Abstract:
A very lightweight tubular building element for the construction of reinforced concrete floors and roofs; providing the formwork for the casting in place of the structural concrete and a high quality finished ceiling at the same time. It is a single component that can be installed easily and efficiently without heavy equipment or special craftsmanship; afterward the component is not removed, but stays permanently integrated in the concrete floor or roof. It forms a deck that is impervious, eliminating cumbersome cleaning during construction and leakage afterward, saving the common need of a costly waterproofing membrane over the slab. The formwork deck, composed of a plurality of the invention component, weighs less than four (4) pounds per square foot; and a single component for a common 15 feet span weighs less than 30 pounds, which can be easily handled by only one laborer. Furthermore, in forming the concrete, the plurality of this component creates hidden closed air spaces in the slab that saves concrete, reduces the overall weight of the building and provides better thermal insulation in comparison with a conventional solid concrete slab of same span, thickness and strength.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This is a continuation-in-part of application Ser. No. 09/433, 593 filed on Nov. 2, 1999. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a single very light tubular building element for the construction of reinforced concrete intermediate floors/ceilings and roofs. The single building element provides the formwork for the casting in place of the structural concrete and also provides for a high quality finished ceiling at the same time. It is intended for simple installation without heavy equipment into building parts. A series of members are often intended to form an exposed surface when used as a floor or ceiling.  
           [0003]    A series of members are constructed and often arranged to be the primary means of containing and supporting a panel or slab of concrete as it cures. An interconnected series of members, according to the present invention, also form a continuous mortar impervious formwork for a concrete slab, and presents an attractive permanently exposed ceiling surface.  
         PRIOR ART  
         [0004]    There have been many suggestions for use of either or both temporary or permanent form members to construct building parts of concrete. These form members can be temporary in nature since they are removed after concrete cures, or can be contained in concrete as permanent parts.  
           [0005]    For example:  
           [0006]    U.S. Pat. No. 5,953,880 teaches a modular building system of extruded hollow thermoplastic structural components of rectilinear cross-section. These members are made of a special thermoplastic mixture said to resist the elements and are characterized by a fire-resistant outer skin. The concrete is poured inside the thermoplastic components which have internal apertures through which the concrete can flow from one member to another member in a group when they are joined as a wall panel, for example. When the members are to be used in construction of a roof, concrete cannot be used, and metal inserts are called for to assist in stiffening.  
           [0007]    U.S. Pat. No. 5,729,944 discloses the use of thermoplastic structural components as permanent formwork. The forms can be used in a series to construct various structures. Concrete is poured inside the thermoplastic components which have internal apertures through which the concrete can flow from one member to another member when they are joined as a wall panel.  
           [0008]    U.S. Pat. No. 5,397,096 is illustrative of conventional concrete forming techniques to manufacture a ribbed, reinforced concrete slab. The forming system utilizes concrete displacement pans supported on temporary framework. The patent discloses the problem of concrete leaking out of joints. The leaking material normally is without aggregate, and is sometimes referred to as mortar. When the concrete slab or slab cures, workers must remove the hardened mortar with a chisel, or the like, providing an unsatisfactory surface finish. The bottom surface is neither planar nor finished. The patent suggests the use of additional members to forestall the leakage of mortar.  
           [0009]    U.S. Pat. Nos. 4,557,031 and 5,216,863 are illustrative of other expedients to join extruded plastic form members for use in containing concrete inside. The members are normally a part of the cured concrete structure or building component.  
           [0010]    U.S Pat. No. 5,535,565 is illustrative of a containment including a plurality of panels that are interconnected by connector columns and fused together by the passing of electrical current through conductors received within such elements at their points of intersection. The panels are interconnected by sliding one adjacent panel over another panel. A gasket is interposed between a pair of panels to create a watertight environment.  
           [0011]    U.S. Pat. No. 5,535,565 is illustrative of a highly sound insulating clay tile for the construction of floors that has an outer substantially parallelepiped shape with symmetrical, laterally projecting portions that act as shoulders for the support of each tile by prefabricated reinforced concrete floor beams.  
           [0012]    While the field of reinforced concrete formwork is well-developed, there is still the need for a relatively inexpensive easy-to-use system to form ribbed-concrete slabs with structural formwork components. The system should not be as labor intensive as prior art arrangements. It should use components that are lightweight and yet will control elastic deformation such as is often encountered when steel and aluminum alloy formwork is used to make such ribbed structures. Moreover, each element should be easily aligned with an adjacent member, the alignment means providing an impermeable alignment between adjacent members. Thus, eliminating the need of additional members (e.g. gaskets) or fusing of the adjacent members to accomplish impermeability.  
