Abstract:
A supporting system for use between two opposing supports comprised of at least two joists and at least one bridging member. The joists span between the opposing supports and are adjacent to each other. The joists each include bridging holes. The bridging members are between the adjacent joists and the bridging members are adapted to engage the bridging holes in the joists.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]    This patent application relates to U.S. Provisional Patent Application No. 60/514,622 filed on Oct. 28, 2003 entitled SINGLE WEB COLD FORMED JOIST, U.S. patent application Ser. No. 10/721,610 filed on Nov. 25, 2003 entitled SEGMENTED COLD FORMED JOIST, U.S. patent application Ser. No. 10/974,964 filed on Oct. 28, 2004 entitled COLD-FORMED STEEL JOISTS, and U.S. patent application Ser. No. 12/461,367 filed on Aug. 10, 2009 entitled LOWER CHORD COLD-FORMED STEEL JOISTS and incorporates by reference subject matter of these applications in its entirety herewith. 
     
    
     FIELD OF INVENTION  
       [0002]    This invention relates to cold-formed steel joists and to assemblies of such joists to provide structural support for floors and roofs in the building construction industry, such as support including fire rated steel-concrete composite structures. Both top chord and bottom chord supported joists are included as aspects of the said invention. 
       BACKGROUND OF INVENTION  
       [0003]    Joists are commonly used in the construction industry to span a distance between opposing walls and provide a structural support for a floor, roof or the like. Joists can be comprised of a variety of materials including softwood, wood based laminates, and metal, particularly steel. 
         [0004]    Steel joists can be constructed in an open web configuration, which generally consists of spaced apart upper and lower chord members which extend longitudinally thereof and are fastened together by a zig-zag web. Such open web joists are typically manufactured from hot-rolled steel structural members namely the upper and lower chords and the webs. The webs typically can be comprised of hot-rolled steel rods, which are formed into a zig-zagged pattern and welded to the upper and lower chords. Integral parts of the web are the end angled supports that connect the ends of the lower chord to the upper chord to counter load stresses at the ends of the joist. Open web joists are normally top chord bearing meaning that they are supported by the underside of the top chord, so that the top chord extends longitudinally beyond the bottom chord and the end angle supports to provide bearing interface with the opposing walls. 
         [0005]    Open web joists are by their nature highly customizable in terms of their load bearing capabilities. Both chords and the zig-zag web can be made from different thickness of steel, and the members constituting the zig-zag web can vary in thickness along the length of the joist. The webs are open in the sense that there is a space between the rods longitudinally along the central web section that can receive utilities such as wires, pipe work, air ducts or the like. Open web joists can be concentric, meaning that the load being supported exerts forces that substantially pass through the centres of gravity of the joists. If the joists are loaded otherwise, they are termed eccentric. 
         [0006]    The joist industry has introduced various types of composite steel-concrete non-combustible floor and roof systems for the construction industry, in which the top chords are embedded into a concrete slab, such a slab having both load bearing and fire resistant properties. Examples of composite joists can be found in U.S. Pat. Nos. 5,941,035, 4,741,138, 4,454,695 and U.S. Publication No. 2002/0069606 A1. A composite joist design permits the top chord member of a joist to be designed with less steel in comparison with non-composite systems since the concrete slab when properly bonded to the upper steel joist provides additional load support for the floor or roof system. 
         [0007]    Generally speaking, for a structural joist member to be composite it must have means to mechanically interlock with the concrete to provide sheer bonding. It is generally difficult and costly to design steel and concrete composite floors using steel joists. Simply affixing vertical studs to the top chord is forbidden by safety regulations in many jurisdictions which state that structural members cannot have objects extending above a structural floor member that will encumber the walking path of a worker. 
         [0008]    The methods for providing sheer bonding between the joist and the concrete in a composite joist are generally expensive to produce in the prior art. 
         [0009]    Furthermore, camber (defined as a slight arch added to the joist) has been introduced into the open web joist technology to offset the deflection associated with dead loads such that only the live load deflection of the joist needs to be accounted for in designs of the joist. However large machines or jigs are needed to impart the camber to the chords of the joist where typically the web resists the cambering process. 
         [0010]    Moreover, hot-rolled open web joists are typically coated or finished with a coloured primer. Steel joists manufacturers typically use large tanks of paint into which completed welded joist assemblies are dipped to receive a coating of primer paint. However, the process has become more expensive due to environmental considerations when using dipped tanks containing volatile solvents. 
         [0011]    Furthermore construction with open web joists is dependent on skilled labour which in many instances sets the critical path schedule on many construction projects during busy construction season periods when skilled labour is in highest demand. Because both the manufacture and usage in construction are labour intensive, open web steel joists are costly, so that their use is viable only in larger commercial and industrial structures requiring spans near 40 feet and above. 
