STRUCTURAL MEMBER

Abstract: A composite structural member (10) is fabricated by springing together two generally 'C' section components (11), each of which has a web (12) with a pair of ribs (16) extending along it, upper and lower main flanges (13) terminating at their edges in sub-flanges (14) directed towards each other, and each sub-flange terminates in a lip (15a, 15b) which is directed back towards the web (12). The lips (15a, 15b) of each component engage respectively outer and inner surfaces of the ribs (16) of the other component, thereby inhibiting displacement of contiguous flanges (13), and maintaining a high moment of inertia which inhibits excessive deflection of the member (10) under load.

Description: STRUCTURAL MEMBER This invention relates to a composite structural member which can be used for example as a post, beam, rafter, floor joist, or for other purposes in building or agricultural construction, fencing and other general purposes. BACKGROUND OF THE INVENTION It is already known to make use of a hollow section for a post, beam or the like, and for example-re erence can be made to the Australian Patent 524516 which illustrated a balustrade having rectangular section spacers between balusters, the Australian Patent 577328 which showed a fencing assembly comprising substantially vertical pillars and upper and lower longitudinal members which were secured between and to adjacent pillars, and vertical members extending between the upper and lower transverse members, wherein the posts and the vertical members were hollow section members. Further reference of more relevance is a hollow beam available from Hunter Douglas Limited of 338 Victoria Road, Rydalmere, New South Wales, as a "R.F. Beam". The invention herein is compared with that product (regarded by the inventors as an excellent product) . With all the prior art known to the Applicant, there is none wherein it is possible to have a continuous section which can span long distances and has the advantage of a box-like section, is capable of being formed by a roll-forming process, can be readily assembled by hand, and will resist bending forces, yet does not include fasteners, welding or other securing means to resist shear forces. If a hollow section composite structural member is fabricated by two similar 'C section components, as in the Hunter Douglas R.F. beam, best results are obviously achieved if there are two laminae of metal comprising the extreme fibres of the beam, that is, where maximum stress and deflection of the metal occurs under loading. The side walls which are under less stress need only be single thickness. However, under load conditions, distortion of the beam can occur, and this can be associated with displacement of the inner metal laminae which contain the extreme fibres, thereby losing some e fectiveness. If fasteners are utilrsed to retain the contiguity of the metal laminae, a little strength is lost due to the existence of fastener apertures. An object of the invention iε therefore to provide a cross-sectional shape of a two-component beam wherein contiguity is retained between inner and outer laminae having the extreme fibres, without the use of fasteners. It iε a further object to provide a shape wherein the components can be readily roll-formed, and after roll-forming, can be readily sprung together to form the hollow section composite beam, but retain its shape and full strength * p to failure. BRIEF SUMMARY OF THE INVENTION In this invention, a composite structural member is fabricated by springing together two generally 'C section components, each of which has a web with a pair of ribs extending along it, upper and lower flanges terminating at their edges in sub-flanges directed towards each other, and at least one sub-flange terminates in a lip which is directed back towards the web. A lip of each component engages an inner surface of a rib of the other component, thereby inhibiting displacement of contiguous flanges, and maintaining a high moment of inertia which inhibits excessive deflection of the member under load. More specifically, the invention consists of a pair of generally r C-section components of identical constant cross- sectional shape, each having two spaced parallel main flanges, a web flanking the main flanges and joining a first pair of corresponding edges thereof, sub-flanges parallel to the web extending generally towards each other from a second pair of corresponding edges of the main flanges, and a return stiffening lip directed towards the web from at least one of the sub-flanges, said web having a pair of inwardly formed ribs defined by inwardly directed wall portions, said at least one lip of each one of the 'C-section components engaging an inner surface of a said inwardly directed wall portion of a