IMPROVED FLOORING PANELS

The present invention relates to flooring panels, particularly for buildings.

Many modern buildings are constructed with a framework of steel or reinforced concrete columns supporting horizontal beams at the level of each floor. Floor panels are then placed on or made composite with the beams to form each floor. The floor panels may be of the order of 10m by 2.5m so that four panels fill a square 10m by 10m bay in the frame and are connected to each other or the beams at their edges and ends.

Conventionally such floor panels have been made of reinforced or prestressed concrete, though proposals to use pultruded fibre-reinforced composites have also been made. Floors may also be cast in place with concrete or made of composite construction such as a preformed metal deck with a concrete finishing slab. Concrete floor panels of this type are heavy, increasing the load that must be bourne by the framework, and up to 30cm thick, reducing the number of floors, and hence usable area, that can be achieved in a given height of building.

Structural sandwich plate members are described in US 5,778,813 and US 6,050,208, which documents are hereby incorporated by reference, and comprise outer metal, e.g. steel, plates bonded together with an intermediate elastomer core, e.g. of unfoamed polyurethane.

These sandwich plate systems may be used in many forms of construction to replace stiffened steel plates, formed steel plates, reinforced concrete or composite steel-concrete structures and greatly simplify the resultant structures, improving strength and structural performance (e.g. stiffness, damping characteristics) while saving weight. Further developments of these structural sandwich plate members are described in

WO 01/32414, also incorporated hereby by reference. As described therein, hollow or solid forms may be incorporated in the core layer to reduce weight and transverse metal shear plates may be added to improve stiffness. Hollow forms generate a greater weight reduction than solid forms and are therefore often advantageous. The forms may be made of lightweight foam material or other materials such as wood or steel boxes, plastic extruded

shapes and hollow plastic spheres.

Where floor panels, especially of concrete, are cast in place, until the floor panels have set, they do not have any structural strength. Thus, the framework that is constructed first must be designed so as to be able to support the dead load of the flooring system and additional framework or shuttering to support the concrete before it curves. Thus, in some cases, the framework of a building needs to be constructed to have a strength greater than is ultimately required in the finished building. This of course increases costs and delays construction of the building. It would therefore be desirable to provide a flooring system for a building taking up its full strength immediately upon installation.

It is an aim of the present invention to provide a structural sandwich plate member that is particularly well-suited to use in floors of buildings.

According to the present invention, there is provided a structural sandwich panel comprising first and second outer metal plates, an edge member fixed between the outer metal plates in an edge of the panel and a core bonded to the outer metal plates and arranged to transfer shear forces therebetween, wherein the edge member comprises: an inner part fixed between the outer metal plates; and an outer part projecting beyond the outer metal plates and having a plurality of through-holes therein arranged to receive respective bolts to fix the panel to another structure. By bolting pre-fabricated floor panels via preformed holes in projecting edge members to suitable points on the building framework, the flooring system can immediately take up its structural function, without imposing a significant dead load on the structure and also taking advantage of the features of structural sandwich panels or plate members. This therefore both speeds construction and avoids the need to construct the building framework so as to be able to bear a significant dead load prior to installation of the flooring system.

The floor panels can be fabricated on site or, desirably off-site in factory conditions. The latter may increase accuracy and enable manufacture of the flooring panels to proceed in parallel with erection of the framework.

The materials, dimensions and general properties of the outer plates of the structural sandwich plate member of the invention may be chosen as desired for the particular use to

which the structural sandwich plate member is to be put and in general may be as described in US-5,778,813 and US-6,050,208. Steel or stainless steel is commonly used in thicknesses of 0.5 to 20mm and aluminium may be used where light weight is desirable. Similarly, the plastics or polymer core may be any suitable material, for example an elastomer such as polyurethane, as described in US-5,778,813 and US-6,050,208 and is preferably compact, i.e. not a foam. The core is preferably a thermosetting material rather than thermoplastic.