           [0013]    Further, the members making up the formwork should not be filled with concrete, to create the slab. Similarly, the members should include an easy device for placement of reinforcement bars without the need of manual tying or securing of the reinforcement bars together.  
           [0014]    It is also desirable to have the ability to incorporate the formwork into the slab and have it serve as an impervious formwork base, eliminating cumbersome cleaning during construction and leakage afterward, and saving the common need of a costly waterproofing membrane over the slab. The formwork should serve for the casting in place of the structural concrete and also should provide for a high quality finished ceiling at the same time, eliminating the need to plaster and otherwise enhance the aesthetic appeal of the ceiling. Finally, the formwork should facilitate hung ceiling installations and also be easily penetrable to hold threaded screws and the like.  
         BRIEF DESCRIPTION OF THE INVENTION  
         [0015]    There is provided an elongated tubular member arranged to be interconnected in a series. Each member is constructed of extruded thermoplastic material, is relatively thin walled, and light in weight. In a preferred embodiment, it will weigh less than four pounds per square foot, i.e., the individual members weigh about 2 pounds per linear foot, so that a 5 meter long member weighs about 32 pounds and can be handled by only one laborer without need of special equipment. It is intended to be incorporated in structural, reinforced ribbed concrete slabs used in roofs and floors.  
           [0016]    The members serve as a continuous mortar impervious formwork on the bottom of a poured concrete slab while it is curing. It thus avoids the leakage of concrete mortar through formwork joints during concrete pouring and cure time which leakage can result in honeycomb void defects that cause the structure to be prone to possible future corrosion of steel reinforcement contained in the concrete slab. Such corrosion is often difficult and costly to repair.  
           [0017]    The formwork permanently serves as the bottom of the slab. It is an impervious barrier of the type essential for roof construction and thus eliminates the need for an exterior waterproofing membrane. The formwork has transverse, flexural strength and stiffness sufficient to resist vertical and lateral construction loads without significant deformation. It can bear the weight and pressure of wet concrete, needing but few transverse intermediate temporary supports directly under the hollow elements which make up the formwork. For example, a line of 4×4 wooden purlines, spaced about five feet apart over 4×4 wooden shores, also spaced about five feet apart, or equivalent simple systems of metal purlines and shores can be used.  
           [0018]    The members are generally formed of a PVC (polyvinyl chloride) alloy conforming with Uniform Building Code (UBC). Any UBC conforming extrudable and light weight similar material of equal or better strength and durability will be suitable. This general type of theremoplastic is lightweight and easily formed by extrusion with many integral convenient features, but has lower modulus of elasticity (stiffness) than most other construction materials. For example, the modulus of elasticity of steel is more than sixty times more than in thermoplastic and the modulus of elasticity for aluminum is more than thirty times more than in thermoplastic.  
           [0019]    The center section is like the hat crown and the wings are like a hat brim. A member is defined by a top and a parallel bottom wall interconnected by parallel side walls which are substantially perpendicular to the top and bottom walls. There is an internal generally horizontal wall between the enclosing side walls. Above that internal horizontal wall and limited by the top and side walls is formed a closed rectangular box-like conduit when viewed from an end. In that rectangular space, it is easy to install a band of fiberglass mat to improve thermal insulation of the concrete slab, if desired. Below that internal horizontal wall and connecting it with the bottom and side walls, there is a web of three shorter longitudinal internal walls. One of them is a longitudinal vertical wall extending from the center of the horizontal internal wall (at a central intersection) to the center of the bottom wall. In one embodiment, the other two web walls are symmetrical, sloped down and outward from the center intersection. The side wings taper from a relatively thick area adjacent the side wall to the narrowest area at the end where there is a finger or groove. The sloped walls, side wall bottom wall, and bottom left and right intersections between the bottom wall and side walls are thickened in the area where the wings join the side walls thereby forming an area better able to absorb bending stress which reduces consequent deformation from the side wings when wet concrete is poured above them.  
