Patent Publication Number: US-8112965-B2

Title: Assembly and method for the construction of monolithic tiered concrete slabs

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to provisional application Ser. No. 60/914,909 filed Apr. 30, 2007, herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The accepted methods of constructing concrete structures designed with a plurality of tiered or stepped levels, such as seating for lecture halls, theaters or stadiums or stairways, is usually determined by the size of the project. Structures, like sports stadiums, are large enough in size to benefit from the ability of using large customized concrete ‘gang type’ forms that require external means of load transfer from one section of the form to another. Forming smaller structures, like a classroom lecture hall, will often typically be built ‘by hand’ one component at a time. 
     The use of ‘gang type’ forms to build the larger structures can usually provide greater control over dimensional accuracy and installed costs due to a faster cycle of setting the forms, placing the concrete and stripping the forms. Employing ‘hand built’ construction practices for smaller structures can provide dimensional accuracy but there is increased risk of failure due to the reduced size of the components and fasteners, though the construction cycle will be longer and the labor cost will be higher. The decision ultimately comes down to whether there is enough labor savings to offset the investment in the ‘gang type’ forms. If the reuse and the labor savings can&#39;t be realized with ‘gang type’ forming methods, then ‘hand built’ forms are used for the construction, with the acceptance of higher labor costs and associated risks. 
     It is known in the industry to utilize expanded polystyrene (EPS) foam blocks as a form that supports the tread portion of a tiered concrete floor, for example, for the seating area of a cinematic movie theater. This prior art method does not form a concrete riser, such that the structure does not have the integrity of a monolithic tiered concrete slab having interconnected concrete risers and treads. Typically, this prior art method utilizes a permanent steel plate as the riser. In the event of a fire, the steel plate transfers heat to the underlying foam blocks, which then can melt such that the concrete treads are not evenly supported and eventually fail. 
     Another prior art method of forming a tired concrete slab requires a base with compacted granular fill which must be retained in a sloped arrangement. Retaining walls are used for retention of the sloped fill material. The retaining walls add additional time and expense to these projects. 
     Therefore, it is a primary objective of the present invention to provide an improved assembly and method for forming a monolithic tiered concrete slab or stairway. 
     Another objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway having a curved riser face. 
     Another objective of the present invention is the provision of an assembly and method for forming a monolithic tiered concrete slab or stairway for various uses, including auditorium and lecture hall seating. 
     Another objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway having minimal heat transfer properties. 
     Still another objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway having interconnected concrete treads and risers. 
     Yet another objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway which is customized to each individual project. 
     A further objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway which is easy to use. 
     Still another objective of the present invention is the provision of an assembly and method for forming a tiered concrete slab or stairway which is economical and durable. 
     These and other objectives will become apparent from the following description of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is directed toward a riser interface assembly and method for constructing a monolithic tiered concrete slabs and stairways using a combination of components that will promote the accurate and efficient construction of a plurality of tiered levels involving riser faces and treads. The distinguishing characteristics of this construction system and method relate to its secure ‘interface’ between the supporting base, whether permanent or temporary, and the forms for the riser faces. Since very few projects have the same dimensional requirements, it is necessary for a system to be customizable, for example, to accommodate either straight or radial designs. This method uses pre-manufactured, project specific components that are supplied as a system. These ‘made to order’ parts are assembled at the jobsite more rapidly, more accurately, and with more stability than typical job built forming methods. The benefits of the ‘gang type’ forms can therefore be realized on smaller projects using the assembly and method of the present invention. 
     The system components include the following: 1) a permanent, engineered base material, such as, but not limited to, EPS foam that is configured to the lineal, radial, or tapered profile of the project, 2) structural interface elements such as boards (laminated wood veneers, oriented wood strands, or composites) or metal components that are bonded and/or mechanically attached to the engineered fill or base material, 3) special form ties (most often made of, but not limited to, welded steel wire) and 4) riser face forming element such as temporary, very smooth boards (laminated wood veneers, oriented wood strands, or composites with a plastic face to the concrete) or permanent riser faces such as concrete or metal, and 5) sufficient structural framing and forming hardware behind the riser face to control the desired configuration of the concrete riser, whether straight or radial. 
     The system, as described, is not intended to alter the design requirements of the structural, tiered concrete slabs or stairways. It should be noted that, the substitution of EPS blocks as a permanent base material, in lieu of compacted granular material, can eliminate the retaining walls that are needed to restrain the lateral pressure caused by compaction forces. EPS blocks are designed, tested and rated according to ASTM standards; specific live and dead loads can be permanently supported without the risk of settling. Structural reinforcing requirements should be engineered to meet the specific needs of the intended application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial plan view of a tiered concrete slab conforming to the radial requirements of a lecture hall (as an example). 
         FIG. 2  is a sectional view taken along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a partial plan view showing EPS foam blocks set in position to form a curved tiered concrete slab. 
         FIG. 4  is an enlarged partial plan view of the EPS foam blocks of  FIG. 3 . 
         FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 4 . 
         FIG. 6  is a partial plan view similar to  FIG. 1 , with the structural interface elements added to the EPS blocks. 
         FIG. 7  is an enlarged partial plan view of one of the structural interface elements showing a fastener and fastening points to the EPS blocks. 
         FIG. 8  is a similar partial plan view with the riser face forming element in place. 
         FIG. 9  is a partial plan view of one of the structural interface elements with a wire riser face form tie mounted thereon. 
         FIGS. 10 and 11  are similar to  FIG. 9  and show alternative embodiments for mounting the riser tie to the interface element. 
