Abstract:
A flooring of pre-stressed deck construction having an elongate decking extending along the flooring is provided. The decking has an upwardly facing asymmetrically profiled channel formation whereby the neutral axis is above a central horizontal plane. A tension rod extends between stressing brackets secured to each end of the decking and is located below the neutral axis of the decking along the length of the decking. Each stressing bracket is secured to upwardly extending sidewalls of the channel above the tension rod. The decking is attached to the girder framework of a building.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of copending International Application No. PCT/GB2004/001949 filed May 6, 2004 which designates the United States, and claims priority to Great Britain application no. 0310916.2 filed May 13, 2003 and Great Britain application no. 0327976.7 filed Dec. 2, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to flooring, and in particular to flooring of the pre-stressed deck construction.  
       BACKGROUND  
       [0003]     Many buildings, particularly industrial and high-rise buildings are constructed by erecting a steel girder framework with the above-ground floors consisting of steel decking supported by the beams of the girder framework and the decking itself supporting a concrete floor. The floor spans are limited by the bending stresses in the decking due to the weight of the concrete floor, and the deflection of the decking and concrete floor. In order to increase the floor span, it is known to prop the decking at mid-span until the concrete floor has set and reached adequate strength. However, this strength achieving time can be of the order of four weeks, and meanwhile the presence of the props restricts further construction activity. In addition, the props are costly and there is the additional time and cost of fitting and removal. Alternatively, the decking may be supported by means of additional “secondary beams” secured to the beams of the girder framework, but again these are an additional expense. Furthermore, the presence of the secondary beams restricts the passage of services, e.g. gas, water and electricity pipes and cables, through the floor space. As a further alternative, the flooring may be formed of pre-stressed concrete, but this is very costly to produce and transport to the site. In addition, large capacity lifting gear is required to position the flooring.  
         [0004]     To avoid or minimise these disadvantages for large floor spans, it is known, for example in U.S. Pat. No. 3,712,010, to introduce an upward camber, and hence a positive bending moment, in the decking prior to pouring the concrete floor thereon. This arrangement is intended to counteract the downward deflection and negative bending moment in the decking due to the weight of the concrete floor, to allow a larger floor span to be used without the stress and deflection limits being exceeded. U.S. Pat. No. 3,712,010 discloses two methods of achieving this initial upward camber and positive bending moment. In the first method, embodied as shown in FIGS.  1  to  8  and  13  to  17 , there is a tension rod or tendon extending between the ends of the decking. This tension rod is located in an upwardly facing channel of the decking, which is shaped to be symmetrical about a central horizontal plane, the neutral axis of the decking. The tension rod is secured to brackets attached to the ends, or upwardly bent ends, of the decking, so that it is only at the centre of the span that the tension rod is significantly below the neutral axis of the decking. In consequence, the positive bending moment induced in the decking when the tension rod is tightened will be very small, and the stress in the rod has to be substantial to achieve the desired effect, thereby requiring high-grade steel. Furthermore, since the load induced on the ends of the decking through the brackets or bent ends is wholly or largely on the bottom surface of the decking, there will be a negative bending stress induced at the ends of the decking. This further reduces the positive bending stress induced at the centre of the decking span. There is the additional time consuming and costly operation of welding the tension rod to the centre of the decking in the embodiment of FIGS.  5  to  8  and  13  to  17 . In the embodiment shown in FIGS.  9  to  12  the tension rod is located in the downwardly facing channel of the decking. Even in this case the tension rod is attached to the decking above the neutral axis (see  FIG. 12  in particular), in order to maximise the inclination of the tension rod, generating some negative bending stresses at the ends of the decking as in the above described embodiments. Furthermore, this embodiment introduces the complexity of the centrally disposed post to form the upward camber in the decking, and effectively requires independently applying tension to both ends of the tension rod. The assembly of the post to the decking is a time consuming and costly operation, and exposes the construction to the risk of fire. In addition, this construction may interfere with the passage of services through the floor space. WO 88/01330 discloses a floor channel and tension rod disposed beneath the neutral axis of the channel. However, the neutral axis of the channel is below the central plane, and this low neutral axis, will cause undesirable higher bending stress in the upper horizontal part and lower stresses in the bottom part of the section.  