           [0020]    In a second embodiment, the two sloped walls extend symmetrically, are sloped down and outward from a first set of two symmetrical points very close to the center intersection of the horizontal internal wall, through the side walls, and rest at points on the wings near the left and right intersections between the bottom wall and the side walls. Because the sloped walls rest on the wings, they act as tensors and increase the stiffness of each wing sufficient to counter deformation caused by vertical forces acting downward on the top of the wings. In this embodiment, there is no need to taper the thickness of all members connected at the bottom right and left intersections as there is when using the embodiment described above.  
           [0021]    There are wing-like webs extending outwardly from each side of each member, having a lower surface, which is substantially on the same plane with the outside lower surface of the bottom wall. The outermost end of one wing has an upwardly extending finger or tongue; and the outermost end of the second wing has a groove like an inverted U, arranged upwardly with the opening facing down. The finger and groove serve as an alignment means. The groove-ending wing fits easily above the tongue-ending wing in a lapping relationship between adjacent members when such members are laid up in a series prepared to receive wet concrete. Since each member has always both wing ending types, for proper lap matching, all members for a formwork deck shall be laid with the tongue wing ending on the same side; that side corresponding with the direction in which the installation proceeds.  
           [0022]    The construction technique of the present invention facilitates hung ceiling installations to form a plenum through which heating and air conditioning pipes or ducts are passed.  
           [0023]    Further, the construction facilitates the accurate arrangement of steel reinforcing bars because of the unique construction of parts. The invention permits the construction of ribbed reinforced concrete slabs with about one-half the weight of concrete, which might otherwise be required, which slabs are both resistant and stiff.  
         OBJECTS OF THE INVENTION  
         [0024]    It is an object of the invention to provide lightweight, thermoplastic structural formwork members constructed and arranged to be interconnected in a series to serve as formwork for ribbed concrete slabs.  
           [0025]    Another object of the invention is to provide lightweight, inexpensive, and easy to install structural members for use in constructing ribbed concrete slabs.  
           [0026]    Another object of the invention is to provide formwork for ribbed concrete slabs that forms a continuous impervious structure, eliminating the needs for exterior waterproofing membranes when used in roof construction.  
           [0027]    It is another object of the invention to provide formwork which has the longitudinal and transverse flexural strength and stiffness sufficient to resist the weight of the wet and vertical and lateral construction loads , yet needing few transverse intermediate temporary supports while the concrete cures.  
           [0028]    It is another object of the invention to provide ribbed concrete formwork having a pleasant appearing exposed surface capable of being used as a finished ceiling with regular longitudinal features or embossing which can be formed during the extrusion process at no extra cost.  
           [0029]    Another object of the invention is to facilitate hung ceiling installation in commercial and institutional buildings where it is necessary to have a plenum for heating and air-conditioning pipes and duct work above the ceiling. The formwork provides outward indicia or other markings indicative of areas in which hanger means for the ducts and pipes may be located with assurance of sufficient holding strength of easily penetrated material, for example, to screw in hangers for the hung ceiling, ducts, and pipes.  
           [0030]    Another object of the invention is to facilitate installation of thermal insulation for the ribbed slab.  
           [0031]    It is yet another object of the invention to facilitate the accurate and easy installation of steel reinforcing bars and/or splice bars in association with the formwork before pouring of the concrete.  
           [0032]    Yet another object of the invention is to provide for construction of ribbed reinforced concrete slabs using about one-half the normal weight and volume of concrete as compared to conventional forming techniques.  
           [0033]    These and other objects, features, and advantages of the present invention will be more clearly understood and appreciated by review of the following detailed description of the disclosed embodiments and by reference to the appended drawings and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a vertical cross-section of one embodiment of a structural member according to this invention;  
         [0035]    [0035]FIG. 2 is an alternate preferred structural member according to this invention in cross-section;  
         [0036]    [0036]FIG. 3A is a partial cross-section of a portion of two adjacent members of the type shown in FIG. 1, having a reinforcement chair with one reinforcement bar;  
         [0037]    [0037]FIG. 3B is a partial side view of the arrangement of the reinforcement chair of FIG. 3A;  
         [0038]    [0038]FIG. 4A is a partial cross-section of a portion of two adjacent members of the type shown in FIG. 2, having a reinforcement chair with a plurality of reinforcement bars (or, alternatively, a reinforcement bar and a splice bar);  
         [0039]    [0039]FIG. 4B is a partial side view of the arrangement of the reinforcement chair of FIG. 4A;  
         [0040]    [0040]FIG. 5 is a transversal cross-section of a series of the tubular members  9  in a ribbed concrete slab  60 ;  
         [0041]    [0041]FIG. 5A is a detail of FIG. 5 showing a reinforcing bar  53  in the concrete slab  60  above the longitudinal alignment means of an adjacent pair of the tubular members;  
         [0042]    [0042]FIG. 5B is a perspective view of a ribbed concrete slab according to this invention;  
         [0043]    [0043]FIG. 6 is a schematic side elevation of an arrangement of slabs of the type shown in FIG. 5, supported on vertical walls.  
