Throughout the specification, the invention is described with reference to the orientation for use in metal decking where a notional centre plane of the sheet is generally horizontal. This, however, should not be construed as limiting the invention to that orientation, as the decking may be laid in orientations that are offset from horizontal. Accordingly, reference to a particular orientation is to be construed to encompass these other orientations.

Background Composite structure includes the use of metal decking which provides the formwork for casting of a concrete slab over the decking, and the tensile reinforcement to the structure on curing of the slab. Composite structures of this type are widely used in the formation of floors or roofing particularly in high rise buildings.

Traditionally, the metal decking is formed from a plurality of decking members which are laid adjacent one another in either abutting or overlapping relationship.

These decking members are traditionally formed from sheet metal strip which are subsequently cold formed by a roll forming and/or pressing operation.

One such decking member is currently manufactured by the applicant under the trade mark WdeK. This decking member is formed with longitudinal edge margins which are shaped to include an overlap portion at one margin and an

underlap portion at the other margin. The member includes intermediate ribs and pans and is arranged to be laid with other said members with the overlap portion of one member interlocking with the underlap portion of adjacent member so as to be able to form a continuous deck.

The design of the interlock formed by the lap connection needs to withstand the considerable loading which is applied when the concrete, or other setable material, is cast onto the deck. With the presently available WdeK member, the overlap is interlocked with the underlap by a process whereby the sheet which incorporates the overlap is presented to the already laid sheet at an angle to the horizontal to enable the underlap to locate within the overlap and then rotated to the horizontal whereby the interlocking parts become fully interengaged with the underlap being trapped within the overlap.

The lap connection between the adjacent sheets has proved satisfactory in resisting the induced forces on casting the slab. However, the mode of connection of one slab to another whereby the sheet needs to be presented at an angle to the already laid sheet, has proved inconvenient and difficult to manipulate in some circumstances.

Summary of Invention According to a first aspect, the invention is directed to a decking member having opposite longitudinal edges which are shaped to form respective overlap and underlap portions and which are arranged to form a lap connection in interconnecting the overlap portion of the member with the underlap portion of another member, wherein in forming the lap connection, the overlap portion is arranged to engage the underlap portion under the application of downward pressure and wherein by that engagement, the members are operative to be caused to have a component of lateral movement on the application of

continued downward pressure.

According to a second aspect, the present invention provides a metal decking member for use in a composite structure, the member having opposite longitudinal edges, the margins adjacent these longitudinal edges being shaped to include an overlap portion at one margin and an underlap portion at the other margin, the member being arranged to be laid with other said members with the overlap portion of a member forming a lap connection with the underlap portion of an adjacent member so as to be able to form continuous decking, wherein the overlap and underlap portions incorporate complementary engagement surfaces and are configured so that when forming a lap connection between one said member and another said member, the underlap portion is able to locate within the overlap portion with the members generally horizontal, and wherein once the underlap portion is located in the overlap portion, the complementary engagement surfaces of the respective portions are arranged to interengage so as to cause said members to move laterally on continued movement of one engagement surface across the other engagement surface, to form said lap connection.

In one form, the members are caused to move laterally apart on continued movement of one engagement surface across the other.

In one form, the member is profiled to include pans adjacent each of the longitudinal edge margins of the member, and at least one longitudinal extending rib located intermediate the edge margins.

In one form, the overlap portion comprises spaced apart inboard and outboard walls which are interconnected by a bridge portion, the inboard wall comprising an inner engagement surface that extends upwardly and outwardly relative to an adjacent part of the member, and the outboard wall includes an inwardly directed tail portion so that the overlap portion incorporates a downwardly facing opening which extends from the inboard wall to an

inner edge of the tail portion. This inner engagement surface forms one of the complementary engagement surfaces of the lap and wherein the underlap is designed to be received within the opening.

In one form, the underlap portion comprises an upstanding wall that has an outer engagement surface that extends upwardly and inwardly relative to an adjacent part of the member. In this way, the outer engagement surface extends over the adjacent part of the member and forms the other of the complementary surfaces of the lap connection.