said web rib of the other ' C-section component. This arrangement has a number of advantages:- Firstly, in having identical cross-sectional shape, the tooling for production is simplified. Secondly, the structural member, when under load and placed with the webs parallel to the plane of the load direction, can provide effective upper and lower extreme fibres of the section of double metal thickness, the intermediate portions being a single metal thickness of the webs. Thirdly, it is possible to stagger joints in an elongate member which may for example be required for a fence rail with a minimum loss of strength at the joint locations. Fourthly, when subjected to moist conditions, most if not all of the overlapping joints can be in a water shed mode so that ingress of moisture is minimized. DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the invention is described hereunder in some detail with reference to and iε illustrated in the accompanying drawings wherein:- A first drawing represents the closest art known to the Applicants, Fig. 1 is a fragmentary perspective view of a composite structural member according to the invention, Fig. 2 illustrates the springing together of two roll- formed components of identical cross-section to fabricate a structural member, Fig. 3 illustrates diagrammatically a typical usage of the members, in the construction of a building, and Fig. 4 illustrates a test arrangement in which the deflection was tested against load applied, the results being shown below. The first drawing illustrates the closest prior art known to the Applicants, that is the aforesaid Hunter Douglas R.F. Beam. Referring first to Fig. 1, the hollow structural member 10 comprises two identical member 'C-section components 11 each of which is formed from sheet metal and compriseε a web 12 flanking two main flanges 13 each of which ter inateε along corresponding edges in an inturned sub-flange 14, and each of the sub-flangeε 14 is provided with stiffening lips 15a and 15b extending along its inner edge. (In some instances the lip 15a is omitted. ) Each web 12 is provided with a pair of spaced ribs 16 defined by inwardly directed sloping wall portions 17, and upon assembly, lips 15a and 15b of each of the 'C-section components 11 engage respective outer and inner surfaces of the inwardly directed wall portions 17. It is this engagement which assists inhibition of displacement of the contiguous main flanges 13 of the two member components 11, even when no fasteners are used to retain them. The main flanges 14 are also provided with ribs 18 which are deεirable in the roll-forming, and also stiffen the main flanges. The outside dimension 'd' across the width of one main flange 13 which carries the inner of the lips 15 is two metal thicknesses less than the corresponding width 'D' of the flange which carries the outer of the stiffening lips 15. With this arrangement it is relatively easy for each component 11 to have its inner stiffening lip inserted within the other, and the outer stiffening lip over the outer surface of the other component 11, and the stiffening lips then bear against the inwardly directed wall portions of the ribs 16 to inhibit disengagement. The illustrations show the sections 11 each having been formed of identical cross-sectional shape by a roll-forming process. However the invention is not necessarily limited to the roll-forming process and in some embodiments it is desirable to produce the sections by an extrusion process, for example of structural aluminium. The assembly which is shown provides a structural member 10 which has very substantial strength because if load is applied vertically to the assembly of Fig. 2, upper and lower chords of the structural member have double metal thickness and the strength of the compoεite member iε conεiderable even without the use of fasteners which may however be added to compensate for the shear forces which exist when the member is subjected to loading. However for light duty purposes, it is not necessary for the members to be joined together as a composite structural member but each section can be used individually and separately. This is of considerable advantage in building operations for example wherein lighter sections are required for some elements of the building and stronger structural members for upper elements. In Fig. 3, identical section structural members are used for posts 21, rafters 22, tie beams 23 and struts 24. The purlins required are not illustrated. A roof support bracket 25 comprises side plates 26 spaced apart by two L-shaped spacers 27 to form, in effect, three sockets 28 (for the post 21), 29 (for the tie beam 23), and 30 (for rafter 22). A ridge support asεembly 32 comprises plates forming two sockets 33 for raf ers, joined together by fasteners