         [0044]    FIGS.  7 -A,  7 -B and  7 -C are schematic illustrations of the elastic deformation of the cantilever and the maximum deflection at the tip when subject to uniform load w, and attached to an elastic element.  
         [0045]    [0045]FIG. 8A is a cross sectional view of markings on a ceiling when using the tubular construction members according to this invention (the markings are exaggerated in this view).  
         [0046]    [0046]FIG. 8B is a cross sectional view of the bottom walls and wings showing only the marks when using tubular construction members according to this invention.  
         [0047]    [0047]FIG. 9 is a partial cross section of two adjacent members aligned via an alignment means having a longitudinal lobe. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0048]    In FIG. 1 there is shown a tubular structural member  9  according to this invention. It can be generally described as shaped like a top hat in cross-section with an upright central crown and a flat brim about its bottom. It consists of a bottom surface, a top wall  10 , interconnected by a pair of substantially parallel sidewalls  12  and  13 . Protuberances  24  and  25  provide a mechanical anchorage to the tubular member after the concrete cures, to prevent any separation of the member from the concrete in the event that loads are hung at the bottom of the side walls (e.g. to avoid sliding of the member).  
         [0049]    There is a horizontal wall  18  substantially centrally of the member  9 , parallel to the top  10  and the bottom wall or floor  11 . There is a vertical wall  19  interconnected between the bottom wall  11  and the horizontal wall  18  at a central intersection  26 . There are sloped walls  20  and  21  which extend downwardly and outwardly at the same angle to the left and right of the central intersection of the horizontal wall  18  and the vertical wall  19 , with respective opposite ends thereof intersecting the comers formed by the intersection of bottom  11  and side walls  12  or  13 , respectively. Areas  22  and  23  are referred to as the bottom left and right intersections.  
         [0050]    There is a wing extending outwardly from each side of the member  9 , forming the brim of the top-hat cross-section. The right-hand wing  16  terminates in an upwardly extending finger or tongue  17 . The left-hand wing  14  terminates in a receiving member  15  having an opening to receive the finger  17 . In a series of members  9 , as shown, for example, in FIG. 3, the finger  17  or  17 ′ is encompassed within a receiving member  15  having an opening or groove to fit the finger  17 . Finger  17  and the receiving member  15  act as an alignment means that serves only to align a series of adjacent members according to this invention. The alignment means does not transmit between the adjacent members any structural load. Rather, each one of the matching wings is able to support independently the load directly above each wing.  
         [0051]    The walls (sloped walls, side walls, bottom walls) and wings connecting at the bottom left and right intersections are tapered in thickness thereby providing bending stiffness against rotation of these corners. The tapering of the wings increases the stiffness of the wings which serves to absorb bending stress and reduce consequent deformation caused by the vertical construction loads of the wet concrete forces.  
         [0052]    Each of the interior walls  20  and  21  tapers from bottom left and right intersections  22  or  23 , respectively, to the central intersection  26 . The drawings are substantially to scale and in the illustrated preferred embodiment, the taper of walls  22  and  23  is from about four millimeters at the area  22  or  23  to about two millimeters at the area adjacent to  26 . The vertical wall  19  is about two millimeters thick in the preferred embodiment. The horizontal wall  18  is about 1.5 millimeters. The top wall  10  is about 3.2 millimeters.  
         [0053]    The bottom wall  11  likewise tapers from the center where it is about two millimeters to a thickness of about four millimeters just before the bottom left and right intersections  22  or  23 . The wings  14  and  16  taper from about four millimeters adjacent to a wall  12  or  13  to about 2.5 millimeters just before the alignment means  15  or  17 . In this embodiment, the receiving member  15  of the alignment means is about 2.5 millimeters in thickness. The receiving member  15  is curved and in the shape of an upside down “U.” The outer surface of the curved section of the receiving member  15  has a diameter of about 7.7 millimeters. The height is about 9.5 millimeters from the bottom surface of the wing  14  to the top of the curve of the receiving member  15 . The curved portion ends 2.5 millimeters from the bottom of the wall to allow insertion of a finger  17 . Finger  17  is about 2.6 millimeters thick and the opening or groove of the receiving member is about 3.0 millimeters wide.  