         [0012]    An alternative approach to the open web steel joist is the cold-formed steel joist. Cold-formed steel structural designs have been used in floor and roof joists in the building construction trade for some time. However prior art cold-formed steel joists have found limited application due to the high costs of construction assembly, and are not cost effective for span lengths much above 24 feet usage is restricted to single and multi-family housing, and to commercial low rise structures. 
         [0013]    Provided that light gauge steel is used, cost effective mass manufacture of cold-formed steel joists is practical because highly automated cold forming operations such as roll-forming are commercially available. Joists in the prior art are produced by cold-forming a single piece of sheet metal into a joist comprising a top chord, a web and a bottom chord forming a continuous single structure, and are predominately used in bottom chord bearing conditions. These joists are generally eccentric in that the load forces do not pass through the centre of gravity of the joist. The most common example from prior art is the C-shaped joist which has a cross sectional profile like the letter C. Other examples of cold rolled constructions are shown in U.S. Patent Publication Nos. 2002/0020138 A1 and 2003/0084637 A1. 
         [0014]    Composite fire rated floor structures constructed using cold-formed joists are commercially available. Examples are Hambro D510 and Speed Floor both of which have end attachments that are welded, bolted or screwed onto a single strip cold-formed section to provide a top chord bearing joist. However these provide only limited load capacity due to the nature of the localized connection of the end attachments to the cold-formed joist member. Further, they are costly to produce. Cold-formed joist manufacturers provide holes longitudinally along the central web section that are sized to receive utilities for follow-up trades. Since cold-formed joist material can be pre-finished (i.e. the coils of steel can be galvanized or painted) the manufacturing process is less harmful to the worker and environment than the open web coating process described above. 
         [0015]    Although cold-formed joists possess superior surface finishes, and can be mass manufactured in a cost-effective manner because there is very little dependency on manpower involved relative to the open web joist technology, current state of the art cold-formed joist technology does not fully exploit the inherent strength to mass ratio of steel, nor does it optimize material usage throughout the length of the joist. The same thickness of steel is used in both of the chords and the web, this thickness being constant along the length of the joist. Eccentric designs have a tendency to be unstable under load due to a mechanical moment about the longitudinal axis. Consequently substantial bracing is required between joists to counteract this effect. 
         [0016]    These properties compare unfavourably with the open web steel joist where the chords and the web may be of different thickness and the web member thickness may be varied over the span length in response to loading requirements. 
         [0017]    Accordingly, a joist and method of producing said joist that can utilize the beneficial attributes while avoiding the drawbacks from each of the open web joist technology and cold-formed joist technology is desirable. Further, it is desirable to manufacture the joist using automated cold-forming methods as opposed to the labour intensive welding and handling methods employed in open web steel joist construction. It is also desirable to have cost effective fire rated composite floors and roofs based on cold-formed steel joists integrally attached to a concrete slab. 
         [0018]    Also both open web and cold-formed steel joist floor and roof structures normally require bridging systems, comprising steel members spanning the gap between joists in a floor or roof assembly, to stabilize the assembly from any lateral movement or rotational movement about the longitudinal direction in response to applied loading. It is common practice to weld bridging in place between open web joists, while cold-formed joist systems have bridging structures that commonly use screws or welding for fastening. Consequently a cost effective means to provide bridging between joists is highly desirable. 
       SUMMARY OF THE INVENTION 
       [0019]    A supporting system for use between two opposing supports comprised of at least two joists and at least one bridging member. The joists span between the opposing supports and are adjacent to each other. The joists each include bridging holes. The bridging member are between the adjacent joists and the bridging members are adapted to engage the bridging holes in the joists. 
         [0020]    The joists may include an upper chord, a web and a lower chord. The bridging holes may be formed in the web. The bridging holes may be formed in at least one of the upper chord and lower chord. 
         [0021]    The bridging members may include generally horizontal bridging members. The bridging members may further include criss-crossed bridging member attached to the generally horizontal bridging members. 
         [0022]    The bridging member may be a diaphragm assembly. The diaphragm assembly may include a steel plate. 
         [0023]    The bridging member may further include horizontal bridging members and the steel plate may be attached to the horizontal bridging members. The steel plate may have a hole formed therein. 
         [0024]    Each bridging may be adapted to be snapped in place. 
         [0025]    The bridging holes are a plurality of spaced apart bridging holes. 
         [0026]    The upper chord and lower chord may each include at least one inner flange and the bridging holes may be formed in the inner flanges. 