         [0005]     It is an object of the present invention to provide flooring of pre-stressed deck construction that overcomes, at least to a substantial extent, the disadvantages of the known constructions.  
       SUMMARY  
       [0006]     The invention provides flooring of pre-stressed deck construction comprising an elongate decking having an upwardly facing channel formation extending therealong, having a tension rod extending between the ends of the decking and located in the channel below the neutral axis of the decking along the length of the decking, wherein the formation is asymmetrically profiled whereby the neutral axis is above a central horizontal plane.  
         [0007]     Preferably, the flooring comprises a stressing bracket secured to each end of the decking, the tension rod being connected to each stressing bracket. Each stressing bracket may be secured to the decking above the tension rod. The stressing brackets may be secured to upwardly extending sidewalls of the channel. The tension rod may extend through a loading bush located in each stressing bracket. Each stressing bracket may be formed of sheet material bent to provide a load face and upper, lower and two opposed side flanges, each flange extending substantially perpendicular to the load face. The loading bush may be located in an aperture in the load face.  
         [0008]     Connection means may connect the tension rod to the decking at a mid location therealong.  
         [0009]     The connection means may be a support clip, which may be of a resilient material. The support clip may be of spring steel. Heat insulation material may be disposed between the tension rod and the decking. The insulation material may be polypropylene, or preferably porous mineral fibre.  
         [0010]     The decking may have upper flanges extending laterally of the channel, and the flanges may have interlocking formations extending along their longitudinal edges, whereby a decking may be mutually engaged in side-by-side disposition with an adjacent decking. The decking may have a male formation extending along the edge of one upper flange and a female formation extending along the edge of the other upper flange and adapted to receive a male formation of another decking.  
         [0011]     The flooring may comprise a supporting girder framework with the decking being attached to the girder framework. In this case, the stressing bracket may be attached to the girder framework. The girder framework may comprise an I-beam having upper and lower flanges, in which case the stressing bracket may be secured to the upper flange of the I-beam, and may be secured to the underside of the upper flange. The stressing bracket may be secured to the flange of the I-beam by means of screwed studs. The screwed studs may bear on the flange through a countersunk collar. The studs may extend upwardly of the upper flange of the I-beam and into a concrete floor supported by the decking.  
         [0012]     The flooring may comprise lateral rods extending transversely of the decking. The lateral rods may be supported above the decking by spacer blocks. The lateral rods may be connected to the decking and may be connected to the interlocking formations of the decking. The lateral rods may be connected to the interlocking formations by means of connecting clips. The connecting clips may be of a resilient material, and may be of spring steel.  
         [0013]     The concrete floor may have at least one cavity therein. The cavity may be lined with a waterproof material, which may be a plastics material. The cavity lining may contain water, which may be heated or cooled. The cavity lining may have a plug in an aperture therein, the plug being of a material adapted to melt in the event of a fire in the proximity of the flooring. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention will now be described with reference to the accompanying drawings in which:  
         [0015]      FIG. 1  is a perspective view of a length of decking,  
         [0016]      FIGS. 2 and 3  show respectively the development and folded stressing bracket,  
         [0017]      FIG. 4  is a longitudinal section through the end of a decking attached to the girder framework,  
         [0018]      FIG. 5  is a lateral centre-span section through two adjacent deckings,  
         [0019]      FIG. 6  is an end view of two adjacent deckings,  
         [0020]      FIG. 7  shows a support clip of  FIG. 5  to an enlarged scale,  
         [0021]      FIG. 8  shows a connecting clip of  FIG. 5  to an enlarged scale,  
         [0022]      FIG. 9  shows stacked units during transportation, and  
         [0023]      FIGS. 10 and 11  are side and plan views respectively of an alternative support clip. 