         [0054]    The sidewalls  12  and  13  are about 2.5 millimeters thick from the top wall  10  to the area where the horizontal wall  18  extends across the interior of the member  9 . From there, the side walls  12  and  13  taper from about 2.5 millimeters to approximately 4.0 millimeters at the bottom left and right intersections  22  and  23 , respectively, in order to increase the stiffness of the bottom left and right intersections. The wing  16  is about 37.1 millimeters from a sidewall to the outer surface of the upwardly extending finger  17 . The finger extends upwardly about 9.3 millimeters. The wing  14  is approximately 32 millimeters from the wall  12  to the outside surface of the receiving member  15 .  
         [0055]    In FIG. 2, there is shown a preferred embodiment of a tubular structural member according to this invention. The design of this alternative embodiment eliminates the need to taper the walls of any member connected at the bottom right and left intersections  221 ,  222  (side wall, bottom wall or wing) to control within acceptable limits the deformation of the wings caused by the weight of the wet concrete.  
         [0056]    [0056]FIG. 2 shows an embodiment that has a top  201 , a bottom wall  202 , and opposed parallel sidewalls  203  and  204 . There is a horizontal wall  205  centrally located of the member  200 , parallel to the top  201  and the bottom wall  202 . There is a vertical wall  206  interconnected between the bottom wall  202  and the horizontal wall  205  extending from the horizontal wall at a central intersection  220 . A first and second sloped wall  207  and  208  extend downwardly and outwardly at the same angle from a first set of right  209  and left  210  points proximate to the central intersection  220 . The sloped walls  207 ,  208  extend through the side walls  203 ,  204 , with opposite ends thereof joined at the wings  215 ,  216  at a second set of right and left points  211 ,  212  proximate to the bottom right and left intersections  221 ,  222  formed by the bottom wall and sidewalls. In other words, the opposite ends of the sloped walls  207 ,  208  rest on the wings  215 ,  216  at a point proximate to the intersection  221 ,  222  of the sidewalls  203 ,  204  and bottom wall  202 .  
         [0057]    In the embodiment of FIG. 2, the tensors,  207 ,  208  intersect the wings at points  211 ,  212 , respectively, which should be proximate to the bottom left and right intersections  221 ,  222 . The tensors cover a portion of the wings between the bottom left and right intersections  221 ,  222  and points  211 ,  212  and form a triangle that is void of concrete. The portions of the side walls (below the intersection of the tensors with the sidewalls) and the portion of the wings between  211 ,  212  and  221 ,  222  respectively, are kept small to make these portions very rigid. As a result, the points from which the wings cantilever is from points  211 ,  212  to the free ends of the wings. The result is that the bending moment at the attached end of the cantilever (points  211 ,  212 ) and the deflection at the tip of the free end of the wings is greatly reduced. Therefore, there is no need to taper any wall or wing as there is in the first embodiment.  
         [0058]    To further increase rigidity of the section of the member below the horizontal wall, the side walls from the right and left intersections  221 ,  222  to the horizontal wall  205  may be thicker ( 203   b  and  204   b ), about 3.2 millimeters thick, than the sidewalls that extend from the horizontal wall  205  to the top walls  201  ( 203   a  and  204   a ), which are about 2.5 millimeters thick.  
         [0059]    The top wall is longer to extend slightly beyond the side walls to form small protuberances  240 ,  241  which provide a mechanical anchorage to the tubular member after the concrete cures, to prevent any separation of the member from the concrete in the event that loads are hung at the bottom of the side walls. Protuberances  240  and  241  are approximately 4 millimeters thick and project outward about 3 millimeters.  
         [0060]    The sloped walls  207 ,  208  are thinner, about 1.5 millimeters in thickness because they are not intended to provide any bending stiffness, but act as a tensor. The horizontal wall and vertical wall are each about 2.0 millimeters thick and the top wall is about 3.2 millimeters thick. The bottom wall or floor is about 3.0 millimeters thick. The wings are about 3.0 millimeters thick. Overall, the thickness of each wall and wing has a thickness of 3.2 millimeters.  