         [0027]    The supporting system may include a plurality of joists and a plurality of bridging members. 
         [0028]    The bridging members include an upper bridging member and a lower bridging member. 
         [0029]    The bridging members may be generally L-shaped. 
         [0030]    These and other objects and features of the invention shall now be described in relation to the following drawings: 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  illustrates a prior art open web steel joist (OWSJ); 
           [0032]      FIG. 2  illustrates a prior art cold-formed C-shaped joist; 
           [0033]      FIG. 3  illustrates one embodiment of the invention, a concentric top chord bearing segmented web steel joist; 
           [0034]      FIG. 4  illustrates segments of a segmented web; 
           [0035]      FIG. 5  is a perspective view of a second embodiment of the invention showing a concentric top chord bearing, cold-formed joist having three web segments; 
           [0036]      FIG. 6  is a side elevation view of  FIG. 5 ; 
           [0037]      FIG. 7  is a cross sectional view along the line  7 - 7  of  FIG. 5 ; 
           [0038]      FIG. 8  illustrates a side-view of a plurality of joists having bridging members; 
           [0039]      FIG. 9  is a side elevation view of a plurality of joists having both horizontal bridging and crossed bridging members; 
           [0040]      FIG. 10  is a perspective view of a concentric top chord bearing segmented web cold-formed joist to be used in a composite floor or roof structure; 
           [0041]      FIG. 11  is a side elevation view of  FIG. 10 ; 
           [0042]      FIG. 12  is a cross sectional view along the lines  12 - 12  of  FIG. 10  and also showing a concrete slab attached thereto; 
           [0043]      FIG. 13  is a side elevation view of a composite floor system having a plurality of joists; 
           [0044]      FIG. 14  and enlargement  14   a  are perspective views showing a bottom chord bearing version of another embodiment of the invention; 
           [0045]      FIG. 15  is a perspective view showing a top chord bearing version of another embodiment of the invention; 
           [0046]      FIG. 16  is a cross sectional view of the web only through line  16 - 16  of  FIG. 6 ; 
           [0047]      FIG. 17  is a cross sectional view of the web only along the line  17 - 17  of  FIG. 6 ; 
           [0048]      FIG. 18  is a partial side elevation view of a segmented web; 
           [0049]      FIG. 19  is a top view of  FIG. 18 ; 
           [0050]      FIG. 20  is a top expanded view of region  20 - 20  in  FIG. 18  showing a rivet joining two segments of a web; 
           [0051]      FIG. 21  is a partial side elevation view of the reinforcing member  84  shown in  FIG. 5 ; 
           [0052]      FIG. 22  is a partial view of  FIG. 21 ; 
           [0053]      FIG. 23  is a partial top plan view of the reinforcing member; 
           [0054]      FIG. 24  is a cross-sectional view of further embodiments of the joist wherein the web and the bottom chord are cold-formed from the same sheet of steel; 
           [0055]      FIG. 25  is a cross-sectional view of further embodiments of the joist wherein the web and the bottom chord are cold-formed from the same sheet of steel; 
           [0056]      FIG. 26  and enlargement  26   a  are perspective views of a bottom chord bearing composite version of another embodiment of the invention; 
           [0057]      FIG. 27  is a perspective view of a top chord bearing composite version of another embodiment of the invention; 
           [0058]      FIG. 28  is a schematic view of an automated assembly line for the manufacture of cold-formed joists; 
           [0059]      FIG. 29  is a cross section view through the line  116 - 116  of  FIG. 14 ; 
           [0060]      FIG. 30  is a side elevation view of an embodiment of one end of a bottom chord bearing composite cold-formed joist bonded to a concrete slab and integrated into a side wall; 
           [0061]      FIG. 31  is a partial enlarged view of  FIG. 30 ; 
           [0062]      FIG. 32  is a cross sectional view through line  112 - 112  of  FIG. 26 ; 
           [0063]      FIG. 33  is a side elevation view of a plurality of another embodiment of the invention with horizontal bridging between joists; 
           [0064]      FIG. 34  is a side elevation view of a plurality of another embodiment with diaphragm bridging; 
           [0065]      FIG. 35  is a side elevation view of one end of a bottom chord bearing cold-formed joist supported by a foundation wall and supporting a stud wall; 
           [0066]      FIG. 36   a  is a top plan view of the reinforcing flap of  FIG. 35 ; 
           [0067]      FIG. 36   b  is a perspective view of the reinforcing flap of  FIG. 35 ; 
           [0068]      FIG. 37  shows top and plan views of a further reinforcing flap of  FIG. 35 ; 
           [0069]      FIG. 38  is a bottom chord bearing embodiment of the invention illustrating the reinforcing end flaps; 
           [0070]      FIG. 39  is a side elevation view of  FIG. 38 ; and 
           [0071]      FIG. 40  is a cross sectional view of an alternate embodiment of a cold formed joist in a composite floor or roof structure 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0072]    In the description that follows, like parts are marked throughout the specification and the drawings with the same respective reference numbers. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order to more clearly depict certain features of the invention. 
