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FIELD OF THE INVENTION 
     This invention relates to an apparatus for bracing a pair of parallel joists or beams. 
     BACKGROUND OF THE INVENTION 
     Use of bracing between joists in floor construction is well known. One objective of bracing is to prevent joists from moving out of a square alignment with the floorboards they are supporting. Without bracing, joists may rotate about a horizontal axis resulting in floors that “squeak” due to a gap developing between the bottom of the floorboard and the non-horizontal surface of the joist. Bracing also strengthens the overall joist structure by distributing the load between joists. 
     A wide variety of bracing systems have been utilized, the traditional and most common being a pair of wooden members arranged in an X-pattern between a pair of joists. Such a brace system does not produce a consistently strong product, as the quality of wood for each brace may vary considerably. Wood braces have a tendency to warp as they dry, thus moving from their optimal support position. Further, the nailing of wood braces to joists can result in splitting of the brace where it is nailed to the joist, thus reducing structural strength. 
     Although various building regulations exist to specify the distance between floor joists, these regulations are not always adhered to. To reduce costs in a building that does not require standard spaced floor joists, fewer joists are installed resulting in a greater distance between joists. In addition, errors in construction can result in joists not being consistently spaced. Braces of fixed length will not support joists that are separated by variant lengths. 
     U.S. Pat. No. 457,664 discloses steel crossbraces designed to fit over the tops and bottoms of joists and to be adjustably connected by a nut and bolt. Such a brace requires that the bracing be installed before the floor is laid and will raise the floor above the joists in the area where the floor contacts the brace. In order to provide a level, squeak resistant floor, the installer must add material to the joists between the braces or recess the floor where it contacts the braces. 
     U.S. Pat. Nos. 3,077,009 and 3,102,306 disclose an adjustable brace and a method for manufacturing the brace. Such braces lack a secure connection to the joists and will detach from the joist if the joists warp so that the compression they provide upon the brace no longer exists. 
     U.S. Pat. No. 4,246,736 discloses a one piece bracing system of fixed length. Since the brace attaches only to the topmost section of each joist, it is less able to brace against joist twisting. 
     U.S. Pat. No. 4,794,746 discloses a bracing system of fixed length. The problem with fixed length braces is that if the joists are not spaced apart a distance equal to the length of the brace, the brace will either be too long to fit between the joists or be too short to adequately support the joists. 
     U.S. Pat. No. 5,301,486 discloses a cross brace that uses wooden components, each of which requires precise cuts to be made in order for the components to fit. Constructing such a brace would be costly and time consuming. As mentioned earlier, wood braces have a number of problems that make them less than optimal as bracing members. 
     Thus, there is a need for an inexpensive, strong, adjustable and easily installable joist bracing apparatus. There is also a need for a bracing apparatus that reduces bounce and vibration in floor systems such as I-joist supported floors. The present invention meets these criteria. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect the invention is directed to an apparatus for bracing a pair of adjacent joists comprising: a pair of load distribution members; fastening means for fastening the load distribution members in opposing positions to the pair of adjacent joists; a spanning member for rigidly connecting the load distribution members together to brace said adjacent joists; and connecting means for connecting the spanning member to the load distribution members at one of a plurality of adjustable positions, to accommodate different spans between the pair of adjacent joists. 
     Further embodiments of the invention include a connector arm portion for extending at an angle from the load distribution member to receive the spanning member. Also, the connecting means comprises a plurality of apertures defined in the connector arm portion and a plurality of tabs protruding from the spanning member, the tabs being sized to removably fit into the apertures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following drawings: 
     FIG. 1 is a side view of a joist bracing apparatus in accordance with the present invention, installed between two joists; 
     FIG. 2 is a perspective view of a load distribution member for the joist bracing apparatus of FIG. 1; 
     FIG. 3 is a side view of the load distribution member of FIG. 2; 
     FIG. 4 is a sectional view of the load distribution member of FIG. 2, taken along line  4 — 4 ; 
     FIG. 5 is a perspective view of one end of a spanning member for the joist bracing apparatus of FIG. 1; 
     FIG. 6 is a perspective view of one end of an alternative embodiment of the spanning member; 
     FIG. 7 is a perspective view of one end of an alternative embodiment of the spanning member; 
     FIG. 8 is a perspective view of one end of an alternative embodiment of the spanning member; 
     FIG. 9 is a vertical cross-sectional view of an alternative embodiment of the spanning member; 
     FIG. 10 is a vertical cross-sectional view of an alternative embodiment of the spanning member; 
     FIG. 11 is a side view of the joist bracing apparatus installed between a series of floor joists; 
     FIG. 12 is a perspective view of an alternative embodiment of the spanning member; 
     FIG. 13 is a perspective view of an alternative embodiment of the load distribution member; 
     FIG. 14 is a plan view of the intersection of two load distribution member flanges; 
     FIG. 15 is a perspective view of one end of the spanning member of FIG. 12; and 
     FIG. 16 is a cross-section of the spanning member of FIG.  12  and the load distribution member of FIG. 13 in a mated position viewed along line A—A of FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, a joist bracing apparatus in accordance with the present invention is shown generally as  10 . The joist bracing apparatus  10  includes a pair of load distribution members  12  and a spanning member  14 . Joist bracing apparatus  10  is shown partially installed between two I-beam floor joists  16  in FIG.  1 . 