With the above arrangement, the overlap portion is operative to be moved under a downward pressure to interlock with the underlap portion of an adjacent member whilst both members are generally horizontal. During this connection, the underlap portion is initially received within the opening of the overlap portion so that the engagement surfaces of the underlap and overlap portions move into engagement, and wherein on continued movement under downward force, the members are caused to move laterally apart by movement of one engagement surface across the other engagement surface to the fully interlocked position. When in the interlocked position, the underlap portion is retained within the overlap portion as the inwardly directed tail portion of the overlap prevents the underlap from being released on vertical displacement of the interlocked members.

In one form, the outboard wall of the overlap is generally perpendicular to a notional centre plane of the member.

In one form, the underlap portion includes a distal portion which is turned out of the plane of the upstanding wall and wherein when in use, this distal portion locates adjacent an inner surface of the bridge portion of the overlap.

In a further aspect, the present invention provides a metal decking member for use in a composite structure, the member being formed from sheet metal and having opposite

longitudinal edges; the margins adjacent these longitudinal edges being shaped to include an overlap portion at one margin and underlap portion at the other margin, the member being arranged to be laid with other said members with the overlap portion of a member inter- engaging with the underlap portion of an adjacent member so as to form a lap connection; the overlap portion comprising spaced apart inboard and outboard walls which are interconnected by a bridge portion, the inboard wall comprising an inner engagement surface that extends upwardly and outwardly relative to an adjacent part of the member, and the outboard wall includes an inwardly directed tail portion so that the overlap portion incorporates a downwardly facing opening which extends from the inboard wall to an inner edge of the tail portion; and the underlap portion comprising an upstanding wall that has an outer engagement surface that extends upwardly and inwardly relative to an adjacent part of the member.

In operation, when the members are generally horizontal, with the underlap portion initially received within the opening of the overlap portion, the lap connection is formed on applying downward pressure to the overlap portion, so that the engagement surfaces of the underlap and overlap portions move into engagement, and wherein on continued movement under downward pressure, the members are caused to move laterally apart by movement of one engagement surface across the other engagement surface to a fully interlocked position, and wherein when in the interlocked position, the lap connection is made with the underlap portion being retained within the overlap portion.

In a further aspect, the present invention provides a method of laying decking members on an underlying structure to form continuous decking for a composite structure; the method comprising the steps of: a) providing a plurality of decking members, each

member made from sheet metal and having a notional centre plane and incorporating an overlap portion and an underlap portion at respective longitudinal edges of the member; b) locating a first member on the underlying structure; c) presenting a second decking member for interlocking with the first member with the centre plane of the second decking member being generally parallel with the centre plane of the first decking member and the overlap portion of the second member being disposed over the underlap portion of the first member; d) moving the overlap portion onto the underlap portion so that the underlap portion engages with an inner surface of the overlap, and when once engaged, the engaging surfaces bias the members to move laterally under the downward pressure, the lateral movement causing said underlap portion to move into a fully engaged position with the overlap portion wherein the underlap portion is retained in said overlap portion.

Brief Description of the Drawings It is convenient to hereinafter describe an embodiment of the present invention with reference to the accompanying drawings. The particularity of the drawings and the related description is to be understood as not superseding the generality of the preceding broad description of the drawings. In the drawings: Fig. 1 is a symmetric view of a metal decking member; Fig. 2 is an end view of the metal decking member of Fig. 1; Figs. 3a to 3d illustrate a lap connection between two said decking members of Fig. 1; and Fig. 4 is a section view of a composite structure formal using the decking member of claim 1.

Detailed Description of Preferred Embodiment Referring firstly to Figs. 1 and 2, a metal decking member 10 is disclosed which is used as part of a composite structure. In use, the decking member 10 is made from sheet metal strip which is subsequently cold formed. Suitable metal strip includes sheet steel that incorporates a corrosion resistant coating such as coated steel strip. The gauge of the steel strip may vary but is typically between 0.75mm to 1. 3mm.

