WO 2006/125248 PCT/AU2006/000670 1 STRUCTURAL STEEL DECKING PANEL FIELD OF THE INVENTION The present invention relates to structural steel decking and in particular to 5 structural steel decking constructed from profiled steel on which concrete is poured to form a composite slab. BACKGROUND OF THE INVENTION Light-gauge steel decking is used as permanent formwork in the construction 10 of composite slabs. During construction it must support the construction dead and live loads and stacked materials applied or placed on its top face prior to the concrete setting. An example of steel decking is shown in Figure 1 in an end view. With this 15 steel decking, overlap and underlap portions are provided within the trailing side and leading side edges, respectively. These overlap and underlap portions allow multiple decking sheets to be connected by lap joints formed by the overlapping and underlapping portions. This is achieved by relative rotation between the decking panels. Problems with the aforementioned 20 decking panel and other similar panels include the need to tilt one panel with respect to another to get engagement of the lap joint the difficulty of accommodating longitudinal curvature of the panels if they are cambered, unwanted separation of the lap joint and leakages through the lap joint. 25 Engaging lap joints by tilting panels is problematic for a number of reasons. Firstly, it can be difficult to hold the panels at the correct angle and engage the joint under normal site conditions unless the installer is forward of the sheets already laid where there are no sheets to stand on. Secondly, the joints need to be tight once fitted together, otherwise they leak (and the soffit may not be flat WO 2006/125248 PCT/AU2006/000670 2 with a vertical step across the joint), but this requires that both the underlap and overlap portions are straight longitudinally when being fitted together, which severely limits the maximum amount of vertical deflection of the underlap joint that can be tolerated between supports, and also prevents the 5 sheets from possibly being significantly pre-cambered to reduce the final vertical deflection of the deck under wet concrete. Finally, reliably making this type of joint tight is difficult in practice when the sheeting base metal thickness is varied during manufacture. 10 It is an object of the present invention to provide an improved decking panel that overcomes at least some of the aforementioned short comings of the prior art. SUMMARY OF THE INVENTION 15 According to a first aspect of the invention there is provided a structural steel decking panel for supporting construction loads and material including wet concrete and subsequently reinforcing the concrete after it has hardened, the decking panel including: a trailing pan portion terminating at a trailing side edge; 20 an overlap portion within the trailing side edge for retainably receiving an underlap portion of a matching panel; an intermediate pan portion spaced apart from and parallel to the trailing pan portion; a first upstanding rib joining the trailing pan portion to the 25 intermediate pan portion; a leading pan portion terminating at a leading side edge, the leading pan portion narrower than the trailing pan portion; an underlap portion within the leading side edge for engagement with an overlap portion of a matching panel; and WO 2006/125248 PCT/AU2006/000670 3 a second upstanding rib portion joining the intermediate pan portion to the leading pan portion, wherein the overlap portion and the underlap portion are shaped complementary to each other such that matching adjacent panels can be snap 5 fitted together without relative rotation of said matching panels. Preferably the overlap portion defines an elongate downward facing mouth having inner walls. i0 Preferably the inner walls of the overlap portion are resiliently displaceable away from each other to allow them to snap fit over the under lap portion of a matching adjacent panel. Preferably the inner walls of the overlap portion are initially upwardly 15 converging so as to provide a lead-in section for the underlap portion of a matching adjacent panel. Preferably the inner walls of the overlap portion diverge at a position above the lead-in section. 20 Preferably the lap joint is substantially leak-proof to minimise the leakage of water and mortar when concrete is poured on top. According to a second aspect of the invention there is provided a structural 25 steel decking panel for supporting construction loads and material including wet concrete and subsequently reinforcing the concrete after it has hardened, the decking panel including: a trailing pan portion terminating at a trailing side edge; an overlap portion within the trailing side edge for retainably receiving WO 2006/125248 PCT/AU2006/000670 4 an underlap portion of a matching panel; an intermediate pan portion spaced apart from and parallel to the trailing pan portion; a first upstanding rib joining the trailing pan portion to the 5 intermediate pan portion; a leading pan portion terminating at a leading side edge, the leading pan portion narrower than the trailing pan portion; an underlap portion within the leading side edge for engagement with an overlap portion of a matching panel; and 10 a second upstanding rib portion joining the intermediate pan portion to the leading pan portion, wherein the overlap portion defines an elongate downward facing mouth having inner walls that are initially upwardly converging so as to provide a lead-in section for the underlap portion of a matching adjacent 15 panel. Preferably the inner walls of the overlap portion are resiliently displaceable away from each other to allow them to snap fit over the under lap portion of a matching adjacent panel. 