AU2004224895A1

AU2004224895A1 - Structural element

Info

Publication number: AU2004224895A1
Application number: AU2004224895A
Authority: AU
Original assignee: BlueScope Steel Ltd
Current assignee: BlueScope Steel Ltd
Priority date: 2003-10-28
Filing date: 2004-10-28
Publication date: 2005-05-19

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): BLUESCOPE STEEL LIMITED Invention Title: "STRUCTURAL ELEMENT" The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 c- STRUCTURAL ELEMENT o Technical Field 00 This invention relates to structural beams made from a plurality of tn components of respectively different materials.

00 The term "beam" as used herein includes within its scope, an elongated elementary part of a suspended floor slab.

C More particularly the invention relates to such beams of the kind comprising a base beam, a strip of profiled sheet material displaying a plurality of parallel ribs spaced apart by pans and projecting upwardly from the plane of the pans, which strip extends longitudinally of the base beam with said ribs extending transversely of the base beam and a layer of reinforced concrete overlying the strip.

Background Art It is well known that when a beam is supported at two points and bears a load between those points, it necessarily flexes downwardly under the load. As a result, upper parts of the beam are subjected to longitudinal compression and the lower parts are subjected to longitudinal tension. In a homogeneous beam of uniform cross-section, there is a so-called neutral layer between the upper and lower parts, which is neither compressed nor tensioned. However the neutral layer is subjected to a longitudinal shear resulting from the total of the tensile forces below it and the total of the oppositely directed compressive forces above it. Thus the longitudinal shear to be resisted by the neutral layer is greater than that for any other layer.

Moreover, in general, it may be said that the closer a layer is to the neutral layer then the greater is the shear it is required to resist.

In a composite beam, although the generality of lower parts in tension, uipper parts in compression, and a maximum longitudinal shear therebetweeni still applies, 3 the position is more complex. The distribution of longitudinal shear stress within o the beam depends not only on its cross-sectional shape but also on the elastic 00 properties of its several components and the integrity of their connections eachi to each insofar as the transfer of horizontal shear forces therebetween is concerned.

It3 00It has been found that conventional composite beams of the kind to which the invention relates, wherein the material of the base beam and the profiled sheet is typically steel, and the concrete reinforcement has comprised one or more substantially planar, substantially horizontal, steel rod or wire meshes or grids, embedded in the concrete above the crests of the said ribs, are prone to incipient shear failure of the concrete at positions between the ribs and substantially in the plane of the crests of the ribs. It is not clear whether this arises because of longitudinal slippage between the base beam and the profiled strip, or between that strip and the concrete, or both, but it has been proposed to alleviate the problem by introducing longitudinal shear stress transfer connectors between the base beam and the concrete and reinforcing elements in the concrete positioned between neighbouring ribs, which elements include multiple parts intersecting horizontal shear planes in the concrete, in particular planes at or near the crests of the ribs.

Those prior art proposals are exemplified by the published specifications WO 96/06994 and DE 1609322.

As seen in both of those prior art specifications the said reinforcing elements have comprised relatively complex folded meshes or fabricated cages (WO 96/06994) or elaborate, multiple component assemblies requiring considerable onsite installation work (DE 1609322).

c Summary of the Invention.

0 An objective of the present invention is to provide a composite beam of the kind to which the invention relates including a reinforcing element providing multiple portions extending through horizontal shear planes at or near a level corresponding to the level of the crests of the ribs, which is cheaper to make and easier to install, by comparison with those elements proposed hitherto. The Sinvention achieves that objective by utilising a reinforcing element in the form of an 0 open-wound, helical coil of rod or wire able to fit between neighbouring ribs of the profiled sheet when extending transversely of the base beam at a level within the concrete such that a lower part of the element is below the plane of the crests and an upper part is above the plane of the crests.

Preferably the mathematical helix to which the helical coil conforms is generated with reference to the surface of a right cylinder of circular cross-section.

However the helix may be generated with reference to the surfaces of cylinders of other cross-sections, for example of elliptical or polygonal cross-section, including square, rectangular and triangular cross-sections, with or without rounded corners, and the term "helical coil" is to be construed accordingly.

Therefore, the invention consists in a composite beam of the kind comprising a base beam, a strip of profiled sheet material extending longitudinally of the base beam and comprising a plurality of spaced apart, parallel ribs separated by pans, which ribs project upwardly to crests at a higher level than the pans and extend transversely of the base beam, a layer of reinforced concrete overlying the strip, and a plurality of shear stress transfer connectors affixed to the base beam and extending therefrom into the concrete, wherein the concrete is reinforced by a plurality of reinforcing elements, each of which elements is an open-wound, helical coil of rod or wire, and is positioned partly within a space between neighbouring ribs of the.

profiled sheet so as to extend transversely of the base beam, with a bottom part c below a plane extending between the crests of its neighbouring ribs and a top part o that is above that plane.

