TITLE: FLOOR/CEILING CONSTRUCTION METHOD FIELD OF THE INVENTION The present invention relates to a method of construction and in particular to a method of constructing a composite concrete floor or ceiling for single or multi-storey buildings.

BACKGROUND OF THE INVENTION There are a variety of construction techniques for producing floors and ceilings for single and multi-storey buildings. Most require substantial framework to support appropriate formwork into which concrete is poured. Significant quantities of concrete are generally required in order to provide the required structural integrity for the resulting floor/ceiling. In many cases, steel reinforcement is incorporated into the floor to provide sufficient tensile or flexural strength, as well as to minimise shrinkage and to control cracking.

A recently developed construction technique, which has found considerable commercial success, is the subject of Australian Patent Application No. 74258/96 and is shown in figure 6. This construction system involves using a number of parallel, spaced apart, prestressed reinforced concrete beams 100, generally of an inverted»T»shape, extending across the intended area of the floor/ceiling to support the formwork. Suitable formwork 150 is then laid between each concrete beam. Concrete 200 is then poured on top of the formwork to cover the beams 100 to a desired depth, and allowed to cure.

Optionally, shrinkage control mesh 175 may be laid over the beams prior to pouring the

concrete. Ceiling lining 280 may be attached to the underside of the beams 100 if desired. In one particular known embodiment of this process, the formwork is constructed from 12 mm thick flat fibre reinforced cement sheets.

Generally, the beams 100 are spaced apart at intervals of around 400 mm. At this distance, the flat fibre reinforced cement formwork sheets comply with Australian standard AS3610. That is, they can support a worker walking across and between the beams and, subsequently, the weight of the wet concrete poured on top of the formwork.

There is, however, a limit to the weight which is supportable by formwork of this type.

The flat formwork sheets, for example, are generally around 10 to 20 mm thick. If it is desired to place the concrete beams further apart to reduce the cost of the floor/ceiling, the formwork sheets must be stronger to support higher bending stresses and a greater weight of wet concrete. This requires the flat fibre reinforced cement formwork sheets to be either thicker and/or more fully compressed to increase their strength. Both these options substantially increase the cost of this construction method.

The present invention seeks to overcome one or more disadvantages of the prior art, or at least to provide a useful alternative.

DISCLOSURE OF THE INVENTION Accordingly, in a first aspect, the present invention provides a method of constructing a floor/ceiling, said method comprising the steps of. (a) defining a floor/ceiling area by means of a peripheral boundary; (b) forming corrugated generally planar sheet material substantially from fibre- reinforced cement;

(c) covering at least a major portion of said floor/ceiling area with a layer of said corrugated sheet material for use as permanent formwork; (d) filling said floor/ceiling area to a suitable depth with concrete; and (e) allowing the concrete to cure so as to form the floor/ceiling.

The term»fibre reinforced cement»as used herein includes both autoclave and naturally cured product formed from cement, fibre reinforcement and optionally other additives, whether manufactured by»Hatschek»,»Magnani», extrusion or other processes, with or without post formation pressing.

The term»planar»as used herein indicates that the sheet extends generally in one plane, in the sense of not being bowed, twisted or arched. The definition is not limited to flat sheets, and includes sheets having regular corrugations or similar formations, provided that the general extent of the sheet lies substantially in one plane, or the lowermost extremities (i. e. the»valleys») of the corrugations lie substantially in one plane.

Unless the context clearly requires otherwise, throughout the description and the claims, the words’comprise’,’comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of»including, but not limited to».

Preferably, said method includes the further steps of. (a) positioning an array of substantially parallel elongate structural members across the floor/ceiling area;

(b) positioning the corrugated sheet material between adjacent pairs of said structural members such that ridges and valleys of the corrugations extend generally transversely to the structural members; and (c) pouring the concrete to a depth sufficient at least partially to cover the structural members.

In a preferred embodiment, the ridges and valleys of the corrugations of the sheet material extend substantially at right angles to the longitudinal axes of the structural members.

Preferably, the structural members take the form of beams formed substantially from roll formed or pressed sheet metal. Ideally, the metal beams are spot welded, riveted, bolted, glued or clinched to form a closed section, for enhanced rigidity.