     In the preferred embodiment, each load distribution member  12  is constructed from a single piece of stamped sheet metal. Load distribution member  12  may be manufactured in a number of different lengths to accommodate the various depths of floor joists, shown as length A in FIG.  1 . As shown in FIGS. 1 and 2 each load distribution member  12  has a planar portion  18 . Planar portion  18  has, on its longest edges, longitudinal support ribs  20 . Support ribs  20  are arcuate in shape and provide longitudinal strength to load distribution member  12 . This longitudinal strength allows each load distribution member  12  to distribute the vertical load on a joist over the surface of the joist and the surfaces of the adjoining joists, thus helping to dampen movement in the floor. One end of planar portion  18  has a speed prong  22 . Speed prong  22  is designed to temporarily fasten load distribution member  12  to the surface of a floor joist  16  when the speed prong  22  is hit with a hammer and thus driven into the surface of a floor joist  16 . The other end of planar portion  18  has a pair of squaring tabs  26 . Squaring tabs  26  extend from the rear face of load distribution member  12 . Squaring tabs  26  when placed upon the interior horizontal face  27  of I-beam floor joist  16  serve as a squaring or levelling indicator to ensure that load distribution member  12  is substantially vertical prior to fastening to floor joist  16 . In the case of floor joists that are not of I-beam type construction, squaring tabs  26  are either driven into the face of the floor joist or bent back to be parallel with planar portion  18 . Planar portion  18  contains a plurality of apertures  28  to allow for more permanent attachment of load distribution member  12  to floor joist  16  through the use of fasteners  30  such as nails, screws or the like. 
     Planar portion  18  has integrally hingeably attached to it a connector arm  32 . Connector arm  32  is integrally formed during manufacture by making cuts on three sides of a rectangle in planar portion  18  and stamping the central portion of the rectangle to form a U-shaped channel, thus defining connector arm  32 . The edge of connector arm  32  remaining attached to planar portion  18  is reinforced by a pair of hinge support ribs  34 . Hinge support ribs  34  protrude above the surface of the planar portion  18 . Connector arm  32  has a plurality of adjustment apertures  36  sized to accept adjustment tabs  38 , discussed further below, of spanning member  14 . 
     FIG. 4 is a sectional view of load distribution member  12  taken along line  4 — 4  of FIG.  2 . Connector arm  32  is formed with a central U-shaped channel to provide a larger surface area and thus a stronger support than that which would be provided by a flat surface. Adjacent to each side of the central U-shaped channel of connector arm  32  are connector arm flanges  37 . Adjustment apertures  36  extend through connector arm flanges  37 . 
