AU2006322634A1 - Composite formwork for concrete slabs - Google Patents

Description

WO 2007/065204 PCT/AU2006/001829 1 Composite formwork for concrete slabs Field of the invention This invention relates to composite formwork structures for use in concrete slabs, and to slabs incorporating such structures. The invention is particularly applicable to 5 metal formwork structures, in which the metal is most commonly steel, and is of primary application in the formation of suspended concrete slabs. The invention is however, generally applicable to slabs in any orientation and location. Background of the invention A common method for providing successive floors in multi-storey buildings is to 10 cast suspended concrete slabs in situ. Formwork for this purpose typically comprises an array of interlocking or overlapped decking members each in turn comprising a base plate having spaced generally parallel ribs separated by pans. This formwork must be propped from the floor or slab below at intervals determined by the strength and bending characteristics of the decking members. Conventional decking arrays are 15 propped by plywood tableforms on lines of props at 2-3 metre intervals. When concrete is poured onto the decking array and profiled to a selected depth, the ribs in the base plates key the decking array to the concrete. In due course, the propping can be removed when the concrete has reached a sufficient degree of curing. Since each successive slab provides the underlying support for propping the next 20 overlying slab, the rate of concrete curing determines a minimum rate of progress in casting a vertical succession of slabs. A further contributor to the costs involved is the labour required to erect and dismantle the propping. There have been a number of proposals for strengthening formwork structures with elongate metal reinforcement members that form part of or are structurally fixed to 25 the base plate, for example, so as to extend generally parallel to the ribs. Australian patent 707101 and international patent publication W002/101168 disclose various forms of structural formwork members for use in concrete slabs, including a configuration sold commercially as TrussdekM. In one form, the strengthening member WO 2007/065204 PCT/AU2006/001829 2 is a lattice girder of longitudinal and transverse chords, each lattice girder being secured within a respective pan of the decking. In another form of the composite formwork member, each strengthening member is an inverted channel that can be configured to define a void in the overlying slab. 5 In composite slabs cast on formwork comprising these base plates with additional reinforcement members structurally fixed to the plates, the reinforcement members are incorporated into the slabs. Typically, other reinforcement elements such as metal mesh or spaced reinforcement bars are supported on or from the decking structure for additionally reinforcing the slab according to the required structural specifications. 10 It will be appreciated that any reference herein to a prior disclosure is not to be taken as an admission that the disclosure is or was common general knowledge in Australia or elsewhere. It is an object of this invention to provide a composite formwork structure that may be assembled in a decking formwork in which greater spans can be achieved 15 without propping the decking while casting a slab on the decking. Summary of the invention It has been appreciated that the object of the invention can be achieved by employing metal reinforcement members of a particular form fixed to and upstanding from the base plate of the decking components. 20 The invention accordingly provides, in a first aspect, a composite formwork structure for use in concrete slabs, including: a metal base plate; a plurality of elongate metal reinforcement members structurally fixed to the metal base plate; WO 2007/065204 PCT/AU2006/001829 3 wherein each reinforcement member is wider normal to the base plate than parallel to the base plate, includes a flat face that abuts and is continuously or intermittently fastened to a surface of the metal base plate, and further includes a web upstanding from and substantially normal to 5 that surface. Preferably, the metal base plate has spaced generally parallel ribs separated by pans. The plurality of elongate metal reinforcement members are fixed to the pans so as to advantageously extend generally parallel to the ribs. Advantageously, the reinforcement members extend further from the respective 10 pan than the ribs. In one embodiment, said reinforcement members are, or include, a metal beam, eg. a steel beam, of channel cross-section having a pair of longitudinally extending flanges. In this embodiment, the aforesaid flat face that abuts and is continuously or intermittently fastened to a surface of the base plate, or pan, is provided by one of the 15 flanges of the beam. Preferably, in the just-mentioned embodiment, the steel beam of channel cross section is a hollow flange beam. Suitable such beams are described and illustrated in international patent publication W02004/11367. In another embodiment, the reinforcement members are, or include, a metal 20 beam, eg. a steel beam, of C configuration in cross-section. In a still further embodiment, the reinforcement members are, or include, a rectangular tube arranged with its longer dimension normal to the base plate. In a still further embodiment of the invention, the reinforcement members are, or include, a metal I beam, eg. a steel I beam. In this case, the web of the I is the relatively 25 wider web upstanding from and substantially normal to the surface of the base plate.

