Patent Publication Number: US-2003233801-A1

Title: Apparatus and method for composite concrete and steel floor construction

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to the construction of buildings such as large open span buildings. The present invention more particularly relates to composite floor systems and a novel design for joists used in such a floor system and installation of such joists.  
       BACKGROUND OF THE INVENTION  
       [0002] Many multi-story commercial buildings and some multi-story residential buildings are constructed primarily of steel and concrete. In many instances, the floors in these multi-story buildings may be constructed by spanning steel joists between structural walls or beams and laying a supporting material such as plywood, metal pan or other type of decking material along or near the top portions of such joists. This supporting material forms a support structure or surface onto which concrete is poured. Generally, the lower chords of the joists form the framework from which ceilings are hung.  
       [0003] Composite floor systems have been employed in multi-story building construction for many years and improvements are constantly being sought, both in the materials used in the composite floor systems and the methodologies used to erect the buildings that incorporate composite floor systems. The development and sophistication of these structural systems has gradually extended to encompass many varieties of steel and concrete floor construction, the result of which has been to measurably reduce the cost of steel framing for multi-story buildings in the industry.  
       [0004] It will be appreciated that the purposes of composite floor construction are to save considerable steel weight and cost, as well as to reduce depth and deflection. In view of the foregoing, it should be appreciated that it would be desirable to provide additional methodologies for constructing various types of composite floor systems that are simpler and less expensive to install, using existing materials and components to the extent possible.  
       SUMMARY OF THE INVENTION  
       [0005] The composite floor system of the present invention comprises a plurality of joists at least partially embedded in the concrete slab of the floor system. In the most preferred embodiments of the present invention, each of the joists is formed from a single piece of cold rolled sheet metal and, in at least one orientation, exhibits a substantially “Z-shaped” or “C-shaped” cross section along a longitudinal axis. In addition, for certain applications, a novel mounting bracket may be affixed to each end of the joists to provide for an underslung installation.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0006] The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and:  
     [0007]FIG. 1 is a partial perspective cut-away view of a composite floor system in accordance with a preferred embodiment of the present invention;  
     [0008]FIG. 2 is a vertical section view of a composite floor system in accordance with a preferred embodiment of the present invention;  
     [0009]FIG. 3 is a vertical section view of a composite floor system in accordance with an alternative preferred embodiment of the present invention;  
     [0010]FIG. 4 is a flowchart depicting a method of constructing a composite floor system in accordance with a preferred embodiment of the present invention;  
     [0011]FIG. 5 is a perspective view of a mounting bracket used in constructing a composite floor system in accordance with a preferred embodiment of the present invention;  
     [0012]FIG. 6 is a perspective view of a joist used in constructing a composite floor system in accordance with a preferred embodiment of the present invention;  
     [0013]FIG. 7 is a perspective view of a joist in accordance with an alternative preferred embodiment of the present invention;  
     [0014]FIG. 8 is a side view of a joist in accordance with an alternative preferred embodiment of the present invention; and  
     [0015]FIG. 9 is a side view of a joist in accordance with an alternative preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
     [0016] The present invention relates to a composite floor system and parts and formwork therefore and erecting method for use in the construction of buildings such as large open span commercial or residential buildings. The present invention is particularly concerned with composite floor systems made from steel and concrete with a novel method of attaching joists used in such a floor system.  
     [0017] Referring now to FIG. 1, a partial cut-away view of a composite floor system  100  in accordance with a preferred embodiment of the present invention is shown.  
     [0018] Composite floor system  100  comprises: a first support structure  105 ; a second support structure  115 ; a plurality of joists  160  suspended in place by a plurality of mounting brackets  150 , with joists  160  extending between support structures  105  and  115 ; a plurality of removable spanner bars  170  selectively inserted into slots  135  of joists  160 ; a support platform  140  placed over and resting on spanner bars  170 ; a concrete slab  110  poured in place and supported by support platform  140 ; and a reinforcing material  190  embedded in concrete slab  110 . In the most preferred embodiments of the present invention, mounting brackets  150  have a plurality of apertures formed in the body thereof and the apertures are designed to provide a means for attaching mounting brackets  150  to joists  160 . Mounting brackets  150  may be attached to joists  160  by screws, bolts, welding, or other appropriate attaching means, with one mounting bracket  150  being attached to either end of each joist  160 . Once mounting brackets  150  are in place, joists  160  can be positioned between support structures  110  and  115 .  
