HIGH STRENGTH STRUCTURAL MEMBERS

Abstract: A structural member (1) is thin walled and hollow. The walls (4, 5, 6, 7) of the member (1) have a series of protrusions (2) or depressions (3) formed in the general plane of each wall (4, 5) which act to strengthen the member (1). The depressions (3) in one wall (4, 5) abut the inner surface of an opposing wall (6, 7) to provide a resistance to crushing of the member (1). The position and alignment of the protusions (2) and depressions (3) can be altered to suit the intended use of the structural member (1). Structural members may be lintels, I-beams or of other structural shape and will have a lower mass when compared to members of the same strength.

Description: HIGH STRENGTH STRUCTURAL MEMBERS This invention relates to cold formed metal structural members and in particular longitudinal cold formed metal structural members that are not solid or uniform throughout their longitudinal cross-section. Currently structural members are produced by one of three recognized techniques. These techniques are: 1) a hot rolling process 2) a cold extrusion process 3) a cold bending process Existing structural members that are produced from those traditional techniques are constrained in their effectiveness by the longitudinal cross section geometry able to be fabricated by the technique and by other limitations peculiar to the process route associated with the technique. In the case of hot rolled structural members the relevant structural properties of the end product are principally governed by the parent metal's chemistry specified and the continuous solid longitudinal cross-section geometry of the member. The technique, and the structural members that result, have the following disadvantages in relation to engineering, physical and structural effectiveness: 1)' the metal in the internal and central regions of the structural member contributes little to the overall effectiveness of the member's structural performance. 2) the technique only produces structural members that are continuously solid and uniform throughout their longitudinal cross-section (solid angles, channels, beams etc.) 3) the technique does not enable increased strength to be achieved by cold working without subsequent additional processing. 4) the technique does not enable aesthetic or corrosion resistant surface treatment (paint, galvanising, etc. ) to be achieved without additional subsequent processing. In the case of cold extruded structural members the resultant structural properties of the end product are principally governed by the parent metal chemistry specified and the uniform and continuous longitudinal cross-section geometry of the member. The technique, and the structural members that result, have the following disadvantages in relation to engineering, physical and structural effectiveness: 1) The technique only produces structural members that are continuous uniform throughout their longitudinal cross-section. 2) the technique does not enable increased strength to be achieved by cold working without subsequent additional processing. 3) the technique does not enable aesthetic or corrosion resistant surface treatment (paint, galvinising, etc. ) to be achieved without additional subsequent processing. In the case of structural members formed by the cold bending technique, the resultant structural properties of the end product are principally governed by the parent metal's physical and chemical specification, the amount of cold work performed and the uniform and continuous longitudinal cross-section geometry of the member. Similar to both of the above, the technique and structural members that result have the following disadvantages. 1) The technique only produces structural members that are continuous uniform throughout their longitudinal cross-section. The present invention aims to overcome all of the above disadvantages by providing a new concept in structural members which are not solid or uniform throughout their longitudinal cross-section and are produced by a technique which combines continuous cold bending and embosing of the member's outer walls. The resultant product comprises a thin heavily cold worked outer skin which encapsulates a reinforced centre cavity to stiffen and brace the member without contributing additional weight. The technique and the structural members that result have the following advantages over existing structural members. 1) major reductions in weight are achieved by the replacement of internal and central region metal with wall coined bracing. SUMMARY OF THE INVENTION In a broad form of the invention there is provided a hollow structural member having at least one depression in a wall of the member, the, or each, at least one depression abutting an opposing face of said member. Preferably the at least one depression comprises a plurality of depressions. The depressions are installed to provide internal bracing and stiffening to the member and act as a substitute for the solid internal and central regions in the case of member produced by the hot rolling technique. They also provide the source of additional cold work to improve the physical properties of the wall metal. Preferably the depressions are spaced regularly along the longitudinal direction of the member. Preferably the depressions are longitudinal. Preferably the longitudinal directions of the depressions are parallel to the longitudinal direction of the member. Preferably the depressions are of equal length. BRIEF DESCRIPTION OF THE DRAWINGS ig 1 shows a perspective of one embodiment of the invention. ig 2 shows a perspective of a second embodiment of the invention ig 3 shows a plan view of the embodiment of Fig 1 ig 4 shows a cross-section of the embodiment of Fig 1 ig 5 shows a plan view of another form of the invention ig 6 shows a plan view of yet another form of the invention DETAILED DESCRIPTION OF THE INVENTION Referring to figures 1, 3 and 4 there is shown a hollow lintel bars 1. The lintel bar 1 is a hollow section bar formed from cold rolled high strength steel sheet, although other alloys could be used, depending on the usage. The bar is formed of a single sheet of steel rolled into a thin walled hollow L shape. The overlapping section 20 may be welded, or left unwelded. The bar could, however, be manfactured from two or more strips of steel, if this were desired. The lintel is roll-formed by conventional techniques into the hollow L section and the