         [0073]      FIG. 1  illustrates a prior art open web joist construction  2  consisting of an upper chord assembly  4  spaced from a lower chord assembly  6 . The chords are joined together by a zigzag web  8  which is generally connected to the upper and lower chord assemblies  4 ,  6  by a number of means including welding or the like. 
         [0074]      FIG. 2  illustrates a prior art cold formed joist construction  10  roll-formed from a single strip of light gauge steel, having a web portion  12  having a plurality of holes  14  disposed therethrough for receiving utilities such as wire or the like, and having upper and lower chords  11  and  13  respectively. 
         [0075]      FIGS. 3 and 5  illustrate two similar embodiments of the invention, namely top chord bearing concentric joists, which comprise an assembled joist  20  having a first or upper chord member  22  spaced from a second or lower chord member  24 . A steel web member  26  is also disclosed. The web member  26  is fastened to the upper and lower chord members  22  and  24  by fastening means  28 . The fastening means can comprise of a variety of fastening means such as bolts and nuts, screws, welding or spot clinches (not shown) or rivets  30  as shown in  FIG. 7   
         [0076]    The upper and lower chord members  22  and  24  are produced from single sheets of steel. The joist can be formed in a concentric fashion as shown in  FIG. 7  where the upper and lower chord members  22  and  24  are substantially symmetrically disposed about web  26 . 
         [0077]    In these embodiments the upper chord member  22  is cold-formed to present a substantially flat upper load bearing surface  34  which is formed as shown in  FIG. 7  to present lower load bearing wings or extensions  36  and  38 . The upper load bearing surface  34  is in contact with the lower load bearing extensions  36  and  38  so as to produce a rigid and structurally solid member which may be fastened together by the spot clinch  32 . The spot clinch process is conducted in the manner well known to those persons skilled in the art and generally consists of a mechanism which pushes material by a plunger (not shown) to present a mushroomed head  40  as shown so as to secure the members together. 
         [0078]    The upper load bearing surface  34  and lower load bearing extensions  36  and  38  are disposed in this case symmetrically about the web  26 , the direction of which defines the “Y” axis  27  as shown in  FIG. 7 . Accordingly, the upper load bearing surface  34  in concert with the lower load bearing extension  36  on one side of the axis  27  defines a horizontal extension  42  while the upper load bearing surface  34  to the right of the Y axis  27  in concert with the lower load bearing extension  38  defines a horizontal extension  44  disposed on the other side of the axis  27 . The lower load bearing extensions  36  and  38  are cold-formed spaced apart web receiving tabs  46  and  48  as shown. The upper portion  50  of the web  26  may include a plurality of holes  52  which are adapted to receive the fastening means  28 .  FIG. 7  shows an example of a fastening means  28  comprising a rivet  30  that fastens the web  26  to the upper chord  22  at the tabs  46  and  48 . 
         [0079]    The spot clinches  32  in combination with the cold-formed chords connect the two folded portions  34  and  36  and  34  and  38  to reduce the width to thickness ratio of the section to avoid local buckling. The spot clinch  32  in combination with the cold work forming increases the yield strength of the steel part. 
         [0080]    As shown in  FIG. 7  the lower chord  24  is similarly constructed by forming sheet metal to present a lower chord surface  54  bent so as to present lower chord extensions  56  and  58  symmetrically disposed about axis  27 . The lower chord  54  with the lower chord extensions  56  and  58  define lower chord horizontal extensions  60  and  62  in this case symmetrically disposed about the web  26 . The lower chord extensions  56  and  58  present two spaced apart web receiving tabs  64  and  66  which are adapted to receive the lower portion  68  of the web  26 . The lower chord is also fastened to the lower part of the web  26  by rivets or other means 
         [0081]    The web  26  can include a plurality of utility holes  72  which provide an access for utilities such as electrical wires, air ducts or the like. The holes  72  as shown are circular although any configuration can be produced including square holes or the like. Furthermore, the holes  72  can include a cold-formed lip  74  as shown in  FIG. 16 . The holes  72  lighten the total weight of the joist  20  while the cold-formed lip  74  adds rigidity to the web structure  26  particularly in the direction of the “Y” axis  27 . 
         [0082]    The web  26  may also include a plurality of stiffening means  80  to stiffen of the web member  26 . 
