Patent Publication Number: US-2011047933-A1

Title: Profiled steel deck

Description:
This invention relates to a profiled steel deck inter-alia for inclusion in flooring which comprises a composite of the steel deck and a concrete layer which traditionally contains a steel mesh, reinforcing bars, and/or metallic/plastics fibres. More especially the invention relates to a cold-rolled profiled steel deck which, in use, receives a layer of poured concrete to produce a steel/concrete composite floor panel, and to a composite floor panel which includes a profiled steel deck bonded to a layer of concrete. 
     Profiled steel decks for use inter-alia as components of steel/concrete composite floor panels are used widely in the building industry. Examples of cold-formed steel decks can be found in GB1361448, U.S. Pat. No. 4,453,364, U.S. Pat. No. 4,675,238, U.S. Pat. No. 5,056,348 and GB2397074. As will be seen from these documents, conventionally cold-formed steel decks comprise one or more crests and troughs separated by inclined webs. The crests, webs and troughs extend over the full span of the deck with the open sides of the deck extending across the deck width. Typically, the span of a deck is of the order of 3 to 5 metres and the width is generally between 500 mm and 1000 mm. Also typically, a steel gauge of between 0.75 and 1.2 mm is employed. 
     The methodology for the design of cold-formed thin gauge steel decks differs from that for the design of general structural steelwork (for members in bending) in terms of bending stress. In structural steelwork, the bending stresses are reduced whereas in cold-formed section design, the yield stress of the steel remains unchanged but the individual elements which make up the profile are reduced in area. Hence, it is important to ensure that all the individual elements of a cold-formed steel deck are as nearly fully effective as possible, that is to say that there is no or limited reduction in element area. 
     By “fully effective” is meant that all material of a profile is acting to resist bending. From this it follows that by keeping the profile of a steel deck fully effective there will be no reduction in section properties, these properties including inertia (second moment of area), and section modulus. It is accepted that a deck is “fully effective” if its elemental compression width (ie the flat areas of the deck surface) divided by the deck thickness is in the region of 30. 
     Stiffeners are used to improve the stiffness of a crest or trough of a profiled deck and to enhance the shear bond characteristics of the concrete and steel components of a deck. Previously, the elemental compression widths of stiffeners have been small when compared with the elemental compression widths of the respective crests and troughs. 
     One object of this invention is to provide a cold-rolled steel deck which is fully effective, or substantially so, and which provides a highly effective shear bond with the concrete layer of the composite floor panel. This objective is essentially achieved by significantly reducing the elemental compression width of the deck. By “elemental compression width” is meant the combined width of those parts of the deck which are in compression in use of the deck. These parts are essentially the flat areas of the crests, stiffeners and the troughs of the deck. Thus, each crest has an elemental compression width which is equal to the distance between the points of intersection of the webs and the crests and the flat element(s) of the crest. Similarly, each stiffener has an elemental compression width. A point of intersection is the point at which a web, if extended, would interest the crest, if extended. The elemental compression width of a stiffener is the distance between the points of intersection of the sides of the stiffener and the flat surface of the stiffener. Again, the points of intersection are the points at which the flat surface, if extended, would intersect the stiffener sides, if extended. 
     Accordingly, in one aspect the invention provides a profiled deck roll-formed from a steel sheet to define at least one pair of crests, a stiffener upstanding from the surface of each crest, a trough positioned between the or each pair of crests, and inclined webs extending between the sides of the trough and the neighbouring sides of the crests, the boundary between each web and crest defining a corner having a smooth curvilinear profile, the profiled deck being characterised in that the elemental compression width of each crest is no more than four times the elemental compression width of the respective stiffener, and that the radius of each curvilinear corner is not less than 33 mm. 
     In a preferred embodiment the elemental compression width of each crest is no more than 3.5 times that of the elemental compression width of the stiffener upstanding from its surface. In a further preferred embodiment the elemental compression width of each crest is no more than 2.5 times that of the elemental compression width of the stiffener. 