first stage of the rolling mill rolls depressions 3 and protrusions 2 into the sheet. The rolling of the protrusions 2 and depressions 3 places sections of the sheet under tension or compression, enhancing the load bearing capability of the metal In the embodiments shown, the protrusions 2 and depressions 3 are formed on the inner horizontal wall 4 and inner vertical wall 5, while outer walls 6 and 7 remain planar. However, depending on the intended usage, the outer walls 6 and 7 could be deformed in a similar fashion. The depressions are formed so as to have a planar base 8 which abuts against the inner faces 9 and 10 of outer walls 6 and 7. Thus a load applied to the bar tending to crush the hollow section will be resisted. The depressions 3 and protrusions 2 are, in this embodiment, aligned parallel to the longitudinal direction of the bar. However, depending on the intended use they could be positioned at various angles to the longitudinal direction, or even at 90 * thereto. Referring to Fig 3 the protrusions and depressions are aligned along lines parallel to the bar longitudinal direction and repeat themselves at regular intervals. Protrusions 2a and 2c are aligned along one line 11 and protrusions 2b and 2d are aligned along another line 12. Similarly, depressions 3a, 3b and 3c are aligned along a line 13 parallel to the lines 11, 12 of protrusion 2. In the embodiment shown protrusions 2a and 2b occur on respective lines 11 and 12 at equal distances from the end 14 of the bar 1, and protrusions 2c and 2d also occur at the same spacing from protrusions 2a and 2b respectively. In the embodiments show the protrusions repeat along respective lines 11 and 12 at regular intervals. In a similar fashion depressions 3a, 3b and 3c are all spaced along line 13, parallel to the bar longitudinal direction. The depressions 3 are displaced axially relative to the protrusions 2 such that they overlap. This ensures that there are no lines of weakness generated perpendicular to the longitudinal direction. The length of the depressions 3 and their axial spacing, in this embodiment, are the same as that of the protrusions 2. However, if required, the axial length, spacing and/or relative position of the depressions can be altered compared to that of the protrusions. Even the relative positions of depressions 3 along lines 13 and 14, or protrusions 2 along lines 11 and 12, could be shifted. Thus, in an alternative embodiment protrusions 2a and 2b could only partially overlap, rather than fully as shown in the drawings. Although the embodiments of figures 1 to 4 shown all protrusions and depressions parallel to the axial direction other variations are possible. Referring to Figure 5 there is shown an alternate arrangement of depressions. The depressions 30 are comprised of a first set 31 aligned parallel to the elongate direction of the member 29, while another set 32 are aligned at 90 * thereto. The first and second sets of depressions, 31, 32 alternate in both the elongate and transverse directions but do not overlap. Referring to Figure 6 there is shown a variation of the embodiment of Figure 5. In this embodiment, while still alternating transversly and longitudinally, the first and second sets of depressions 31, 32 overlap to create cross-shaped depressions 33. It is clearly envisaged that the position and alignment of the protrusions and depressions can be altered to suit the intended use of the bar. Thus an alternate version of the lintel bar could have protrusions 2 along line 11 still parallel to the bar direction but protrusions 2 along line 12 could be rotated by 45° to the axial direction. Similarly there is no restriction on the protrusions/depressions having a straight shape. Curved protrusions and or depressions are also envisaged. Although the arrangement of protrusions 2 and depressions 3 has been described with reference to the horizontal face 4 the above discussion applies equally to the vertical face. Furthermore it should be noted that the arrangement of protrusions 2 and depressions 3 on the vertical face 5 may be chosen independently of the arrangement on the horizontal face. Thus, as an example, protrusions/depressions on vertical face 5 may be alleged at 45° to the axial direction, but those on the horizontal face may be parallel to the axial direction. Although the invention has been described with reference to lintel bars it is to be realised that the invention can be applied to any structural member i.e. I beams, U-channel, etc. Furthermore the surface deformation of the walls of the members provides substantial strengthening. Thus although the invention has been described with reference to a hollow member, the invention provides structural members merely having one or more depressions/protrusions in the wall, but the member itself not being hollow. Thus such a non-hollow member will be thin walled, but with the walls being corrugated. Many other modifications may be made to the invention described by those skilled in the art without departing from the spirit or scope of the invention.

Claims: The Claims 1. A hollow structural member having at least one depressions in a wall of the member, the, or each, at least one depression abutting an opposing face of said member. 2. The member of claim 1 being an elongate member and the at least one depression comprising a plurality of depressions spaced regularly along said elongate direction. 3. The member of claim 2 wherein the depressions are elongate depressions. 4. The member of claim 3 or claim 4 wherein the depressions are all of the same length. 5. The member of any one of claims 3 to 5 wherein the depressions comprise a first set aligned in one direction and second set aligned in another direction. 6. The member of claim 8 wherein at least a portion of said first set overlap a portion of said second set. 7. The member of any one of claim 1 to 7 comprised of cold roll formed metal sheet. 8. The member of any one of claims 1 to 8 wherein the member is comprised of a single piece of metal. 9. The member of any one of claims 1 to 9 wherein the member also includes at least one protrusion in a wall. 10. The member of any one of claims 1 to 10 wherein the depressions and/or protrusions are roll formed in the wall of the member.

Inventors: JOHNSON MICHAEL IAN, JOHNSON, MICHAEL, IAN
Applicants: JOHNSON MICHAEL IAN, JOHNSON, MICHAEL, IAN
Application year: 1990
Main classification: E04C3
IPC codes: E04C2, E04C3