     
    
     DETAILED DESCRIPTION  
       [0024]     Referring now to  FIG. 1 , there is shown a length of decking  10 . The decking  10  has, in use, an upwardly facing channel  11  formed by a base  12  and sidewalls  13 . Ribs  14  are formed in the base  12  and sidewalls  13  for stiffening purposes. In addition, the decking  10  is formed with upper flanges  15  that are also provided with stiffening ribs  14 . The channel  11  tapers downwardly, and the upper flanges  15  are considerably larger than the base  12 . In consequence of this profile of the decking  10 , the neutral axis is as high as is practicably possible above the centre line of the section, as shown. This maximises the dimension between the neutral axis and the applied tension. One upper flange  15  is formed with a female interlocking formation  16  along its free edge, which is adapted to receive a male interlocking formation  17  formed along the free edge of the other upper flange  15 . By this means adjacent deckings  10  may be attached to each other as shown in  FIGS. 5 and 6 . This construction provides a vertical shear interlock and lateral thrust load transfer between adjacent deckings  10  that assists inter-decking load sharing in either direction;  
         [0025]     At each end of decking  10  there is provided a stressing bracket  20  as shown in developed and folded configurations in  FIGS. 2 and 3 . The stressing bracket  20  is formed of sheet material, preferably steel, bent to provide a load face  21  and upper, lower and two opposed side flanges  22 ,  23 , and  24  respectively. When the stressing bracket  20  is bent into shape, each flange  22 ,  23 ,  24  extends substantially perpendicular to the load face  21 . In addition, side flanges  24  are further bent to form top flanges  25 . An aperture  26  is provided in the load face  21 , holes  27  are provided in side flanges  24 , and holes  28  are provided in top flanges  25  for purposes to be described below. A torsion plate  29  may be provided, for example at mid-span, as a precautionary strengthening of the decking  10 . This would abate possible twist distortion during transportation.  
         [0026]     Referring now to  FIG. 4  there is shown a stressing bracket  20  secured to the end of a decking  10 . The side flanges  24  of the stressing bracket  20  are secured by means of bolts or rivets through the holes  27  to the sidewalls  13  of the decking  10 . With these bolts or rivets being in a near-vertical sidewall  13  of the decking  10 , shear loads from the decking  10  are transferred effectively to the stressing bracket  20 . As a more economical alternative for factory prepared units, the stressing bracket  20  may be resistance spot welded. The stressing bracket  20  effectively bears onto a stiffened compression zone at the end of the decking  10  beneath the neutral axis. Pure axial compression stress can be developed in this zone. The end of span shear forces associated with the weight of the decking  10  are taken through the near vertical sidewalls  13  of the decking  10 , and transferred via the bolts, rivets or welding to the bracket  20 . This arrangement minimises combined stress effects in the compression zone and the shear sidewalls  13 . A tension rod  40  passes through a loading bush  41  located in the aperture  26  in the load face  21  stressing bracket  20 . Nut  42  on the end of tension rod  40  is tightened to tension the rod  40  and apply a bending stress to the decking  10 . Since the tension rod  40  is below the neutral axis of the decking  10 , the bending stress applied to the decking  10  is positive, causing upward arching of the decking  10 . Also, since the attachment of the stressing bracket  20  to the decking  10  is above the tension rod  40 , there is no negative bending stress applied to the ends of the decking  10 . In fact, the positive bending stress applied is enhanced by this configuration.  
         [0027]     The stressing bracket  20  is secured to the top flange  43  of an I-beam  44  forming part of the girder framework of the building. For this purpose, shear studs  45  pass through countersunk holes in the top flange  43  and through the holes  28  in top flanges  25  of the stressing bracket  20 . A nut  46  on the bottom of the shear stud  45  secures the stressing bracket  20  and the I-beam  44  together. In known constructions, the shear studs are welded to the flange of the girder framework, but this is a time consuming and expensive operation. With the present arrangement, the shear studs  45  bear on the flange  25  through a countersunk collar  47 , and assembly of the decking  10  to the girder framework  44  is simplified and less costly than was the case previously. Furthermore, this attachment of the stressing brackets  20  to the I-beams  44  using the shear studs  45  creates a rigid structure providing lateral restraint to the girder  44  to prevent lateral deflection under load.  
