Abstract:
A precast composite building system usable for walls, roofs, and floors of buildings, comprising a concrete composite panel element having embedded steel I-beams, wire mesh, embed plates, and steel tension reinforcement bars interconnected vertically, horizontally, and angularly by columnar elements rigidly fixed to the supporting foundation, embedded into the panel elements affixed to a transverse steel beam so as to form a perimeter tie-beam connection structure to which additional floor, roof, and wall elements are attached, forming a unitary, superior, load-bearing structure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to building construction and specifically to the construction of precast composite steel I-beam reinforced concrete panels and the method of interconnecting the precast panels to create floors, roofs and walls in a unitary integrated structure having high wind resistance and increased structural load bearing capabilities. 
     2. Description of Related Art 
     The advantages of reinforced concrete has long been known in the building industry, such as higher fire ratings and improved seismic and weather resistance. Concrete walls, floors and roofs have been commonly used in buildings, however pouring on site on forms built onto trusses or joists is slow and labor intensive. Thus, precast concrete building construction panels set into place and joined together to create a structure on site gained acceptance as a method to reduce the time, labor and material costs. The prefabricated panels, however, are not without problems if improperly prepared or installed. Without proper reinforcement or adequate joining of adjacent panels, cracking, questionable structural integrity, and diminished resistance to the forces of nature may result. 
     Many configurations have been employed utilizing prefabrication of concrete panels to construct buildings; for instance, U.S. Pat. No. 5,987,827 to Lord provides concrete panels formed utilizing a horizontal casting platform and having interlocking abutting joints. The structural integrity of the Lord system is provided wholly by the concrete and embedded reinforcement, requires integral wall panel footing and vibrator compactor for alignment, does not provide for prefabricated roof panels and requires multistory panels to be fabricated in one section thereby rendering the system impractical for off site construction and shipping. 
     The present invention described herein employs integral steel beams as a column in the wall panels, tilt up alignment adjustability independent of the footing design, continuous welded interpanel connection of steel S-beams forming a structural perimeter joining system, and provides for integral concrete roof panels which can accommodate multistory panel fabrication and transportation without much difficulty. 
     A precast panel interconnection system relying on concrete keys and keyways and which does not provide for prefabricated roof panels or multistory floor and wall panels is disclosed in U.S. Pat. No. 5,865,001 to Martin. The present invention does not utilize an interlocking panel construction. 
     U.S. Pat. No. 5,761,862 to Hendershot is a building system utilizing a connector assembly at the end of each panel spanning the vertical section of the panel corrugated edge and extruding steel reinforcement, precast corner sections, tongue and groove roof panel connections, integral precast footings, and structural tensions transmitted primarily by wire mesh and steel reinforcement. The present invention uses embedded steel plates welded panel to panel, even at the corners, the panel edges being beveled with no extruding steel, a continuous S-beam perimeter which accommodates structural tensions and shearing, conventional slab and footing construction, and no tongue and groove roof connection. In addition, the Hendershot system requires a post installation concrete pour while Applicant&#39;s system is wholly constructed on-site from prefabricated components. 
     U.S. Pat. No. 3,952,471 to Mooney teaches a precast concrete construction system with an integral concrete column structure included in the wall panels, an installation of protruding upright anchor bolts at the time of foundation construction and plates welded across panel joints for inter-panel connections. The present system employs embedded S-beam column members in the wall panels, steel plate embeds or anchor bolts after panel installation and a continuous perimeter S-beam connection. 
     U.S. Pat. No. 3,724,157 to Miram incorporates complex architecture of removable fasteners and internal steel reinforced panels and plates welded across the panel joints. Miram requires existing structural framework to attach the precast panels to at installation and post installation of steel beams spanning the panel joints. The present invention uses steel S-beams embedded in the wall panels as integral column structures, a continuous perimeter S-beam connection, no pre-installation structure to support the wall panels, and welds plates between panels embeds. 
     U.S. Pat. No. 4,472,919 to Nourse details a monolithic composite panel construction based on embedded steel channels and does not address the construction of complete structures. The present invention herein is a method of constructing a building utilizing wire mesh reinforced concrete with embedded S-beam columns for use in constructing multi-story buildings interconnecting the same elements for wall, floor and roof components. 