         [0061]    Points  211 ,  212  are about 8.0 millimeters from the bottom left and right intersections  221 ,  222  of sidewalls  203 ,  204  with bottom wall  202 . The distance from the bottom and right intersections to the finger  17  is about 33.6 millimeters. The distance from point  211  to the finger is about 25.6 millimeters. The distance from the bottom left intersection  222  to the receiving member is about 36.2 millimeters. The distance from point  212  to the receiving member is about 20.5 millimeters.  
         [0062]    In the construction of the embodiments shown in FIGS.  1 , and  2 , all comers, both inside and outside, should be rounded to aid in the extrusion process.  
         [0063]    In FIG. 3A, which is a partial cross-section of some adjacent parts of an adjacent pair of structural members  9 , there is shown a wing  14  having a receiving member  15  with an opening which has received within it an upwardly extending finger or tongue  17 ′ on a wing  16 ′ of an adjacent member  9  for alignment and water-proofing purposes. The fitting relationship is such that mortar will not flow through the alignment means, thus making the deck impermeable in nature. The alignment means includes a wing  14  that has a receiving member  15  about 0.04 millimeters wider than the thickness of finger  17  to allow easy assembly, and the end of the receiving member  15  rests on top of wing  16 ′ and that contact is made tighter with the weight of the concrete. No fastening device or securing device is necessary to secure the alignment of adjacent members. This arrangement is constructed and arranged to provide a simple way to align the members while preventing passage of mortar, thereby creating an impermeable formwork,  
         [0064]    It is not necessary to align the members of the present invention via the aligning means to form a deck. Each member could simply have fingers at both ends of each wing, fingers of opposite adjacent members lying side to side. The purpose of the alignments mean is to create an impermeable deck. The wing of a member having a receiving member laps the finger of an adjacent wing. Because the wing having the receiving member is longer and laps over the finger, it is subject to a slight increased deflection when receiving wet concrete than that of the wing having the finger. This difference in deflection of the wing having the receiving member causes the receiving member to press down contacting the adjacent wing (see FIG. 9 showing point of contact as  401 ).  
         [0065]    The present invention also includes a reinforcement chair  50  to support reinforcement bars. The chair  50  is removably mountable on the receiving member  15  of the alignment means. FIG. 3A shows a reinforcement chair  50  made also of extruded plastic, having an upward opening  51  to receive a reinforcement bar  53  and a downward opening  52  to mount the receiving member  15  of the alignment means. In this embodiment, the downward and upward openings are curved in nature to cooperate with the curved alignment means. The downward opening  52  is of sufficient size to engage in a close-fitting but loose relationship with the outer surface of revolution of the opening of the receiving member  15 . The downwardly opening  52  closely conforms to the outer surface of revolution of receiving member  15  and has legs that extend to the top of wings  14  and  16 . The upper opening  51  is sized to accept a reinforcing bar  53  in a close-fitting snap-on relationship. The legs are long enough to prevent the reinforcement chair  50  from falling to either side.  
         [0066]    In FIG. 3B there is shown a side elevation of a portion of the parts of FIG. 3A, indicating the relationship of the reinforcing bar  53 , the reinforcement chair  50 , and the plane in which the upper surface of the wing  14  exists. The chairs are spaced about four feet apart. The chairs are about one-half to three-quarter inches long, measuring along the axis of a reinforcing bar or “rebar” as they are sometimes called.  
         [0067]    In FIG. 4A there is a shown a second embodiment of the reinforcement chair of this invention. The shape of the reinforcement chair  80  is rectangular in nature and would, for example, serve to cooperate with the alignment means shown in FIG. 2. No embodiment is limited to cooperate with a particular reinforcement chair and thus, may be interchangeable as long as the alignment means are of the same shape for cooperation with the reinforcement chair.  
         [0068]    [0068]FIG. 4A shows a reinforcement chair  80  that is elevated with legs  81 ,  82  above the receiving member  15  of the alignment means. The chair includes a downward opening formed by the two bottom legs,  81  and  82 , and an upward opening formed by two upper legs  83 ,  84  to receive a plurality of reinforcement bars  90  (or a reinforcement bar and a splice bar). A horizontal bar  86  extends almost the length between the sidewalls of two adjacent members and serves to divide the upper legs  83 ,  84  from the bottom legs  81 ,  82 , and also to support the plurality of reinforcement bars. Because of the elevated nature of the reinforcement chair  80 , it is necessary to have a horizontal bar  86  that nearly extends the length between two sidewalls of two members in order to prevent the chair from falling to one side once the wet concrete is poured. Moreover, this embodiment serves to comply with fire codes and other regulations normally imposed in school buildings and other like buildings.  
