SLABS FOR FALSE FLOORS

Abstract: False floors are constructed using quadrilateral slabs or tiles (10, 60) which are mounted on supporting columns or legs (15, 102). Each slab or tile has a diagonal line of weakness, permitting the tile to yield about the line of weakness to form two joined, triangular portions. The slabs or tiles are conveniently, but not necessarily, constructed as pre-cast concrete slabs, with a slot (11, 62) providing the diagonal weakness. A panel comprising a plurality of connected slabs or tiles, each having the features of the present invention, is also described. Preferably such panels are hexagonal.

Description: TITLE; "SLABS FOR FALSE FLOORS" TECHNICAL FIELD This invention concerns slabs used to create false floors. False floors, in this specification, are floors which are supported above a true floor or above a roof on pedestals. Among the purposes for which a false floor may be constructed are: a) to provide a trafficable surface over a roof or over a floor requiring protection; b) to provide a space in which heat insulation or sound attenuation members can be located; and c) to provide a cavity for electrical wiring or other services. BACKGROUND ART At present, false floors are constructed of rectangular slabs or tiles which are supported on packing blocks or column supports set under the four corners of each slab or tile. Typically, these slabs or tiles are pre-cast reinforced concrete members or are pressed steel members filled with concrete or particle board. Unless the floor or roof above which the false floor is located is planar and the column supports are of uniform height, the slabs or tiles are not supported on all four supports simultaneously. Planar floors and uniform column supports, however, are rare and either the slabs or tiles rock about the pivot provided by two of the supports, or each slab has to be supported on adjustable jacks at each corner or has to be carefully packed to ensure that it is supported evenly on all four supports. Rocking slabs produce an unsatisfactory false floor. Careful jacking or packing at each support, however, adds considerably to the cost of the installation of the false floor. DISCLOSURE OF THE PRESENT INVENTION It is an object of the present invention to overcome the disadvantages of the existing construction of false floors and provide a slab or tile construction which can be securely mounted on support columns which do not have their top surfaces in precisely the same plane, without the need for special jacking or packing of the slab or tile. This objective is achieved, according to a first aspect of the present invention, by the provision of a quadrilateral floor slab with a diagonal line of weakness built therein. When such a slab is unevenly supported at its four corners, the application of pressure to the slab causes the slab to yield along the line of weakness until the slab becomes, effectively, two triangular slabs, joined along the line of weakness, with each triangular slab being supported at its three corners. If the slab is a pre-cast reinforced concrete slab, it will crack along the line of weakness. The above-noted objective is also achieved, according to a second aspect of the present invention, by forming a rectangular slab as two triangular slabs, joined along a corresponding side by a hinge or by a flexible joint. Thus, according to a first aspect of the present invention, a slab for use in the construction of a false floor comprises a quadrilateral pre-cast slab of concrete or the like, characterised by the provision of a line of weakness in the slab, the line of weakness being located along a diagonal of the quadrilateral slab. The line of weakness may be formed by the provision of a groove extending along a diagonal of the slab, or by any other suitable construction. Preferably, for ease of construction of false floors over substantial areas, the quadrilateral shape will be a parallelogram. The most useful shapes are the rectangle, square and rhombus. Also, according to a second aspect of the present invention, a slab for use in the construction of a false floor comprises a pair of slabs, each slab having the shape of a triangle, said slabs being joined along a corresponding side by a flexible joint. The flexible joint may comprise a hinge construction. Typically, the triangular shape will be either an equilateral triangle (to produce a slab having a rhombus shape) or a right-angled triangle (to produce a slab of rectangular shape - including a square). A panel formed as a plurality of slabs, each constructed in accordance with the first or second aspect of the present invention, is a useful realisation of the present invention. These and other features of the present invention will become more apparent from the following description of embodiments of the present invention, in which reference will be made to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of one embodiment of a floor slab constructed in accordance with the first aspect of the present invention. Figure 2 is a sectional view at II-II of the floor slab of Figure 1. Figure 3 shows, using a schematic sectional view at III-III of the slab of Figure 1, the mounting of the slab of Figure 1 on a planar floor, using support columns of equal height. Figures 4 and 5 are similar drawings to Figure 3, illustrating the way in which the slab of Figure 1 yields when the floor above which it is mounted is not planar and/or the support columns are not of equal height. Figure 6 is a perspective sketch of another embodiment of the first