     In U.S. Pat. No. 5,678,372 to Thompson a system of adjacent reinforced preformed panels are joined to one another at undulating confronting edges wherein alternating reinforcement bars are connected to an arrangement of elongated bars and a zigzag reinforcement bar by a wet knit joint completed by introduction of concrete. Although employable for floors, walls, and roofs like the present invention, the present invention uses welded steel plates to attach the bevel-edged (not alternating steel bar reinforced concave/convex segments) panels together, S-beams embedded in the wall panels as integral column structures, a continuous perimeter S-beam connection, and no concrete poured at time of installation. 
     BRIEF SUMMARY OF THE INVENTION 
     A precast building system and method comprising an integrated structural support panel or wall which provides an increase in structural load-bearing capacities and subsequent reduction in structural mobility as compared to existing precast and composite building systems. The resulting structural panels are not limited to use as bearing, retaining, shear and architectural walls, but can be used as floor and roof panels as well. Additionally, regardless of the particular structural application for a which a given panel is applied, the basic design of the composite panel remains the same, which yields improved efficiency in planning, design and construction. The floor panels can be cast with varying degrees of negative camber based on the size of the panel being cast, the element being flipped over after removal from the casting mold to accommodate for the camber so the panel will lay flat when used for a floor surface. The panels can be manufactured as precast or on-site cast, providing maximum efficiency in the logistical implementation of a construction project. Further, the system incorporates the longstanding advantages of precast construction techniques of arbitrary design shapes and rapid assembly while providing the improvement of an I-beam as both a continuous perimeter tie-beam enhancing load reinforcement and providing columnar support, unavailable for instance with a bar joist which would likely collapse when similarly used. 
     The composite steel beam-to-concrete panel provides for the use of a uniform structural element for all parts of a given structure, expediting the planning and erection phases. The system is manufactured as structural panels on site, or delivered by conventional transportation as precast panels to the construction site. Many of the characteristics of traditional precast panel construction are maintained, however, incorporation of the I-beam within the panel element constitutes a significant structurally advantageous difference in the forming, structural embedding, casting, handling, and erection of the elements as compared to traditional precast construction. 
     The building system is comprised of a concrete slab of about a 3-inch desired thickness and ranging up to about 50 feet in desired length, featuring an embedded S-shaped steel I-beam, conventional steel wire-mesh, embedded plates, and conventional steel tension reinforcement bars (deformed steel rods). The I-beam provides columnar and flexural support for wall, floor, and roof structures. When used as columnar supports, the embedded I-beams are welded or otherwise anchored to the foundation, and are also welded to the continuous perimeter S-shape I-beam tie beam structure. When employed as flexural members to support roofs or floors, the embedded I-beams are welded to the continuous perimeter S-shape I-beam tie beam structure. Adjacent wall, floor and roof panels are structurally connected with steel weld plates. 
     According to standard industry practices, a mold or form is constructed according to the panel element dimensions and support requirements. The component reinforcement, including but not limited to S-beam shapes, wire-mesh, tension bars and embed plates are fixed in place. Concrete of standard aggregate and post curing compressive strength, preferably a minimum of 3,000 psi, is poured, allowing sufficient curing time to achieve sufficient strength. The panel is then removed from the mold by a claw-like custom lifting technique, and is ready for transport or on-site erection. 
     A fundamental feature of the system is the manner in which the composite elements are interconnected to form an integral structure. The columnar element support beams embedded in the panels are welded or otherwise affixed to a transverse steel beam (tie-beam) which forms a continuous perimeter connection structure. The transverse beams can also serve as flexural support for floor and roof elements, e.g., withstanding bending loads imposed by the floor or roof panels, as well as providing structural integrity for wind resistance. In addition to this continuous perimeter flexural and tensile support structure, the columnar elements are rigidly affixed to the supporting foundation. Further, inter-element connections are formed at the panel interfaces to connect panels together, providing additional structural integrity. The resulting structure exhibits superior structural load-bearing characteristics in both compressive and tensile loadings, while providing maximum efficiency in construction expediency and overhead reduction. 
     The object of the invention is to provide a precast concrete I-beam reinforced panel which, when interconnected using the beams and embedded plates, is interchangeably usable for floors, walls, and roofs to construct a superior structurally load-bearing building which is cost and time efficient and resists most hurricane force winds. 