     FIG. 5 is a perspective view of one end of spanning member  14 . The ends of spanning member  14  are identical. Spanning member  14  is sized to adjustably connect to load distribution members  12  between a pair of floor joists. In the preferred embodiment spanning member  14  is manufactured in lengths of: twelve inches, sixteen inches, nineteen inches and twenty-four inches to accommodate a wide variety of installation requirements. As shown in FIG. 1, lengths A, B, C and D may all vary, depending upon the dimensions of the joist selected and the installation distance between joists. The variety of possible lengths for spanning member  14  allow the correct spanning member  14  to be selected over a wide range of possible joist configurations. Spanning member  14  has a plurality of adjustment tabs  38  that are sized to lockably fit adjustment apertures  36  of connector arm  32 . Adjustment tabs  38  are finger-like in structure and integral to spanning member  14 . Adjustment tabs  38  are created during the manufacture of spanning member  14  by cutting a finger-like shape into the surface of spanning member  14  leaving the base of adjustment tabs  38  connected to spanning member  14 . Adjustment tabs  38  are then bent along the base attached to spanning member  14  to an angle of approximately ninety degrees below the top surface of spanning member  14 . The finger tip ends of adjustment tabs  38  are preferably arcuate in shape to permit rapid connection with adjustment apertures  36 . Any reasonable number of adjustment tabs  38  may be stamped into spanning member  14 . Spanning member  14  may be constructed in a variety of cross-sectional forms as will be discussed further below. The preferred embodiment as illustrated in FIG. 5 has a planar top surface from which the adjustment tabs  38  project downward. On each side of the top surface are shoulders shown generally as  42 , each shoulder  42  having a vertical wall  43  connected to a spanning member flange  45 . The shoulders  42  serve to protect the adjustment tabs  38  from becoming bent prior to installation, for instance by someone accidentally stepping on the spanning member  14 . The shoulders  42  further serve to support the adjustment tabs  38  and prevent the adjustment tabs  38  from bending in use. 
     FIG. 6 shows an alternative embodiment for spanning member  14 , having no shoulders. Adjustment tabs  38  are formed by cutting slits into the vertical side walls of spanning member  14 . 
     FIG. 7 shows an alternative embodiment for spanning member  14 , having no shoulders and a peaked top surface. Adjustment tabs  38  are formed by cutting slits into the vertical side walls of spanning member  14 . 
     FIG. 8 shows an alternative embodiment for spanning member  14 . The spanning member  14  has spanning member flanges  45  with upturned end walls  46 . Adjustment tabs  38  are created during the manufacture of spanning member  14  by cutting finger-like shapes into the surface of spanning member flanges  45  leaving the base of adjustment tabs  38  connected to spanning member  14 . Adjustment tabs  38  are then bent to an angle of approximately ninety degrees below the surface of spanning member flanges  45 . The finger tip ends of adjustment tabs  38  are preferably arcuate in shape to permit rapid connection with adjustment apertures  36 . 
     FIG. 9 shows an alternative cross-sectional shape for spanning member  14  having an outwardly extending rib  40 . 
     FIG. 10 shows an alternative cross-sectional shape for spanning member  14  having an inwardly extending rib  42 . 
     Although the preferred embodiment utilizes a spanning member  14  of the configuration as illustrated in FIG. 5, any number of configurations may be selected that are cost effectively produced and provide sufficient load bearing strength. For example, the adjustment tabs  38 , shelves  45  and walls  46  of FIG. 8 could be combined with the cross-sectional configuration of FIGS. 7,  9  or  10 . 
     FIG. 11 shows joist bracing apparatus  10  installed between a series of conventional wooden joists  48 . The joist bracing apparatus  10  are shown installed in a zig-zag pattern for optimal load distribution. 
     FIG. 12 shows another preferred embodiment of the spanning member  14 . Spanning member  14  has a spanning member body  50  and two pairs of spanning member side walls  52 . Each pair of side walls  52  are generally parallel to each other and extend at 90° degrees from spanning member body  50 . As shown, one pair of sidewalls  52  extend above spanning member body  50  and, the other pair of spanning member side walls  52  descend below spanning member body  50 . Spanning member side wall  52  intersects an arcuate trailing edge  54  located toward the central portion of spanning member  14 . Each spanning member side wall  52  has a locking prong  56  located centrally in the spanning member side wall  52  beneath the plurality of adjustment tabs  38 . The locking prong  56  serves to lock the connector arm  32  to the spanning member  14  once they are engaged. 
     Spanning member body  50  also includes a pair of ribs  58   a  and  58   b . In the preferred embodiment one of ribs  58   a  or  58   b  is recessed into spanning member body  50  and the other rib extends above the surface of spanning member body  50 . The ribs  58   a  and  58   b  serve to provide longitudinal rigidity to the centre portion of the spanning member body  50 . 
     FIG. 13 shows the preferred embodiment of distribution member  12  designed to be connected with the spanning member  14  of FIG.  12 . In this embodiment of distribution member  12 , connector arm  32  has a pair of opposed connector arm side walls  68 . Each side wall  68  is angled at slightly greater than 90° from planar portion  18 . This allows the side walls  68  to bend to form a friction fit with sidewalls  52  of spanning member  14 . The end  69  of each connector side wall  68  has a tapered edge  69 , to eliminate a sharp edge at the terminus of connector side wall  68 . Distribution member  12  has at one end a distribution member flange  70  extending at approximately 90 degrees from planar portion  18 . Planar portion  18  and distribution member flange  70  contain a plurality of apertures  28  through which nails, screws, or the like may be inserted to secure distribution member  12  to a joist. 