20 Preferably the inner walls of the overlap portion diverge at a position above the lead-in section. Preferably the lap joint is substantially leak-proof to minimise the leakage of 25 water and mortar when concrete is poured on top. Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying Figures. These WO 2006/125248 PCT/AU2006/000670 5 embodiments are illustrative and are not meant to be restrictive of the scope of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE 5 INVENTION Preferred embodiments of the invention are illustrated in the accompanying representations in which: Figure 1 is an end view of a background art structural steel decking panel; 10 Figure 2 is a cross-sectional view of a decking panel according to a first embodiment of the invention, showing overlapping with a portion of identical decking panel; Figure 3 is a similar cross-sectional view to that of Figure 2 but shows only a single decking panel with features removed; 15 Figure 4 is an isometric view of the decking panel in Figure 3; Figures 5, 6 and 7 are similar to that of Figure 2, but show progressive engagement of one panel with a joining panel with panels supported across their width by intermediate steel beams; Figures 8, 9a and 9b are similar to Figures 5, 6 and 7 but show the area 20 of the lap joint in more detail; Figures 10 and 11 are similar to Figures 3 and 4 but show an alternative embodiment where the stiffening features of the panel are removed; and Figures 12a and 12b show an alternative embodiment of the invention. Figure 12c shows a further alternative embodiment of the underlap 25 portion of the snap-joint shown in Figures 12a and 12b. Figures 13a and 13b show an alternative embodiment of the snap-joint of the invention. Figures 14a and 14b show yet another embodiment of the snap-joint of the invention.
WO 2006/125248 PCT/AU2006/000670 6 A first embodiment of the invention is illustrated in Figures 2, 3 and 4. Referring to Figures 3 and 4, the steel decking panel 10 includes a trailing pan portion 20 that terminates at a trailing side edge 22. Within the trailing side 5 edge, an overlap portion 24 is provided for retainably receiving an underlap portion 54' of a matching panel. An intermediate pan portion 30 is spaced apart from and parallel to the trailing pan portion 20. The decking panel 10 also includes a first upstanding rib 40 joining the trailing pan portion 20 and the intermediate pan portion 30. A leading pan portion 50 terminating at a 10 leading side edge 52 is also included. An underlap portion 54 within the leading side edge 52 is provided for engagement with an overlap portion 24' of a matching panel. Finally, the decking panel 10 includes a second upstanding rib portion 60 joining the intermediate pan portion 30 to the leading pan portion 50. 15 The trailing pan portion 20 is wider that the leading pan portion 50 so that, when a matching panel is joined side by side at the underlap portion 54 of the panel and the overlap portion 24' of the matching panel to form a two part pan portion 70 (shown in Figure 2), a lap joint is formed off centre within the 20 two part pan portion. The overlap portion 24 is shown in more detail in Figure 8. The overlap portion 24 defines an elongate downward facing mouth having inner walls 23 and 26 that are initially upwardly converging so as to provide a lead-in 25 section for the underlap portion 54 of a matching adjacent panel. The initially upward converging section 23 is joined to a divergent section 25. The initially converging and then diverging inner walls 23 and 25, "respectively", allow a snap fit to occur as is progressively illustrated in Figures 9a and 9b.
WO 2006/125248 PCT/AU2006/000670 7 In progressing from Figures 9a to 9b, the inner walls 23 and 25 on the one hand and 26 on the other hand are resiliently displaced away from each other to allow them to snap fit over the underlap portion 54'. 5 Referring to Figures 5, 6 and 7 it can be seen that the panel 10 can be installed flat on narrow supports 90 and does not have to be tilted at an angle to the horizontal to obtain engagement of the joint. This allows panels to be dropped down while the installers stand on the previous sheet. The length of the leading pan portions 50 and 50' are considerably shorter than the lengths of 10 the trailing pan portions 20 and 20'. This improves the stiffness of the underlap and limits its movement, thus assisting the joint to snap together when a force is applied as indicated by arrow 97 in Figure 6. The stiffness of the underlap becomes increasingly important as the span between supports 90 increases. 15 Once the joint has been formed as is shown in Figure 7, the panels are difficult to separate because the contact force inside the lap joint is inclined significantly to the horizontal plane, and the long pan on the opposite side of the lap joint is much more flexible which reduces the magnitude of the 20 upwards force potentially pulling the overlap off the underlap, which would lead to joint failure. A critical loading situation for the lap joint is if heavy downward loads are applied to the decking panel on the underlapping side of the lap joint. 25 Not only does off-centreing of the lap joint improve the performance of the lap joint from an installation and separation point of view, off-centreing is also very desirable when placing shear connectors.