     In accordance with these and other objects which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of the finished composite element. 
     FIG. 2 is a perspective partial cross-sectional view of the finished element before removal from the mold. 
     FIG. 3 is a partial side elevational cross-sectional view of the panel element mold and embed. 
     FIG. 3A is a partial side elevational cross-sectional view of the panel element mold and embed as used in an on-site casting of the system elements. 
     FIG. 4 is a side elevation cross-sectional view of the panel element. 
     FIG. 5 is a side elevation cross-sectional view of the standard inter-element connection. 
     FIG. 5A is a side elevation cross-sectional view of two interconnected panels at the connection junction. 
     FIG. 6 is a top plan cross-sectional view of the standard inter-element corner connection detail. 
     FIG. 7 is a perspective view of the panel element lifting apparatus. 
     FIG. 8 is a side elevation cross-sectional view of the panel element lifting apparatus applied to the I-beam. 
     FIG. 9 is a perspective view of a panel element in preparation for lifting or removal from the mold. 
     FIG. 10 is a perspective view of a panel element as in lifting or installation after removal from the mold. 
     FIG. 11 is a perspective cross-sectional view of a junction of two lower story wall panels, one upper story wall panel, and a floor panel. 
     FIG. 12 is a perspective cross-sectional view of the floor panel and connection shoe. 
     FIG. 13 is a side elevation view of joined wall panels. 
     FIG. 14 is a side elevation view of a wall panel and foundation connection. 
     FIG. 15 is a perspective view of an alternate embodiment of a panel foundation connection. 
     FIG. 16 is a perspective view of the preferred embodiment of a panel foundation connection. 
     FIG. 17 is a side elevation cross-sectional view of the wall-to-floor panel connection with floor panel beams parallel to wall. 
     FIG. 18 is a side elevation cross-sectional view of the wall-to-floor panel connection with floor panel beams perpendicular to wall. 
     FIG. 19 is a side elevation cross-sectional view of a structural steel frame for floor/roof panel bearing. 
     FIG. 20 is a side elevation cross-sectional view of the roof-to-wall panel connection along an exterior wall panel. 
     FIG. 20A is a top plan cross-sectional view of the roof-to-wall panel connection at wall corners. 
     FIG. 21 is a side elevation cross-sectional view of the roof-to-wall panel connection along exterior walls. 
     FIG. 22 is a cross-sectional side elevation view of the entire structure. 
     FIG. 23 is a perspective view of the typical L-angle bracket used in panel connections. 
     FIG. 24 is a perspective view of the typical studded L-angle bracket used for foundation connections. 
     FIG. 24A is a side elevation view of the typical studded L-angle bracket used for foundation connections. 
     FIG. 25 is a perspective view of a typical weld-plate used for inter-panel connections. 
     FIG. 26 is a perspective view of a panel embed plate with L-shaped steel embed rod. 
     FIG. 27 is a perspective view of the typical wire-mesh reinforcement used in the panels. 
     FIG. 28 is a perspective view of a typical studded embed plate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, the invention will now be described in detail with regard to the best mode and preferred embodiment. The present invention is the uniform precast steel I-beam reinforced concrete panel for walls, floors, and roofs and the method of interconnection of these panels on site to form a highly wind resistant integrated unitary structure. 
     The precasting of the panel  35  off-site, shown in FIGS. 2 and 3, consists of welding studs  31  to an S-shape steel I-beam  32  at about six-inch intervals, centered along the bottom flange  54  of the I-beam. Conventional wire mesh  33  is introduced into the mold  34  extending to the perimeter of the mold over which the S-shaped I-beam  32  is placed, each end of the I-beam resting atop opposing edges of the mold  34 . The wire mesh  33  (shown in perspective in FIG. 27) is supported underneath by spacers  48  which raise the mesh off the bottom surface of the mold approximately one inch to allow for a reasonable amount of concrete cover over the mesh to reduce the potential of the mesh rusting due to the presence of moisture accumulated in the cement should the depth of the mesh within the slab be shallower. 