     [0019] While support structures  110  and  115  are depicted as a block wall and an I-beam respectively, it should be understood that these are merely representative of the types of support structures that may be utilized in conjunction with the present invention. In practice, support structures  105  and  115  may be any type of structure capable of supporting the load of composite floor system  100 , including columns, load-bearing interior walls, etc. Apertures  165  are provided for the installation of various utilities such as electrical lines, plumbing pipes and other similar purposes.  
     [0020] Once joists  160  are in place, removable spanner bars  170  are inserted into the body portion of joists  160  by inserting the ends of spanner bars  170  into apertures  135 . Apertures  135  are most preferably spaced equidistant along the body portion of joists  160  so that cooperating pairs of apertures  135  can be aligned to receive alternate ends of removable spanner bars  170 . The location and number of removable spanner bars  170  used for supporting a given concrete slab  110  can be determined by performing load analysis calculations for composite floor system  100 .  
     [0021] With the appropriate number of removable spanner bars  170  in place, support platform  140  can be installed. Support platform  140  rests on and is supported by removable spanner bars  170 . Support platform  140  provides a form for defining the bottom of concrete slab  110  and also provides stability to the overall structure prior to the pouring of concrete slab  110 .  
     [0022] After support platform  140  has been completed, reinforcing material  190  is placed over the top of joists  160 . Reinforcing material  190  is typically a welded wire mesh and is provided to add additional strength and stability to concrete slab  110  and will be embedded within concrete slab  110 . Finally, concrete slab  110  can be poured in place over support platform  140  and reinforcing material  190 . Support platform  140 , in concert with joists  160 , removable spanner bars  170  and support structures  105  and  115 , support concrete slab  110  while it hardens and cures. After an appropriate period of time, such as approximately one or two days, spanner bars  170  and support platform  140  can be stripped from joists  160 . Concrete slab  110  maybe further reinforced in the usual way to carry all loads between any vertical walls and columns.  
     [0023] It should be noted that, after positioning joists  160  as shown in FIG. 1, the top chord of each joist  160  is suspended slightly above the top edge of support structures  105  and  115 . However, at least a portion of each joist  160 , including the lower chord of each joist  160 , is located between support structures  105  and  115 . This is in contrast to typical floor construction methods where the lower chord of joists  160  are commonly resting on top of support structures  105  and  115 . This allows a composite floor to be constructed using less blocking or bracing than typical with other methods. Additionally, although joists  160  are depicted as being ‘underslung” in this particular exemplary embodiment, it should be noted that in at least one alternative preferred embodiment of the present invention, joists  160  may be installed so that the lower chord of each joist  160  is resting on top of support structures  105  and  115 .  
     [0024] Referring now to FIG. 2, a composite floor system  200  in accordance with a preferred embodiment of the present invention is shown. Composite floor system  200  comprises a concrete slab  210 ; a plurality of joists  230 ; a reinforcing material  220 ; a plurality of spanner bars  270 ; a plurality of handles  240  attached to spanner bars  270 ; a support platform  260 ; a hat channel  250 ; and a ceiling  280 .  
     [0025] Reinforcing material  220  is a welded wire fabric or rebar mat placed over the upper chords of joists  230 , prior to the pouring of concrete slab  210 . In the most preferred embodiments of the present invention, reinforcing material  220  is a welded wire fabric with a mesh-like appearance. However, it should be noted that any other reinforcing material capable of developing the required structural capacity may be used as well. Reinforcing material  220  is typically draped over the upper chords of joists  230  and hangs in a catenary-like shape between the joists to provide the most effective reinforcement. Reinforcing material  220  is completely encased with the boundaries of concrete slab  210 .  
     [0026] Support platform  260  is suspended on spanner bars  270  prior to the pouring of concrete slab  210 . Support platform  260  is used as a form for defining the bottom surface of concrete slab  210 . Support platform  260  also provides a degree of lateral stability to the structure of composite floor system before concrete slab  210  is poured. After concrete slab  210  has been poured and allowed to cure for an appropriate amount of time, spanner bars  270  are removed by using handles  240  and support platform  260  may be stripped from concrete slab  210  and may be reused in subsequent concrete pouring operations. Hat channel  250  is attached to joists  230  and ceiling  280  is attached to hat channel  250 .  
