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BACKGROUND OF THE INVENTION 
     The invention relates to suspended ceilings and, in particular, to grid elements that eliminate or reduce the number of mid-span suspension wires or like elements required to adequately support the ceiling assembly. 
     PRIOR ART 
     Commonly, the grid of a suspended ceiling is supported by wires depending from overhead structure such as an overlying floor or roof. There are circumstances, as in corridors, where the plenum or space above the ceiling is occupied by utilities, such as air and wire ducts, making it difficult or impractical to use wires for carrying the weight of a ceiling. In other circumstances, there may only be a limited number of places to attach wires to the overhead structure and/or to the grid elements. In still other circumstances, labor and overall installation costs can be lowered where the number of wires needed for an installation is reduced. 
     There have been proposals such as disclosed in U.S. Pat. No. 7,240,460 and U.S. patent publication US 2010/0257807 A1 for free span suspended ceilings. 
     SUMMARY OF THE INVENTION 
     The invention provides a ceiling grid system with high moment of inertia grid runner, end brackets and wall mounted runner end supports. Optional elements of the system include splice plates and runner-to-runner cross hanger brackets. The disclosed system is capable of spanning an area without or with limited overhead wire support. 
     In the disclosed embodiment, the high moment of inertia grid runners are primarily used as main runners or tees that cooperate with cross runners in a generally conventional manner. End brackets are manually attached to main runners typically at the grid installation site after the main runners are confirmed to fit or have been cut to fit the span across which they are to be installed. 
     Preferably, an end bracket interfits with the physical characteristics of the main runner so that only a single screw fastener is required to rigidly fix the bracket to the runner. 
     The disclosed grid runner end supports are in the form of roll formed sheet metal channels that are affixed to the walls at the edge of the ceiling. The channel flanges can be of different widths so that the channel can be oriented with a wide or narrow flange visible from the space below the ceiling. The flanges have inturned hems that are engaged by tab elements of the end brackets for a quick snap-in provisional mounting. An end bracket can be locked on the channel at a desired location with a screw fastener through a web of the channel. 
     In moderate span length applications such as in a corridor of 8 foot (or metric equivalent) for an acoustical ceiling, the disclosed system can eliminate the need for intermediate overhead support wires or like members. In longer spans, the system can reduce the number of suspension wires that would otherwise be required. For such longer spans, a splice plate is provided to enable the high moment of inertia grid runner to be connected end-to-end. Additionally, the splice plate can be bent into a right angle for connecting intersecting grid runners to the main runner. 
     A cross brace clip is disclosed that suspends a high moment of inertia grid runner with an identical grid runner to reduce the number of necessary suspension wires and/or enable a main runner to be suspended where no directly overhead structure is available for its support. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a corridor ceiling embodying aspects of the invention; 
         FIG. 2  is an enlarged fragmentary perspective view of an end area of grid runners and a support channel of  FIG. 1 ; 
         FIG. 3  is an enlarged fragmentary perspective view of a main grid runner with a narrow lower flange and a support channel inverted from that shown in  FIG. 2 ; 
         FIG. 4  is an elevational view of an end clip for a main runner shown in a pre-bent condition; 
         FIG. 5  is an edge view of the clip of  FIG. 4 ; 
         FIG. 6  is a top view of the clip of  FIG. 4 ; 
         FIG. 7  is an elevational view of a splice plate for the main runner; 
         FIG. 8  is an edge view of the splice plate of  FIG. 7 ; 
         FIG. 9  is a fragmentary perspective view of two main runners joined with the splice plate of  FIG. 7 ; 
         FIG. 10  is a perspective view of main runners intersecting at 90 degrees and joined by the splice plate of  FIG. 7 ; 
         FIG. 11  is a view similar to  FIG. 10  with a cross-runner joined to a main runner with the splice plate of  FIG. 7 ; 
         FIG. 12  is a perspective view of a cross brace clip for supporting a main runner from an identical transverse main runner; 
         FIG. 13  is a front view of the cross brace clip; 
         FIG. 14  is a side view of the cross brace clip; and 
         FIG. 15  is a top view of the cross brace clip. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates a suspended ceiling grid  10  suitable for supporting conventional acoustical panels or tiles in a corridor  11 . It will be understood that various aspects of the invention are applicable to suspended ceilings apart from hallways or corridors and the like. By way of example, the corridor  11  can be nominally 8 foot in width (or metric equivalent). The grid  10  comprises parallel main runners  12  located on 4 foot centers. Cross runners  13 , nominally 4 foot long, extend transversely between the main runners  12 . Nominal 2 foot cross runners  14  are disposed between cross runners  13 . 
     As is conventional, cross runners  13 ,  14  have end connectors assembled in receiving slots  17  of the main runners  12  and cross runners  13 . Ends of the main runners  12  and cross runners  14  are supported by wall channels  19 . 