The present invention will be described below with reference to exemplary embodiments and the accompanying schematic drawings, in which: Figure 1 is a cross-sectional view showing the connection of structural sandwich plate members according to an embodiment of the present invention to a beam;

Figure 2 is a cross-sectional view showing the connection of structural sandwich plate members according to another embodiment of the present invention to a beam;

Figure 3 is a cross-sectional view showing a structural sandwich plate member according to another embodiment of the present invention mounted to a beam and supporting a curtain wall;

Figure 4 is a cross-sectional view showing another connection of two structural sandwich plate members according to an embodiment of the present invention; and

Figure 5 is a flow diagram of a method of manufacturing a building according to the invention.

In the various drawings, like parts are indicated by like reference numerals.

Figure 1 shows two floor panels 10a, 10b according to embodiments of the invention bolted via edge members 20 to a beam 40 forming part of the framework of a building. The building may be any form of building constructed with a structural framework that supports a flooring system and curtain walls. The present invention is particularly applicable in buildings such as office blocks, apartment blocks, shopping centres (malls) or the like and may also be used in off-shore structures. As a floor panel, the plate preferably presents a generally flat upper surface but the lower surface need not be flat and either or both surfaces may be provided with recesses, trenches, grooves or openings to accommodate utility

conduits and outlets. Both vertical and horizontal passages may also be provided within the floor panel for utility conduits.

Each floor panel 10a, 10b shown in Figure 1 is a structural sandwich plate member that comprises upper and lower outer plates (faceplates) 11, 12 which may be of steel or aluminium and have a thickness, for example, in the range of from 3 to 8mm, more preferably 3 to 5mm. Edge members 20, described further below, are provided between the face plates 11, 12 around their outer peripheries to form a closed cavity. In the cavity between the face plates 11, 12 is a core 13, described further below. This core may have a thickness in the range of from 15 to 200mm; in many applications 25 to 55mm is preferable. The overall dimensions of the plate member in plan may be from 2 to 4m width by 8 to 10m length. A preferred size is 3m by 9m. Plate members may be made in standard sizes or tailor-made to specific shapes and/or dimensions.

The core 13 may take various different forms but its major structural component is a main core layer 14 of plastics or polymer material (preferably a thermoset, compact elastomer such as polyurethane as discussed above) which is bonded to the face plates 11, 12 with sufficient strength and has sufficient mechanical properties to transfer shear forces expected in use. The bond strength between the layer 14 and face plates 11, 12 should be greater than 3MPa, preferably greater than 6MPa, and the modulus of elasticity of the core material should be greater than 200MPa, preferably greater than 250MPa. For low load applications, where the typical use and occupancy loads are of the order of 1.4kPa to 7.2kPa, the bond strength may be lower, e.g. approximately 1.0MPa, but sufficient to provide the required resistance, based on safety indices associated with construction for all anticipated loads, including use and occupancy loads, construction loads and wind, earthquake and temperature loads. In this embodiment, the core 13 also includes a plurality of hollow box-shaped forms

15 enclosing voids 16. The size and material of the forms 15 are chosen so that the overall density of the forms is lower than the density of the material of the main core, preferably less than 50% of the density of the material of the core layer 14, or preferably less than 25% and most preferably less than 10%. The purpose of the forms 15 is essentially to take up space within the core and thus reduce the amount of the main core material required whilst

maintaining or even increasing the desired spacing between faceplates 11 and 12. This reduces cost both directly as the forms are less expensive by volume than the main core material and secondly because the weight of the panels is reduced which may enable savings in the building's framework. The forms 15 do not need to contribute to the overall structural strength of the floor panel 10a, 10b but if the floor panel 10a, 10 is formed by injection of the main core layer 14, the forms 15 must have physical properties sufficient to withstand pressures and temperatures arising during casting and curing of the main core layer 14. The size, shape and distribution of forms 15 within the core is chosen so that a sufficient number of ribs and/or columns of main core layer material extend between and bond to faceplates 11 and 12 at regular intervals across the length and width of the member 10a, 10b. If the forms

15 run continuously along or across plate members, they may also be used for utility conduits or air ducting. The forms 15 do not have to be hollow, e.g. if made of a suitable lightweight material such as a foam, or may be filled with lightweight material, which may be insulating and/or fire resistant. A particularly useful material for the forms is expanded polystyrene, having a density of 20-40g/l, which may be provided, e.g., either as spheres or ribs.