     Referring now to FIGS. 1 and 3, embed plates  38  with studs  31   a  (shown in FIG. 28) and rigid displacement blocks  36  are set in at intervals along the opposing longitudinal sides of mold  34 . Concrete, preferably about 3,000 psi, however greater psi can be used, is poured in even layers into the mold  34  until the surface of the bottom flange  54  of each I-beam  32  is flush with the surface of the concrete, thereby embedding the I-beam studs  31 , the wire mesh  33 , studded embed plates  38 , and displacement blocks  36  into the concrete to form a composite three-inch thick panel  35 . The panel can range in width to about 50 feet and in length to about 50 feet, depending on structural requirements. One or more I-beams are spaced apart in parallel arrangement a maximum of 4 feet apart across the panel. 
     In FIG. 3, the preferred embodiment is shown with a rigid displacement block  36 , attached to the mold  34  to allow for lateral recesses containing steel embed plates  38 . Spacing and dimension vary by application, however, it is preferred that the embed plates are about 12 inches from the leading adjacent edge of the panel at both ends with one or more embed plates spaced between as shown in FIG. 1. A steel weld plate  42 , shown in closeup in FIG. 25, is welded across the embed plates  38  and connects the panels, then the recesses are filled with bonding cement  37  to form a continuous and uniform surface as shown in FIGS. 5,  5 A, and  6 . FIG. 3A shows how panel  35  is cast on site using a block of wood  56  to reinforce and stabilize the form  34   a  positioned on the existing foundation slab  55 . 
     In the wall panel corner connections, conventional reinforcement bars (rebars)  39 , usually about 30 inches in length, are welded to the steel embed plates  38 , forming an L-shape as shown in FIG. 26 before being introduced into the mold  34 . The rebars  39  are positioned to extend away from the mold face at a 90 degree angle to provide embed plate  38  anchorage for corner connections shown in FIG.  6 . Studs  31   a  on the embed plates  38  shown in FIG. 28 can be substituted for the rebar to hold the embeds in place. 
     Referring to FIGS. 2,  3 ,  3 A, and  5 A, the concrete is allowed to cure and is treated according to industry standards. Typically, all longitudinal leading edges are beveled  47   a  at about 45 degrees by placement within the mold of a longitudinal pyramidal rod  47  along the length at the junction between the bottom and side walls of the mold  34  or form  34   a . The pyramidal rod  47  takes up space, preventing concrete from flowing into the mold edge region, creating an approximately 45-degree bevel on the edge of the panel element. The beveled edge  47   a  shown in FIG. 5A serves to create an increased surface area and bonding angle for the elastic joint grout weatherproofing. 
     In FIGS. 7,  8 , and  9 , the panel is lifted from the mold by the top flange  54   a  of I-beam  32  using a winch connected to the aperture  67  in the structural T-shaped bracket  40  on the U-shaped steel claw  41 . Each claw  41  is secured in place using a chain  57  hooked to the top and bottom of the S-shaped I-beam  32  to keep the claw  41  from sliding toward the middle of the I-beam. 
     In FIG. 10, the panel  30  is lifted, lateral and horizontal movements are assisted by lifting devices using chains  57   a  having J-hooks  59  inserted through an aperture  58  located at the upper end of the I-beam  32 . Lifting, placing and basic erecting maneuvers of the panels  30  are similar for all uses, and is executed in a manner customary in the precast/tilt-up industry. Once lifted, the panel can be placed on any carrying means, such as a truck (not shown) for transport to the construction site. 
     In FIGS. 5,  5 A,  6 , and  13 , two panels,  61  and  61   a , whether to be along a planar side of the building or at a corner connection, are joined by aligning each set of two abutting embed plates  38  over which is welded a weld plate  42  to form a rigid connection between the two panels. 
     FIG. 20A shows an alternate way of connecting wall panels  61  and  61   a  at a corner by a welding cap plate  50  over the junction of two columnar I-beams  32  and two tie-beams  43 . 