     The main runners  12  have the general cross section of an inverted tee with a hollow upper generally oval reinforcing bulb  21 , a vertical web  22  depending from the bulb, and a flange  23  symmetrically disposed about a lower edge of the web. The illustrated bulb  21  is substantially wider than it is tall. By way of example, but not limitation, the main runner  12  can have a height of about 2¾ inch which, when compared to a typical 1.640 inch height conventional intermediate duty main grid runner, is relatively tall. The height of the main runner  12 , width of its reinforcing bulb  21  and heavier gauge results in a runner that has a high moment of inertia about its longitudinal bending axis. Consequently, the runner  12  can support a relatively high load distributed along its length. For example, the main runner  12 , formed of 0.022 inch thick G-30 hot-dipped galvanized steel place on 4 foot centers such as is shown in  FIG. 1  can readily support an acoustical ceiling of conventional tile. The illustrated main runner  12  can support 12 pounds per foot across a span of 8 foot without intermediate support wires, straps, rods or the like. 
     The ceiling load on a main tee  12  is transferred at each end to a respective wall channel  19  through an end bracket  26 . The end bracket  26  is shown separately in  FIGS. 4-6  and with main and cross runners  12 ,  13  in  FIGS. 2 and 3 . The end bracket  26  is preferably a sheet metal stamping. The bracket  26  can be marketed in the generally flat configuration illustrated in  FIGS. 4-6  making it easier for a technician to carry a plurality of the brackets in a pouch or box. For use, the technician manually bends the bracket  26  across a vertical line determined by a center line of a vertical slot  27  that serves locally to weaken the bracket for this bending purpose. A portion  28  of the bracket  26  to the left of the slot  27  in  FIG. 4  is engageable with a main grid runner  12  and a portion  29  to the right is engageable with a wall channel  19 . The bracket  26  has a central horizontal shallow channel  31  with an elevation and width enabling it, on the left portion  28  to register with a reinforcing bulb  32  of a conventional grid runner of nominal 1½ inch height as shown in  FIG. 2 . A narrow horizontal slot  33  enables an upper region of the left bracket portion  28  to be removed for clearance purposes by cutting the region off at the dotted lines  34 ,  35 . Two other horizontal slots  36 ,  37  can be used in a seismic application with a screw located in either slot and an associated grid runner. Holes  38  are provided to receive screw fasteners for fixing the bracket  26  to a grid runner  12 ,  13  and to the web of a wall channel  19 . 
     The wall channel  19  is preferably roll formed of sheet metal of, for example, G-30 hot dipped galvanized steel of 0.020 inch thickness. The illustrated channel  19  has flanges  41 ,  42  of different widths and extending generally perpendicularly from a common web  43 . The wider flange  41  is, for example, nominally 1 inch wide and the narrow flange  42  is nominally ½ inch wide. These flange dimensions correspond to the flange face width of standard and narrow face commercially available grid common in the industry. The channel flanges  41 ,  42  have inturned hems  44  associated with marginal edges  45  of the metal strip forming the channel  19 . The flanges  41 ,  42  are spaced to receive the height of the main runner  12 . 
     As shown in  FIG. 1 , the channels  19  are secured to a wall  15  at ceiling height with one of their flanges  41  or  42  at or essentially at the plane of the grid surfaces which remain visible when ceiling tile are installed on the grid flanges. The other flange  42  or  41  is situated above this visible plane. The main runners  12  may be supplied with a length that exceeds a standard corridor width. For example, if the corridor under construction has a nominal 8 foot width, main runners  12  can be provided at a length of 8 foot 6 inches, so that any actual run out of the corridor can be accommodated. End brackets  26  are field installed on the main runners  12  so that the main runners can be first properly cut to length, typically at each end, to center the grid  10  as dictated by slots  17  in the main runners. The cross runner connector receiving slots  17  ( FIG. 2 ) are spaced along the length of the main runner  12  on, for example, 6 inch centers. 
     The end brackets  26  have resilient tabs  48 - 50  on upper and lower edges of the channel engaging portion  29 . The upper tab  48  extends the full length of the portion  29  and a lower middle tab  49  extends between outlying lower tabs  50 . With reference to  FIG. 2 , the outlying lower tabs  50  are proportioned to snap into engagement with the inner edges  45  of the hem  44  of the wide channel flange  41  and the upper tab  48  is proportioned to snap into engagement with the narrow flange hem edge  45  when the bracket portion  29  is pushed into the channel  19 . This snap fit is a convenience to the installer since the bracket  26  (and the main runner  12  if it is attached) is/are immediately held in the channel while being horizontally adjustable. When in a proper position, the bracket  26  is fixed to the channel web  43  with a self-drilling screw  40  or other suitable fastener through a hole  38  in the portion  29 . The bracket  26  can be fixed to a main runner  12  with a single self-drilling screw  40 . Upper and lower edges  52 ,  53  of the runner engaging portion  28  of the end bracket are proportioned to fit closely with the bottom of the reinforcing bulb  21  and top of the flange  23  when positioned against the main runner web  22 . When held against the web  22  by a single self-drilling screw  40  or other fastener positioned in a hole  38 , the bracket  26  cannot perceptibly rotate relative to the main runner  12  and, consequently, the main runner cannot droop at the bracket under the weight of the ceiling. 