     In a still further embodiment, the elemental compression width of each crest is between 1.5 and 3.5 times the elemental compression width of the stiffener upstanding from its surface. 
     Preferably, the radius of each curvilinear corner is between 33 mm and 40 mm. 
     The sides of each stiffener are preferably re-entrant. 
     The or each trough may also include one or more stiffeners upstanding from its surface. If two such stiffeners are provided, they are preferably positioned substantially equidistant from the neighbouring web. 
     In another aspect the invention provides a composite floor panel comprising a profiled deck roll-formed from a steel sheet to define at least one pair of crests, a stiffener upstanding from the surface of each crest, a trough positioned between each pair of crests, and inclined webs extending between the sides of the trough and the neighbouring sides of the crests, and a layer of concrete bonded to the surface of the deck, the floor panel being characterised in that the elemental compression width of each crest is no more than four times the elemental compression width of the respective stiffener. 
     Returning now to the five listed documents referred to previously, the crests and troughs of the first four documents are generally flat with the corners between the crests and the inclined webs defined by sharp angles. Thus the bend radii of these and similar profiled steel decks are small, generally no more than between 5 mm and 10 mm. A consequence of such a bend radius is that the elemental compression width of each crest is relatively large leading to low deck inertia. 
     Furthermore, the surfaces of the crests of the decks disclosed in these four documents are generally planar or are formed with channels extending along the span of the deck. Planar deck surfaces having no stiffeners have significantly reduced stiffness and shear bond characteristics. The presence of spanwise extending channels marginally increases the deck stiffness but does not provide any or at best a limited increase in shear bond properties. 
     GB2397074 discloses a profiled steel deck in which the corners between the webs and the crests are curved to define corners having a bend radius of between a minimum of 15 mm and a maximum of 30 mm. In GB2397074 each crest is formed with an upstanding stiffener and two channels extending along the span of the deck. The elemental compression widths of each such crest is approximately 6.5 times the elemental compression width of the respective stiffener. 
     Whereas profiled decks as disclosed in GB2397074 will perform better than the decks disclosed in the other four documents, profiled decks as disclosed in GB2397074 suffer from certain features which adversely affect their performance. Essentially these features include relatively large elemental compression widths caused by a smaller than necessary bend radii, and relatively short crest stiffeners. 
     The initial purpose of the bend radii of a profiled deck is to link the crests of the deck to the adjoining inclined webs. This function is achieved by corners having small or larger bend radii. Secondly, and more importantly, the size of the bend radii affects the performance of a profiled steel deck under compression. 
     The Applicant has established that larger bend radii than those presently proposed have the effect of reducing the elemental compression widths of the profiled deck and consequently enhance its performance under load. 
     The crests of a profiled deck under simple and continuous construction (that is when concrete is poured onto the upper surface of the deck) define the major parts of the profile under compression. To minimise the elemental compression widths of the crests is therefore important. This is because these elemental widths have a direct function of the crests&#39; ability to act in compression. In other words, the shorter the elemental compression width of a deck element, the better it will perform in use. 
     The Applicant has also established that a larger than normal bend radius which effectively shortens the elemental compression width of each crest of the deck increases the vertical shear/buckling capacity of the web. 
     In summary, the bend radii of the profiled decks disclosed in GB1361448, U.S. Pat. No. 4,453,364, U.S. Pat. No. 4,675,238 and U.S. Pat. No. 5,056,348 are minimal. The crests will, therefore, perform poorly under compression. The bend radius of the profiled deck disclosed in GB2397074 is higher with subsequent increases in performance under compression. However, the elemental compression widths of the crests and the troughs are still large leading to a reduced ability to act efficiently under compression and a lower web vertical shear and buckling capacity. 
     Surprisingly, the Applicant has discovered through extensive tests that a bend radii significantly above the maximum proposed previously can be employed to achieve a significant improvement in the performance of a deck without any profile instabilities being generated. Indeed, profiled steel decks in accordance with this invention exhibit significantly enhanced ability to act under compression by providing reductions in the elemental compression widths of the elements of the profiled deck and increases in the vertical shear and buckling capacity. 