         [0069]    The upper legs, lower legs and horizontal bar are about 2.0 millimeters thick. The length of the horizontal bar is about 63 millimeters. The distance between the adjacent members in FIG. 4A is about 64.7 millimeters. The opening between the two upper legs is about 13 millimeters wide and the opening between the two lower legs is about 8 millimeters wide. The length of the chair is about 15 millimeters.  
         [0070]    [0070]FIG. 4B shows a side view of the reinforcement chair shown in FIG. 4A. The reinforcement bar  90   a  is directly on top of another reinforcement bar  90   b  due to the upper legs  83 ,  84 . Ordinarily, reinforcement bars are placed right next to each other in the same horizontal plane and tied together manually for purposes of keeping such bars together in place. This embodiment avoids any manual securing of the reinforcement bars. A laborer need only drop in place the reinforcement bars or reinforcement bar and splice bar in the chair.  
         [0071]    In FIG. 5 there is shown a plurality of the members  9  in a ribbed concrete slab  60 . There is shown a wire mesh reinforcement sheet  61  laid on the top surface of the series of the plastic members  9 . A series of parallel reinforcing bars  62  are tied to the sheet  61  arranged parallel to the reinforcing bars  53 , which reinforcing bars  53  are supported by a series of reinforcement chairs  50  (not shown). As can be seen, there is formed a series of hollow enclosed valleys. At the bottom of each valley, the mating alignment of adjacent members are engaged in mortar impervious contiguous relation.  
         [0072]    Looking for the moment at FIG. 5A, which is a detail of a portion of FIG. 5, parts are enlarged to better show the relationship of reinforcing bar  53  in the concrete slab  60 .  
         [0073]    In FIG. 5B, there is shown a perspective view of a portion of a slab construction, shown in FIG. 5 in which the hollow tubular nature of the member  9  can be better appreciated. This view emphasizes the lightweight nature of a ribbed slab using a series of hollow thermoplastic members according to this invention.  
         [0074]    In FIG. 6, there is shown a ribbed concrete slab as it might be supported in a building. Element  63  is an outside wall and element  64  is an intermediate wall or beam support. Thermoplastic members  9  and  9 ′ are shown in an appropriate fashion supported by the walls  63  and  64 . Top rebar  62  is placed exactly above the intermediate supports as shown in FIG. 6. The exposed nature of the ceiling is likewise schematically demonstrated. In FIG. 6, we have shown concrete poured about the ends of the slabs on top of the walls. There are simple means, like tape, provided to prevent uncured concrete from entering the plastic members  9  and  9 ′. The top rebar  62  serves to resist the reverse bending force that occurs above the intermediate support and also to avoid cracking through the joint between  9  and  9 ′. A series of such top rebars is similarly positioned across all such interior joints over the length and width of the structure.  
         [0075]    Now turning to FIGS.  7 A- 7 C, as stated above, the wings project outward from the bottom left/right intersections (Tube) in the same plane of the bottom, as if extensions of the bottom wall formed a ceiling. The concrete ribs of the slab are formed between the side walls of the parallel adjacent members and have the wings of those members forming the bottom of each rib and matching their edges to prevent leakage of the mortar from the wet concrete above them. In the first and second embodiment, the match of the wings is at the center of rib bottom form. Each wing carrying structurally and independently the wet concrete above it, being in cantilever from the side wall in one embodiment and mostly in cantilever (from the points  211 ,  212  outward in FIG. 2) in the second embodiment.  
         [0076]    FIGS.  7 A- 7 C illustrate the elastic deformation of the cantilever and the maximum deflection at the tip when subject to uniform load w, and attached to an elastic element.  
         [0077]    [0077]FIG. 7A shows the deformation assuming the cantilever element is elastic but the attachment (rest of the member) of it is absolutely rigid. The tip deformation will be called Δ 1 .  
         [0078]    [0078]FIG. 7B shows the deformation assuming the cantilever is absolutely rigid, but the attaching element (rest of the member) is deformable when subject to the bending moment caused by the cantilever element. The elastic deformation of the attaching element will be a rotation of the attaching plane, represented by the angle ø. The tip of the cantilever will move downward a distance Δ 2 =ø×S.  