In a further alternative (not shown) the inner part of the core 13 is a corrugated metal, e.g. steel, plate with the corrugations at least partly filled by a foam or other lightweight filler material. Preferably the corrugations are substantially completely filled so that the inner core, comprising corrugated plate and filler material, presents substantially flat outer surfaces. The corrugated plate may have embossments or openings to increase composite action with the foam or elastomer bonded to it. The filler material need not contribute significantly to the strength of the panel and hence many materials are suitable. It should be of lower density than the material of the main core layer 14, preferably less than 50% of the density of the material of the main core layer 14, more preferably less than 25% and most preferably less than 10%. Both open and closed cell foams may be used but if the panel is manufactured by injection (see below) closed cell foams may be preferred to limit ingress of the material of the main core layer 14 and in such cases it is desirable that the filler material have sufficient strength to substantially maintain its shape during the casting process. A suitable filter material is polypropylene foam with a density of from 40 to 50 kg/m ³ . The

filler material is preferably cast onto the corrugated steel plate. Also, preformed foam sections may be glued to the corrugated metal plate. The filler material preferably contains fire retardants so that it does not ignite under fire conditions mandated by relevant building codes. Other materials, such as a ceramic coating, may be inserted into the core or bonded to the corrugated metal plate to act as a thermal break, thereby increasing the fire resistance of the plate member.

The corrugated plate and filler are arranged so that on the major faces of the inner part of the core, parts of the corrugated plate are exposed and bonded to the main core layer 14 with similar strength to the bond between the main core layer and the faceplates. The total area of the exposed parts of the corrugated plate on each of the major faces is sufficient to transfer shear forces from either faceplate through the elastomer to the corrugated metal plate and to stabilise the faceplate to prevent local buckling. The total area is preferably in the range of from 10 to 45% of the total area of the face, more preferably in the range of from 20 to 40% and most preferably in the range of 25 to 35%. If the panel is elongate, corrugations of the corrugated plate preferably extend substantially parallel to the longest dimension of the panel. The exposed parts are in that case elongate strips and may have a width in the plane parallel to the major faces of the panel in the range of from 50mm to 200mm.

The corrugated plate may have a thickness in the range of from 0.5mm to 5mm and may be perforated, especially in the webs b, to facilitate casting of the filler material onto the corrugated plate. Surface treatments, such as adhesives, roughening, cleaning or embossing, may be applied to the corrugated metal plate to enhance its bond to the main core layer 13 and/or the filler material. The main core layer, each side of the inner core, preferably has a thickness of 10mm or more and may have a thickness of between 10 and 25% of the total core thickness.

Edge members 20 are provided in at least one, or preferably two edges of floor panels 10a, 10b. In the case where a floor panel is mounted at opposite ends to respective girders of the framework, for example where the floor panel is in the middle of a bay, edge members 20 are provided in the opposite short ends of the panel. Where the panel is to be mounted to girders of the framework along three or four sides, e.g. where the panel is at the edge of a

bay or fills a bay on its own, edge members 20 may be provided on three or four sides of the panel. Floor panels in the middle of a bay may be provided in their long edges with edge members of different design that facilitate inter-connection of floor panels, e.g. by bolting. An example of such an edge member is described below. Edge member 20 is a solid bar of metal having a generally rectangular cross-section.

One edge of the edge member 20 is thinned so that when this edge is fitted between the face plates 11, 12 of a plate member 10a, 10b, the outer faces of faceplates 11, 12 and the edge member 20 are substantially flush. Note that in Figure 1 the sandwich plate members 10a, 10b have a thickness in their main parts substantially greater than the thickness of the edge member 20 but an angle plate 12a forming an extension to lower faceplate 12 reduces the effective thickness of sandwich plate members 10a, 10b at their edges to be substantially the same as the thickness of the edge member 20.