         [0083]    The stiffening means  80  comprises a first stiffening means  82  and a second stiffening means  84 . The first stiffening means  82  generally consists of the ends of the web segment  26  being bent to form a stiffening tab  82  which is disposed at approximately a 90 degree angle from the web  26 . The second stiffening means  84  may consist of a hollow embossed rib structure  86  as illustrated in  FIG. 21 . 
         [0084]    The hollow rib structure  86  can be produced by a variety of means and in one example is produced by a punch (not shown) which pushes the web material  26  to present the stiffening structure  84 . The stiffening structure has two spaced side walls  88  and  90  as well as upper and lower walls  92  and  94  and stiffening front wall  96 . The stiffening front wall  96  has stiffening holes  98  which are adapted to receive bridging members  170  and  171  in a manner to be more fully particularized herein. 
         [0085]    Furthermore, the web  26  can comprise a plurality of web segments  104 ,  106  and  108 , as shown in  FIG. 4 , in which, as an example, three segments are shown. Each of the web segments  104 ,  106  and  108  are adapted to be fastened to one another. In particular, the web segments  104 ,  106 ,  108  include a first stiffening means  82  which comprise sheet metal flaps which are bent at substantially 90 degrees from the web material  26 . The first stiffening flaps  82  may include a plurality of holes  110  which are adapted to receive fasteners such as rivets, nuts and bolts, or may receive spot clinches to secure the plurality of web segments  104 ,  106 , and  108  together to form a web  26 . The web segments  104 ,  106 , and  108  also include second stiffening means  84 , shown in  FIG. 3 . 
         [0086]    The web segments can either all have the same thickness or have different selected thickness. For example the web segments can be thicker at the ends of the joist than segments in the middle of the joist since the shear stresses under load are greater at the ends than in the middle. 
         [0087]    The joist shown in  FIGS. 3 and 5  include angled end support members  140  that secure the ends of the lower chord  24  and upper chord  22 . 
         [0088]    A structural assembly comprising a plurality of joists  20  partially shown at  FIGS. 8 and 9  can define a supporting surface  160  to support a platform  162  such as a roof or floor. Each of the joists  20  as shown in cross section comprises spaced apart cold-formed steel upper and lower chord members  22  and  24  and a steel web  26  intermediate between upper and lower chord members  22  and  24 . Fasteners  28  are utilised to fasten the web to the upper and lower chords and the top surface of upper chords  22  define the supporting surface  160 . 
         [0089]    A plurality of bridging members  170  and  171  may be used to connect adjacent joists  20  together as shown so as to stiffen the said joist assembly. Parallel bridges  170  may be used as shown in  FIG. 8 , or may be accompanied by criss-crossed bridges  171  that are appropriately fastened to the horizontal bridges  170  at  173  as shown in  FIG. 9 . The fastening of the bridges  170  to the joists  20  through holes in the embossed features  84  is shown in greater detail in  FIGS. 21 ,  22  and  23 , effectively creating a snap in place connection without the use of tools. 
         [0090]    The bridge members such as  170  may be formed in an L-shaped cross section from sheet steel to produce a first surface  172  and a second surface  174 . The second surface  174  is slotted at  176  as shown and the width W of surface  174  is less than the depth D of the hole  98  to permit the end  178  of the bridging member  170  to be inserted into the hole  98  and then rotated so as to lock the edges of the slot  176  against the reinforcement face  96  adjacent the hole  98 . Criss-crossed bridging members  171  may then be added and fastened as shown in  FIG. 9 . 
         [0091]      FIGS. 12 and 13  illustrate another embodiment of the invention defining a composite floor or roof structure. In particular, the upper chord  22  can be cold-formed so as to present horizontal extensions  190  symmetrically disposed about the central web  26  and presents spaced apart vertical extensions  192  and  201  adapted to receive the top portion  50  of the web  26  to define a vertical extension  194 . A rivet  196  may be utilized to fasten the upper chord  22  to the web  26  as shown. 
         [0092]    A steel deck  198  is adapted to rest on the top surface of the horizontal upper chord extensions  190  as shown in  FIGS. 12 and 13 . A wire mesh  205  is added. Thereafter concrete  206  can be poured onto the deck  198  so as to produce a floor or ceiling. Since the vertical extensions  194  are embedded into and bonded with the concrete  200 , a very solid composite floor system is produced. The vertical extension  194  can also include a generally horizontal concrete engaging extension  202  that runs along the length of the chord  22 . Since the horizontal concrete engaging extension  202  runs along the length of the chord  22 , the possibility of snagging a worker&#39;s foot or clothing is minimized thereby adding to the safety feature of the joist prior to pouring of the concrete  206  over the deck  198 . 