     [0027] With the composite floor system of the present invention, it is possible to utilize standard-sized materials to form the support structure for the concrete slab. For example, the spacing of joists  230  may be advantageously fixed at approximately four-foot centers, thereby enabling the use of readily available and inexpensive standard 4′ by 8′ sheets of plywood for support platform  260 . It should also be recognized that, in accordance with contemporary construction practice, such plywood panels would be treated with a release coating, such as oil, to avoid adherence of concrete slab  210  to plywood used in support platform  260 . Such a release coating enables the ready stripping of support platform  260  beneath concrete slab  210  with a minimum loss of formwork due to accidental destruction. Alternatively, support platform  260  may be constructed from typical steel pan formwork or some other material known to those skilled in the art that provides sufficient strength to support concrete slab  210 .  
     [0028] Referring now to FIG. 3, a composite floor system  300  in accordance with an alternative preferred embodiment of the present invention is shown. Composite floor system  300  is similar to composite floor system  200  as shown in FIG. 2 above, but the cross section of the joists used in composite floor system  300  is different than joists  230  used in composite floor system  200 . Composite floor system  300  comprises a concrete slab  310 ; a plurality of joists  330 ; a reinforcing material  320 ; a plurality of handles  340  attached to spanner bars  370 ; a support platform  360 ; a hat channel  350 ; and a ceiling  380 .  
     [0029] Reinforcing material  320  is a welded wire fabric or rebar mat placed over the upper chords of joists  330 , prior to the pouring of concrete slab  310 . In the most preferred embodiments of the present invention, reinforcing material  320  is a welded wire fabric with a mesh-like appearance. However, it should be noted that any other reinforcing material capable of developing the required structural capacity may be used as well. Reinforcing material  320  is typically draped over the upper chords of joists  330  and hangs in a catenary-like shape between the joists to provide the most effective reinforcement. Reinforcing material  320  is completely encased with the boundaries of concrete slab  310 .  
     [0030] Support platform  360  is suspended on spanner bars  370  prior to the pouring of concrete slab  310 . Support platform  360  is used as a form for defining the bottom surface of concrete slab  310 . Support platform  360  also provides a degree of lateral stability to the structure of composite floor system before concrete slab  310  is poured. After concrete slab  310  has been poured and allowed to cure for an appropriate amount of time, spanner bars  370  are removed by using handles  340  and support platform  360  may be stripped from concrete slab  310  and may be reused in subsequent concrete pouring operations.  
     [0031] Referring now to FIG. 4, a flowchart depicting a method  400  of constructing a composite floor system in accordance with a preferred embodiment of the present invention is shown. First, a mounting bracket may be attached to each end of each joist (step  410 ). It should be noted that this is an optional step because the joists may be placed on top of supporting walls or beams. In underslung installations, the mounting brackets will be installed and the joist will be suspended between the support structures instead of resting on top of the support structures. Next, the joists are positioned on the supporting structures by placing the bearing plate (shown in FIG. 5) of each joist on top of the supporting structures (step  420 ). If the mounting brackets are not used, then the bottom chord of the joists may be placed directly onto the supporting structures.  
     [0032] Next, a plurality of removable spanner bars are positioned between each pair of joists (step  430 ). Then, the support platform for the concrete slab is positioned on top of the removable spanner bars (step  440 ). As previously mentioned, the support platform may be any material capable of supporting the load of the concrete slab. After the support platform is in place, the reinforcing material is positioned by draping it over the upper chords of each of the joists (step  450 ). The reinforcing material is typically a welded wire mesh material well known to those skilled in the art. Once the reinforcing material has been positioned, the concrete slab can be poured over the support platform and allowed to cure (step  460 ). Finally, after the concrete slab has been allowed to sufficiently cure, the removable spanner bars and the support platform can be stripped from the underside of the concrete slab (step  470 ).  
     [0033] Referring now to FIG. 5, a mounting bracket  500  used in constructing a composite floor system in accordance with a preferred embodiment of the present invention is shown. Mounting bracket  500  comprises a body portion  510 ; a bearing plate  520 ; a plurality of wall or beam attachment apertures  530 ; a plurality of upper chord attachment apertures  540 ; and a plurality of web attachment apertures  560 . In a typical application, one mounting bracket  500  will be used on each end of a joist and mounting brackets  500  are used to support the joist over the span between the structural support elements such as walls or beams. Mounting brackets  500  may be adapted for either end of a joist (i.e., left and right-handed mounting brackets).  