Spaced along the length of edge member 20 are a plurality of recesses 21 and through-holes 22 by which the sandwich plate members 10a, 10b are fixed using bolts 34 and nuts 35 to corresponding holes in the flange 41 of a girder 40 forming part of the framework of the building. The through-holes in the edge member and flange may be slightly oversized to accommodate any fabrication errors: in a preferred embodiment the through-hole 22 in the edge member 20 is elongate in a first direction and the through-hole 42 in the flange 41 is elongate in a perpendicular direction. The recess 21 are sufficiently large to accommodate the head of bolt 34 and a tool required to tighten it. Recess 21 should also be sufficiently deep to accommodate the full height of the head of bolt 34. After installation of the panels, the recess 21 may be filled in with a suitable filler, or covered by a plate or whatever architectural floor covering is to be used in the building. The spacing and number and size of bolts required to fix the sandwich plate member floor panels 10a is determined by the expected loads. Standard bolts or tension control bolts may be used.

As illustrated in Figure 1, two sandwich plate floor panels 10a, 10b are fixed to a girder 40, one to either side. Any resulting space between edge members 20 for the two panels may be filled with an expansion joint filler 37 of conventional type. Angle irons 42 may be attached, by any convenient manner, to vertical pillars of the building framework to provide additional support to the floor panels 10a, 10b if required or desired.

Figure 2 shows the edge members 20 used to connect alternative floor panels 10'a, lO'b according to another embodiment of the invention to a girder 40 in essentially the same manner. Floor panels lO'a, lO'b are the same as the panels described above save as discussed below. The alternative floor panels lO'a, lO'b are substantially thinner than panels 10a, 10b and may, for example, have a core that is wholly formed of the main core layer 14 or a core partially filled with hollow forms 17, e.g. in the form of polypropylene spheres. This form of core is sometimes known as bubble core and is further described in WO 2005/051645, which document is hereby incorporated in its entirety by reference.

In an embodiment, the forms 17 comprise hollow, solid skin polypropylene balls having a diameter substantially equal to the distance D between the outer plates 11, 12. The balls 17 may be arranged in orthogonal rows and columns so that substantial gaps are left between them. This arrangement of forms is particularly appropriate where the major loads in use are directed along the lateral and longitudinal directions. These gaps fill with core material which bonds the outer metal plates together. Because of the curvature of the balls, the core material forms column-like structures extending directly between the outer plates and bonded to the plates over a wide area. Thus the bond strength compared to a solid core is reduced by no more than about 5% and the shear transfer capability is maintained.

The balls 17 may also be closely packed in a hexagonal array. This results in a higher floor panel as the proportion of the core cavity that is occupied by the main core layer 14 is reduced. This arrangement is also particularly suited to applications in which the major loads will lie on oblique directions. The balls 17 may naturally fall in this configuration so reducing manufacturing costs.

Two layers or more of balls may also be used. This enables a thicker floor panel to be made without increasing the spacing of the column-like structures of the core. Preferably, the balls of one layer overly the balls of the other layer but in lower load applications the balls may be close packed in the vertical direction as well as in the horizontal direction. The different layers of forms need not all be the same, however it is preferred that there are 5 or fewer layers.

In general, the forms 17 should not tesselate in a plane parallel to said outer metal layers and have principal dimensions in the range of from 20 to 200% of the distance

between said outer metal layers. The term "principal dimensions" is intended to refer to the diameter of a sphere, the major and minor diameters of an ovoid, the length, depth and breadth of a cuboid, etc.. In the case of irregular shapes, the principal dimensions may be regarded as the dimensions of the smallest rectangular box in which the shape will fit. By using forms that are comparable in dimensions to the gap between the metal layers, and hence relatively small compared to the lateral dimension (length and/or width) of the plate member, any shape of plate can be manufactured using standard mass-produced forms, without the need for hand adaptation. The exact shape of the form is not crucial in many cases, though additional advantages can be obtained with specific shapes. It is required that the forms do not tesselate so that there are spaces between them for the core material which bonds to the outer plates. The shape and arrangement of the forms can be varied to vary the proportion of the volume between the outer plates that is occupied by core material.

The forms may be arranged in a single layer or multiple layers. In the case of multiple layers, it is preferred in some applications that the forms of one layer directly overly the forms of the layer below so that there are parts of the core material extending perpendicularly between the outer metal layers. Where there are multiple layers of forms, an interlayer may be provided between the layers of forms. The layer may be made of a high tensile strength material such as metal, a high tensile strength fabric, such as Kevlar(TM) or Spectra(TM), fibre reinforced plastic, other suitable fabrics, mesh or ceramic sheets to improve the blast and/or ballistic resistance of the plate member. The layer may be perforated or shaped to allow flow of core material throughout the core during fabrication and to enhance the shear strength between the layers. The layer may also be used to assist the placing of the forms - e.g. to determine the spacing between layers or the relative positions of the forms in different layers - and thereby enhance the performance of the plate member.