aspect of the present invention. Figure 7 is a view (similar to that of Figure 2) of the slab of Figure 6. Figure 8 is a perspective sketch of an embodiment of the second aspect of the present invention. Figure 9 is a sectional view of the slab of Figure 8, taken at the diagonal of the slab which is transverse to the adjacent sides of the two triangular slabs which form the composite slab of Figure 8. Figures 10, 11 and 12 illustrate panels which have been constructed as an assemblage of slabs having the features of the present invention. Figures 13 and 14 are sectional views, partly schematic, in the direction X-X of Figure 10, showing alternative constructions of the panel of Figure 10. - 6 - DETAILED DESCRIPTIONS OF ILLUSTRATED EMBODIMENTS The floor slab 10 shown in Figures 1 and 2 is substantially square (a square being one example of a rectangle, which is a particular form of parallelogram, which is a preferred form of the quadrilateral shape of the present invention). It has a groove or slot 11 formed along one diagonal, which creates a line of weakness in the slab along this diagonal. Typically, the slab 10 will be of pre-cast, reinforced concrete, and will be a square having sides of 500mm or 600mm and a thickness in the range from 20 to 40mm. In such slabs the reinforcing mesh 12 (see Figure 2) will normally be positioned about 2 or 3mm from the bottom surface of the slab and the groove 11 will extend from the upper surface of the slab to about 1mm above the top of the reinforcing material 12. These dimensions are not limiting. The groove 11 may be created by including a strip of particle board or similar material in the mould for the slab when the concrete is poured into the mould. With this approach, strength for the slab may be provided by a strong membrane attached (for example, by gluing) to the top of this particle board strip, instead of by reinforcement in the concrete. The particle board remains in the groove or slot 11. A convenient way of forming an open groove 11 is to stretch a tape, having a thickness of 1mm, across the mould for the slab after the reinforcing mesh has been positioned and before the concrete is poured. After the slab has been cast with the tape in this position, the tape can be removed, thus creating groove 11. ~ Another technique for forming the groove or slot 11 is to provide an extending thin flange or knife edge on the lower surface of the press that is used to compact the concrete in the mould for the slab (most slabs will be formed using a pressure compaction process). When the compaction of the slab is effected, the projecting flange or knife edge creates the groove or slot 11 in the slab. Other techniques may be used to form the slot or groove 11. 5 The slab 10 shown in Figures 1 and 2 has two preferred, but optional, features. These are the _ chamfer 13 on the slab at each end of the groove or slot 11, and the provision of one or more small holes 14 in the side walls. 0 The chamfer at the corner of the slab is preferred to reduce the possibility of a weakness to abrasion at the acute angle formed by an edge of the slab and the contiguous inside face of the groove 11. When all the slabs have a chamfer 13 on the corners at the 5 ends of the slot or groove 11, and the slabs are assembled such that the slots or grooves 11 of four adjoining slabs come to a single point, a square hole is formed at that point. (If the chamfer is not at right angles to the direction of slot 11, the hole at this point will have a non-square, polygon shape.) This hole can be filled with a plug of resilient material (such as PVC, rubber or neoprene). Preferably, the plug used for this purpose has a cross-section which matches the shape of the hole, and has a slight taper so that it has to be tamped into position (to assist in securing the assembled slabs in their required locations). If the plug is longer than the thickness of the slab, the top of the plug can be cut off flush with the top of the assembled slabs. If the plug contains metal wires or is otherwise manufactured so that it conducts electricity, it can be used to remove unwanted static electricity from a carpet or other floor covering laid on top of the false floor formed by the assembled slabs. For this purpose, the plugs will have to contact earthed conductors on the top of the supporting columns for the assembled false floor. The holes 14 in the sides of the slabs are provided to enable small resilient plugs, inserted into the holes, to form connections between the adjacent faces of assembled tiles (which also assists in securing the assembled slabs in their required positions). As shown in Figure 3, when a floor 16 is planar and the support columns 15 for the slabs of a false floor are of uniform height, the slabs 10 will be supported evenly at their four corners, in the same manner as a conventional floor slab would be supported. However, as shown in Figures 4 and 5, when the tops of the - 9 - supporting columns 15 do not all lie in the same plane, and pressure is applied to the top of a slab 10, it will deform until all its four corners are supported on the columns 15. Because the slab 10 is rigidly constructed, this deformation requires the slab to crack along its diagonal line of weakness, as shown at reference 17 in Figures 4 and 5. With such deformation or yielding of the slab, the width of the slot 11 will either increase (as shown in Figure 4) or decrease (see Figure 5). Thus, for most practical purposes, the slot or groove 11 should be at least 1mm in width. It will be appreciated that the