     Typically, the channel  19  is secured to a wall by self-drilling drywall screws  55  ( FIG. 2 ) through the channel web  43 , any wall facing material such as drywall, and into studs  54 . An upper flange  42  or  41  of the channel  19  stiffens the channel web  43  and prevents it from pulling away from the wall to which it is attached due to the weight of the ceiling. Consequently, there is no need to align a bracket  26  or, more importantly, a grid runner  12 , with a wall stud  54  ( FIG. 1 ) so that the bracket would be anchored directly to a stud. 
     From the foregoing, it will be seen that for the spans of about 8 feet the runners  12  and the acoustical ceiling elements they carry are supported exclusively at their ends. The brackets  26  are capable of fully providing this support although a support contribution can be provided by a lower channel flange  41  or  42 . 
     In  FIG. 3 , a main runner  112  has a narrow flange face as would the other main and cross runner in a ceiling installation. The wall channel  19  is inverted from its position in  FIG. 2 . In this orientation, the narrow flange  42  will be visible from below and will match the appearance of the grid runners where they are of the narrow face design. In instances where the wall channel  19  is of the orientation in  FIG. 3 , the end bracket tabs  50  are bent up by the installer and the middle tab  49  can engage the adjacent hem edge  44  of the narrow flange  42 . 
     In the foreground of  FIG. 2  is illustrated the end bracket  26  supporting a conventional cross runner  14 . The horizontal channel  31  is proportioned to receive a reinforcing bulb  32  of the runner  14  while a lower part of the portion  28  abuts a web  58  of the runner. For seismic service, a screw can be positioned in the slot  37  and the reinforcing bulb. 
       FIGS. 7 and 8  illustrate a splice plate  61  useful for joining the ends of a pair of main runners  12  in the manners illustrated in  FIGS. 9 and 10 . The splice plate  61  is generally rectangular in front view, being formed, for example, of 0.030 inch gauge hot-dipped galvanized steel sheet. The plate  61  has notches  62  along its upper and lower edges at its mid-section. A shallow horizontal rib or channel  63  is stamped in the body of the plate  61 . A central vertical slot forms a line of weakness to permit the plate  61  to be manually bent into a right angle. Elongated horizontal slots  66  are stamped in the plate channel  63  on both sides of the vertical slot  64 . Several holes  67  are provided for screws used to attach the plate to a grid runner.  FIG. 9  illustrates the plate  61  joining a pair of main runners  12  together in end-to-end alignment. Upper and lower edges  68 ,  69  of the plate  61  fit closely between the reinforcing bulb  21  and the flange  23  when the plate is abutted against the web  22  of a main runner  12 . The fit of the plate  61  thereby prevents any perceptible rotational movement relative to the main runner to which it is attached. Any of the holes  67  or slot  66  may be used to accept a screw for attaching the plate to a main runner  12 . 
       FIG. 10  illustrates use of the plate  61  to join a main runner  12  with an intersecting main runner. Note that the width of the slot  64  avoids interference between areas of the channel  63  when the plate  61  is bent into a right angle. 
       FIG. 11  illustrates use of the splice plate  61  to join a main runner  12  with an intersecting conventional cross runner  13  or  14 . The channel  63  is configured to receive the reinforcing bulb  32  and a lower part of the plate half to abut the web  58  of the conventional grid runner. 
     A physical situation may exist where a main runner  12  cannot be supported exclusively at its end. For example, may be an absence of a suitable attachment point for a suspension wire or strap overlying the main runner or runners involved.  FIG. 12  illustrates a cross brace clip  71  that can be useful in such situations. The clip  71 , shown in detail in  FIGS. 13-15 , is a monolithic sheet metal stamping of, for example, 0.050 inch hot dipped galvanized steel. The clip  71  has the general geometry of a right angle. An upper planar part  72  of the clip  71  has several holes  73  for receiving self-drilling screws for attachment to the web  22  of a main runner  12 . Upper and lower edges of the part  72  are spaced to closely fit between the reinforcing bulb  21  and flange  23  of a main runner  12  so that the part cannot perceptively rotate relative to the main tee when it abuts the web  22 . The clip  71  includes a triangular extension  74  in a vertical plane perpendicular to the planar part  72 . An offset web  76  joins the extension  74  to a depending planar part  77 . Holes  78  in the depending planar part  77  receive self-drilling screws for attachment to the web  22  of a main runner  12  below and transverse to the main runner to which the upper planar part  72  is attached. It will be seen from  FIG. 12  that the cross brace clip  71  supports the lower main runner  12  from the overlying main runner  12 . 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.

Summary:
Components for constructing a ceiling grid across a span free of or with a limited number of suspension wires including main runners with a relatively high moment of inertia secured at their ends with brackets to wall moldings on opposing walls.