A particularly preferred form is a spherical hollow ball having a diameter substantially equal to 1/N of the distance between said outer metal layers, N being a natural number between 1 and 5. The balls may for example have a diameter in the range of from 20 to 100mm and can be used in single or multiple layers in plate members with core

thicknesses in the range of from 20 to 100mm. Balls made of polypropylene are particularly suitable and may be solid or preferably hollow with a solid skin. Solid balls provide less weight reduction but may still be advantageous as they are cheaper than the elastomers preferred as the main core material. Such balls are widely available and cheap to manufacture.

The forms may also be provided with a plurality of protrusions so as to increase the spacing between the forms, and hence the proportion of the core cavity occupied by core material. The protrusions may also be arranged to determine the relative shapes and positions adopted by adjacent forms and hence the shape of the void space that is filled by core material, e..g. to ensure a continuous mass of core material. A mesh, e.g of wire, may be used to assist the placing of the forms and space them apart from each other and/or from the metal layers.

A floor panel according to an embodiment of the invention that lies along the edge of a building can be arranged to project over a supporting beam and support a curtain wall. This provides a convenient way of providing a desired contour to the outside of the building through the use of floor panels of custom shapes. An arrangement to effect this is shown in Figure 3.

Floor panel 10c comprises upper and lower faceplates 11, 12 and a core 13 which may be solid or provided with forms as in any of the above described embodiments. It is mounted to girder 40 and extends outwardly of girder 40 (to the left in Figure 3) to provide a cantilevered section that supports curtain wall 50. It will be appreciated that the core 13 may differ between the cantilevered sections and internal section to meet different structural requirements. For instance, in the internal section of the floor panel the core 13 may be provided with forms whereas in the cantilevered section it may be solid to provide additional rigidity.

To fix the floor panel 10c to the girder 40, a plurality of cylindrical inserts 26 are provided in the panel 10c, extending between upper and lower faceplates 11, 12. Each insert 26 has a through-hole to receive bolt 34 and a recess 27 on its upper side to receive the head of bolt 34 and the tool required to tighten it. Bolts 34 fix the panel 10c through corresponding through-holes in the flange 41 of girder 40. As before, the through-holes in

the insert 26 and the web 41 may be oversized to accommodate manufacturing errors, e.g. by being elongate in perpendicular directions. In an embodiment, the line of inserts 26 in floor panel 10c is staggered so that alternate inserts lie either side of web of girder 40. Inserts 27 are preferably fixed to faceplates 11, 12 by welding prior to injection of the main core layer 14 and then can also serve as spacers to support and restrain the faceplates during the injection and curing of main core layer 14. In some circumstances it may also be possible to fit the inserts 26 after casting of the main core layer 14, but in that event care will need to be taken that heat generating steps such as drilling and welding do not damage the core 13. The free end of floor panel 10c supports the curtain wall 50. To provide an aesthetically pleasing arrangement, niches 51 can be provided in the curtain wall 50 to conceal bolts 38 which fix the curtain wall to the floor panel 10c. Bolts 38 engage through metal sleeves 19 defining further through-holes through the panel 10c. As with the inserts 26, the through-holes and sleeves 19 are preferably put in place prior to injection and curing of the main core layer 14, but may also be installed afterwards. The edge member 25 shown is a simple bar defining a clean edge to the panel. However in an alternative embodiment, the edge panel may be of a type with a protrusion and through-holes so that the curtain wall 15 may be fixed to the edge member 25. A seal 52 may be provided between sections of the curtain wall 50.

Figure 4 shows in cross-section another arrangement for connecting, to each other and to a beam, two floor panels 10a, 10b according to an embodiment of the invention. In the figure, the cores of the panels 10a, 10b have been omitted for clarity.