Alternatively, however, the structural members may be formed from reinforced concrete or other suitable materials. Moreover, the structural members need not take the form of beams, but could include masonry columns or walls for example.

Preferably, the structural members have a cross-sectional profile in the form of an inverted»T», a lower section of which extends outwardly from an upper section on each side to define a longitudinally extending shoulder, the opposing shoulders of adjacent structural members being adapted to locate and support the intermediate formwork sheet.

The corrugated sheet is designed, at least in a preferred embodiment, to withstand a construction point loading, due to the impact of falling objects or foot traffic without failure. Advantageously, being formed from fibre reinforced cement, it is also compatible with the concrete topping and bonds chemically to it, without the need for

supplementary fastening means, while the corrugations enhance the mechanical keying between the two components.

In one preferred variation, the method includes the additional step of covering an upper surface of the corrugated sheet material with a layer of substantially flat planar sheet material prior to pouring the concrete. Optionally, an underside surface of the corrugated sheet material may also be covered with a layer of flat planar sheet. The upper and lower flat sheets are preferably also formed from fibre reinforced cement.

This not only provides certain aesthetic improvements but substantially reduces the quantity of concrete to be poured into the formwork as well as providing insulating cavities. In some embodiments, the cavities conveniently provide for cable ducting through the floor.

In this way, also, a temporary composite formwork decking of enhanced structural strength can be formed by sandwiching the corrugated sheet between the top and bottom flat sheets. In this arrangement, the decking exhibits enhanced impact strength against construction point loading, accessibility for traffic of other trades on site, prolonged dry strength of the corrugated sheet due to protection against wetting during concreting, improved insulation properties, and reduced weight on foundations due to less volume of concrete topping being required.

According to a second aspect, the invention provides an elongate corrugated formwork sheet for constructing a floor or ceiling in accordance with the method defined above, said formwork sheet having substantially parallel corrugated longitudinal edges and substantially parallel rectilinear transverse edges, wherein valleys and ridges of the corrugations extend substantially parallel to the transverse edges.

Preferably, in use, the corrugations extend substantially transversely to the structural members.

Preferably, the transverse edges of each formwork sheet are configured to overlap with the transverse edge of an adjacent formwork sheet, such that in use at least one corrugation adjacent the end of each formwork sheet nestingly engages a complementary corrugation of an adjoining sheet. Such an arrangement is particularly helpful in correctly positioning the overlapping formwork sheets. It also increases the seal between the formwork sheets to reduce loss of concrete through the formwork.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the nature of the present invention may be more clearly understood, preferred embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a corrugated sheet suitable for use in accordance with a first embodiment of the invention; Figure 2 is a perspective view of two corrugated sheets of the type shown in figure 1, placed in situ between structural members, in accordance with the invention; Figure 3 is a perspective view of the corrugated sheets of figure 1 extending between structural members and covered by additional flat formwork sheet in accordance with a further embodiment of the invention; Figures 4 and 5 are cross-sectional views of floor/ceilings constructed in accordance with the embodiments of the invention as shown in figures 2 and 3 respectively; and

Figure 6 is a cross-sectional view showing a construction technique according to the PRIOR ART.

BEST MODE OF PERFORMING THE INVENTION The formwork shown in Figure 1 comprises a generally planar corrugated sheet 10, constructed from fibre reinforced cement. In the embodiment shown, the corrugated sheet has asymmetrical curvilinear corrugations 15. However, it will be understood that other corrugation profiles such as square, triangular, pantile, trapezoidal or the like may alternatively be used, whether symmetrical or otherwise.

Turning now to Figure 2, this drawing shows a plurality of parallel spaced apart structural beams 20 extending across the area of the intended floor/ceiling. The cross- sectional profile of each structural beam takes the shape of an inverted»T», with the lower section extending outwardly beyond the upper section on each side, to define a longitudinally extending shoulder 21. The corrugated formwork sheets 10 extend respectively between adjacent structural beams 20, supported by the opposing shoulders.

