Beam for a grid in a suspended ceiling

Abstract: A compression relief section (40) in a beam (23) in a grid (22) for a suspended ceiling (20) that permits controlled collapse of the section during a fire, whereby the ceiling (20) is kept relatively intact. The section (40) has a channel (42) formed from the web portion (27) of the beam (23), and a crushed bulb (26) with a hump (55), along with a flange (31), that fold from compression forces, while resisting such forces. There is no interference between the folding portions and the ceiling panels when the section collapses.

Description: The invention relates to a beam for a grid that supports panels in a suspended ceiling, wherein the beam is in cross section in the form of an inverted T and comprises a web to be vertically mounted, a flange having sides extending outwardly from one end of the web, a bulb on the other end of the web, and a compression relief section collapsing under compression forces in the beam created during a fire and including a cut-out in the bulb having a notch that causes the bulb to fold upwardly under the compression forces, a cut-out in the web having a taper extending downwardly to the flange for folding the flange under the compression forces at least downwardly, and an under compression forces outwardly folding base formed from the web between the two cut-outs that have substantially the same length. Grid beams in a suspended ceiling, under normal conditions, are subject only to vertical loads from panels and accessories. Hanger wires, anchored to the structural ceiling above the suspended ceiling, generally located 1,2 m (4') apart on the main beam, provide support for such horizontal main beam. Cross beams are supported from the main beams. Both beams support panels. The beams are of an inverted T cross-section, and are formed by roll forming light sheet metal strip. Under normal conditions, the beams are subject to primarily vertical loads. In the event of fire, however, the beams in the grid are subject to compressive forces in the manner of a column that supports a vertical load, although the load is applied horizontally at the ends of the beam. Under heat, the beam seeks to expand longitudinally, and since the ends are constrained at the walls of the room, the beams buckle, unless the build up of compression forces is relieved. If the beams buckle, the panels are no longer supported in position, leaving the structural ceiling above the suspended ceiling exposed to the high heat of the fire. With the fire resistant panels in place, the structural ceiling is protected against the fire. A prior art way of keeping the beams, which act as a horizontal column under a compressive load during a fire, relatively intact, is to provide in the beam relief joints that permit the beam to collapse longitudinally, while keeping the beam relatively straight. Such joints are shown, for instance, in U.S. Patents 4,606,166 and 5,349,803. US-A-3 965 631 discloses a fire rated grid-member for a suspended ceiling with controlled expansion means comprising a rectangular cut-out in the web having a central notch on its lower side directed with its peak to the flange, while the opposed sides of the bulb above the cut-out are crimped together into planar abutment resulting in an upward protrusion and folding lines along which, if in case of a fire compression forces act on the beam, the beam is laterally displaced, i.e. the longitudinal alignment of the beam is lost. The beam of the generic kind is disclosed in US-A-3 589 089. The cut-outs in the web and the bulb weaken the beam in this area. In order to maintain sufficient strength for supporting the panels, the cut-outs have to be as small as possible which means that a controlled beam collapse under compression forces in case of fire can be problematic. It is the object of the invention to provide a beam of the generic kind that maintains strength in the compression relief section even though material is removed in creating this section and which resists compression loads created by a fire without twisting or bending until the instance of collapse, which is to occur in a controlled manner such that after the collapse the beam continues to support the panels to act as a fire barrier. This object is achieved with the beam of the generic kind which is characterized by stiffening sides extending from the base providing a channel having an U-shaped cross-section, by a notch into each of the stiffening sides at the longitudinal center of the channel to provide a controlled collapse point, and by a slightly elevated hump formed from the bulb by an inward crush of one side of the bulb, wherein the notch of the cut-out in the bulb extends below the hump. If the panel, i.e. a drywall panel, is fixed to the flange of the grid, the height of the cut-out of the web advantageously provides the necessary space for taking up the flange folding upwardly into it under the compression forces. The compression relief section of the beam of the invention has a notched channel in the web and a crushed and notched bulb. The section collapses and the beam contracts when the compression forces from a fire build-up in the