modules comprising the hollow core element and the upper and lower skin sheets are fabricated to lengths required for building floor, roof or bridge spans and, when joined by welding or otherwise joining the upper and lower skin sheets of adjacent elements along their full lengths, provide a floor or roof deck structure of a large span with horizontal stresses distributed omnidirectionally. A post-stressing tensile system redistributes and reduces the load on the roof deck by about one-half. Small building decks utilizing the stress redistribution system can be combined to build a large span roof in which multiple tensioning systems are coordinated to simultaneously effect the load redistribution.