     [0034] Body portion  510  is shaped similar to a piece of steel angle with a 90° bend at the midpoint. Bearing plate  520  is attached to body portion  510  by welding or other suitable attachment methods. Bearing plate  520  serves to distribute the load of any joists attached to mounting bracket  500  over a larger surface area, thereby minimizing any undesirable load concentrations that may result in structural failure.  
     [0035] Wall or beam attachment apertures  530  are used to securely attach mounting bracket  500  to the top of a supporting or load-bearing structure, such as a wall or a beam, if required. While bolts or screws may be inserted through apertures wall or beam attachment apertures  530 , thereby attaching mounting bracket  500  to a wall or beam, in certain applications mounting bracket  500  will be welded in place and apertures  530  will not be used.  
     [0036] Upper chord attachment apertures  540  are used to securely attach the upper chord of a joist to mounting bracket  500 . As with wall or beam attachment apertures  530 , bolts or screws may be inserted through upper chord apertures  530 , thereby securely attaching mounting bracket  500  to the upper chord of a joist. It is anticipated that the upper chord of the joist may be welded to mounting bracket  500  in certain applications.  
     [0037] Web attachment apertures  560  are used to secure the body of a joist to mounting bracket  500 . As previously explained in conjunction with upper chord attachment apertures  540  and wall or beam attachment apertures  530 , bolts or screws may be inserted through web apertures  560 , thereby attaching the body portion of a joist to mounting bracket  500 . Once again, it is anticipated that mounting bracket  500  will be welded directly to the joist for certain applications. Mounting bracket is connected to a joist and the joist is then positioned as shown and described in FIG. 1.  
     [0038] Referring now to FIG. 6, a joist  600  used in constructing a composite floor system in accordance with a preferred embodiment of the present invention is shown. Joist  600  comprises a body portion  620  an upper chord  630  and a lower chord  660 . Upper chord  630  and lower chord  660  are substantially parallel to each other and substantially perpendicular to body portion  620 . Upper chord  630  has a flange  635  that is extends outwardly from body portion  620  and forms approximately a 50° angle with the plane defined by body portion  620 . Similarly, lower chord  660  has a flange  665  that extends outwardly away from body portion  620  in a like fashion.  
     [0039] Body portion  620  defines a plurality of body apertures  650 . Body apertures  650  are used to support spanner bars that, in turn, are used to support the decking material that will form the surface for the concrete slab when the concrete is poured in place. The spanner bars may be inserted to support the plywood or other material suspended between a plurality of joists  600  and to stabilize the plurality of joists  600  prior to the pouring of the concrete slab. Optional aperture  695  may be used to provide for the installation of utilities such as electrical and plumbing lines.  
     [0040] Upper chord  630  defines a plurality of apertures  640  spaced along the length of upper chord  630 . Apertures  640  are positioned horizontally in upper chord  630  and allow the portion of the concrete above upper chord  630  to be connected with the portion of the concrete slab beneath upper chord  630 . Apertures  640  are concrete-engaging mechanisms that act as an additional shear transfer mechanism. Much of the interface shear is accomplished by the combination of the concrete and steel reinforcement gripping and adhering to the embedded portion of upper chord  630 , upper flange  635 , and the upper portion of body  620 . Lower chord  660  may also have apertures  640  formed therein. In the most preferred embodiments of the present invention, upper chord  630  is entirely encased within the concrete slab during the pouring of the concrete slab. Optional apertures  695  are provided for the installation of various utilities such as electrical lines, plumbing pipes and other similar purposes.  
     [0041] As shown in FIG. 6, joist  600  has a cross section that is substantially “Z-shaped,” or reverse “Z-shaped, depending on the orientation of joist  600 . Further, joist  600  exhibits rotational symmetry around a longitudinal axis of symmetry  610  of body  620 . Rotational symmetry means that when joist  600  is rotated 180° around axis of symmetry  610 , the cross sectional shape of joist  600  will remain substantially, if not exactly, the same. The length of joist  600  will be determined by the specific application. Although not shown in FIG. 6, it should be noted that “stiffening” of joist  600  may be included for additional strength. Stiffening is a process of providing a corrugated-type body portion for joist  600  and is well known to those skilled in the art.  