     In FIGS. 11 and 22, the vertical wall panels are tied together by means of a continuous tie-beam  43  welded at bottom flange  64 , positioned perpendicular to, and on top of, the cross-sectional end of columnar I-beams  32  embedded within the composite wall panels  61 . In FIGS. 13,  14 ,  15 ,  16 , and  22 , the wall panel  30  is positioned on the foundation  55  with the base of the columnar I-beam aligned with a studded base plate  44 , the structural concrete slab  35  of the panel  30  is positioned on foundation ledge  70  which is present on the perimeter of the foundation. This assures that the panel I-beam columns  32  carry the structural load of the building. Any gaps or crevices between the panel  30  and the foundation ledge  70  are filled with bonding cement  37 . The bases of such columnar I-beams in wall panels  61  are welded or bolted to studded base bracket  44 , shown in closeup in FIGS. 24 and 24A, embedded afoot each of the vertical S-shaped I-beams into the structural foundation  55 . Alternatively, the I-beam  32  can be secured with a steel L-angle bracket  51  welded to the web of the I-beam at the base. The typical L-angle bracket  51 , shown in closeup in FIG. 23, is bolted to the foundation  55  using standard anchor bolts. 
     The horizontal panels, e.g., floor panels  60 , which have embedded I-beam supports perpendicular to the continuous wall perimeter tie-beam  43 , are supported at the end walls by welding a shoe  45  on the top of the flange  54  of floor panel I-beam  32 . The shoe  45  is typically about a nine and one-half inch long and three-inch deep S-shape, which is attached through longitudinal welds along the panel&#39;s I-beam flange. The standard weld length is about six inches and the bearing depth is about three and one-half inches. The top flange of the shoe  45  is flush with the top surface of the floor panel  60  and the shoe  45  is fully embedded into the concrete. The shoe is then welded to the continuous S-shape tie-beam  43  shown in FIGS. 12,  18 , and  22 . For floor panel with embedded I-beams which span the direction parallel to the continuous tie-beam  43  as seen in FIGS. 11 and 17, the floor panel  60  contains an embed plate which is welded to the top of the tie-beam. 
     Referring now to FIGS. 19,  20 ,  20   a ,  21 , and  22 , a structural support matrix of tubular steel shapes  53  and W-shape I-beams  52  can be erected to form a support structure for floor and roof elements. The W-shape I-beams  52  are not embedded in the panels, but act as truss elements. FIG. 20A illustrates a corner connection between two wall panel elements  61 , a cap plate  50  is welded over two cornering continuous tie-beams  43 . In FIGS. 19,  20 , and  21 , an inclined W-shape I-beam  52 , having vertical web stiffeners  69 , is miter cut and welded flush on the cap plate  50 . Along the interior wall element sections, a tubular steel column  53  may be welded in place on the upper flange  65  of the continuous tie-beam  43  to provide sufficient height and bearing support for the W-shape steel beams  52 . 
     In FIGS. 5,  5 A, and  6 , a filler rod  46  with sealer applied thereon is inserted to fill the gap between abutting panels. In succession, the remaining void space is then filled with filler cement  37  to about one-third of the joint depth and enclosed to the outside by impervious permanently elastic joint grout  49 . 
     When casting the panels  35  on site, as shown in FIG. 3A, all of the above applies, however, instead of using an oil-treated prefabricated steel mold, a form  34   a  is set up in which the concrete is cast. The concrete may be poured onto an existing floor slab  55  that has been treated with form oil. 
     Once a suitable structural foundation  55  is in place, preferably with embed plates, the wall panels may be installed. The embed plates  38  are set in the foundation concrete at the time the foundation is poured along the periphery of the foundation edges where wall panels are to be installed as shown in FIG.  14 . The typical embed spacing is 48 inches. The wall panels  35  depicted in FIG. 10 are lifted by a crane (not shown) and positioned for installation above the ledge  70  of foundation  55  with the wall panel embedded columnar I-beam aligned with, and resting directly on, the exposed foundation embed plate as seen in FIG.  14 . The panel is secured in place by industry standard tilt-up panel bracing. The columnar embedded I-beam  32  is then welded directly to the studded base plate  44  on the existing foundation, as shown in FIG. 14 or, alternatively, as shown in FIG. 15, the I-beam may be welded to an L-angle anchor plate  51  which is secured to the foundation  55  with standard expansion bolts. This process is repeated for all first floor wall panels. 
     Referring to FIG. 13, adjacent wall panels  61  and  61   a  are then structurally connected with steel weld plates  42  which span the adjacent panel-to-panel embed plates  38  located along the vertical edges of adjacent panels. At places where adjacent wall panel elements form a corner, steel weld plates  42  are fully welded to embed plates  38  set in the interior corners of the wall sections, as well as being fully welded to each other to form a corner connection as seen in FIG.  6 . 
