Patent Publication Number: US-7721497-B2

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

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/198,018, filed on Jul. 17, 2002, now U.S. Pat. No. 7,017,314, which application is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to the construction of buildings such as large open span buildings and more particularly relates to composite floor systems and a novel design for joists used in such a floor system and installation of such joists. 
   2. Background Art 
   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. 
   In the past, concrete and steel floor construction methods have included open-web steel joists placed in position spanning structural supports with a concrete slab poured on decking supported by the joists. Generally, an open-web steel joist is a joist in the form of a truss having horizontal top and bottom chords joined by a web comprising tension and compression members triangulating the space between the top and bottom chords. 
   While the chords may be of many shapes, typically, the top and bottom chords each comprise a pair of steel angle bars, the top chord angle bars being arranged with one leg of each bar extending horizontally outward at the top of the truss, and the other leg of each bar extending downwardly on opposite sides of the web. The bottom chord angle bars are arranged with one leg of each bottom chord angle bar extending horizontally laterally outward at the bottom of the truss, and the other leg of each bottom chord angle bar extending vertically upward on the opposite sides of the web. Decking for supporting the concrete slab is laid on and fastened to the horizontal leg of the top chord angle bars at the top of the joist, and a concrete slab is the poured on the decking. Using this typical construction methodology, there is no structural integration of the concrete slab to the joists and the slab and joists function as separate entities with the slab constituting a “dead load” on the joists without materially contributing to the strength of the overall structure. 
   In another construction method, the upper ends of the web members project upwardly above the upper horizontal legs of the top chord angle bar for anchorage in the concrete slab to form a composite slab and joist construction in which the slab may, to some extent, become a compression member sharing part of the load. It has been found that this type of construction does not obtain the full potential of a composite slab joist construction, and has certain disadvantages. For example, the effective anchorage is between the slab and the upper ends of the web members so that transfer of stress between the joists and the slab occurs only at the upper ends of the web members. Furthermore, the slab is necessarily placed above the level of the supporting structure for the joists. In addition, the decking is formed with slots to enable the web member to protrude into the concrete forming the composite section. This creates another problem, namely, that the slots must be exactly aligned along the length of the building and the joist must also be perfectly aligned. 
   Yet another construction method employs an open-web steel joist in the form of a truss having a web, a top chord and a bottom chord. The top chord comprises a pair of steel angle bars arranged with one leg of each of the angles extending horizontally outward from a position on the truss below the top of the truss, and the other leg of each angle extending upwardly to the same height on opposite sides of the web and terminating below the top of the web. Decking is laid on the horizontal legs of the top chord, and concrete is poured on the decking to embed the vertical legs of the top chord angle bars and the upper ends of the web in the concrete slab to create a composite floor structure. In this construction, the top chord is below the top of the web member and composite action is obtained primarily by embedding the portion of the web extending above the top of the top chord into the concrete slab. 
   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. While many of these various methods for forming composite floor systems have enjoyed some commercial success in achieving the stated goals, there is a continual search for even more effective and efficient methods for constructing these composite floor systems. 
   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 
   The composite floor system of the present invention comprises a system of joists, where each of the joists has a top chord, a bottom chord and a web, including tension and compression members in the space between the top chord and the bottom chord and secured to the top and bottom chords, and the top chord of the joist having a substantially cruciate or cross-shaped cross section about a longitudinal axis of the upper chord. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and: 
       FIG. 1  is a partial perspective cut-away view of a composite floor system in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 2  is a vertical section view of a composite floor system in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 3  is a flowchart depicting a method of constructing a composite floor system in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 4  is a perspective view of the top chord of joist in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 4   a  is a perspective view of the top chord of a joist in accordance with an alternative preferred exemplary embodiment of the present invention; 
       FIG. 5  is a side cutaway view of a joist in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 6  is a perspective view of a joist and metal decking installation in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 7  is a side view of the top chord of a joist in accordance with a preferred exemplary embodiment of the present invention; 
       FIG. 8  is a side view of the top chord of a joist in accordance with a preferred exemplary embodiment of the present invention; and 
       FIG. 9  is a side view of a structural support system for constructing a composite floor system in accordance with a preferred exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
   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 using joists with a novel top chord member. 
   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. Composite floor system  100  comprises: a first primary support structure  105 ; a second primary support structure  115 ; a plurality of joists  160  suspended and extending between support structures  105  and  115 ; a plurality of removable spanner bars  170  selectively inserted into slots formed in the body 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, joists  160  may also comprise a series of concrete-engaging mechanisms to further connect slab  110  with the supporting structure formed by joists  160 . 