reinforcing material 12 used in pre-cast concrete slabs of this type has to be chosen with reference to (a) the thickness of the slab (which effectively becomes a tile when it is thin), (b) the location of the reinforcing material within the slab or tile, and (c) the load capacity of the slab or tile. The selection of the type and location of the reinforcing material is an engineering exercise which persons of skill in this art can readily perform. If, as a consequence of the chosen reinforcement material, the slab or tile becomes too stiff to flex and crack as shown in Figures 4 and 5, the reinforcing material may have to be weakened immediately below the diagonal slot or groove 11 in the slab or tile. This can be effected, when a wire mesh is used for reinforcing, by cutting through (or partially cutting through) at least some of the mesh wires that lie directly underneath the slot or groove 11. When using a reinforcing mesh 12 in the slabs or tiles of the present invention, it has been found to be advantageous to locate the mesh approximately 2 mm clear of the underside of the slab or tile. If the tensional reinforcement could be located closer to the underside of the slab, then either the tension forces that oppose the flexing of the slab are increased, or a smaller gauge of reinforcing material may be used to provide a slab with the same torsional strength. To locate a torsional reinforcement at the bottom of the slab, a reinforcing mesh with lugs on its uppermost side, able to be bonded into the concrete of the slab, is preferred. Alternatively, a mesh formed from flat wires which are twisted into the vertical plane between each cross-wire (thus increasing the area that is bonded to the concrete) may be used. Such special types of reinforcement mesh, however, add to the cost of production of the slab or tile, and the additional cost of fabricating such special reinforcement mesh can be counterbalanced by ensuring that a conventional mesh is located at the correct height in the concrete. The reinforcement of the slab or tile may be achieved by using a mesh or other structure fabricated from a polycarbonate or other strong plastics material, instead of the conventional steel mesh. An alternative slab construction to that described above is illustrated in Figures 6 and 7. In this embodiment of the present invention, the slab or tile 60 is formed as a concrete block 61 which is bonded to the top of a tray 63 which forms the base of the slab or tile. The tray may be a steel tray, or it may be formed from a polycarbonate material or from another strong plastics material. The tray 63 may be deformed or have lugs projecting upwardly from it to key into the concrete block 61. In this embodiment of the present invention, the diagonal line of weakness of the slab or tile 60 can be created by providing the groove or slot 62 in the cast material. Additionally, or alternatively, the tray 63 can be weakened along the line of a diagonal, or the tray 63 can be formed as two triangular metal dishes, bonded together by fabric (for example, reinforcing mesh) in the concrete block 61 (the groove or slot 62 may then become an optional feature, depending on the strength of the slab and the use to which it is to be put). The weakening of the tray along a diagonal may be achieved by cutting into the tray along the line of the diagonal, by forming a series of incisions in the tray along the line of the diagonal, by forming a series of holes along the line of the diagonal, or by deforming the tray to create an upwardly-extending ridge along the line of the diagonal. Another way of constructing a slab in accordance with the first aspect of the present invention is to construct a shell of a plastics material in the required shape of the slab, and subsequently to inject lightweight concrete or other suitable material into the shell. The line of weakness in the slab can be formed in the plastic shell in the same way as the line of weakness may be created in the tray 63 of the embodiment of Figure 6. Instead of using a plastics material, the shell may be constructed by spot welding an upper and a lower steel tray, to form the shape of the slab. Yet another way of constructing a slab in accordance with the first aspect of the present invention is to cast a slab of lightweight concrete or other suitable material, then to mould a shell of a strong plastics material around all or part of the cast material. Again, the diagonal line of weakness can be created, in the moulded plastic coat, by any one of the techniques that may be used to weaken the tray 63 of the embodiment illustrated in Figure 6. The embodiment of the second aspect of the present invention, shown in Figures 8 and 9, comprises a pair of right-angled triangular slabs or tiles 80 joined along their adjacent hypotenuses by a hinge or flexible joint 81. The joint 81 may be of any flexible material - including metal - and may conveniently be incorporated into the slab or tile during the simultaneous casting of the blocks 80. The joint 81 may be replaced by a suitable hinge construction. In the slab or tile illustrated in Figure 8, there is chamfer 83 at each corner of the slabs 80 which are at the end of joint 81, and a series of holes 84 in the side walls of the blocks 80. The chamfer 83 and the holes 84 perform the same functions as the chamfer 13 and holes 14 of the slab or tile 10 of Figure 1. Thus no further explanation of these features is required. In the illustrated embodiments of the invention that have been considered so far, the slab or tile has