Abstract:
A beam comprised of sub-components capable of extending or contracting in overall length is provided. The beam consists of a twin-beam structure that provides travel support for two end beam components that are movable with respect to one another to extend or contract the length of the resulting variable length beam. Extension or contraction of the variable length beam can be accomplished manually or, in a preferred embodiment, by means of a screw drive. The variable length beams facilitate the fabrication of reusable, adjustable width deck-forming panels used in the construction of cast-in-place bridge deck slabs supported by parallel structural beams.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to bridge building. In one of its more particular aspects it relates to a variable length beam which is useful for fabricating reusable, adjustable width deck-forming panels used to construct cast-in-place concrete bridge deck slabs supported by parallel structural beams. 
         [0003]    2. Description of the Related Art 
         [0004]    Bridges provide grade separation to facilitate the efficient transport of vehicles, pedestrians and rail systems over roads, railways, chasms, water, and other obstructions. 
         [0005]    A typical bridge consists of a series of foundation substructures to transfer loads into the earth, and a superstructure to transfer loads to the substructure. The majority of bridges built use a system of parallel beams, either pre-cast concrete or steel, to span the distance between foundation elements. Typically, the system of parallel beams will be braced at regular intervals and normal to their centerlines by a horizontal structural member referred to as a “diaphragm”. The space between these parallel beams is commonly referred to as a “bay”, the width of which is typically between 4 and 12 feet. The superstructure surface, which carries traffic loads, is provided by forming a steel reinforced concrete bridge deck, which is formed and cast in place over the bridge beams. 
         [0006]    The cast-in-place bridge deck must be temporarily supported by a system of falsework that is usually suspended from the structural beams. A large variety of systems exist in the marketplace that employ hanger assemblies or threaded rod to hang vertically, or near vertically, from the structural beams, which are in turn used to support transverse joist members that will ultimately transfer the deck dead load to the structural beams by supporting a plywood surface onto which the cast-in-place concrete is poured. 
         [0007]    The entire temporary falsework system can be adjusted vertically to account for beam deflections caused by the weight of the concrete and reinforcing steel. 
         [0008]    The spacing and size of the temporary transverse joist beams vary, dependent upon the spacing between the parallel bridge beams and the load that needs to be supported. A reusable temporary deck forming falsework system needs to be able to be adjusted to variable bay widths for different bridges. 
         [0009]    Once the cast-in-place concrete deck has been poured and cured, the temporary falsework system must be stripped from beneath the finished deck. 
         [0010]    Numerous methods of constructing the falsework decking system exist in the marketplace today. Concrete forming systems comprised of steel component pieces used to carry construction loads are commercially available in the world-wide marketplace. These component pieces are manufactured in a wide variety of sizes and shapes, and can be combined into myriad configurations, much like a large “Erector set”, in order to support horizontal and vertical loading conditions. Using these members in a horizontal capacity to function as transverse joist members is a standard practice in cast-in-place bridge deck forming. However, no component piece that will allow transverse joist members to be configured into a continuously variable length has yet been provided. 
       SUMMARY OF THE INVENTION 
       [0011]    A transverse joist member designed to provide a continuously variable length would revolutionize the forming and stripping of the temporary falsework, allowing it to be fabricated off-site in modular panels, hung in place as a complete unit, designed to fit between structural beam diaphragms, adjusted to elevation, and stripped as a complete unit from the underside of the finished deck. Only slight modifications to the panels will be necessary, by removing a small portion of the plywood sheet and adjusting the continuously variable length transverse joist member to establish the new joist length. Adding or subtracting stringer beams as needed and replacing the portion of plywood sheet needed to fill in the panel will yield a system ready for the next use. In some instances it may be necessary to add or subtract a combination of fixed beam components to develop a new joist length. 
         [0012]    The present invention provides a variable length beam, which can be used in combination with a fixed length support beam to continuously adjust the length of the combination. Since support beams typically comprise a combination of fixed length beam components (1′-6″, 3′-0″, 6′-0″, and 12′-0″ beam components), attaching a beam component which is continuously adjustable in length will enable the resulting combination to be used across the full range of bridge deck bay widths seen in the heavy highway construction industry throughout the world today. The variable length beam component will allow deck formwork joist beams, for example, to be adjusted to the precise width required to fit between bridge beams. 
         [0013]    The present invention comprises a uniquely fabricated twin-beam structure that acts as a travel support to two slightly modified pre-existing end beam components, typically two 1′-6″ beam components, that are movable with respect to one another to extend or contract the length of the twin-beam structure. The two pre-existing beam components, which are currently available in the marketplace, each has a pair of oppositely facing side channels. They are modified by replacing one of two pre-existing end-plates on each end beam component with a plate welded between the oppositely facing side channels. Stop tabs are provided at each end of the two travel support beams. Two side plates are added to the outside flanges of each of the pre-existing beam components to stiffen the members for load transfer and to serve as predetermined stop sites for the stop tabs on the ends of the travel support beams. The modified members, referred to above, reside at opposite ends of the variable length beams. The twin travel support beams are connected with a central stiffener assembly and are fabricated to move within the cross-section of the end beam components. Aligned slots and holes in the top and bottom flanges of the end beam components and the travel support beams are used for placement of structural bolts that lock the variable length beam into its required length. The overall length of the variable length beam can be adjusted by manually sliding the two end beam components along the travel support beams. 