         [0093]    The shear bond between the extensions  194  and  202  and the concrete may be increased by using rivets spot clinches or the like to increase the surface area of contact between the concrete and the top chord. Despite the asymmetry provided by the horizontal engaging extension  202 , this embodiment of the joist is substantially concentric since the extensions  194  and  202  are bonded to the concrete and the steel-concrete composite effectively distributes the applied load to each joist through its centre of gravity 
         [0094]      FIG. 24  illustrates another embodiment of the invention which includes an upper cold-formed steel chord  22  fastened to a steel web  26  by fasteners  30 . In the embodiment shown, the bottom chord  24  is a cold-formed extension of the web formed so as to present a horizontal extension  250  and  252  which may be of double thickness as shown and may be hole clinched (not shown) and may be disposed symmetrically or asymmetrically about the plane of the web. 
         [0095]      FIG. 25  illustrates another embodiment of the invention, similar that shown in  FIG. 24  where the upper chord  22  has a single layer of sheet metal which is bent to produce the horizontal extensions  190  spaced apart to accommodate the end  50  of web  26  so as to define an upper vertical extension  194  having a horizontal concrete engaging extension  202 . The horizontal concrete engaging extension  202  can include a plurality of hole clinches to further strengthen the bond between the concrete and the upper chord  22  and thereby increase the shear strength of the composite. Clearly different further embodiments are possible wherein the bottom chord, being a cold-formed extension of the web, may have different forms being symmetric or asymmetric about the web axis, and in parts being of different multiples of the web thickness. 
         [0096]    In the following, methods to locate and affix the joist to the opposed supporting walls are described. The joist  20  can be supported along the bottom chord  24  as shown in  FIGS. 30 and 31  illustrating a bottom chord bearing composite joist embodiment  20  supported by the bottom chord  24 . 
         [0097]    In particular the ends  400  of the joist are disposed within the lower stud wall  402  and upper stud wall  404  as shown. The lower stud wall  402  includes a stud wall track  406  which is generally a flat piece of sheet steel  408  bent at its ends so as to present a solid surface to the joist. The upper stud wall  404  includes a similar stud wall track  406 . The stud walls  402  and  404  also includes a floor joist track  412  adjacent the end  400  of joist  20 . 
         [0098]    The view of the joist  20  seen in  FIG. 30  can have a number of configurations as described in the context of the composite joist including that shown in  FIG. 12 . The composite joist is constructed in the manner previously described. An erection clip  414  can be utilized so as to locate the joist  20  prior to pouring the concrete to produce the composite joist. In particular the erection clip  414  comprises a general J-shaped clip in cross-section which is secured to the bottom of the stud wall track  406  and extension  202 . Once the concrete  200  is poured, the composite cold formed steel joist is supported by the bottom chord  24  at the ends  400  of the joist  20 . 
         [0099]      FIG. 35 , together with the enlargements depicted in  FIGS. 36   a  and  36   b , illustrates another bottom chord bearing embodiment of the invention supported by the foundation walls and supporting the stud walls in a residential home. 
         [0100]    In particular the joist  20  rests on a foundation  401  having a bearing support  410 . The end  400  of the joist  20  includes a reinforcing flap  82 , which provides support against the compressive forces arising from loads applied through the stud wall  404 , and is further particularized in  FIGS. 36   a  and  36   b . In particular the flap  82  is cut along cut lines  600 ,  602  and  604  so as to present portions  620  and  622 . In particular portions  620  and  622  are folded along fold lines  606  and  608 . Thereafter portions  620  and  622  are further folded along fold lines  621  and  623  so as to present wing portions  624  and  626  which are adapted to contact respectively the lower surface of upper chord member  22  and upper surface of lower chord member  24  as best shown in  FIG. 35 . Fastening means may be utilized to fasten the reinforcing wings  624  and  626  to upper and lower chord members  22  and  24  so as to further rigidify and strengthen the joist  20 . 
         [0101]    Wooden or metal backing plates  412  are also utilized as shown in  FIG. 35 . Wooden pieces  414  may also be disposed as shown. The upper chord  22  provides a support surface for supporting plywood  416  or the like. 
         [0102]    Further end reinforcing members  700  may be utilized which comprises an elongated section of sheet metal having web contacting portions  702  and rigidifying portions  704  extending generally perpendicular to the web contacting portions  702 . The ends of the rigidifying portions  704  are bent at  706  and  708  and adapted to contact the upper chord  22  and lower chord  24  respectively. Furthermore fastening means may be utilized to fasten the rigidifying section  700  to web  26  and upper and lower chords  22  and  24 . 