     Thus, a deck in accordance with the present invention which is fully effective and has reduced elemental compression lengths will span greater distances when compared with presently available decks as exemplified by GB1361448, U.S. Pat. No. 4,453,364, U.S. Pat. No. 4,675,238, U.S. Pat. No. 5,056,348 and GB2397074 which have deck profiles which are not fully effective. Applicant has established that a deck in accordance with this invention will, for a given steel gauge, provide increases in span length in excess of 10%. Any increase in span length results in a reduced requirement for structural steelwork and consequent significant build cost savings. 
     As mentioned previously, each crest of the profiled deck disclosed in GB2397074 is formed with an upstanding stiffener. The effective width of each such stiffener is relatively small, that is to say about 16% of the crest width between its radiussed corners. Applicant has established that, surprisingly, by increasing the compression width of each stiffener the inertia of the profile is improved leading to improvements in the performance of the deck under construction and in use. 
     Applicant has also established that for an efficient profiled deck it is very important to have as large a deck inertia as possible because this will reduce the construction stage deflection which, in turn, reduces the levels of ponding. Ponding is a term associated with deck deflection and the required concrete volume to achieve a desired concrete level for the composite product. In other words, the less a deck deflects during pouring of concrete, the less concrete is used to achieve the desired concrete level leading potentially to significant savings in build cost. The increase in stiffener length of profiled decks in accordance with the present invention increases the stiffness of the deck and reduces ponding leading to significant savings in build cost. 
     A profiled deck in accordance with this invention will not only span greater distances when compared with the other known decks but also has the potential of reducing gauge thickness of the steel sheet from which the deck is roll formed. In practise, an achievable reduction in gauge thickness from, say, 1.2 mm to 1.00 mm can provide a cost saving circa 15 to 20%. Further gauge reductions to 0.75 mm and below are possible with a deck profile in accordance with this invention. 
     When spans require propping, a profiled steel deck in accordance with this invention will use less props in the floor construction stage because of its greater vertical shear capacity and bending resistance leading to further cost savings. 
     All of the foregoing advantages and cost savings are consequent on the features of the profiled deck set out in the appended claims; thus, the invention sets out to provide a profiled steel deck having enhanced performance and reduced material and build costs during fabrication of the steel deck. 
    
    
     
       The invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: 
         FIG. 1  is an end view of a profiled steel deck in accordance with the invention; 
         FIG. 2  is an end view to an enlarged scale of that part of the deck marked “A” in  FIG. 1 ; 
         FIG. 3  is a view taken in the direction of arrow “B” of  FIG. 2 ; 
         FIG. 4  is an end view to an enlarged scale of that part of the deck marked “C” in  FIG. 1 ; 
         FIG. 5  is a scrap view from above of that part of the deck shown in  FIG. 4 ; 
         FIG. 6  is an end view to an enlarged scale of a stiffener rib of the deck marked “D” in  FIG. 1 ; 
         FIG. 7  is an end view of an alternative stiffener rib to that shown in  FIG. 6 ; and 
         FIG. 8  is a side view of a connection between neighbouring decks in accordance with the invention. 
     
    
    
     The profile of a deck in accordance with the invention is produced by subjecting a suitably sized normally rectangular sheet of steel cut from a coil to a cold forming process. In this process the sheet is passed between a series of forming rolls whose rolling surfaces are shaped to impose on the sheet the required profile. 
     Typically, the gauge of the steel to be roll formed is between 0.75 and 1.2 mm, although other steel gauges may be employed. The steel is preferably galvanised and may be coated with a textured polyester film for protective purposes. 
     As will be seen from the drawings, the profiled deck has two generally parallel crests  2  which extend along the span of the deck, a trough  4 , end laps  6  and webs  8  which join the trough and the end laps to the crests. Each end lap terminates in either a male  10  or female interlock  12 . The interlocks co-operate with those of neighbouring decks to create the required span of floor to be covered. 
     The width of the profiled deck is typically 600 mm or 800 mm. 