In this arrangement, the two floor panels 10c, 10b have perimeter bars 30a, 30b in at least one edge which serve both to define the cavity for the core and provide a means for connection to adjacent panels or the building structure. Each perimeter bar 30a, 30b comprises a main part 31 which has a thickness equal to the space between the faceplates 11,

12 of the panels 10a, 10b and a width sufficient to provide a seal and a landing for the faceplates to be welded to it. The main part 31 may be approximately square in cross- section.

Integral with the main part 31 of the perimeter bar 30 is a projecting flange 32 by which the panels are corrected to each other or the structure. In an embodiment, as

illustrated, the projecting flange 32 is approximately half the thickness of the main part 31 and parallel to the plane of the panel. To enable an aligned connection between panels, all of the projecting flange 32 lies on one side of a plate bisecting the perimeter bar and parallel to its panel and preferably one face 32a of the projecting flange 32 lies on the bisecting plane. The perimeter bars 30 are installed on the panel so that on one side the projecting flange is above the bisecting plane and on the opposite side the projection flange is below the bisecting plane. Then, panels can be quickly installed by resting the projecting flange 32 of one panel on that of its neighbour. Spacers can be used between the flanges to adjust the height of one panel but this is preferably avoided by making the one face 32a of each projecting flange 32 lie accurately on the bisecting plane. A further alternative is to make perimeter bars of two different but complimentary profiles whereby the plane of connection can be located as desired.

To fix the panels together, the projecting flanges can be connected together by nuts 34, bolts 35 and washer 36 through holes 33, which may be pre-formed at specific locations or drilled in-situ. Other means of fixing the flanges together - such as rivets, welding or adhesives - may also be used.

As shown in Figure 4, a vertical plate 40, e.g. the web of a girder, may be welded to the perimeter bar. If necessary, one faceplate can be cut back to accommodate this.

A preferred method of constructing a building including floor panels according to the invention is shown in Figure 5. The manufacture of SPS panels or members Sl is preferably performed off-site and involves: placing the outer metal layers 11, 12, edge members and any forms or spacers in a mould to define a cavity; injecting liquid plastics of polymer material into the cavity through an injection port; and causing or allowing the plastics of polymer material to cure to form the main core layer 14.

After curing, the injection ports and vent holes are filled, e.g. with threaded plugs, and ground flush with the surface of the outer metal plate. It is to be noted that even if a single continuous cavity is present prior to injection, multiple injection ports and vent holes

may be provided to ensure complete filling.

If the floor panel is to be provided with recesses, grooves or openings, e.g. for utility conduits and outlets, or other surface features, such as fixing or lifting points, these are preferably formed in or on the outer metal plates prior to injection of the core. Grooves and other indentations can be formed by known techniques such as milling, cutting, bending, rolling and stamping as appropriate to the thickness of the plate and size of feature to be formed. Details can be attached by welding. Tubes to define passageways through the floor panel, e.g. for utility conduits, can be put in place prior to injection of the material to form main core layer 14. It is also possible to form such features after injection and curing of the main core layer 14, by coring for example, but in that case measures may need to be taken to ensure that the heat generated by activities such as welding does not deleteriously affect the core 13.

In some circumstances it may be possible to avoid the use of a mould by welding edge plate or perimeter bars to the outer metal plates so that the panel forms its own mould. Depending on the compressibility and resilience of the inner core, it may be necessary to provide restraints to prevent deformation of the outer metal plates due to the internal pressures experienced during injection and curing of main core layer 14.

It should be noted that after the core has cured, the faceplates and perimeter bars are bound together by the core 13 so that in some cases the fixing of the perimeter bars to the face plates need only be sufficient to withstand loads encountered during the injection and curing steps, and not necessarily loads encountered during use of the floor panel 10. To improve sealing of the cavity, gaskets or sealing strips can be provided between the edge plates or perimeter bars and face plates.

Independently of the manufacture of the panels, the construction of the building and erection S2 of the structural frame work can proceed on site. Once the framework construction has advanced to a suitable point, the floor panels can be delivered and simply bolted in place at which point they will directly contribute to the strength of the structure. With the floor panels in place, any necessary fire proofing, utilities and architectural finishes can be installed S4 to complete the building. It will be appreciated that the above description is not intended to be limiting and that

other modifications and variations fall within the scope of the present invention, which is defined by the appended claims.