Background to the Invention Access flooring systems define a space between an underlying original floor, and a suspended supporting surface. Telecommunications, computer and electrical wires, air conditioning ducting and piping and other wiring, cabling or piping systems can be positioned in this space and can be accessed as necessary.

Access floor panels need to be sufficiently strong to withstand both high human and equipment loading, yet sufficiently light that they are not cumbersome to install, or remove where cable or other access is required.

For this reason, an access floor panel basically has a metal casing surrounding a lighter fill material core.

Typically the fill material core is a timber based bonded product, or can be a natural or synthetic fibrous based bonded product which provides both strength and lightness.

In forming such access floor panels, the fill material core is positioned between an upper metal plate and a lower metal plate, and the plates are joined together to define the casing (e. g. by being clamped together along their edges, welded, glued etc.) Access floor panels can be positioned in a supporting

grid like frame located on the original floor, and which spaces the panels at a pre-determined distance above the original floor. The frame is typically formed from metal, and thus the contact between the panels and the frame is metal-to-metal contact, as is the contact between adjacent panels. This metal-to-metal contact can make the panels noisy (e. g. squeaky or scratchy), but it can also result in the panels fastening to each other or becoming fastened to the frame (e. g. through friction, cold welding, intermetallic corrosion etc).

For these reasons, panels have been produced in the art wherein the lateral or side walls are inclined, so that the region of contact between adjacent panels is along the upper edges thereof. However, because the panel side walls are inclined outwardly their load bearing capacity decreases, and eg. thicker plate sections or core material needs to be employed.

Examples of such arrangements are shown in GB213065, W099/18305 and WO01/86094. In these documents the panel comprises an outer casing comprised of a base plate with upstanding side walls and a top plate with downwardly extending side walls. The walls are joined together along each lateral side of the panel, with the resultant join forming part of the panel side wall once the panel has been formed. However, in W099/18305, both the join 17,21 and the side wall 16 are inclined inwardly with respect to the upper covering element 19.

W001/86094 discloses a similar join to W099/18305, but in this case the join 17 is located in a recess 18.

This enables the outer surface of the join to be aligned with and remain at the same level as the outer lateral surface of a folded down flap of the top plate 14, and also enables a rib profile 103 (as shown in Figure 3) to be attached along the side of the panel.

It would be advantageous if an alternative panel arrangement to those shown in GB213065, W099/18305 and WO01/86094 could be provided.

Summary of the Invention The present invention provides a panel for elevated floors comprising first and second casing elements for enclosing a core material therein to define the panel, with the first element providing an in-use panel upper casing and the second element providing an in-use panel lower casing; the first element being joined to the second element along one or more sides of the panel, wherein the join is located in a recess at the panel side such that an outwardly facing surface of the join is inset from the remainder of the panel side.

By arranging for the join to be inset in this manner, the present inventor has observed even less panel interference with a supporting frame or adjacent panel, and increased panel strength over the panel shown in eg.

W001/86094.

Preferably the join extends generally vertically in use, preferably subtending a right angle to the panel upper and lower casings. This further increases the load bearing capacity of the panel at its side walls.

Preferably the panel is arranged such that, in use, at least a major portion of the join is positioned within a lower portion of the or each side. The inventor has observed that this position of the join further improves the structural strength.

Preferably to define each panel side, the first element has an edge region extending along its side which

in use is folded downwardly, and the second element has an edge region extending along its side which in use is folded upwardly, with the respective first and second edge regions being further folded to lap over each other to define the join.

Preferably, in this regard, in use the first edge region extends downwardly and inwardly, and the second edge region extends upwardly such that, in side profile, the first edge region subtends an acute angle with respect to the panel upper casing, and the second edge region is generally orthogonal to the panel lower casing.

Preferably in forming the panel, the first edge region is bent intermediate its edges such that, in side profile, and moving down from the panel upper casing, a first bend causes the first edge region to bend further in towards the panel to subtend an even more acute angle with respect to the panel upper casing and a second bend causes an end part of the first edge region to then bend out so as to be generally orthogonal to the panel upper and lower casings.

Preferably in this regard, the generally orthogonal part of the first edge region is located adjacent to the second edge region.

Preferably end portions of both the generally orthogonal part of the first edge region and the second edge region are lapped over each other to define the join.

In this regard, the portions can be spot welded, crimped, clamped etc to further define the join.

Preferably the first and second bends combine to define the recess in the panel side, in which the join is then located.

In the finished panel, it is most preferred that a core material is positioned between the first and second elements, the core material having a profile that generally matches the interior shape of the first and second elements when joined to each other. In this regard, the core material can help in the formation of the panel, providing a substrate around which the folds and bends can be made.

Preferably the first and second elements each comprise a metal plate which is subsequently folded/bent to define the resulting panel.

The core material preferably comprises a panel core formed from wood, bonded wood chip, bonded synthetic or natural fibre, bonded calcium sulphate, gypsum fibreboard etc. and shaped to have said matching profile.