been square or substantially square. As recited earlier in this specification, other quadrilateral shapes, including a rhombus, may be used for the slabs or tiles. Some (or all) of the slabs or tiles used in a false floor may be provided with a small, covered opening, through which conduits and wiring may pass to the sub-floor space, and through which ther_e is an access to the cavity formed beneath the false floor. A modification of the present invention is the production of a composite panel comprising an assemblage of slabs or tiles which are constructed in accordance with the present invention. Two examples of this modification are illustrated in, respectively, Figures 10 and 11. Figure 10 consists of a panel for use in the construction of a false floor which comprises nine square slabs. Typically, the panel is a square of side length 500mm or 600mm, and contains nine square slabs, each having a side dimension of about 200mm and a diagonal line of weakness 101. The line of weakness may be established by any suitable technique described above. In the illustrated embodiment of Figure 10, on the underside of each triangular slab portion, there is provided, at each corner, a leg 102 (see Figures 13 and 14). The legs may be moulded with the slab or attached to it later. In an alternative arrangement (not illustrated), each triangular section is provided with a single leg or support column at one of its corners, and solid dowel bonding is used to connect the corners of the triangle remote from the leg-carrying corner to the corresponding corners of the adjacent triangle. A layer of floor covering material (for example, carpet, as shown at 106 in Figure 14) may be bonded to the top of individual slabs of the panel to act as a binding membrane for the slabs and to provide a flexible bonding between adjacent triangular sections. An edge strip 105 is usually provided around the side of each composite panel. Similar considerations apply to the panel illustrated on Figure 11, which is equivalent to an assemblage of small triangular slabs. Figure 12 shows how three rhombus-shaped slabs, constructed in accordance with the present invention, with each triangular portion 120 of a slab connected to its adjacent triangular portions by hinges 121, and with supports 122 at each corner of a triangular portion 120, form a composite hexagonal panel. The advantage of hexagonal panels is that when they are used to construct a false floor, portions of the floor can be removed to provide access to the sub-floor and the buttressing (that is, the lateral thrust) of the remaining panels ensures that these panels do not move sideways to close or reduce the opening to the sub-floor. This "closing" phenomenum is often experienced with conventional false floor constructions, and is known as "creep" in computer floors. It will be appreciated that "creep" makes it difficult to replace floor panels, and can endanger the stability of a false floor. With panels of the type shown in Figures 10, 11 and 12, having a side length in the range from 150mm (in the case of a hexagonal panel) to 600mm (square or rectangular panels), it is possible to reduce the thickness of each triangular component of the panel to about 6mm. If the legs 102 and 122 give a sub-floor clearance of about 12mm, an overall height for the false floor is about 18mm. This arrangement is particularly suitable for use in buildings where the floor to ceiling height is about 2.4 metres. A convenient method of constructing panels of the type illustrated in Figures 10, 11 and 12 is to mould the panels in one piece, using a rigid plastics material (or a metal). The edges adjoining each rigid triangular portion are formed as thin strips of material by any suitable pressing technique. The thickness of each of these thin strips is such that it will flex and yet remain integrated with the triangular portions it connects. INDUSTRIAL APPLICATION OF THE INVENTION The major applications of the present invention have been mentioned already in the first paragraph of this specification. It may be noted that, when buildings are constructed, the extent to which a floor may depart from being flat is recognised throughout the world by the standards laid down by each country. In Australia, for example, the standards laid down in AS 1480-1982 and AS 1509-1974 result in a requirement that a concrete floor in an office block must be flat to within 25 mm in a distance of 7.3 metres when the formwork is removed from the floor. Subsequently, some creep deflection of the cast floor is likely. Observations of office buildings in general use have shown that a departure from flatness of 50mm in 7.3 metres is acceptable to tenants of the office buildings. A square slab of side 500mm, constructed as shown in Figure 1, with a diagonal groove 11 of width 1mm, is able to provide a stable false floor above such a cast concrete floor. It will be appreciated by civil engineers that the present invention is particularly suited for the construction of false floors over curved shapes such as domes, or over the surface formed by the intersection of inclined planes. When used to provide a protective surface or a sound-isolating surface, the joints between the assembled slabs will usually be filled with a jointing strip, mastick material, putty or the like. A floor covering (such as carpet) may be laid on top of a false floor formed by an assembly of the slabs of the present invention. The floor covering may be bonded to the false floor by adhesive, or by using mechanical clips (such as plastic plugs).