   Each joist  160  comprises a top chord  161 , a bottom chord  162  and an intermediate connecting web member  165 . Each top chord  161  and bottom chord  162  is most preferably affixed to connecting web members  165  by welding or some other suitable method. Each top chord  161  defines a cross section that is substantially cross-shaped along the longitudinal axis of each joist  160 . Intermediate connecting web member  165  may be a single connecting member or may be multiple discrete connecting members. Further details about joists  160  are presented in conjunction with  FIG. 4 ,  FIG. 4A , and  FIG. 5 . 
   While support structures  105  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. 
   Once joists  160  are in place, removable spanner bars  170  are inserted into the lower portion of joists  160  by inserting the ends of spanner bars  170  into a series of apertures formed in the lower portion of the top chord of joists  160 . 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 . 
   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 . 
   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  may be further reinforced in the usual way to carry any loads between any vertical parallel walls and joists  160 . 
   It should be noted that, after positioning joists  160  as shown in  FIG. 1 , the bottom portion of each top chord of each joist  160  is resting on the top edge of support structures  105  and  115 . However, a vertical leg portion of each top chord of each joist  160  protrudes above the top edge of support structures  105  and  115  and becomes embedded in concrete slab  110 . 
   Referring now to  FIG. 2 , a sectional view of 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 . 
   In the most preferred embodiments of the present invention, each joist  230  comprises a top chord fashioned from two discrete components, a first upper angle  215  and a second upper angle  225 . In the most preferred embodiments of the present invention, first upper angle  215  and a second upper angle  225  are typically joined together by conventional welding methods and techniques, such as a fillet weld along their common longitudinal edges. 
   It should be noted that in another preferred embodiment of the present invention, first upper angle  215  and second upper angle  225  may be an integral member, formed via extrusion or some other suitable process. In either case, first upper angle  215  has an upward vertical component that is embedded in concrete slab  210  and second upper angle  225  has a downward vertical component that is fixedly attached to the central open web portion of each joist  230 . Additionally, each joist  230  has a first lower angle  245  and a second lower angle  255 . First lower angle  245  and second lower angle  255  are affixed to opposite sides of the central open web portion of each joist  230  and each further comprises an upward vertical component and a horizontal component. 
   Reinforcing material  220  is a welded wire fabric or rebar mat placed over the upward vertical component of each first upper angle  215  of each joist  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 . 
   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 then be reused in subsequent concrete pouring operations. Hat channel  250  is attached to joists  230  and ceiling  280  is attached to hat channel  250 . 
   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 . 
   Referring now to  FIG. 3 , a flowchart depicting a method  300  of constructing a composite floor system in accordance with a preferred embodiment of the present invention is shown. First, the joists are positioned on the supporting structures by placing the joists on top of the supporting structures (step  320 ). 
   Next, a plurality of removable spanner bars are positioned between each pair of joists (step  330 ). Then, the support platform for the concrete slab is positioned on top of the removable spanner bars (step  340 ). 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  350 ). 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  360 ). 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  370 ). 
   Referring now to  FIG. 4 , an upper chord  400  of a joist used in constructing a composite floor system in accordance with a preferred embodiment of the present invention is shown. Upper chord  400  comprises a first upper angle  410  and a second upper angle  420 . Each of first upper angle  410  and a second upper angle  420  has a cross section that forms approximately a 90° angle. First upper angle  410  comprises an upward vertical leg portion  416  and a horizontal leg portion  414 . Second upper angle  420  comprises a downward vertical leg portion  422  and a horizontal leg portion  424 . Horizontal leg portions  414  and  424  are located in substantially the same horizontal plane. In this specific embodiment, upward vertical leg portion  416  and downward vertical leg portion  422  are not co-planar but are slightly offset and are contained within substantially parallel planes. First upper angle  410  and second upper angle  420  may be joined by any suitable method, such as welding. 
   Apertures  440  are formed in downward vertical leg portion  422  and are sized and positioned to receive the end portions of removable spanner bars, such as those depicted in  FIG. 2 . As shown in  FIG. 4 , a section of downward vertical leg portion  422  has been removed, thereby allowing horizontal leg portions  414  and  424  to rest flat on top of a load-bearing structure for support of the joist to which top chord  400  is attached. In typical applications, downward vertical leg portion  422  will extend to some point within the space defined by the load-bearing structures while horizontal leg portions  414  and  424  will extend over the top of the load-bearing structures to the approximate mid-point of the load-bearing structures, as shown in  FIG. 1 . 