     Each web and crest is linked by a corner  14  having a smooth curvilinear profile whose radius is at least 33 mm. The radius should not exceed 40 mm to prevent profile instabilities being generated. A corner radius of 34 mm is preferred and is shown in the drawings. 
     It has been found that such a corner radius significantly reduces the elemental compression width of each crest thereby substantially increasing the ability of the deck to act in compression. A curvilinear profile increases the bending capacity of the deck and adds strength particularly in the corners  14  between the crests  2  and the neighbouring webs  8  to inhibit failures which can occur with more conventional profiled decks. 
     Upstanding from the upper surface of each crest is a stiffener  16 . Each stiffener  16  has re-entrant side walls  18  and a generally planar upper surface  20 . The re-entrant shaping of the side walls adds to the shear bond capacity of the profiled deck and enhances, the ability of the deck to bond effectively with the poured concrete layer when under compression. The stiffeners are produced during the roll forming process and add substantially to the stiffness of the deck and also define shear connectors between the steel deck and the concrete layer which is poured over the upper surface of the deck during construction. The re-entrant sides of each stiffener allows hangers to be supported from the stiffener interiors. As will be seen from the drawings, the corners between each stiffener and the adjoining crest surface are curvilinear. 
     Projecting from the upper surface of each stiffener  16  are a linear array of embossments  22 . These can be seen more clearly in  FIG. 5 . As shown, the embossments are generally of square shape with rounded corners. Typically the embossments are 25 mm across and are spaced apart by 50 mm. The embossments add stiffness and shear bond capacity. 
     The size of each stiffener  16  is larger than that found in conventional profiled decks to improve the inertia of the profile and reduce the elemental length of each crest adjacent to the respective stiffener. In the illustrated deck, the elemental compression width L 2  of the upper surface of each stiffener is between one quarter and one third of the elemental compression width L 1  of the respective crest. The ratio of the elemental compression width of each crest and that of each stiffener of a deck in accordance with this invention is between 4 to 1 and 1 to 0.5 to 1. 
     As mentioned previously, an increase in profile inertia (deck stiffness) reduces deck deflections in the composite floor construction stage. Reductions in deck deflection reduce the levels of ponding during concrete pouring and provides commensurate reductions in the required volume of concrete with consequent savings in build costs. 
     As will be seen more readily from  FIGS. 2 and 3 , each web  8  is formed with two vertically spaced linear rows  26 ,  28  of outwardly projecting embossments  30 . Each embossment is generally circular in plan and the radius of the embossments of the lower row  26  is typically 4 mm and that of the embossments of the upper row  28  is typically 5.2 mm. The spacing between the centres of neighbouring embossments of each row is typically 34 mm and that between the centres of the two rows is typically 36.3 mm 
     The embossments of the upper row  28  are displaced linearly with respect to those of the lower row whereby each upper embossment is positioned above a land portion of the respective web. 
     The embossment rows  26 ,  28  extend along the entire span of the webs  8  and assist bonding of the steel profile and the poured concrete during production of the composite floor panel. 
     The trough  4  is formed with two upstanding ribs  32 , 34  separated by a plane surfaced land  36  through which shear stud connectors can pass to connect the steel web to supporting beams or the like prior to concrete pouring. The shape of alternative ribs can be seen from  FIGS. 6 and 7 . 
     Each end lap  6  is formed with either a male or female interlock  10 , 12 . The interlocks extend along the entire length of the deck and enable two or more decks to be joined as shown in  FIG. 8  to produce a deck of any required width. 
     To produce a composite floor panel a steel deck in accordance with the invention is positioned on supports above the floor area to be covered and joined through its interlocks to produce the required floor panel area. Concrete is then poured in situ over the deck and allowed to set. The profile of the deck promotes an efficient bond to the concrete and the profile inertia during pouring ensures low ponding of the concrete. 
     It will be appreciated that the foregoing is merely exemplary of profiled decks in accordance with the invention and that various modifications can readily be made thereto without departing from the true scope of the invention as set out in the appended claims.