         [0014]    In a preferred embodiment of the present invention the two end beam components are moved by a horizontal screw drive with screw drive receiving plates welded between their oppositely facing side channels at one end in lieu of the standard end-plates. One screw drive receiving plate is a clockwise-threaded plate and the other is a counterclockwise-threaded plate. Side plates are added to the side channels to stiffen the components for load transfer and to serve as predetermined stop sites for the stop tabs on the ends of the travel support beams. One end of the screw drive, referred to herein as the proximal end, has a clockwise or standard thread. The other end, referred to herein as the distal end, has a counterclockwise or reverse thread. The screw drive also acts as a structural component to provide load transfer to the twin travel support beams. The screw drive has a centrally located bevel gear affixed to its horizontal shaft that is driven by a smaller bevel gear on a vertical shaft that is aligned to it tangentially and kept in a fixed alignment by keeper plates on the screw drive shaft. A user can apply torque to the head of the vertical shaft, causing the variable length beam to mechanically extend or contract in overall length. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a first embodiment of the variable length beam of the present invention in a contracted state; 
           [0016]      FIG. 2  is a perspective view of the embodiment of  FIG. 1  shown in an extended state; 
           [0017]      FIG. 2(   a ) is a cross-section of the embodiment of  FIG. 2  along the line  2 ( a )- 2 ( a ); 
           [0018]      FIG. 3  is an exploded perspective view of the variable length beam of  FIGS. 1 and 2 ; 
           [0019]      FIG. 3(   a ) is an exploded perspective view of a second embodiment of the variable length beam of the present invention; 
           [0020]      FIG. 4  is an enlarged view of the screw drive shown in  FIG. 3(   a ); 
           [0021]      FIG. 5  is a top view, partly in phantom, of the variable length beam of  FIGS. 1 and 3 , shown closed, with a breakaway piece at the far right, which represents any of the aforementioned fixed beam components; 
           [0022]      FIG. 6  is a cross-section of the variable length beam of  FIGS. 1 ,  3 , and  5  along the line  6 - 6  of  FIG. 5 ; 
           [0023]      FIG. 7  is a top view, partly in phantom, of the second embodiment of the variable length beam of the present invention as shown in  FIG. 3(   a ); 
           [0024]      FIG. 8  is a cross-section of the variable length beam of  FIGS. 3(   a ) and  7  along the line  8 - 8  of  FIG. 7 ; 
           [0025]      FIG. 9  is a bottom perspective view of two panels placed on either side of a diaphragm of a bridge in construction showing use of the variable length beam of the present invention, with the area over the diaphragm constructed with fill-in stringers and decking; 
           [0026]      FIG. 10  is a perspective view, partially broken away, of an assembled bridge panel, showing use of the variable length beam of the present invention; 
           [0027]      FIG. 11  is a perspective view of multiple adjustable panels, with Detail A, a blow-up, illustrating the use of the variable length beam of the present invention in such adjustable panels; and 
           [0028]      FIG. 12  is a side elevation of an adjustable panel suspended from hangers, showing the use of the variable length beam of the present invention in such adjustable panels. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The present invention provides a variable length beam which is useful in bridge construction, especially in adjusting the dimensions of falsework support beams used in cast-in-place bridge deck forming. Although the variable length beams of this invention could be used by themselves as support members in any number of load transfer configurations, their most advantageous use is in combination with fixed length components to create joists which support a system of parallel stringers in panels of varying widths. For example, a variable length beam comprised of two modified 1′-6″ components can be used with one or more standard length components of 1′-6″, 3′-0″, 6′-0″, or 12′-0″ to provide beam lengths which are not otherwise readily available. Some of the advantages of such use are as follows:
       eliminating the waste of dimensional lumber (ultimately discarded and replaced) used as transverse joist members which are cut to fit the variable bay width experienced from one bridge to another;   providing a reusable, panelized form system, that is easily configurable to varying bridge girder spans and bay widths;   reducing the time allocated to deck forming and stripping on a job-site by allowing the majority of the forming to be completed off-site, and eliminating the need to disassemble the form system when stripping from the completed cast-in-place concrete deck;   increasing the level of worker safety by minimizing the time spent elevated and tied off on the structural bridge beams;   reducing the overall cost of constructing cast-in-place concrete bridge decks by decreasing the time expended to form and strip the deck falsework system; and   decreasing the impact of construction upon the traveling public by requiring less construction time and bringing the new bridge on-line more quickly.       
 
         [0036]    The invention will be better understood by reference to the drawings, in which similar parts are indicated by use of the same reference numeral in each of the figures in which that part is depicted. 