         FIGS. 12-14  are section drawings showing the steps in the process for creating the tiered concrete slab using the riser interface assembly according to the present invention. 
         FIG. 15  is an enlarged partial elevation view showing the hardware and framing lumber used with the riser tie. 
         FIG. 16  is an enlarged side elevation view of one of the structural interface elements with a welded wire riser face form tie thereon, and having the riser face form and framing lumber attached to the tie. 
         FIG. 17  is a partial view of an alternative permanent concrete face panel used with a riser tie. 
         FIG. 18  is a partial plan view of the present invention arranged for forming a stairway with an intermediate landing. 
         FIG. 19  is a sectional view taken along line  19 - 19  of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The assembly and method of the present invention is intended for use in the construction of a monolithic, reinforced, tiered concrete slabs  10 , or stairways  12 , formed in straight rows or about a radius. Each row of the tiered concrete slabs or stairways has a riser  16  and a tread  18 . The assembly begins with a plurality of EPS foam blocks  20  which are positioned adjacent each other, as seen in  FIGS. 3 and 12  of the drawings. The blocks  20  each have a front edge  22 , a rear edge  24 , opposite sides  26 , a bottom  28  and a sloped top  30 . The adjacent blocks  20  define a joint  32  there between. The drawings show the assembly used in creating curved tier levels, although it is understood that straight tier levels can be formed in a similar manner by abutting the adjacent sides  26  of the EPS blocks  20 , there between as in the curved tiers. As seen in  FIGS. 12-14 , the height dimensions of the blocks  20  increasing from the front row A to the rear row of the tiered slab, thereby forming a continuous, smooth, sloping upper surface from front to back. Also, when a curved or radial slab profile is to be formed, the width of the EPS blocks  20  increases from the front row A to the rear row, as best seen in  FIGS. 3 and 12 . 
     The structural interface elements  34 , shown in cross hatching in  FIG. 6 , are placed over the joints  32  between adjacent EPS blocks  20 , and also preferably at the midpoint of the EPS blocks  20 , such that the interface  34  extends linearly from the front row to the back row, as seen in  FIGS. 6 and 8 . A minimum width of 12″ is preferred for the element  34  to assure the structural stability of lateral concrete pressures exerted against the riser face forming element. The interface elements  34  may be secured to the EPS blocks  20  using adhesive and/or mechanical anchors, such as the barbed pins  36  shown in  FIG. 7 . 
     The fixed length, or adjustable length, riser face form ties  38  are mechanically attached to the interface elements  34  using any convenient fastener, such as screws, extending through front and rear L-shaped angle feet  40 . Typical methods of fabricating the angled feet  40  include steel clips welded to the wire tie  38  or a looped wire feature that is integral with the riser tie  38 . As an alternative to feet  40 , an integral looped wire  41  may be provided for receiving fasteners, as seen in  FIG. 11 . The riser tie  38  includes a triangular wire body  42 , with the wires preferably being welded together, with break-back cones  44  which position the riser face form  46 , as best seen in  FIG. 16 . The form ties  38  must be attached to the structural interface element  34  in a secure manner. This tie  38  can be produced as a singular unit or as a series of ties connected together sharing common structural parts.  FIG. 19  illustrates an example wherein double ties have a single wire connecting the identical ties. This system does not require the use of supplemental bracing to achieve dimensional accuracy. According to the architectural design, the riser form face  46  extends vertically, such that the riser  16  of the tiered steps is vertical, as seen in  FIG. 14 . Ties  38  can be fabricated to the exact requirements of all building codes. The face form  46  may be removably mounted to the riser tie  38 , such as shown in  FIGS. 15 and 16 , or alternatively, may be a permanent face panel  48  made of concrete or other material, as seen in  FIG. 17 . 
     The method of forming the tiered concrete slabs  10  or stairways  12  of the present invention is schematically shown in  FIGS. 12-14 . Once the ground or support base  50  is graded, the foam blocks  20  are mounted thereon, and preferably anchored thereto, as seen in  FIG. 12 . If the slabs  10  or stairways  12  are to be formed on top of dirt or other particulant material, anchoring pins can be driven downwardly through the foam blocks  20  and/or the dirt or material so as to maintain the blocks in the desired position. 
     The next step in the method is to attach the structural interface elements  34  to the foam blocks  20 , preferably using adhesive and/or mechanical anchors. In the best mode, the riser face form ties  38  are mounted on the structural interface elements  34 . If required, shims can be placed under the mounting feet  40  to assure accurate positioning. Then, the riser face forms  46 , walers and hardware are mounted on the riser ties  38 . As required, the riser face forms  46  will create a smooth, curved riser surface when the blocks  20  are set in a radial alignment around the center point of the riser faces. Similarly, straight or lineal riser configurations will be parallel and accurately positioned. Steel reinforcement rods (not shown) can be positioned, as known in the industry. The concrete  52  is then poured, finished on the treads  18 , and allowed to cure. The last step in the process is to remove the riser face forms  46  and framing lumber, unless the permanent face panel  48  is utilized. The structural interface elements  34  and the riser ties  38  remain buried in the concrete  52 . 
     It is understood that this system and method can be used on sloped earth (or particulate material), or on decking (whether temporary or permanent), without the EPS foam blocks  20 . 
       FIGS. 18 and 19  show the assembly as used to form steps  12  with a landing  54 . Each step includes a riser  16  and tread  18 . 
     The invention has been shown and described above with the preferred embodiments, and it is understood that many modifications, substitutions, and additions may be made which are within the intended spirit and scope of the invention. From the foregoing, it can be seen that the present invention accomplishes at least all of its stated objectives.