WO 2007/065204 PCT/AU2006/001829 4 In a second aspect, the invention provides a composite slab, eg. a composite concrete slab, including composite formwork structure according to the first aspect of the invention. Brief description of the drawings 5 The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figures 1 to 4 are respective cross-sectional views of composite formwork structures in accordance with successive embodiments of the invention; Figure 5 is a fragmentary perspective view of the composite formwork structure 10 illustrated in Figure 4; and Figure 6 is a view similar to Figure 4 of a composite concrete slab incorporating formwork as a reinforcement component of the slab. Detailed description of the embodiments All of the illustrated embodiments of the invention have in common a profiled 15 metal base plate or sheet 20 having spaced generally parallel ribs 22, 122, 222 separated by pans 24. At opposite longitudinal edges of the plate or sheet, complementary rib segments facilitate interlocking of adjacent plates to form an assembled decking. For the purposes of illustration, different forms of ribs 22 and pans 24 are depicted in successive drawings. It will be seen that these rib forms include 20 dovetail configuration ribs 22 (Figures 1 and 4), narrow inverted channels 122 (Figure 2), and pressed lipped channels (Figure 3). In the eventual cast product, these ribs key the base plate to the curing concrete and so prevent lateral relative displacement of the two. To prevent relative longitudinal displacement in a conventional manner, the ribs are typically interrupted by deformations that receive wet concrete during pouring of the 25 slab.

WO 2007/065204 PCT/AU2006/001829 5 There may also be secondary shallow ribs 32 for enhancing the rigidity of base plates 20. In order to strengthen the base plates and thereby substantially increase their maximum unpropped span, every second pan is fitted with a reinforcement member, 30, 5 130, 230, 330 that rests on and is structurally fixed to the pan. The reinforcement members project above the pan and significantly above the ribs, ie they extend further from pan 24 than do the ribs 22, 122, 222. Again, for purposes of illustration, each drawing depicts a different form of reinforcement member. Thus, Figure 1 illustrates a steel beam 30 of rectangular channel cross-section having a base web 40 and pair of 10 longitudinally extending flanges 42, 43 at the respective side edges of rib 40. The beam is arranged side-on, ie with one of the flanges 42 resting on and structurally fixed to the pan 24. Figure 2 depicts an embodiment in which the reinforcement member is a rectangular steel tube 130 arranged with its wider sides 140 extending normal to the 15 pan and one of its shorter sides 142 defining a flat face 142a that abuts and is structurally fixed to the surface of the pan 24. In the embodiment depicted in Figure.3, the reinforcement member is an I beam 230 arranged with its flanges 242 abutting and structurally fixed to the pan and its web 240 projecting normal to the pan. 20 Figures 4 and 5 depict an embodiment in which the reinforcement member is similar to that of Figure 1 in overall form but in which the rectangular channel configuration is provided by a hollow-flange steel beam 330 of the kind described and illustrated in the aforementioned international patent application WO 2004/11367. It would be seen that in each embodiment the reinforcement members 30, 130, 25 230, 330 are structurally fixed to the pans 24 so as to extend generally parallel to ribs 22. Moreover, each reinforcement member includes a flat face 42a, 142a, 242a, 342a that abuts and is continuously or intermittently fastened to a surface 25 of the pan 24, WO 2007/065204 PCT/AU2006/001829 6 and one or two relatively wider webs 40, 140, 240, 340 upstanding from and substantially normal to that surface 25. The means of fixing the reinforcement members to their respective pans comprises any convenient metal-to-metal fastening. Suitable techniques include screws, 5 welds and power actuated nails. For most applications and embodiments, the height dimension h for reinforcement members 30,130,230, 330 [ie. the height from pans 24] may typically be in the range 50 to 200mm, preferably between 100 and 150mm, and will usually be around half the thickness of the slab after casting is complete. It is emphasised that this 10 and other dimensions of the reinforcement members will be determined for a given application so as to meet the engineering specifications of the application. Figure 6 is a fragmentary cross-sectional view of a composite concrete slab 300 incorporating several adjacent formwork structures of the form shown in Figure 4. The slab also incorporates an appropriate steel reinforcing mesh, or re-bars, 350 resting on 15 the hollow-flange beams 330, which thereby serve as supports for the mesh or re-bars in place of the array of chairs conventionally used for this purpose. It is found that formwork decking comprising formwork structures of the forms illustrated in Figures 1 to 4 is capable of spanning up to 6 metres during a slab pour without any intervening propping. 20