beam. The section collapses in the manner wherein the channel, bulb, and flange of the beam fold in such a manner that the beam is kept longitudinally aligned, to provide support for the panels. Figure 1 is a perspective view of a suspended ceiling having panels supported on a grid of beams. Figure 2 is an end view taken on line 2.2 of Figure 1 showing a main beam in cross-section supporting panels on the beam flanges. Figure 3 is a perspective view of a main beam compression relief section. Figure 4 is a perspective view of the section of Figure 3 after the section has partially collapsed to relieve compressive forces. Figure 5 is a side elevation of the compression relief section shown in Figure 3. Figure 6 is a side elevation of the section in partial collapse as shown in Figure 4. Figure 7 is a top plan view of the section shown in Figure 3, supporting panels drawn in phantom. Figure 8 is a top plan view of the partially collapsed section of Figure 6, supporting panels as shown in phantom. Figure 9 is a sectional view of a collapsed section, showing the panels the beam continuing to support the panels. Figure 10 is a side elevation showing the section fully collapsed. Figure 11 is a top plan view showing the section fully collapsed. Figure 12 is a cross-section showing the section fully collapsed. Figure 13 is a side elevation showing the section partially collapsed, with the bottom flange folding inward. Figure 14 is a cross-section showing the section being used with dry wall paneling fixed to the beam. As seen in Figure 1, suspended ceiling 20 has panels 21 supported by a rectangular ceiling grid 22. Grid 22 has main beams 23 and cross beams 25. Main beams 23, generally 3,6 m (12') lengths connected together in abutting relationship, are suitably supported at, for instance 1,2 m, (4 foot) intervals by hanger wires anchored in the structural ceiling and connected to the main beams 23 through holes in a web 27 of the beam. The cross beams 25 are supported from the main beams 23. The beams are formed of a strip of sheet metal rolled into a cross-sectional shape having a bulb 26, the web 27 of the two layers 28 and 29, and a flange 31 having opposing sides 32 and 33. A bottom cap 35 extends over the flange sides and is secured to the flange at its edges at 36 and 37. Suitable stitching 38 may extend through the layers 28, 28 of the web 27 to strengthen the web 27. Such beam construction is well known in the prior art. A compression relief section 40 invention has a cut-out 41 in the web 27, a channel 42 in the web 27 that collapses in a controlled manner under compressive forces in the beam, a cut-out 43 in the bulb 26, and a bulb shape 44. Cut-out 41 is desirably of the dimension shown in Figure 5, in inches. It should be understood, however, that such dimensions are merely illustrative for purposes of understanding. The length of the cut-out 41, which is shown as 4,13 cm (1.625 inches) in Figure 5, should be such as to provide relief from compressive forces caused by the heat of a fire, when the section fully collapses, as shown in Figures 10, 11, and 12. Generally, there is a need to permit the beam to contract 8,36 mm per m (0.1 inch per foot) of length of beam in case of fire, so that the dimension shown, 4,13 cm (1.625 inches) is enough to relieve a 36 m (12 foot) section. Alternative dimensions for a cut-out length can be calculated based on the length of beam relieved. It should be understood, however, that the length of the cut-out 41 must permit the section to collapse in the manner shown. The height of the cut-out 41 is such that it permits the channel 42 to fold outwardly from the web 27, without interference from the panel. A feature of the invention is that the compression relief section 40 maintains structural strength in the grid 22 under normal conditions even though the cut-out 41 in the web 27 is large enough so that the folded channel 42 clears the panel 21 when the compression relief section 40 collapses. It is desirable to clear the panel 21 to avoid interference with the panel 21 as the compression relief section 40 collapses, and to avoid any displacement of the panel 21 from the folded channel 42 during the collapse. Cut-out 41 has at the bottom V-shaped comers 45 of a suitable arcuate dimension as shown in Figure 5. The cut-out 41 then tapers down to virtually the flange so that there is the least resistance to the flange 31 folding as set forth below, in the event of a fire. Channel 42, formed from web 27 by stamping or other suitable operation, is U-shaped in cross-section and has a base 46 and stiffening sides 47. Thus, there is formed from the relatively flexible flat web 27, a channel 42 which is relatively rigid. This is important in providing strength to the compression relief section 40, both under normal conditions, wherein the channel shape compensates for, the cut-out 41 of the web 27, and under fire conditions, where the channel 42 contributes to the controlled collapse and continued strength of the action in collapsed condition. A notch 48 is cut into each of the upper and lower sides 47 at the longitudinal center of channel 42 to provide a controlled collapse point when