WO 2006/125248 PCT/AU2006/000670 8 The height of the wedge opening 80 (see Fig.7) in the base of the joint (which takes the form when seen from below of a mock longitudinal stiffener) should not exceed 10 mm. To allow for the possibility of air being trapped in the top of the underlap portion causing air pockets under the top of the joint portion, 5 the overall width of this portion of the lap joint is limited to about 6 mm. With these dimensions, any significant air pockets in the top of this joint will simply be squashed under pressure from shear connectors in the immediate vicinity, thus behaving as a solid slab at ultimate load. Compressive pressure will be transferred over the joint without any detrimental effect due to the 10 limited height of the (wedged) joint base. Neither rib punch-through failure nor rib-shearing failure can possibly occur due to the lap joint as described. The lap joint formed by the overlap portion 24 and underlap portion 54' can come in a variety of forms. While a preferred embodiment has been described 15 in relation to Figures 1 through to 9b, other embodiments such as those shown in Figures 12a, 12b, 12c, Figures 13a and 13 b, and Figures 14a and 14b may be used. In the case of the open type of joint in Figures 13a and 13 b, the gap in the joint above the wedge opening 80 will be crushed and closed up without effecting the strength and ductility of the shear connectors. Neither 20 will it cause undesirable secondary failure modes of the shear connection like rib punch-through or rib-shearing. Therefore, the gap in the top of the open type of joint will close up as occurs for any air pockets formed in the top of the underlap portion in Figure 9b. Referring to figures 12a and 12b, tabs 57 are provided within the underlap 25 portion 54 to enable better control of the snap-fit forces in spite of manufacturing tolerance variations. The width of the tabs and hence the lengths of the portions 58 can be varied.
WO 2006/125248 PCT/AU2006/000670 9 Referring to Figure 12c, a further variation of the underlap portion 54 is shown. With this variation, the snap-fit force is reduced by providing cut-out areas 58 between tabs 57. The cut-outs 58 can be formed in the steel blank before the panel is roll-formed. 5 Referring to Figures 13a and 13b, a further variation of the underlay portion 54 and the overlap portion 24 is shown. Referring to Figures 14a and 14b, a further snap-fit assembly is shown. With 10 this assembly, a swage 29 is provided within the overlap portion 24. The swage enhances the stiffness of the overlap portion 24. Similar swages can be formed within the underlap portion if required. Although swages are not shown with the other joint types described above, they can of course be employed in any underlap or overlap portion. 15 The decking panel 10 has the following features. a) the lap joint exhibits snap-in action whereby the panels can be connected together without having to rotate them into position (see Figures 5 to 7), and also ensures that an essentially leak-proof joint is 20 formed to minimise leakage of water and mortar when concrete is poured on top of the deck; (b) the underlap has side, upper and lower contact points with the overlap which eliminate horizontal or vertical slack in the joint, thus providing a flat soffit and tight-fitting joint for good visual appearance from 25 below (see Figure 9b); (c) the lap joint is off-centered in the flat pan of the decking (see Figure 2) to allow welded studs or other types of shear connectors to be placed in the middle region between the ribs, either through the steel sheeting WO 2006/125248 PCT/AU2006/000670 10 or else directly onto the top flange of the steel beam, which are optimal positions for shear connectors to improve their strength and ductility; (d) off-centreing the lap joint, with the underlap located nearer to the adjoining steel rib, also significantly improves the action of the snap-in 5 joint; (e) the underside of the joint has the same appearance as any other longitudinal stiffener in the pans of the deck, with its geometry allowing the joint to act as a "closed" rib in the vicinity of shear connectors, and therefore without having a detrimental effect on the 10 strength or functionality of the lap joint, or on the strength or ductility of any shear connectors in the pans of the deck; and (f) the shape of the lap joint is such that it will grip the concrete well and develop strong, ductile longitudinal slip resistance in the final composite slab; and 15 (g) The lap joint creates a mock longitudinal stiffener. This stiffener is created efficiently with minimal use of additional sheet metal by its positioning below or within the underlap and overlap portions. The snap-joint discussed above allows longer sheets to be joined, the joints 20 can be tighter, the sheets can be curved or pre-cambered, and changes in base metal thickness can be more readily accommodated. The embodiments of the invention described above have two ribs. In other embodiments of the invention, one, three or more ribs may be used. 25 While the present invention had been described in terms of preferred embodiments in order to facilitate better understanding of the invention, it should be appreciated that various modifications can be made without WO 2006/125248 PCT/AU2006/000670 11 departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.