         [0103]    Moreover  FIG. 38  illustrates an embodiment of a bottom chord bearing cold-formed joist utilizing the reinforcing structure  700  shown in  FIG. 37 . 
         [0104]      FIG. 28  generally illustrates a method of producing the said embodiments of the cold-formed joist. The upper chord  22  can be produced by unrolling a coil of sheet steel  112  along path  114  to a roll forming machine  116  such as sold by Samco machinery located in Toronto, Canada. The roll forming machine  116  can include a station to flatten and cut a selected length of the upper chord member  22 . Similarly, the lower chord member  24  can be produced by unrolling a coil of sheet steel  118  and flattening same along a path  120  to a roll forming machine  116  and then cutting to the desired length. Furthermore, the web  26  can also be produced by unwinding a coil of sheet steel  122  and flattening same at flattening station  123 . A shear  125  can be used to shear the web member  26  to its desired length. Thereafter, the web  26  approaches stiffening section  128  so as to produce the first and second stiffening means  82  and  84  as described. 
         [0105]    The shear  125  can be used to produce the plurality of segmented webs  104 ,  106  and  108 . Each web segment  104 ,  106 ,  108  can have the left hand and right hand stiffening flaps  82  produced by stiffening station  130  and  132 . An appropriate punch  133  is used to produce the second stiffening means  84  as described above in a drawing operation. As well, punch  133  is used to produce holes  72  and area embossments  184 . 
         [0106]    The sheet steel at stations  112 ,  118  and  122  can be galvanized or painted as desired prior to the forming process. Furthermore the roll forming machine  116  may include punches to punch the appropriate holes  52  in the upper and lower chord members  22  and  24  so as to accommodate the appropriate fastening means  28 . 
         [0107]    Alternatively the roll forming machine  116  can include apparatus to spot clinch  32  the members together. 
         [0108]    Accordingly the joist fabricated herein can be coated with a variety of paint colours which are painted prior to fabrication so as to produce a variety of joists having different colours and avoiding the dip painting characteristic of open web joist construction. The invention as described herein presents a number of advantages over the prior art. For example, many open web steel joists in the prior art include a cambering of the upper and lower chords  4  and  6  so as to present a slight arch to increase load bearing capabilities of the joist. Such prior art cambering techniques required working against the web during the cambering process. Applicant&#39;s invention on the other hand presents an advantage since the upper and lower chord members  22  and  24  can be cambered individually and separately from the web  26 . Once the upper and lower chord members  22  and  24  are cambered they can be attached to the web  26  as described since the depth of the said camber is adequately contained within the web receiving tabs  46 ,  48  of the upper chord and  64 ,  66  of the lower chord as depicted in  FIG. 7 . Since the web  26  is not part of the upper and lower chord members  22  and  24  during the cambering process there is substantially less resistance to the cambering. 
         [0109]    Alternate versions of the invention are shown in  FIGS. 14 and 14   a ,  FIG. 15 ,  FIGS. 29  representing bottom and top chord bearing versions; and  FIGS. 26 and 26   a , and  FIG. 27 , representing bottom and top chord bearing versions of a composite joist. In  FIG. 14  and  FIG. 29  a top chord  22  and a bottom chord b are attached by web receiving tabs to a generally planar web  26  that defines a Y-axis  27  of the joist by self piercing rivets  30  or other fastening means such as screws or rivets. Said web has longitudinally spaced holes  72  formed therein each with a cold-formed lip  74  for increased rigidity under load to allow the routing of pipes, wiring, ductwork and such of other trades. Further web stiffening may be provided by cold-formed area embossments  184  as shown disposed along the length of the web at locations chosen to counteract applied loads or may be provided by vertical stiffening embossments such as  84  as previously described. Further stiffening at the ends of the joist are provided by embossed plates  101  attached by fasteners  130  to the end portions of the web, and are sized to counter both compressive and shear stresses near the ends of the joist. Such embossed plates may be fastened on both sides of each end of the joist, and may terminate longitudinally in cold-formed flaps  182  that provide increased stiffness and provide a means of attaching joists at their ends. 