   Additionally, optional concrete-engaging mechanisms  411  and  412  are shown along the lateral portion of upward vertical leg portion  416 . In the most preferred embodiments of the present invention, concrete-engaging mechanism  411  is a raised portion of first upper angle  410  and concrete-engaging mechanism  412  is a recessed portion of first upper angle  410 . While shown as generally rectangular in shape, concrete-engaging mechanisms  411  and  412  may take on any suitable shape, including arcuate projections such as dimples and/or indentations. 
   Additionally, concrete-engaging mechanisms  411  and  412  may be apertures formed in the lateral portion of upper chord  400 . Concrete-engaging mechanisms  411  and  412  are provided to aid in the composite action of the joist employing upper chord  400 . Along with upward vertical leg portion  416 , concrete-engaging mechanisms  411  and  412  are most preferably embedded in the concrete slab during the pouring process. While not shown, additional concrete-engaging mechanism may be formed in horizontal leg portions  414  and  424  to increase the concrete-engaging ability of the composite structure. 
   Referring now to  FIG. 4A , a joist  450  used in constructing a composite floor system in accordance with an alternative preferred embodiment of the present invention is shown. In this specific embodiment, joist  450  is a unitary member and may be formed by extrusion or other similar process. Additionally, joist  450  may include concrete-engaging mechanisms as shown in  FIG. 4 . However, in contrast to  FIG. 4 , upward vertical leg portion  456  and downward vertical leg portion  452  are substantially co-planar. 
   Referring now to  FIG. 5 , a side view of a joist  500  used in constructing a composite floor system in accordance with a preferred exemplary embodiment of the present invention is shown. Joist  500  comprises an intermediate web portion  530  extending between upper angles  510  and  520  and lower angles  540  and  550 . Upper angles  510  and  520  may be fastened together by welding or any other suitable method. Intermediate web portion  530  may be fastened to upper angles  510  and  520  and lower angles  540  and  550  by welding or any other suitable method. An aperture  512  may be formed in the downward vertical portion of upper angle  512  and, if present, is sized and positioned to receive the end of a removable spanner bar. Those skilled in the art will recognize that certain embodiments of the present invention may not use spanner bars and, accordingly, aperture  512  may be unnecessary. 
   Referring now to  FIG. 6 , a perspective view of a joist and metal decking installation for a composite floor system in accordance with a preferred exemplary embodiment of the present invention is shown. As shown in  FIG. 6 , a first end of a section of a sheet of corrugated metal decking  610  is fixed in place on a horizontal leg portion of joist  450 . Each sheet of corrugated metal decking  610  is sized to fit between adjacent joints  450  and the other end of corrugated metal decking  610  will similarly rest on a horizontal leg portion of an adjacent joist  450 . In this fashion, multiple sheets of corrugated metal decking  610  can form a support platform for a poured concrete slab to be used in a composite floor system. The sheets of corrugated metal decking  610  may be attached to joist  450  using any technique or method known to those skilled in the art. This includes welding, metal screw attachment, etc. In this particular embodiment, spanner bars and plywood supports are not used. 
   Referring now to  FIG. 7 , is a side view of the top chord of a joist  450  in accordance with a preferred exemplary embodiment of the present invention. As shown in  FIG. 7 , each vertical leg and each horizontal leg is substantially perpendicular to the other vertical leg and to each of the horizontal legs. Additionally, each horizontal and vertical leg of the upper chord of joist  450  is substantially the same length, represented by length “D.” 
   Referring now to  FIG. 8 , is a side view of the top chord of a joist  410  in accordance with an alternative preferred exemplary embodiment of the present invention. As shown in  FIG. 8 , each vertical leg and each horizontal leg is substantially perpendicular to the other vertical leg and to each of the horizontal legs. Additionally, each horizontal and vertical leg portion of the upper chord of joist  410  is substantially the same length, represented by length “D.” 
   Referring now to  FIG. 9 , a structural support system  900  for a composite floor system in accordance with a preferred exemplary embodiment of the present invention is shown. In this embodiment of the present invention, a primary support member or beam  910  is used to support a secondary support member or joist  920 . Joist  920  rests on one horizontal portion of beam  910  and can be fixed in place or attached to beam  910  at point  930  by any means known to those skilled in the art. For example, point  930  may be representative of a structural weld or a threaded bolt and nut connection. Regardless of the type of attachment used to connect joist  920  and beam  910 , point  930  represents a shear transfer connection and functions as a shear transfer mechanism to enhance the composite nature of the resultant composite floor system. 
   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.