The corrugations extend generally transversely with respect to the longitudinal axes of the beams. In the embodiment shown, the corrugations are at right angles to the structural beams. The beams are ideally roll formed from sheet metal, and spot welded to form a closed section. They may, however, alternatively be formed from reinforced concrete, pressed steel, or other suitable materials. Moreover, at the perimeter and at level step-downs, for example, the structural supporting members may include concrete or masonry walls, columns, or other suitable formations.

With the corrugated formwork sheets 10 in place, concrete 50 is poured so as to cover both the corrugated formwork 10 and structural members 20 as shown in Figure 4.

The concrete covers the upper surfaces of the structural beam 20, typically to a depth of around 25-50 mm The corrugated configuration of the formwork 10 provides a substantial increase in structural rigidity as compared with previously used flat sheet. With such an increase in strength of the formwork supporting the wet concrete 50, the structural members 20 may be spaced relatively further apart. This provides substantial reductions in cost since the number of beams required to cover a given floor/ceiling area is substantially reduced. In this regard, it has been found that a safe and practical increase in the effective span of around 50-100% over conventional spacing can be achieved. This may be increased further with optimised corrugation profiles.

Further, it has been found that due to its corrugated configuration, the formwork sheet can be substantially thinner than conventional formwork. By way of example, the applicant has found that conventional 12 mm thick flat fibre reinforced cement sheeting can be replaced by 6.5 mm thick corrugated sheet at greater beam spacing.

Consequently, the beams and formwork sheeting provided by the present invention are easier and faster to lay and are lighter both during laying and subsequently. This also leads to further reductions in materials and labour costs.

It is preferred that the transverse edges of the formwork sheets are configured to overlap such that at least one corrugation adjacent the end of a formwork sheet is nestled in an overlapping corrugation of the adjoining formwork sheet. Such an arrangement is particularly helpful in correctly positioning the formwork. It also increases the seal

between the formwork sheets. As will be clear to those skilled in the art, with non- corrugated formwork sheets, the seal between overlapping or abutting formwork sheets in not particularly effective. Consequently, concrete can escape through gaps between the formwork sheets leading to increased concrete consumption. Further, such cracks or gaps between the formwork sheets can result in an unsightly end product which may require further finishing. The present invention avoids these difficulties by providing formwork sheets which are corrugated and configured to overlap.

Unexpectedly, it has also been found that corrugated cement sheet with cellulose fibre reinforcement, subjected to impact in preliminary testing, exhibits a non- catastrophic failure mode which is believed to be caused by the ability of the corrugations to arrest cracking. This impact resistant behaviour in fibre reinforced cement corrugates, contrary to flat sheets which failed quickly when their impact capacity was reached, is believed to provide an added safety margin against dynamic and impact loadings of the type which are typically experienced in permanent formwork flooring applications.

In preliminary testing, the failure impact energy in corrugated sheet formed from cellulose fibre reinforced cement was also improved with increasing moisture content from 9% (air-dry condition) to 24% (saturated condition), resulting in a 50% increase in the impact energy (Table 1). This unexpected trend was opposite to that observed in flat sheeting under impact, which exhibited 20% to 30% reduction in the impact energy at failure. This is a significant advantage since moisture from the concrete actually improves the impact resistance of the underlying formwork and contrasts dramatically with other formwork materials which typically become weaker when wet.

Table 1 Failure impact energies in corrugated and flat FC sheeting (air-dry and wet conditions) Failure Energy (Joule) FC Element r. dry t %Change, 9°fo mlc 24% m. c’ from dry tovet 625 mm span 190 286 + 50% 750 mm span 218 327 + 50% Flatsneet Air-dry Wet % Change 1.2°. 0nlc’, 35°fa zlo from dry to wet 400 mm span 408 327-20% 500 mm span 517 354-32%

A further embodiment of the present invention is shown in Figures 3 and 5. In this embodiment, the corrugated formwork sheet 10 is covered by an additional layer of flat formwork sheet 30 prior to pouring of the concrete. This configuration has a number of substantial advantages over the prior art. Firstly, it provides an immediate and reliable work platform for walking over the floor/ceiling area before the concrete is poured.