     A continuous tie-beam  43  is then fabricated by installation of S-shape steel I-beams transverse to, and along the top of, the wall panel columnar embedded I-beams  32 . The tie-beam connection is achieved by directly welding the bottom flange  64  of the tie-beam  43  to the top cross section  66  of the panel embedded I-beam as shown in FIGS. 11,  17 ,  18 ,  20 ,  21 , and  22 . 
     Referring now to FIGS. 12,  18 , and  22 , once the continuous perimeter tie-beam  43  is installed, the second floor panels can be installed. The floor panels are set into place with the floor panel embedded I-beam shoe  45  resting on the tie-beam. The floor panel shoe  45  is then welded directly to the top flange  65  of the tie-beam  43 . Adjacent floor panels  60  are structurally connected by steel weld plates  42  or rods  39  which are welded across embed plates  38  set along the peripheral edges of adjoining floor panels. Once the floor panels  60  are installed, the wall panels  61  are lifted into place on the second floor and secured with industry standard temporary bracing (not shown). The wall panels  61  are aligned on the second floor such that the wall panel embedded columnar I-beam  32  is directly above the continuous perimeter I-beam  43 . The wall panel embedded I-beams  32  are then directly welded to the top flange  65  of the continuous perimeter I-beam  43 . Once the wall panels  61  are in place, adjacent wall panels  61   a  are structurally connected with steel weld plates  42  across the wall panel embeds  38  set along the vertical edges of adjoining panels as shown in FIG. 13. A continuous tie-beam  43  is then fabricated for the walls on the second floor (or any multiple upper floor) by installation of S-shape steel I-beams  32  transverse to, and along the top of, the second floor wall panel columnar embedded I-beams as shown in FIG.  22 . The bottom flange  64  of the tie-beam  43  is directly welded to exposed cross-sectional top edge  66  (shown in FIG. 16) of the embedded columnar I-beam  32 . 
     The installation of roof panels may proceed once all the upper floor wall panels are fully installed. Depending on the particular architectural details of the roof panel placement, two methods are employed to support the roof panel elements. In the case wherein the lower section of a roof panel rests on a wall panel, the roof panel embedded I-beam  32   a  may rest directly on the perimeter tie-beam  43  as depicted in FIG. 22, the roof panel I-beam being directly welded to the tie-beam  43  top flange  65 . In the situation where the wall panel extends above the height of tie-beam  43  top flange  65 , a structural steel tubular shape  53  is used as a column support between the tie-beam  43  and roof panel I-beam  32   a  as shown in FIG.  21 . The columnar support is fully welded at both the tie-beam flange  65  and the I-beam flange. 
     Referring now to FIGS. 19 and 21, in the case where the roof panel  62  cannot rest on an exterior wall panel, a tubular steel column  53  is positioned and affixed to the foundation to support the roof panel. The column has a steel cap plate  50  welded to its upper cross section. The roof panel is welded to I-beam  52  via embeds in the roof panels, then the supporting W-shape steel I-beam  52  is welded to a cap plate  50  supported by tubular steel columns  53 . Once the roof panels  62  are in place, adjacent roof panels are structurally connected with a weld plate  42  or rod  39  which is welded across embed plates  38  (see FIG. 26) set along the outside edge of adjacent roof panels. 
     Once a panel is in place and properly connected, it is ready to bear the design loads. Referring now to FIG. 22, the final interconnected structural assembly  63  of floor, roof, and walls is achieved primarily by welding aligned and adjoining floor, wall, and roof panel elements  60 ,  61 , and  62 , respectively, together horizontally, vertically, and/or inclined, or as other specified parts of a structure (not shown). After the structure  63  is fully erected and installed, all inter-panel joints are sealed with an elastic filler rod  46 , non-shrink bonding cement mix  37 , and an elastic joint sealer  49  as depicted in FIGS. 5 and 5A. All weld plate connections are filled with non-shrink bonding cement mix  37  to provide a smooth finished outer surface. The precast finished building structure  63  as connected is calculated to resist hurricane level wind forces. 
     The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made therefrom within the scope of the invention and that obvious modifications will occur to a person skilled in the art.