Abstract:
A balanced, single-layered web beam for a grid in a suspended ceiling, wherein opposing flanges at the bottom of the web are cantilevered directly from the bottom of the web. When the flanges are equally loaded, the resultant load on the beam passes through the vertical plane of the web, so the beam does not twist or bend.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to beams that form a grid in a suspended ceiling. The beams support either panels laid on top of the flanges of the beams, or drywall sheets attached at the bottom of the flanges of the beams. 
     2. Description of the Related Art 
     Beams used in grids for suspended ceilings of either the panel or drywall type are well known. Such beams, which are similar for both types of ceilings, are formed into an inverted T cross section by continuously passing a strip of metal through rollers that fold the strip longitudinally. 
     The beams carry a vertical load on the flanges only. To avoid twisting and bending in tee beams under such vertical load on the flanges in suspended ceilings, beams symmetrical in cross section are used, so that the beam is loaded in the plane of the web. In the prior art, this is done with a double-layered web, having a flange cantilevered from each layer of the web, wherein the flanges oppose one another horizontally. 
     Beams with a single-layered web have been tried, in an attempt to produce a beam that uses less metal. In such a beam that has a single-layered web, only a single flange is cantilevered from the web. An opposing flange is cantilevered from the first formed flange. Such a beam is unbalanced under a vertical load on both flanges, and is subject to twisting and bending, since it is not loaded in the plane of the web. 
     In U.S. Pat. Re 31,528, incorporated herein by reference, such problems with single-layered webs are discussed with reference to  FIG. 7  of the patent. 
     In U.S. Pat. No. 4,520,609, attempts were made to balance the cross section of a single-layered web beam by adding more material to the top and bottom of the beam on opposite sides of the web. 
     In U.S. Pat. No. 4,713,919, a beam having a web with a full first layer, and a partial second layer, is disclosed. 
     In U.S. Pat. No. 5,979,055, incorporated herein by reference, a beam having a web that is formed partially of one layer, is pieced together. 
     Such prior art beams with a full, or partial, single-layered web were unbalanced and lacked the necessary strength and stiffness to support the loads, unless more and heavier material was used than in a double-layered web beam. This defeated the desire to use a single-layered web beam with its promise of the use of less metal to make the beam. Virtually all beams for suspended ceilings continue to have a double-layered web. 
     BRIEF SUMMARY OF THE INVENTION 
     A balanced beam for a suspended ceiling is formed with a single-layered web that has one flange bent and cantilevered from the bottom of the web, and a second, opposite flange, that is cantilevered from close to the web by a seam that secures the first and second flanges together close to the web. 
     The seam is preferably formed by continuous stitching as the beam is being rollformed, as seen, for instance, in the &#39;055 patent. Other forms of binding, such as spot, or continuous, welding, as well as adhesives, may be used to form the seam. 
     Such a beam in cross section is balanced, and acts to load the beam in the plane of the web, so that any twisting or bending in a beam having a single-layered web is substantially eliminated. 
     The seam also binds the flanges themselves together to produce a bottom member at the base of the single-layered web that stiffens the web itself. 
     Such a single-layered web beam with a seam in the flanges along the web that binds the flanges together near the bottom of web, so that both flanges are cantilevered from the web, provides the equivalent strength and rigidity of a double-layered web formed of the same thickness of strip metal, but without using a second layer of the metal in the web, so there is less metal needed to make the beam. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a partial perspective view of the basic single-layered web beam of the invention, taken from above. 
         FIG. 2  is a partial perspective view of the beam of  FIG. 1 , taken from below. 
         FIG. 3  is a cross sectional view of a prior art beam with a double-layered web. 
         FIG. 4  is a cross sectional view of a prior art beam with a single-layered web. 