Secondly, the amount of concrete required to form the floor/ceiling is substantially reduced since the voids 40 (see Figure 5) between the corrugations are not filled with concrete. Consequently, the floor/ceiling itself is substantially lighter and the beams 20 may be reduced in size as compared with conventional construction methods. Typically, the mean concrete depth is around 75 mm compared with conventional depth of around 100 mm. Moreover, due to the reduced quantity of concrete to be supported by the

formwork, the distance between adjacent structural members 20 may be increased still further.

Surprisingly, greater impact resistance is also achieved. By way of example, when a 6 mm flat fibre reinforced cement sheet was laid on top of a corrugated sheet, a further 43% to 48% gain in impact energy (depending on moisture condition) was observed (see Table 2). This trend indicates that the impact resistance of fibre reinforced cement corrugated permanent formwork elements can be further enhanced using a combination of a corrugate sheet with a flat top sheet.

Table 2 Failure impact energies in corrugates and (corrugate + top flat sheet) assemblies (air-dry and wet conditions) Impact Energy at Failure (Joule) Air-dry condition (9% m/c) Saturated condition (24% m/c) Corrugate Corrugate Corrugate + % Change Corrugate Corrugate + % Change Span only top flat sheet only top flat sheet 625 mm 190 272 + 43 286 422 + 48 750 mm 218 313 + 43 327 490 + 50 In another embodiment, the underside of the corrugated sheets may also be covered by conventional flat sheets 60 (see Figure 5). This provides a smoother more aesthetic underside to the floor/ceiling. It should be noted that the formwork sheets 30 and 60 on the respective upper and lower surfaces of the corrugated sheet 10 can be relatively thin, since it is not necessary that these sheets alone support the concrete. This structural support is provided in large part by the corrugated sheet 10 while the planar formwork sheets 30 and 60 simply cover the corrugated sheet.

By covering of the corrugated formwork 10 with planar formwork sheets 30 and 60, there is a net reduction in the weight of the floor/ceiling. This is the combined result of the voids 40 which mean less concrete is required, the smaller size beams, and/or the wider beam spacing. As a result, there is a consequential reduction in load on the foundations for a single or multi-storey building. Better sound insulation is conveniently also provided, while in some embodiments the voids 40 can be used to provide a mechanism for ducting power/communication cables throughout the building.

Moreover, as discussed above, there is improved impact load capacity during construction.

The present invention thus provides several significant advantages over the cited prior art. Firstly, a corrugated formwork sheet has substantially greater strength and impact resistance than comparable flat formwork sheets. Accordingly, the corrugated sheet can support a greater quantity of concrete thereby allowing the span between the structural supporting members to be increased. Preliminary testing shows a safe and practical effective span increase of more than 50 % and up to 100% over conventional spacing.

Secondly, with such a corrugated formwork sheet, the actual sheet itself can be substantially thinner than conventional formwork due to its corrugated profile. Once again preliminary testing has shown that a flat 12 mm thick sheet can be replaced with a 6.5 mm thick planar corrugated fibre reinforced cement sheet, with greater beam spacing.

Thirdly, the corrugate is a cementitious composite which makes it compatible with the concrete topping in a flooring system. Contrary to the case with steel permanent

formwork, it requires no bonding enhancements such as shear key arrangements or surface-sprayed bonding agents.

Further, the corrugated profile of the formwork sheet reduces the quantity of concrete necessary to provide the desired thickness and structural integrity of the resultant floor/ceiling.

As a result, there are substantial reductions, typically around 25%, in the cost per square metre of the floor/ceiling area. The primary saving in cost is due the reduction in structural beams required to cover the floor/ceiling area.

A further advantage is that because the concrete bonds chemically to the upper formwork layer, the possibility of delamination is virtually eliminated. Even in situations where an aperture needs to be cut through the ceiling or floor, subsequent finishing or refastening of the formwork to the concrete adjacent the aperture is not required. This contrasts dramatically with prior art techniques involving the use of corrugated steel formwork, for example, where sharp edges, corrosion of the formwork and delamination, particularly adjacent exposed edges are common problems. As will be clear to those skilled in the art, the present invention thus provides a practical, commercially significant, and novel advance over the prior art.

Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

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