     FIG. 14 is a plan view of the intersection of two distribution member flanges  70 . Each distribution member flange  70  has a plurality of teeth  72  and recesses  74  that are configured to permit the distribution member flanges  70  of a pair of distribution members  12  mounted on opposing sides of a narrow floor joist to intersect, thus avoiding any potential overlap of distribution member flanges  70 . Each tooth  72  of distribution member flange  70  contains an aperture  28  through which a nail, screw, or the like may be inserted to attach distribution member flange  70  to a joist. 
     FIG. 15 is a perspective view of one end of the preferred embodiment of spanning member  14  as shown in FIG.  12 . Locking prong  56  is shown in a disengaged position within spanning member side wall  52 . Locking prong  56  is created by cutting an elongate locking prong aperture  76  into spanning member side wall  52  and leaving the material cut from locking prong aperture  76  attached at one end to spanning member side wall  52 . This attached material is then bent outwardly from spanning member side wall  52  during manufacture to form locking prong  56 . In use, once connector arm  32  has been inserted into the channel of spanning member  14  locking prong  56  is driven inwardly by using a hammer or the like. This serves to lock connector arm  32  within the channel of spanning member  14 . Locking prong  56  preferably includes a tapered top edge  79  so that its height at engaging end  78  is less than the height of the end remaining attached to spanning member side wall  52 . Further, engaging end  78  is preferably arcuate. Both of these features act as a wedge to ease the locking engagement of locking prong  56  with the edge of connector arm side wall  68 . 
     FIG. 16 is a cross-section of the spanning member  14  of FIG.  12  and the distribution member  12  of FIG. 13 in the engaged position viewed along line A—A of FIG.  15 . In the engaged position the adjustment tabs  38  of spanning member  14  extend through the adjustment apertures of connector arm  32 . Locking prongs  56  firmly engage the edge of connector arm side walls  68 . In the preferred embodiment adjustment tabs  38  are tapered so that they are widest at the base. The width of the base being such as to provide a snug fit of adjustment tabs  38  within adjustment apertures  36 . 
     In use, the user first bends connector arm  32  outwardly from the planar portion  18  of the load distribution member  12 . The load distribution members  12  are preferably shipped with the connector arm  32  non-extended to reduce the volume of packaging required. Once the connector arm  32  has been bent to a desired angle of approximately  45  degrees, the load distribution member  12  is positioned against the floor joist  16  with load distribution member  70  abutting the top most or bottom most exterior surface of a floor joist. The load distribution member  12  is then secured to the floor joist  16  by driving fasteners  30  through apertures  28  into the floor joist  16 . During installation, a first load distribution member  12  is attached to a floor joist  16  with the connector arm  32  extending upwardly and a second load distribution member  12  is installed to an opposing floor joist with the connector arm  32  extending downwardly. The connector arms  32  of the first and second load distribution members  12  are then connected by linking the connector arms  32  with the spanning member  14 . Locking prongs  56  are then struck with a hammer causing them to lock connecting arms  32  within spanning members  14 . For optimal support on a floor, the bracing members should form a zig-zag pattern between the floor joists  16  as shown in FIG.  11 . 
     In an alternative method of use, the joist bracing apparatus  10  may be assembled to a fixed length prior to installation. As each floor joist  16  is installed, a number of assembled joist bracing apparatus  10  are attached to the face of floor joist. The assembled joist bracing apparatus  10  may then be used as spacers to determine where to install the adjacent floor joist. 
     One particular advantage provided in the above described invention is the reduction in bounce and vibration for I-joist floor systems. 
     Although referring to floor joists throughout, this invention is not meant to be restricted to only floor supporting joists. Ceiling joists or other load bearing joists would also benefit from the use of this invention to distribute loads and prevent twisting of the joists. 
     As will be apparent to those skilled in the art, various modifications and adaptations of the apparatus as described above are possible without departing from the present invention, the scope of which is defined in the appended claims.

Summary:
An apparatus for bracing joists comprising a pair of load distribution members and a spanning member. The load distribution members are fastened to adjacent joists and connected together by the spanning member. The load distribution members each have a connector arm which contains a plurality of holes into which tabs on each end of the spanning member are sized to fit. The spanning member can thus connect the load distribution members over a range of distances providing a length adjustable joist bracing apparatus.