the beam 23 is subject to compressive forces. The sides 47 of channel 42 rise above one side of the base 46. As seen in Figure 5, for instance, the sides 47 rise toward the viewer. As seen in Figure 2, the sides 47 rise to the left from the plane of the web 27. A suitable fillet 51 is formed at each of the comers of channel 42 that permits the channel 42 to fold under compression, as described below. The bulb 26 has a cut-out 43 which has a length conforming generally to that of cut-out 41, with a height at the ends substantially that of the entire bulb 26. The amount of metal left at the ends 52, however, should be sufficient to provide a contribution to the structural rigidity of the compression relief section 40, so that the compression relief section 40 under normal grid conditions has the necessary strength to support panels 21 in the ceiling 20. The arc dimension shown at the comers of the cut-out 43 is illustrative. Such a comer provides enough rigidity under normal grid conditions, while permitting the compression relief section 40 to fold under fire conditions, as described below. The bulb 26 itself is partially crushed at 53 to provide a slightly elevated hump 55. Such hump 55 is formed when one side of bulb 26 is crushed inward as seen particularly in Figure 2, at 56. An inverted V-shaped notch 54 in the bulb 26 extends below hump 55. In the event of a fire, main beam 23 heats up, and since the main beam 23 is confined at its ends, compression forces build up. These compression forces cause the main beam 23 to expand. This expansion is then accommodated within the compression relief section 40. Bulb 26, at hump 55, folds upward; channel 42 folds outward; and flange 31 folds downward. The compression relief section 40 is shown partially collapsed in Figures 4, 6, and 8, and fully collapsed in Figures 9, 10, and 11. The collapse is a steady one, in which the compression relief section 40 offers continued resistance to the compressive forces throughout the collapse. Throughout the collapse, the main beam 23 on both sides of the compression relief section 40 remains in longitudinal alignment, so that the panels 21 continue to be supported wherein they stay in place to act as a barrier to the fire heat reaching the plenum space above the suspended ceiling 20. The channel 42 may fold in a manner wherein each of the layers 28, 29 of the channel 42 extend away from one another, as shown in the drawings, or they may fold in a manner wherein the layers 28, 29 of the channel 42 stay together, wherein the channel 42 fold to one side or the other of the web. The main beam 23 stays aligned at the compression relief section 40, in any event. A further use of the invention is in a construction wherein a drywall panel 60 extends over more than one grid opening, and is affixed to the flange 31 of the grid 22 with screws 61 or other fasteners. Such an embodiment is shown in Figure 14. In such construction, when the compression relief section 40 collapses, the flange 31 folds upward into cut-out 41, since the drywall panel 60 resists the downward folding of the flange 31. The height of the cut-out 41 provides the necessary space for such folding upward of the flange 31. The shape of the bottom of the cut-out 41 is such that it does not interfere with such upward folding.

Claims: A beam (23) for a grid (22) that supports panels (21, 60) in a suspended ceiling (20), wherein the beam (23) is in cross section in the form of an inverted T and comprises a web (27) to be vertically mounted, a flange (31) having sides (32, 33) extending outwardly from one end of the web (27) a bulb (26) on the other end of the web (27), and a compression relief section (40) collapsing under compression forces in the beam (23) created during a fire and including a cut-out (43) in the bulb (26) having a notch (54) that causes the bulb (26) to fold upwardly under the compression forces, a cut-out (41) in the web (27) having a taper extending downwardly to the flange (31) for folding the flange (31) under the compression forces at least downwardly, and an under compression forces outwardly folding base (46) formed from the web (27) between the two cut-outs (43, 41) that have substantially the same length, characterized by stiffening sides (47) extending from the base (46) providing a channel (42) having an U-shaped cross-section, by a notch (48) into each of the stiffening sides (47) at the longitudinal center of the channel (42) to provide a controlled collapse point, and by a slightly elevated hump (55) formed from the bulb (26) by an inward crush (56) of one side of the bulb (26), wherein the notch (54) of the cut-out (43) in the bulb (26) extends below the hump (55). A beam according to claim 1, characterized in that the height of the cut-out (41) in the web (27) provides the necessary space for taking up the flange (31) folded upwardly into it under the compression forces if the panel (60) is affixed to the flange (30) of the grid (22).

Inventors: LIN YU, PLATT WILLIAM J, ZIEGLER DANIEL C, LIN, YU, PLATT, WILLIAM J., ZIEGLER, DANIEL C.
Applicants: WORTHINGTON ARMSTRONG VENTURE
Application year: 2001
Main classification: E04B9
IPC codes: E04B9