     [0042] In the most preferred embodiments of the present invention, joist  600  is completely formed of a single piece of cold rolled sheet metal, but may be fabricated in many other ways and additionally reinforced, if necessary. Apertures  640  and  650 , along with optional aperture  695  can be created as part of the overall manufacturing process and any of the various methods for creating apertures known to those skilled in the art may be used. Alternatively, instead of apertures  640 , upper chord  630  may be fabricated with other concrete-engaging mechanisms such as a series of “dimples” or other protrusions that would further assist in firmly fixing upper chord  630  into a concrete slab.  
     [0043] Referring now to FIG. 7, a joist  700  used in constructing a composite floor system in accordance with an alternative preferred embodiment of the present invention is shown. Joist  700  comprises a body portion  720  an upper chord  730  and a lower chord  760 . Upper chord  730  and lower chord  760  are substantially parallel to each other and substantially perpendicular to body portion  720 . Upper chord  730  has a flange  735  that is substantially parallel to body portion  720 . Similarly, lower chord  760  has a flange  765  that is substantially parallel to body portion  720 . Body portion  720  defines a plurality of apertures  750 . Apertures  750  are used to support spanner bars that, in turn, are used to support the decking material that will form the surface for the concrete slab when the concrete is poured in place. Optional apertures  795  are provided for the installation of various utilities such as electrical lines, plumbing pipes and other similar purposes.  
     [0044] Upper chord  730  defines a plurality of apertures  740  equally spaced along upper chord  730 . Apertures  740  allow the portion of the concrete above upper chord  730  to be connected with the portion of the concrete slab beneath upper chord  730 . Apertures  740  are concrete-engaging mechanisms that act as an additional shear transfer mechanism. Lower chord  760  may also have apertures  740  formed therein. In the most preferred embodiments of the present invention, upper chord  730  is entirely encased within the concrete slab during the pouring of the concrete slab. Optional apertures  795  are provided for the installation of various utilities such as electrical lines, plumbing pipes and other similar purposes.  
     [0045] As shown in FIG. 7, joist  700  has a cross section that is substantially “C-shaped,” or “reverse C-shaped,” depending on the orientation of joist  700 . Further, joist  700  exhibits reflective symmetry around a longitudinal axis of symmetry  710  of body  720 . Reflective symmetry means that the upper portion of the cross section of joist  700  is substantially “reflected” beneath axis of symmetry  710 . Further discussion of the symmetry associated with the joists of the present invention is presented in conjunction with FIGS. 8 and 9. The length of joist  700  will be determined by the specific application. Although not shown in FIG. 7, it should be noted that “stiffening” of joist  700  may be included for additional strength. Stiffening is a process of providing a corrugated-type body portion for joist  700  and is well known to those skilled in the art.  
     [0046] In the most preferred embodiments of the present invention, joist  700  is completely formed of a single piece of cold rolled sheet metal, but may be fabricated in other ways and additional reinforcement may be added as needed. Apertures  740 ,  750  and  795  can be created as part of the overall manufacturing process and any of the various methods for creating apertures known to those skilled in the art may be used. Alternatively, instead of apertures  740 , upper chord  730  may be fabricated with other concrete-engaging mechanisms such as a series of “dimples” or other protrusions that would further assist in firmly fixing upper chord  730  into a concrete slab.  
     [0047] Referring now to FIG. 8, a side view of a joist  800  according to an alternative preferred exemplary embodiment of the present invention is depicted. As shown in FIG. 8, the cross-sectional profile of joist  800  is substantially “C-shaped.” However, distance  810  is measurably smaller than distance  820 . Joist  800  will display a rough reflective symmetry about its midpoint.  
     [0048] Referring now to FIG. 9, a side view of a joist  900  according to an alternative preferred exemplary embodiment of the present invention is depicted. As shown in FIG. 9, the cross-sectional profile of joist  900  is substantially “Z-shaped.” However, distance  910  is measurably smaller than distance  920 . Joist  900  will display a rough rotational symmetry about its midpoint.  
     [0049] While certain preferred exemplary embodiments have been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that these preferred embodiments are only examples and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description provides those skilled in the art with a convenient roadmap for implementing the preferred exemplary embodiments of the invention. It should be understood that various changes may be made in the function and arrangement of elements described in the exemplary preferred embodiments without departing from the spirit and scope of the invention as set forth in the appended claims.