The member 10 incorporates longitudinal edges 11,12 and is profiled to incorporate two longitudinal extending ribs 13 and 14 located intermediate the edges 11 and 12.

The ribs are spaced from each other and from the edges 11, 12 by pans 15,16 and 17. Whilst the general profile of the ribs is not part of the invention, in the illustrated form, each of the ribs 13,14 include webs 18,19 which incorporate embossing 21 to strengthen those webs. The webs 18,19 are interconnected by a bridge portion 21 which includes stiffening elements 22. The middle pan section 16 also includes a stiffening element 23.

An illustration of a composite structure 100 made using the member 10 is disclosed in Fig. 4. The member 10 is arranged to be laid with like members 101, 101l, and interconnected along the longitudinal edges 11 and 12 so as to form continuous decking 50. That decking is designed to provide the formwork for a concrete slab 51 which is cast over the upper surface 52 of the decking and also to provide the tensile reinforcement to the slab 51 on curing of the concrete thereby providing the composite structure 100.

To interlock a member 10 with another member, a lap connection 24 is formed between the interlocking members.

To form this connection, one longitudinal edge margin 25 is shaped to include an overlap portion whereas the other longitudinal edge margin includes an underlap portion 26.

Referring to Fig. 2, the overlap portion includes

inboard and outboard walls 27,28 which are interconnected by a bridging portion 29. The inboard wall 27 includes an inner engagement surface 30 which extends upwardly and outwardly relative to the pan section 17. The outboard wall 28 extends generally perpendicular to the plane of the pan section 17 and includes an inwardly directed tail portion 31. With this arrangement, a downwardly facing opening 32 extends from the inboard wall 27 to an inner edge 33 of the tail portion 31.

The underlap portion 26 comprises an upstanding wall 34 that has an outer engagement surface 35 which extends upwardly and inwardly relative to the pan section 15. The underlap portion also includes a distal portion 36 which is turned out of the plane of the upstanding wall 34.

As is illustrated in Figs. 3a to 3d, a lap connection 24 is formed on interconnection of an overlap and underlap portion. To facilitate differentiation between the components at a lap connection 24, one member is identified by superscript and its features are similarly designated.

As illustrated, one member 10 is laid on a supporting structure (not shown) so that the underlap portion 26 of that member is able to be received in the overlap portion 251 of the subsequent member 101 which is being installed.

As illustrated in Fig. 3a, the subsequent member 101 is able to be interconnected with the member 10 whilst it is in a generally horizontal orientation. In particular, the downwardly facing opening 321 formed in the overlap portion 251 is wide enough to be able to receive underlap portion 26 of the member 10.

The overlap portion 251 is pushed down onto the underlap portion 26 until such time as the engagement surface 301 comes into contact with the engagement surface 35 of the member 10 as illustrated in Fig. 3b. By virtue of the orientation of these engagement surfaces 301 and 35, further downward pressure applied to member 101 causes the movement of the engagement surface 301 across the

engagement surface 35. This causes the members 10, 101 to have a component of movement which is laterally apart as illustrated in Fig. 3c. This movement continues until the distal portion 36 of the underlap portion 26 locates within the bridge portion 291 of the overlap portion 251.

When in this position (as illustrated in Fig. 3d) the lap connection 24 is formed. With the underlap portion 26 being effectively retained within the overlap portion 251 it is unable to be released by vertical displacement of the members 10, 101 as the tail portion 311 of the overlap portion 251 prevents release of the distal portion 36 of the underlap.

This lap connection 24 is effective in withstanding and casting of a concrete slab over the lap connection 24 even though the distal portion 36 is not in direct engagement with the tail portion 311. As such, whilst a minor amount of vertical displacement may occur between the members 10, 101, it is not sufficient to open the lap connection 24.

Accordingly, the member 10 provides an arrangement where the members can be interconnected with like members simply and easily to form continuous decking for use in composite structure construction.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word"comprise"or variations such as "comprises"or"comprising"is used in an inclusive sense, i. e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

It is to be appreciated that variations and alterations may be made to the parts previously described without departing from the spirit or ambit of the present invention.