         [0079]    [0079]FIG. 7C represents the actual condition, applying the principle of superposition to the above assumptions made for FIGS. 7A and 7B. The actual deflection of the tip of the cantilever being Δ=Δ 1 +Δ 2 . The analysis shows the importance and the need to control the rotation of the point of attachment of the wing to reduce Δ by reducing Δ 2 .  
         [0080]    As a result, there is a need to provide substantial stiffness both to the wings in cantilever and to the tube at the two bottom comers where these wings are attached, to avoid unpleasant deflection of the wings. In the first embodiment shown in FIG. 1, this is done by providing the bottom left and right intersections formed by the sidewalls and bottom wall (including sloped walls) with bending stiffness against rotation of these comers. The tapered thickness of these walls, thicker at the bottom left and right intersection and thinner at the other ends, is an effective form to obtain the needed rigidity. In the second embodiment, a thin tensor extends out to the top of each wing, reducing the cantilever portion of the wing and the forces that cause rotation of the bottom right and left intersections. With these conditions, the uniform thickness is rigid enough and easy to extrude.  
         [0081]    It can also be appreciated that the structure of this invention, including the plastic members  9  facilitate hung ceiling installation in commercial and industrial buildings where it is necessary to have plenums to pass heating and air-conditioning ducts and pipes. In the embodiment shown in FIGS. 8A and 8B, longitudinal markings  300  at the intersection of the side walls  203 ,  204  with the bottom wall  202  serve to delineate the boundaries of the side walls  203 ,  204  so that a threaded screw or other like material can be placed in the middle  301  of the bottom of the side walls  203 ,  204 . As shown in FIG. 8B, after installation of a slab construction according to this invention, these marked areas  300  will be detectable on the exposed ceiling surface (the variation in thickness of the wings and bottom walls in FIG. 8A and 8B are exaggerated for exemplary purposes). Threaded screws easily penetrate the plastic material from which members  9  are made of and are much less expensive and easier to install than power-driven nails and the like, which normally are used with concrete slabs. The variation in thickness between the wings and sidewalls is about 0.5 millimeters.  
         [0082]    The hollow interior of the structural members  9  and  40  facilitate the installation of thermal insulation, for example, by filling the longitudinal tubular portions with fiberglass, either blown or by inserting pieces of insulation mats.  
         [0083]    Another embodiment for the alignment means is shown in FIG. 9 which includes an alignment means having a finger with a longitudinal lobe  400 . The lobe  400  is a means of separation that serves to ensure that the finger  17  does not come in direct contact with the left inner side of the receiving member  15 , to avoid capillary action to raise water between them. As shown in FIG. 9, the receiving member comes in contact with the wing having the finger at point  401 .  
         [0084]    Use of the members according to this invention facilitates the accurate and precise arrangement of steel reinforcing bars, not only because of the novel seat construction, but because it can be accomplished without the cost of the labor involved in tying reinforcing wires which is the usual practice.  
         [0085]    Construction according to this invention provides for reinforced concrete slabs of about one-half the weight and concrete volume. The slabs are resistant to sagging. Approximately 80 millimeters or 3.25 inches average thickness of concrete (from top of slab to top of wings buried in concrete) can be used to build a roof slab span of about six meters or 20 feet. In residential intermediate size floor slabs, they can be up to about five meters or 16 feet at the same concrete thickness. Conventionally, the latter would require 150 millimeters or six inches in normal ribbed reinforced concrete slab.  
         [0086]    The time and labor required to build a ribbed concrete slab, according to the invention, is substantially reduced for many reasons. For example, the task of placing the formwork is much simpler because the present invention is a single component that can be installed easily and efficiently without heavy equipment or special craftsmanship; afterward the component is not removed, but stays permanently integrated in the concrete floor or roof. Additionally, the amount of time to install slab reinforcement is drastically reduced because there is no need to wire the reinforcing bars in place. Since about one-half the volume of concrete is required, additional time and labor are saved. No formwork stripping is needed. Ceiling plastering, painting and the like can be eliminated.  
         [0087]    In the above description, exemplary dimensions have been given in describing the operation of structural members when incorporated in a ribbed concrete slab forming process. It should be understood by those skilled in the art that other dimensions can be calculated, using conventional techniques, to determine appropriate dimensions for installations other than exemplary ones described herein.  
         [0088]    For performance verification we have used properties of available thermoplastic material. It should be likewise understood that plastic materials other than the exemplary one described above which will provide the properties described to a member made therefrom are considered the functional equivalent of those described herein and can thus likewise be used.