Claims: - 18 - CLAIMS A slab or tile (10, 60) for use in the construction of a false floor comprising a quadrilateral pre-cast slab of concrete or the like, characterised in that the pre-cast slab of concrete or the like has a line of weakness located along a diagonal of the quadrilateral shape. A slab or tile as defined in claim 1, in which said quadrilateral is a parallelogram, and said line of weakness is formed by a slot or groove (11) formed in said concrete slab. A slab or tile as defined in claim 2, in which reinforcing means (12) is included in said concrete slab. A slab or tile as defined in claim 3, in which said slot or groove (11) extends from the top surface of the slab or tile (10) to about 1mm above said reinforcing means (12), and said reinforcing means (12) comprises a mesh which is located above the base of the slab or tile at a distance therefrom in the range from 2mm to 3mm. A slab or tile as defined in claim 3, in which said reinforcing means is located at the base of the slab or tile. 6. A slab or tile as defined in claim 5, in which the reinforcing means comprises a reinforcing mesh with upwardly projecting lugs. 7. A slab or tile as defined in claim 5, in which said reinforcing means comprises a reinforcing mesh formed from flat wire, said flat wire being twisted between cross-wires to increase the surface area of the mesh in a plane perpendicular to the plane of the mesh. 8. A slab or tile as defined in any one of claims 3 to 7, in which said reinforcing means is weakened along said diagonal line of weakness. 9. A slab or tile as defined in any one of claims 2 to 8, further characterised in that said slab or tile has a chamfer (13) at its corners which are located at ' the end of the diagonal line of weakness. 10. A slab or tile (60) as defined in claim 1, further characterised in that said quadrilateral is a parallelogram and said slab of pre-cast concrete or the like is cast upon a metal tray (63). 11. A slab or tile (60) as defined in claim 10, in which said line of weakness is formed by a slot or groove (62) formed in said concrete slab. - 20 - 12. A slab or tile (60) as defined in claim 10 or claim 11, in which said metal tray (63) is provided with a structural weakness along said line of weakness. 13. A slab or tile (60) as defined in claim 12, in which the structural weakness in said metal tray (63) comprises an incision (65), or a line of holes, or a ridged region of said metal tray. 14. A slab or tile (60) as defined in claim 1, in which said quadrilateral is a parallelogram, and said slab of pre-cast concrete or the like is cast upon a pair of triangular metal trays, each of said triangular metal trays having a side adjacent to and parallel to a corresponding side of the other metal tray, whereby said diagonal line of weakness is formed at the region between the adjacent sides of said triangular metal trays. 15. A slab or tile as defined in claim 14, having a slot or groove formed in the concrete or like material along said diagonal line of weakness. 16. A slab or tile as defined in claim 14 or claim 15, including a reinforcing means extending across said diagonal line of weakness. 17. A slab or tile as defined in any one of claims 2 to 16, in which said parallelogram is a rectangle, a square or a rhombus. - 21 - 18. A slab or tile for use in the construction of a false floor, comprising, in combination, a) a pair of triangular slabs (80) of pre-cast concrete or the like, one side of each of said slabs (80) being adjacent to and parallel to a corresponding side of the other of said slabs; and b) a flexible joint (81) extending between said adjacent and parallel corresponding sides, of said slabs. 19. A slab or tile as defined in claim 18, in which each of said triangular slabs (80) has the shape of a right-angled triangle and said adjacent sides are the hypotenuses of the right-angled triangles. 20. A slab or tile as defined in claim 18 or claim 19, in which said flexible joint comprises a hinge. 21. A slab or tile as defined in any one of claims 2 to 20, including at least one hole (14, 64, 84) formed in each side wall of the slab or tile, for receiving a flexible plug. 22. A slab or tile as defined in claim 1, in which the pre-cast slab of concrete or the like is located within a shell, and the line of weakness is created in said shell. 23. A false floor formed by an assemblage of slabs or tiles as defined in any preceding claim, said assemblage of slabs or tiles being mounted on support columns (15) or the like positioned at the corners of the slabs in the assemblage. 24. A panel for a false floor, comprising a plurality of interconnected slabs or tiles, as defined in any one of claims 1 to 22. 25. A panel as defined in claim 24, in which each slab or tile in the panel has two triangular portions, and each triangular portion has a supporting leg (102) under each of its corners. 26. A panel as defined in claim 24, in which each slab " or tile in the panel has two triangular portions, and each triangular portion is provided with a leg under one corner thereof, and the other corners ' of each triangular portion are connected to the respective adjacent corners of adjoining triangular portions by solid dowels. 27. A panel as defined in claim 24, claim 25 or claim 26, in which the panel has a hexagonal shape. 28. A false floor formed by an assemblage of panels as defined in any one of claims 24 to 27.

Inventors: MATTHEWS WILLIAM JOHN, MATTHEWS, WILLIAM, JOHN
Applicants: MATTHEWS WILLIAM JOHN, MATTHEWS, WILLIAM, JOHN
Application year: 1985
Main classification: E04B5
IPC codes: E04F15