Claims (26)

1. A composite formwork structure for use in concrete slabs, including: a metal base plate; a plurality of elongate metal reinforcement members structurally fixed to 5 the metal base plate; wherein each reinforcement member is wider normal to the base plate than. parallel to the base plate, includes a flat face that abuts and is continuously or intermittently fastened to a surface of the metal base plate, and further includes a web upstanding from and substantially normal to 10 that surface.

2. A composite formwork structure according to claim 1, wherein the metal base plate has spaced generally parallel ribs separated bypans.

3. A composite formwork structure according to claim 2, wherein the elongate metal reinforcement members are structurally fixed to the pans so as to 15 extend generally parallel to the ribs.

4. A composite formwork structure according to claim 2 or 3, -wherein said reinforcement members extend further from the respective pan than said ribs.

5. A composite formwork structure according to any one of.claims 1 to 4, wherein said reinforcement members include a metal beam of channel cross 20 section having a pair of longitudinally extending flanges.

6. A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members are metal beams of channel cross section having a pair of longitudinally extending flanges. WO 2007/065204 PCT/AU2006/001829 8

7. A composite formwork structure according to claim 5 or 6, wherein said flat face that abuts and is continuously or intermittently fastened to a surface of the base plate is provided by one of the flanges of the beam.

8. A composite formwork structure according to claim 7, wherein the beam of 5 channel cross-section is a hollow flange beam.

9. A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members include a metal beam of C configuration in cross-section.

10.A composite formwork structure according to any one of claims 1 to 4, 10 wherein said reinforcement members are metal beams of C configuration in cross-section.

11. A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members include a rectangular tube arranged with its longer dimension normal to the base plate. 15

12.A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members are a rectangular tube arranged with its longer dimension normal to the base plate.

13.A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members include a metal I beam. 20

14.A composite formwork structure according to any one of claims 1 to 4, wherein said reinforcement members are metal I beams.

15.A composite formwork structure according to claim 13 or 14, wherein the web of the I is the relatively wider web upstanding from and substantially normal to the surface of the base plate. WO 2007/065204 PCT/AU2006/001829 9

16.A composite formwork structure according to any one of claims 2 to 4, wherein the ribs are formed as dovetail channels.

17.A composite formwork structure according to any one of claims 2 to 4, wherein the ribs are formed as narrow inverted channels. 5

18.A composite formwork structure according to any one of claims 2 to 4, wherein the ribs are formed as pressed lipped channels.

19.A composite formwork structure according to any one of claims 2 to 18, wherein the metal base plate further includes secondary shallow ribs.

20.A composite formwork structure according to any one of claims 2 to 4, 10 wherein a said reinforcement member is fitted to every second pan.

21.A composite formwork structure according to any one of claims 1 to 20, wherein the width of said reinforcement members normal to the base plate is in the range of 50 to 200 mm.

22.A composite formwork structure according to claim 21, wherein said width of 15 said reinforcement members normal to the base plate is in the range of 100 to 150mm.

23.A composite concrete slab, including composite formwork structure according to any one of claims 1 to 22.

24.A composite concrete slab according to claim 23, wherein the width of the 20 reinforcement members normal to the base plate is around half the thickness of the slab.

25.A composite concrete slab according to claim 23 or 24, further including steel reinforcement mesh resting on the reinforcement members. WO 2007/065204 PCT/AU2006/001829 .10

26.A composite concrete slab according to claim 23 or 24, further including steel rebars resting on the reinforcement members.