Brief description of the drawings Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a side sectional view through a panel in accordance with the present invention; Figure 2 shows a side sectional detail of the left hand end of the panel of Figure 1 but with the core removed therefrom; and Figure 3 shows a side perspective detail, similar to Figure 2, and with the core present therein.

Modes for carrying out the invention Referring to the drawings, a panel for an elevated or raised floor system is shown in the form of floor panel 10. The floor panel 10 includes a top plate 12 and a

bottom plate 14, joined to define the panel exterior (or casing). Whilst the panel can be formed simply from top and bottom plates, usually a panel core 16 is positioned between the plates and is optionally fastened thereto by an adhesive.

Typically the top and bottom plates are formed from a metal, such as galvanised or stainless steel, aluminium etc. Typically the panel core is formed from a timber based material, such as wood chip or wood fibre bound together by a suitable polymeric resin, or natural or synthetic fibres bound together by polymeric resin, or from bonded calcium sulphate or gypsum fibreboard etc.

Timber ply may also be employed, as may an appropriately shaped timber block. Typically the exterior profile of the panel core has a shape which matches the interior profile of the top and bottom plates when so joined. In addition, the panel core can be used as a supporting substrate during the formation of the floor panel, providing a surface around which the plates 12,14 can be folded/bent.

Referring specifically to Figure 2, it will be seen that top plate 12 is joined to the bottom plate 14 at a join 18. The join 18 is defined by over-lapping a free edge region 20 of the top plate with a corresponding free edge region 22 of the bottom plate. This defines a join which extends right around the lower periphery of the panel, and which functions as a reinforcing stringer.

The side wall 19 and recess R of the panel are defined as follows. A longitudinal edge zone 24 of the top plate is folded down and inwardly about a fold line 26 in the top plate so that ultimately the edge zone 24 subtends a first acute angle a with the upper part 28 of the top plate 12.

In this embodiment the bottom and lower and upper casings each comprise a single layer of steel. In this case the edge at the fold line 26 will be relatively sharp. If, for example, carpet is installed on top of the panel, sharp edges reduce the grooves that may be formed between two adjacent panels at fold line 26. This has the advantage of reduced carpet wear and tear.

A second edge zone 30 of the top plate 12 is bent further inwardly at bend 32, to partly define recess R, subtending an angle 6 with part 28. A third edge zone 34 of the top plate is defined by bending the plate back outwardly at bend 36, typically so that the third edge zone generally subtends a right angle with respect to the upper part 28 of top plate 12 and also bottom plate 14.

The free edge region 20 extends from third edge zone 34, at bend 38.

The bottom plate 14 is bent at fold line 40 to define edge zone 42, which extends generally orthogonally from the lower part 44 of bottom plate 14. The edge zone 42 is connected to the free edge region 22 by a bend 46. The free edge regions 20 and 22 are lapped over as shown.

The resulting join 18 can be strengthened by bonding the regions 20,22 and zones 34 and 42 together (e. g. using adhesive or welding) or by clamping or crimping those zones. However, the top and bottom plates may be held together at join 18 simply by a friction fit. The inventor has observed that the position of the join 18 at the lower side of side wall 19 results in improved structural strength.

It will also be seen that the resultant join 18 is inset into recess R, and thus inset from the remainder of the panel side wall 19. In this way the join does not in any way interfere with the side wall of an adjacent panel.

As shown in Figure 3, typically a panel core 16 having the appropriate shape formed (eg. machined) therein is positioned between partly bent plates, and then the remaining bends, folds and crimping are conducted by appropriate bending operations (as known in the art).

The resultant floor panel has been observed to have a number of advantages including: a panel that is strong and yet lightweight, having a thinner dimension than prior art panels. a panel that can be fabricated from readily available, and thus cost effective materials. the inset recessing of the join prevents it from interfering with adjacent panels, increases its strength and facilitates its easy insertion into a supporting grid framework.

'the orthogonal disposition of the join increases the panel's load bearing capacity, resisting the tendency of the wall to splay out under load. w The orthogonally disposed join also obviates the need for a supporting grid structure and instead a simple to install pedestal support array can be employed (with the resultant time and cost savings).

The join acts as an in-built stringer around the panel, the effect of which is enhanced by its in- setting in recess R, and hence a grid support structure is not required. the use of an inset, preferably orthogonal joint increases the pre-tension of the so-formed panel, enhancing its resistance to flexing when loaded, thus increasing its load bearing capacity. a thinner core material can also be used when the panel casing tension/strength is increased.

'the preferable location of the join adjacent to the bottom plate of the panel reinforces the

bottom peripheral edge of the panel, thus again increasing its load resistance (c. f. GB2130615 and WO 99/18305). can inclination can still be provided in part of the panel side wall such that adjacent panels only touch at their corner edges (i. e. at the fold line 26) and thus do not interfere with each other during installation or panel removal.

'as a result the friction between the panels (and the resultant noise) is also minimised in use.

Whilst the invention has been described with reference to a number of preferred embodiments it should be appreciated that the invention can be embodied in many other forms.