         [0110]    As shown in  FIG. 29 , the construction of the top chord  22  and the bottom chord  24  of this embodiment may be simplified compared with previously described embodiments. However additional features to those shown previously in  FIG. 7  say are disclosed. In particular the web receiving tabs  46  and  48  of the top chord are shown extended and cold-formed to provide outward protruding inner flanges  45  and  47  respectively disposed generally orthoganally to the web  26 . Said flanges contribute to the overall strength of the joist; and said flanges are formed with holes  198  regularly spaced along the length of the chord and designed to receive snap-in bridging members as shown in  FIGS. 33 and 34 . The bottom chord  24  also shows inner flanges  65  and  67  as cold-formed extensions to the receiving tabs  64  and  66 . Without loss of generality,  FIG. 29  also serves as a cross section view of a top chord bearing version of this embodiment shown in perspective in  FIG. 15   
         [0111]    Perspectives of bottom and top chord bearing composite joist versions of this embodiment are shown in  FIGS. 26 ,  26   a  and  FIG. 27 , and a cross section view through line  112 - 112  is shown in  FIG. 32 . In  FIG. 32 , top chord  22  is attached to the web  26  by fastening tabs  192  and  201  of vertical section  194  by self piercing rivets  196  or other means. The double thickness of steel forming horizontal extension  202  are fastened by rivets  199  as shown or by other fastening means, with the head of said rivet disposed above the top surface of extension  202  in order to increase the surface area on the top surface of extension  202  and so enhance shear bonding with concrete. The bottom chord inner flanges  65  and  67  are formed with regularly spaced holes  198  to receive snap-in bridging members as shown generally in  FIGS. 33 and 34 . 
         [0112]    An alternate embodiment is shown in  FIG. 40  which is similar to the embodiment shown in  FIG. 12 . In this embodiment the joist  700  only includes a top chord  22  and does not include a web or a bottom chord. It will be appreciated by those skilled in the art that this joist would only have application in relatively short spans. Joist  700  includes a concrete engaging extension  202  which includes a vertical extension  194  that extends upwardly from horizontal upper chord extensions  190 . As described above steel deck  198  is adapted to rest on the top surface of the horizontal upper chord extensions  190 . A wire mesh  205  is added and thereafter concrete  200  is poured onto the deck  198 . 
         [0113]    A structural assembly comprising a plurality of joists  20  partially shown at  FIG. 33  can define a supporting surface  160  to support a platform  162  such as a roof or floor. Each of the joists  20  as shown in cross section comprises of spaced cold-formed steel upper and lower chord members  22  and  24  and a steel web  26  fastened between upper and lower chord members  22  and  24 . A plurality of bridging members  170  is used to stiffen the assembly  20 , said bridging members being disposed parallel to the support surface; and said flanges may be connected to adjacent joists at the holes  198  provided by the inner flanges  45  and  47  of the top chord  22  and by the inner flanges  65  and  67  of the bottom chord  24 . Bridging members may be constructed from a length of steel of angled cross section terminated at each end by a feature  270  that fits the holes  198  and allows the bridging member to be snap fastened to inner flanges of adjacent joists. 
         [0114]    A further aspect of this invention is illustrated in  FIG. 34  partially showing a structural assembly of joists  20  defining a support surface  160  supporting a platform  162  such as a floor or roof when both parallel and criss-cross bridging is required. Such combined bridging may be provided by a diaphragm assembly  370  comprising a steel plate  470  affixed by fasteners  670  to upper and lower bridging members  170  each terminated by a snap-in feature  270  at either end. Said steel plate may provide a hole  570  having a cold-formed lip to allow the passage of wiring, pipes and ducting from other trades. Diaphragm assembly  370  providing both parallel and criss-cross bridging may be snap-fastened to adjacent joists by engaging the snap-in feature  270  with the holes  198  provided in the inner flanges of the upper and lower chords. 
         [0115]    The snap-in bridging illustrated in  FIGS. 33 and 34  advances the prior art by substantially reducing the labour and cost involved in the manual assembly of bridging on the construction site. And although  FIGS. 33 and 34  refer to conventional floor or roof structures, the same bridging means may be used without any loss of generality to the construction of composite steel-concrete floors and roofs. 
         [0116]    The support structures described in this invention can be utilized either as floor joists or roof joists for single family residential, multi-family residential, commercial or industrial building construction. Further it will be appreciated by those skilled in the art that the system described herein may be used as a stay in place forming system. Analysis and testing of said structures demonstrate that the prior art is advanced in several regards including:
       more economical bottom chord bearing cold-formed steel joists with spans up to 40 feet   more economical top chord bearing joists capable of mass manufacture and customization   more effective and economical composite floor and roof structures.       
 
         [0120]    Although the joist embodiments as well as the manufacturing operations and use in construction have been specifically described in relation to the drawings, it should be understood that variations in these embodiments could be achieved by a person skilled in the art without departing from the spirit of the invention as claimed herein. 
         [0121]    As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and opened rather than exclusive. Specifically, when used in this specification including the claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or components are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
         [0122]    It will be appreciated that the above description related to the invention by way of example only. Many variations on the invention will be obvious to those skilled in the art and such obvious variations are within the scope of the invention as described herein whether or not expressly described.