         FIG. 5  is a cross sectional view of the beam of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Beams  20  for suspended ceilings are shown in  FIGS. 1 through 5 . Such beams include the prior art beams shown in  FIGS. 3 and 4 , and the single-layered web beam of the invention shown in  FIGS. 1 ,  2 , and  5 . Beams  20  have a bulb  21  at the top of a web  22 . Opposing flanges  23  and  25  extend horizontally away from the web at the bottom of the beam. 
     The vertical panel load, or vertical drywall load, on the beams in a suspended ceiling, is indicated in  FIGS. 3 through 5  by vectors that represent the amount, location, and direction of the load exerted by the panels or drywall in a suspended ceiling. The load on each flange is indicated by numbers  26  and  27  on the prior art beams shown in  FIGS. 3 and 4 , and on the beam of the invention  20  shown in  FIG. 5 . 
     The prior art beam  20  shown in  FIG. 3  has a two-layered web  22 , with each of the flanges  23  and  25  cantilevered from one of the layers of the web  22 . The beam is symmetrical, and hence balanced, in cross section. 
     The prior art beam  20  shown in  FIG. 4  has a single-layered web  22  with a flange  25  cantilevered from the bottom of the web  22 , to the right, and then a second opposing flange  23  cantilevered from flange  25  at location  29 , in a direction to the left. 
     The basic single-layered web beam  20  of the invention, as seen in  FIGS. 1 ,  2 , and  5 , has a single-layered web  22 , with the flanges formed as in the prior art beam  20  of  FIG. 4 . The basic single-layered web beam  20  of the invention also has a seam  40  that runs longitudinally along the web  22  of the beam, that binds flanges  23  and  25  together, so that flange  23  is cantilevered from flange  25  along web  22 . 
     The seam  40  is preferably made as the beam is being continuously rollformed, as by stitching. A form of stitching is disclosed in U.S. Pat. No. &#39;055 cited above. A seam  40  could also be formed by continuous or spot welding, or by adhesives. 
     Seam  40 , in effect, cantilevers the flange  23  from the single-layered web  22  of the basic beam of the invention  20 , so that the result is a balanced beam that is loaded through the plane of the single-layered web  22 . Such basic beam  20  of the invention resists twisting and bending to an extent equivalent to that of a double-layered web beam of a comparable size made of the same thickness metal strip, as seen for instance in  FIG. 3 . The beam of the invention however, uses less metal. 
     In  FIGS. 3 ,  4 , and  5  of the drawings, the loading of the beams  20 , both prior art, and of the invention, is shown through the use of vectors. 
     In  FIG. 3 , load vectors  26  and  27  represent the vertical loading on each of the flanges  23  and  25  of a double-layered prior beam  20 , in either a panel or a drywall suspended ceiling. The resultant load vector  30  of vectors  26  and  27  of such prior art double-layered web beam passes through the plane of web  22 , since the beam is balanced. Such balanced beam creates a maximum resistance to bending and twisting. 
     In  FIG. 4 , there is shown the single-layered beam of the prior art. Again, as in  FIG. 3 , the vectors  26  and  27  represent the loads applied to the beams, either through panel, or drywall, loads. However, because of the beam construction wherein flange  23  is cantilevered from flange  25  at location  29 , the resultant load vector  31  is shown applied at a distance away from the single-layered web, resulting in an unbalanced beam subject to bending and twisting that is not present in the balanced beam of  FIG. 3 . 
     In  FIG. 5 , which shows the basic single-layered web beam  20  of the invention, again, as in the prior art, the beam  20  is vertically loaded on the flanges  23  and  25 , in the suspended ceiling, as shown by vectors  26  and  27 . However, seam  40  binds flange  23  to flange  27  along web  22 , so that in effect both flanges  23  and  25  are cantilevered from web  22 , resulting in a balanced beam. Load resultant  32  passes through the plane of the web, so that the single-layered beam of the invention resists twisting and bending equivalent to a comparably sized two-layered web beam, as seen in  FIG. 3 , but with the use of less metal.