         [0037]    Referring now to  FIG. 1 , the numeral  10  represents a first embodiment of the variable length beam of the present invention having side channels  12  which are provided with end-plates  14 . Travel support beams  16 , which have stop tabs  15 , are fitted within side channels  12 , which receive structural bolts  18  for positioning with respect to travel support beams  16 . Side stiffeners  20  are connected to side channels  12  to strengthen variable length beam  10 . Central stiffener assembly  22  and two modified end-plates  24  are provided midway between the end-plates  14   
         [0038]      FIG. 2  depicts variable length beam  10  in an extended state. In addition to the elements shown in  FIG. 1 , slots  26  are shown in the tops of travel support beams  16  for accommodating structural bolts  18 . Slots are also present in the bottom flanges of travel support beams  16  (not shown). 
         [0039]    From  FIG. 2(   a ), a cross-section of the extended variable length beam  10  of  FIG. 2 , it can be seen that travel support beams  16  are fitted within side channels  12 . Nuts  19  fix the position of structural bolts  18  within slots  26  (shown in  FIG. 2) , thereby controlling the position of side channels  12  relative to travel support beams  16  and adjusting the length of variable length beam  10 . 
         [0040]    The elements making up the variable length beam of  FIGS. 1 and 2  are shown prior to final assembly in  FIG. 3 . Central stiffener assembly  22  and modified end-plates  24  enable manually moving a pair of side channels  12  along a pair of travel support beams  16  to extend or contract the variable length beam of the present invention. 
         [0041]      FIG. 3(   a ) illustrates a preferred embodiment of the variable length beam of the present invention, previously referred to as the second embodiment, in which extension or contraction of the variable length beam is accomplished mechanically by means of a screw drive mechanism  30 , more particularly shown in  FIG. 4 , rather than manually. Modified end plates  27  and  28 , which are threaded, cooperate with screw drive mechanism  30  to enable mechanically moving a pair of side channels  12  along a pair of travel support beams  16 . Modified end-plate  28  has a standard or clockwise thread whereas modified end-plate  27  has a reverse or counterclockwise thread. Screw drive  32  has a clockwise thread to cooperate with the clockwise thread of modified end-plate  28 , while screw drive  34  has a counterclockwise thread to cooperate with the counterclockwise thread of modified end-plate  27 . Screw drive  32  has affixed to it a shaft keeper  36  and a first bevel gear  38 , which is aligned tangentially to a second bevel gear  40  affixed to a vertical shaft  42 , which is mounted within a central stiffener assembly  22 , which serves as a gear housing. Application of torque to the head of shaft  42  will cause bevel gears  40  and  38  to rotate standard thread screw drive  32  and reverse thread screw drive  34  within modified end-plates  28  and  27 , respectively, moving side channels  12  along travel support beams  16  to extend or contract the variable length beam of the present invention. 
         [0042]      FIGS. 5 and 6  show additional details of the first embodiment of the variable length beam of the present invention as illustrated in  FIGS. 1 and 3 , including attachment of a fixed beam component. 
         [0043]      FIGS. 7 and 8  show additional details of a preferred embodiment of the variable length beam of the present invention as illustrated in  FIGS. 3(   a ) and  4 , including attachment of a fixed beam component. 
         [0044]      FIG. 9  shows how the variable length beams of the present invention are used in bridge deck forming. Hanger assemblies  74  support a plurality of joists  56  comprised of variable length beams  10  and fixed length components  76 , which in turn support a plurality of stringers  54 , upon which plywood decking  62  is laid to serve as a base for concrete, which is poured upon plywood decking  62 . The fill-in area over a diaphragm  50  attached to bridge beams  70  is shown at area  58 . 
         [0045]      FIG. 10  shows use of the variable length beams of the present invention in a preassembled deck panel  60  which comprises a series of joists  56  utilizing variable length beams  10  as a part thereof, which joists support a series of stringers  54 , which in turn support plywood decking  62 . 
         [0046]      FIG. 11  shows a series of adjustable panels  60  between bridge girders  70 . The fill-in area  58  occurs at the location of each permanent diaphragm  50 . Detail A shows plywood decking  62  laid upon a series of stringers  54 , which are supported by a series of joists  56  (one shown). The joists are comprised of variable length beams  10  and a fixed component. 
         [0047]    In  FIG. 12  diaphragm  50  is shown between two bridge girders  70  supporting hanger assemblies  74 , which support joists  56 , parts of which are comprised of variable length beams  10 . A series of stringers  54  are supported by joists  56  and support plywood decking  62 , which supports a reinforced concrete deck  72 . 
         [0048]    By creating variable length beams which can be used in joists to construct adjustable panels for supporting bridge decking, a reusable deckwork forming system is provided. 
         [0049]    It will be appreciated that the disclosure and description in the instant specification are set forth by way of illustration and not limitation, and that various modifications and changes may be made without departing from the spirit and scope of the present invention.