through contiguous clamp plates 34. A space exists between side plates 35 within which the upper end of strut 24 is contained. Side plates 36 intermediate the endε of tie beam 23 provide clamping means for the lower end of strut 24. Fig 4 illustrates a deflection testing arrangement wherein a structural member was compared with the illustrated prior art. The representations are accurately drawn, and the overall dimensions of the two sections were identical, the metal thickness identical, but the Applicants' rolled section was necessarily of a softer grade of aluminium (H34 standard half- hard, compared with HI6 structural grade). The relative strengths are as follows: Tensile H34 159 M.Pa Yield H34 134 M.Pa Shear H34 97 M.Pa Tensile H16 179 M.Pa APPLICANTS' H34 PRIOR AUT HI6 ROLL-FORMED ALUMINIUM EXTRUDED ALUMINIUM [crushing occurred] 1 0.045 2 0.150 3 0.215 3.5 0.275 APPLICANTS' GALVANISED STEEL The above tests were conducted independently by the Australian National Railways at their Islington Laboratories in South Australia, on 29th October, 1990. They indicated: (1) A considerable increase in loading before crushing occurred (2) A loεε of strength without fasteners for aluminium, but an increase for steel. The conclusion reached was that the cross-sectional shape of Applicants' member was adequate to avoid the need for fasteners. The deflection/load ratio was within an anticipated range 7 for the steel, assuming a modulus of elasticity of 3x10 . The moment of inertia was less than could be obtained with a drawn tube having the same wall thicknesε as the combined thicknesseε of the components, but the relative costs are much in favour of Applicants' member for the same deflection.

Claims: • THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A composite hollow structural member comprising a pair of generally 'C-section components of identical constant cross- sectional shape, each having two spaced parallel main flanges, a web flanking the main flanges an joining a first pair of corresponding edges thereof, sub-flanges parallel to the web extending generally towards each other from a second pair of corresponding edges of the main flanges, and a return stiffening lip directed towards the web from at least one of the sub-flanges, said web having a pair of inwardly formed ribs defined by inwardly directed wall portions, said lips of each one of the 'C-section components engaging respective inner and outer surfaces of said inwardly directed wall portions of the web ribs of the other 'C-section component. 2. A composite structural member according to claim 1 wherein said rib wall portions of each said 'C-shaped component slope inwardly from said web near but not at said first pair of corresponding edges of the main flanges. 3. A composite structural member according to claim 1 or claim 2 wherein engagement of the component lips with the web ribs retains contiguouε main flangeε of the components in abutment. 4. A composite structural member according to any preceding claim wherein said components are formed by a roll-forming process from flat sheet metal into their said cross-sectional shape. 5. A method of forming a structural member comprising roll- forming flat sheet metal strip into two components each having identical cross-sectional dimensions, and a shape as defined in any preceding claim, and springing the components together to form a hollow section with the lips of each component engaging inner and outer surfaces of said inwardly directed wall portionε, and retaining contiguous main flanges in abutment. 6. A structure comprising a post, rafter and tie beam all according to any one of claims 1 to 4, and further comprising a roof support bracket having sockets the walls of which retain ends of said post, rafter and tie beam. 7. A structure according to claim 6 wherein said roof support bracket comprises a pair of side plates separated by a pair of L-shaped spacerε which define said socketε. 8. A εtructure according to claim 6 or claim 7 further compriεing a ridge εupport aεsembly comprising εocket plateε defining two εocketε each supporting a rafter end, clamp plates on the socket plateε, and faεtenerε εecuring the clamp plates together faσe-to-face. 9. A co poεite hollow structural member subεtantially aε hereinbefore deεcribed with reference to and aε illuεtrated in the accompanying drawingε. 10. A method of forming a εtructural member εubεtantially aε hereinbefore described with reference to and as illustrated in the accompanying drawings. 11. A structure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Inventors: LEWIS SIMON JOHN, ROBINSON MAURICE DESMOND, LEWIS, SIMON, JOHN, ROBINSON, MAURICE, DESMOND
Applicants: PELL MELL PTY LTD, PELL-MELL PTY. LTD.
Application year: 1990
Main classification: F16S3
IPC codes: E04C3