SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a metal decking member being elongate and of a C-section profile including a web and a pair of opposing flanges each including a longitudinally extending rib being configured wherein said rib can interlock with an adjacent rib of an adjacent metal decking member.

Preferably the opposing pair of longitudinally extending ribs are in transverse cross-section shaped complementary to and are substantially aligned with one another. More preferably said pair of ribs protrude inwardly and outwardly, respectively, of the decking member.

Preferably the opposing pair of ribs are in transverse cross-section shaped wherein adjacent interlocked ribs reside within one another to prevent lateral separation of the adjacent metal decking members.

More preferably the outwardly protruding rib of one decking member resides within an inwardly protruding rib of an adjacent decking member.

According to another aspect of the present invention there is provided a metal decking member being elongate

and of a C-section profile including a web and a pair of opposing flanges, one of said pair of opposing flanges being of a lower stiffness relative to the other of said pair of opposing flanges.

Generally the lower stiffness of said one of the flanges is provided by a reduction in the surface area of said one flange relative to the other flange.

Preferably one of said pair of opposing flanges is adapted to interlock with an adjacent flange of an adjacent decking member.

Preferably the opposing flanges each include a longitudinally extending rib being configured wherein said rib can interlock with an adjacent rib of an adjacent metal decking member.

Preferably the metal decking member is of the C- section profile wherein the opposing flanges each having inwardly directed portions. More preferably a free edge portion of each of the inwardly directed portions includes a lip return disposed parallel to the corresponding flange.

Preferably the inwardly directed portions of each of the flanges includes one or more openings. More preferably said one or more openings are defined by longitudinally extending slits formed in the inwardly directed portions which are deformed out of the plane of the corresponding flange. The openings assist in the venting of air which would otherwise be"trapped"as air pockets within the flanges when pouring concrete across the decking member.

Generally the metal decking member is one of a plurality of metal decking members arranged alongside one another to together form metal decking.

It has been found that securing or interlocking of adjacent flanges of adjacent metal decking members of a generally symmetrical configuration restricts or inhibits collapse or rotation of the flanges. In conventional metal decking where the decking members are symmetric and adjacent inwardly and outwardly turned edge portions of the respective adjacent flanges overlap one another, the decking members tend to fail by rotation of the overlapped flanges in the"direction"of overlap.

Preferably the web is longitudinally precambered inwardly of the metal decking member. It has been found that longitudinal precambering of the web is effective in increasing the unsupported span of the metal decking member.

Preferably the longitudinal precamber is up to about 2% measured as the maximum longitudinal offset of the web from a substantially flat plane and expressed as a percentage relative to the length of the web. More preferably the longitudinal precamber is between about 0.4% to 1%. In one embodiment this equates to a precamber of between about 20 to 50 mm for an unsupported span of 5 metres.

Preferably the web in transverse section is precambered inwardly of the metal decking member. More preferably the transverse pre-camber is up to about 5%

measured as the maximum offset of the web from a substantially flat plane and expressed as a percentage relative to the width of the web. Still more preferably the transverse pre-camber is between about 1% to 4%.

BRIEF DESCRIPTION OF THE DRAWINGS In order to achieve a better understanding of the nature of the present invention a preferred embodiment of metal decking will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a sectional view of one embodiment of a metal decking member according to the invention; Figure 2 is a schematic sectional view of another embodiment of metal decking according to the invention; and Figure 3 is a perspective view of a further embodiment of metal decking according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figures 1 and 2 there is a metal decking number 10 being elongate and of a C-section profile including a web 12 and a pair of opposing flanges 14 and 16, respectively. The metal decking member 10 is one of a plurality of decking members such as 10 and 18 located alongside one another to together form metal decking 20 (see Figure 2). The metal decking 20 is designed to be embedded or clad in a concrete slab so as to form a roof or floor. In order to avoid repetition and for ease of reference, similar components of the embodiments of the metal decking members 10 of Figures 1 and 2 have been designated with the same reference numerals.

The adjacent metal decking members such as 10 are of an identical cross-sectional shape being of the C-section profile wherein opposing flanges each include inwardly directed portions 22 and 24. Additionally, each of the inwardly directed portions 22 and 24 include a respective lip return 26 and 28 which is either turned back toward or disposed generally parallel to the corresponding flange 14 or 16.

The flanges 14 and 16 include respective longitudinally extending ribs 30 and 32. The longitudinal ribs 30 and 32 are configured so that adjacent ribs of adjacent decking members interlock to prevent lateral and vertical separation of the metal decking members such as 10 and 18. This interlocking of the ribs 30 and 32 eliminates the need for fasteners to secure adjacent decking members such as 10 and 18 together. In these embodiments interlocking of the ribs such as 30 and 32 is provided by having the ribs 30 and 32 shaped complementary to and substantially aligned with one another so that one of the ribs such as 30 resides within the other rib 32.