         [0028]     Referring now to FIGS.  5  to  8 , there is shown adjacent deckings  10  attached to each other by means of the male interlocking formation  17  of one decking  10  being received in a female interlocking formation  16  of the adjacent decking  10 . At the centre of the span, each tension rod  40  is connected to the decking  10  by means of a spring steel support clip  50 . This provides additional central support for the decking  10  to counteract the bending stresses induced in and mid-span deflection of the decking  10  caused by the weight of the concrete floor  53 . However, unlike the previously known welding attachment, such attachment does not facilitate the transfer of heat through the floor  53  and tension rod  40  to the decking  10 . In addition, heat insulation material  51 , for example polypropylene or porous mineral fibre quilting, is disposed between the tension rod  40  and the decking  10  for the purpose of resisting the spread of fire. For the purpose of preventing, or at least minimising the risk of, shrinkage cracks in the concrete floor  53 , lateral rods  52  are located above the decking  10 . The lateral rods  52  are connected to the decking  10  at suitable intervals by means of spring steel connecting clips  54 . The connecting clips  54  clip to the interlocking formations  16 ,  17  of the decking  10 . By this means, relative longitudinal movement between adjacent deckings  10  is resisted, thereby resisting vertical shear in the concrete floor  53  and providing longitudinal restraint to the girder  44 . A services aperture  48  is shown in the girder  44 . Lightweight spacer blocks  57  of a plastics material, e.g. dense polystyrene, are provided (only one is shown in  FIG. 5 ) to act as a support for the lateral rods  52 . This enables the lateral rods  52  to be located at the optimum height for concrete shrinkage crack control in the floor  53 . In addition, the spacer blocks  57  ensure that the lateral rods  42  are not in damaging contact with the decking  10 . Use of the spacer blocks  57  as a packing/spacer during transportation of the deckings  10  is shown in  FIG. 9 .  
         [0029]     After such assembly, and after tensioning the tension rods  40  to the required upward deflection and stress in the deckings  10 , the concrete floor  53  is poured onto the deckings  10 . As the decking  10  is loaded by the concrete flooring  53 , the pre-camber introduced into the decking  10  by tensioning of the rod  40  will straighten out, followed by sagging to the permissible centre deflection. This creates an end rotation of the decking  10  that will increase the tension in the tension rod  40  and hence reduction of the negative bending stress on the decking  10  caused by the weight of the concrete flooring  53 , Le. the arrangement is partially self-stress relieving. As shown in  FIG. 6 , from which the I-beam  44  has been removed for clarity, the concrete floor  53  envelops the longitudinally grooved shear studs  45  to resist shear in the floor  53  across the I-beam  44 . The countersunk collars  47  reduce the risk of slip between the shear studs  45  and the flange  43 . The floor  53  also envelops the lateral rods  52 , again to resist shear in the floor  53 . To reduce the weight of the floor  53 , and therefore the negative bending stresses induced in the decking  10  by the weight of the concrete floor  53 , voids  55  are created in the floor  53 . The spacer blocks  57  also locate the lateral rods  52  to allow the maximum size of the voids  55 , and in themselves form light voids to reduce the weight of the floor  53 . The voids  55  are lined with a non-degradable material, for example of a plastics material, and filled with water or other fire preventing fluid, e.g. an inert gas such as carbon dioxide. The lining of voids  53  is suspended from the lateral rods  52 . A tube  56  extends from the lined void  55  to the insulation blanket  51 . A plug (not shown) of a material that will readily melt in the event of a fire, is disposed in the tube  56  to allow the water or other fluid to escape in the event of a fire. The water or other fluid may be heated or cooled to provide underfloor heating/cooling if desired.  
         [0030]     Instead of the connecting clips  54 , an alternative form of connecting clip  58  is shown in  FIGS. 10 and 11 . This clip  58  is preferably of resilient steel wire, and has the advantages that it does not project into the concrete floor  53 , it supports the lateral rods  52  at a complimentary level to the spacer blocks  57  and could be of differing sizes to vary the depth of support to the lateral rods  52  for differing ponding depths of concrete floor  53 .  
         [0031]     By means of the invention, a flooring of pre-stressed deck construction is provided that allows for larger spans than was possible heretofore without exceeding stress and deflection limits. For a given dimensional arrangement, because of lower bending stress levels and centre-span deflection, lower grades of steel for the decking and tension rods can be used, thereby resulting in a cheaper construction. The present construction also provides enhanced lateral stiffness and resistance to shear and lateral deflection, resulting in a more efficient supporting girder through the restraint to the compression flange and reduced tendency to cracking of the concrete floor. In addition, the present construction provides greater resistance to heat transfer through the floor and increased safety in fire situations.