WO1999029980A1 - Floor/ceiling construction method - Google Patents

Abstract

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 (10) 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 (10) for use as permanent formwork; (d) filling said floor/ceiling area to a suitable depth with concrete (50); and (e) allowing the concrete (50) to cure so as to form the floor/ceiling.

Description

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 foπnwork 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 foπnwork;

(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 foimation 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 coirugated 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 foim 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 prefeired 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 foπriwork 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

coirectly positioning the overlapping formwork sheets. It also increases the seal between

the formwork sheets to reduce loss of concrete through the formwork.

B.RIEF DESCRIPTION OF THE DRAWINGS

In order that the nature of the present invention may be more clearly understood,

prefeired 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 foimed 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 coirugated 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 foimwork 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 foimwork. 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 prefeired that the transverse edges of the foimwork 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 coixectly 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 foimwork 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 coirugated 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 airest 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 foimwork

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 foimwork and contrasts dramatically

with other foimwork materials which typically become weaker when wet. Table 1

Failure impact energies in corrugated and flat FC sheeting (air-dry and wet conditions)

A further embodiment of the present invention is shown in Figures 3 and 5. In this

embodiment, the corrugated foimwork 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 foimwork, 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

foimwork sheets 30 and 60 simply cover the corrugated sheet. By covering of the corrugated foimwork 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 foimwork sheet has substantially greater strength and

impact resistance than comparable flat foimwork 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 foimwork 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 foimwork, 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

foimwork 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 foimwork, for example, where sharp edges, corrosion of the foimwork

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.

Claims

CL.AIMS:-

1. 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 peimanent 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.

2. A method according to claim 1 including the further steps of:

(a) positioning an array of substantially parallel elongate structural members

across the floor/ceiling area;

(b) positioning the coirugated 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.

3. A method according to claim 2, wherein said structural members take the form of

beams formed substantially from roll formed or pressed sheet metal.

4. A method according to claim 2, wherein said structural members take the form of

beams foimed substantially from timber or reinforced concrete.

5. A method according to any one of claims 2 to 4, wherein said structural members

have a cross-sectional profile generally 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 in use to locate and support the foimwork sheet extending therebetween.

6. A method according to any one of the preceding claims, including the further step

of covering an upper surface of the corrugated sheet with a layer of substantially flat

planar sheet material prior to pouring the concrete.

7. A method according to any one of the preceding claims, including the further step

of covering an underside surface of the corrugated sheet with a layer of substantially flat

planar sheet material, prior to pouring the concrete.

8. A method according to claim 6 or claim 7, wherein said flat sheet material is

foimed substantially from fibre reinforced cement.

9. A method according to claim 8, wherein, during the curing step, the concrete

bonds chemically to the uppermost layer of fibre reinforced cement sheet.

10. A method according to any one of the preceding claims, wherein said fibre

reinforced cement sheet material includes fibre reinforcement consisting substantially of

cellulose fibres.

11. A method according to any one of the preceding claims, wherein said fibre

reinforced cement sheet material includes fibre reinforcement consisting substantially of

asbestos fibres.

12. A method according to any one of the preceding claims, wherein said layer of

corrugated sheet material comprises a plurality of individual corrugated sheets, each

having substantially parallel corrugated longitudinal edges and substantially parallel rectilinear transverse edges with the corrugations extending substantially parallel to the

transverse edges.

13. A method according to claim 12, including the further step of laying the corrugated

sheets such that the transverse edge of each sheet overlaps with the transverse edge of an

adjacent sheet, to provide nesting engagement between the respective overlapping

corrugations of adjoining sheets.

14. A method according to any one of the preceding claims, wherein said corrugated

sheet material is produced by a method involving the Hatschek or Magnani processes.

15. A method according to any one of the preceding claims, wherein said corrugated

sheet material is produced by a method involving extrusion of a fibre reinforced

cementitious mixture through an extrusion die.

16. A method according to any one of the preceding claims, wherein said corrugated

sheet material is formed by a method involving post pressing after green sheet formation

to increase density.

17. A corrugated foimwork sheet foimed substantially from fibre reinforced cement

for constructing a floor/ceiling in accordance with the method defined in any one of the

preceding claims, said foimwork sheet having substantially parallel corrugated

longitudinal edges and substantially parallel rectilinear transverse edges, wherein the

corrugations extend substantially parallel to the transverse edges.

18. A corrugated formwork sheet according to claim 17, wherein the fibre

reinforcement consists substantially of cellulose fibres.

19. A corrugated foimwork sheet according to claim 17, wherein the fibre

reinforcement consists substantially of asbestos fibres.

20. A coiTugated foimwork sheet according to any one of claims 17 to 19, wherein the

transverse edge of each foimwork sheet is configured to overlap with the transverse edge

of an adjacent foimwork sheet, to provide nesting engagement between the respective

overlapping corrugations of adjoining sheets.

21. A corrugated foimwork sheet according to any one of claims 17 to 20, being

formed with generally curvilinear corrugations.

22. A corrugated foimwork sheet according to any one of claims 17 to 21, being

foimed with generally asymmetrical corrugations.

23. A corrugated formwork sheet according to any one of claims 17 to 22, being

foimed with generally square, rectangular, triangular, pantile, or trapezoidal

corrugations.

24. A corrugated foimwork sheet according to any one of claims 17 to 23, produced by

a method involving post pressing after green sheet formation to increase density.

25. A corrugated formwork sheet according to any one of claims 17 to 23, produced by

a method involving extrusion through a die.

26. A corrugated foimwork sheet according to any one of claims 17 to 23, produced by

a method involving the Hatschek or Magnani process.

27. A method of constructing a floor/ceiling, said method being substantially as herein

described with reference to any one of the embodiments of the invention shown in the

accompanying drawings.

28. A corrugated formwork sheet for constructing a floor/ceiling substantially as

herein described with reference to any one of the embodiments of the invention shown in

the accompanying drawings.