The metal decking member 10 of Figure 1 includes a pair of generally C-shaped ribs 30 and 32 which protrude outwardly and inwardly, respectively, of the decking member 10. The C-shaped ribs 30 and 32 are formed in an upright portion of the respective flange 14 and 16. The decking members such as 10 and 18 of Figure 2 include the longitudinal ribs 30 and 32 within the flange adjacent the juncture of the upright portion and the inwardly directed portion of the flange 14 or 16. The ribs 14 and 16 are in this example generally U-shaped in transverse cross-section.

The ribs 30 and 32 of both embodiments are roll formed in the respective flange 14 and 16.

Conventional metal decking members are generally of an asymmetric configuration wherein opposing flanges are turned inward and outward respectively. Thus, the conventional metal decking is formed by overlapping adjacent flanges. The tendency for conventional metal decking is to fail under load wherein the adjacent overlapping flanges collapse or rotate toward the web of one of the decking members. It is understood that the abutting or interlocking flanges of adjacent metal decking members of this embodiment of the invention are less vulnerable to failure in this manner.

According to another aspect of the present invention one of the pair of opposing flanges, such as flange 16 of Figure 2, is of a lower stiffness relative to the interlocking flange 14. This is achieved by reducing the surface area or in this example the width dimension of the inwardly directed portion 24 of the less stiff flange 16 relative to that of the other flange 14. Thus, the less stiff flange 16 has a tendency to deflect or rotate outwardly before the interlocking flange 14. The less stiff flange 16 may be designed to about 90% of the stiffness of flange 14. This reduction in stiffness is provided by reducing the surface area of the portion of the flange disposed above the rib for the less stiff flange relative to the corresponding portion of the other flange. In operation, the load of concrete within the metal decking member such as 18 forces interlocking engagement of the less stiff flange 16 with the flange 14 of the adjacent decking member 10. The adjacent metal decking members 10 and 18 are thus"tied"together without the need for a fastener which is onerous.

Although not illustrated, the inwardly directed portions 22 and 24 may include openings to allow air to vent from the flanges when concrete is poured across the metal decking. The air may otherwise be trapped as air pockets particularly within the area enclosed by the lip returns 26 and 28 of the inwardly directed portions 22 and 24, respectively. The openings are formed by a plurality of longitudinally extending slits in the inwardly directed portions 22 and 24 which are pressed upward out of the plane of the respective flange. In one embodiment the slits are formed as transversely spaced pairs each of a length of about 8 mm and the adjacent inwardly directed portion such as 22 is pressed about 3 mm out of the plane of the respective flange. The slits formed in the flanges also promote the engagement of concrete with the decking member.

Figure 3 illustrates a further embodiment of the invention where the web 16 of the metal decking member 12 is longitudinally pre-cambered inwardly of the metal decking member 12. For clarity the metal decking member is depicted without the longitudinally extending ribs. The metal decking member which ordinarily is embedded in a concrete slab (not shown) is thus capable of spanning an increased distance unsupported. The precamber of the web 16 is in this example about 0.6% measured as the maximum longitudinal offset of the web from a substantially flat plane and expressed as a percentage relative to the length of the web 16. It is understood that the longitudinally precambered web 16 is at least partly deflected toward the flat plane under the significant weight of the concrete slab. Advantageously, this longitudinal precamber provides

minimal deflection of the metal decking member 12 which spans increased distances. In this embodiment the metal decking member 12 spans up to about 5 metres unsupported and includes a longitudinal precamber of about 30 mm which corresponds to 0.6 percent. The unsupported span of 5 metres of this embodiment of the intention compares to a span of up to 3 metres for conventional decking without a longitudinal precamber.

Although not clearly illustrated the web 16 of the metal decking member 12 may also be pre-cambered in transverse sectional profile inwardly. The transverse pre- camber of the web 16 in this example is approximately 2% measured as the maximum offset of the web 16 from a substantially flat plane and expressed as a percentage relative to the width of the web 16. In this example the metal decking member 12 has a width of approximately 300 mm and is roll formed from sheet metal of a thickness of about 1.2 mm.

The longitudinal precamber in the web 16 of the metal decking member 12 is formed by corrugating the web 16. The corrugations (not shown) are oriented transverse and extend partly across the width of the web 16. The transverse corrugations are cold roll formed in the web 16 are sufficiently"light"to provide the preferred longitudinal precamber of up to about 2%. The corrugations may be formed either in the flat strip or in the web 16 once it is formed into the C-section profile. Otherwise, corrugation of the web 16 is performed via corrugting rolls (not shown) in a conventional cold roll forming manner.

Those skilled in the air will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

For example, the longitudinal ribs of the opposing flanges may vary in configuration provided they permit interlocking of adjacent decking members. The less stiff flange may vary in constructions from that described provided it promotes interlocking of adjacent flanges of adjacent decking members. Preferably the web is longitudinally and/or transversely precambered inwardly of the decking member whereby it can span increased distances unsupported. All such variations and modifications are to be considered within the ambit of the present invention the nature of which is to be determined from the foregoing description.

In the preceding summary of the invention, except where the context requires otherwise due to express language or necessary implication, the word"comprising" is used in the sense of"including", that is the features specified may be associated with further features in various embodiments of the invention.