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00 Brief Description of the Drawings.

In By way of example, an embodiment of the invention is described in more 00 detail hereinafter with reference to the accompanying drawings.

Cl Figure 1 is a side elevation of a portion of an assembly of the metal components of a composite beam according to the invention ready to receive a deposit of reinforced concrete to complete the composite beam.

Figure 2 is a diagrammatic side elevation of a reinforcing element, being a component of the beam of figure 1.

Figure 3 is a diagrammatic end view of the reinforcing element of figure 2.

Figures 4 to 6 are views similar to figure 3 of other reinforcing elements, being respectively discretionary alternatives to the component illustrated by figures 2 and 3.

Best Mode of Putting the Invention into Effect.

The assembly illustrated by figure 1 constitutes the metal components of a composite beam according to the invention. That composite beam may be an elongated, elementary part of a suspended, load bearing, floor slab. To that end the composite beam may be one of an array of parallel, spaced apart composite beams extending between supporting structures (not shown) to the right and left of the portion of the assembly shown in the figure.

c The illustrated assembly comprises a base beam4, which may be a o conventional, structural steel, I-beam comprising a web 5, a top flange 6 and a

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00 similar bottom flange (not shown).

A strip of conventional, profiled sheet steel decking 7, displaying a plurality o of parallel ribs 8 spaced apart by substantially co-planar pans 9 and projecting 00 upwardly from the plane of the pans 9 to substantially co-planar crests 10, extends longitudinally of the base beam 4 with the ribs 8 extending transversely of the base beam 4.

In this instance, the decking 7 extends transversely of the base beam 4 to and beyond the base beam of at least one neighbouring composite beam of the array.

That is to say decking 7 is common to a number of composite beams. In instances wherein the composite beam is a stand alone structural item, the equivalent of the decking 7 may be of sufficiently heavy material to enable it to project in a selfsupporting manner beyond the free edges of the flange 6 to a predetennrmined desired extent.

The assembly further comprises a plurality of reinforcing elements 11, each in the form of an open-wound, helical coil 12 of rod or wire lying upon a pan 9 and extending transversely of the base beam 4. It will be noted that a bottom part of each reinforcing element 11 is well below the plane of the uppermost parts of the crests 10, whereas a top part of the element is well above that plane.

The element 11 may readily be manufactured from elongate stock material by laying a leading end portion of the stock material into a few turns of a helical groove formed in the curved surface of a right cylindrical mandrel terminating at a free end of the mandrel. The mandrel may then be rotated to draw further stock material into the groove while allowing the formed helix to feed off said free end.

c1 With the object of disclosing a particular example of an appropriate Sreinforcing element, it is mentioned that the stock material may be steel wire, for

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00 example 7.6 of D500 class. The pitch of the helix may be within the range of from 100 to 150 mm. The diameter of the generating surface may be within the range of 90 to 150 mm. In such instances the individual turn sides will intersect the 00 horizontal shear planes within the concrete at a spacing required by AS 2327.1 and Sthe element will have appropriate strength and ductility.

SIn the present instance, further supplementary reinforcement is provided in the form of a steel mesh or grid of conventional nature, comprising longitudinally extending rods 13 and transversely extending rods 14. The rods 13 and 14 may be wired or welded together at their crossover points. The mesh or grid may merely rest directly upon the crests 10 or may be supported by conventional chairs (not shown) at the discretion of the user.

The preferred helical reinforcing elements have a degree of resilient flexibility enabling the individual turns of the coil to be fairly readily displaced slightly if this should be necessary to avoid obstruction with supplementary reinforcement.

However, as shown by the illustrated embodiment, a transverse rod 14 may be surrounded by the turns of the helical element. This would normally be avoided, but if needed for any reason can be accommodated by the present invention by emplacing each element 11 by "threading" it into position. That is to say by shifting the element axially into position from one side of a composite beam being assembled, while simultaneously rotating the element about its own axis. This manoeuvre is facilitated in preferred embodiments by the aforesaid flexibility of the preferred helical elements.

cI The embodiment of the invention now being described also includes a o plurality of shear stress transfer connectors 15. There are preferably two such 00 connectors associated with each pan 9, disposed one each side of the web 5. Each may be no more than a piece of steel, for example a short length of steel shaft or the like, welded to the flange 6 and projecting therefrom through a neat fitting hole in Sthe associated pan into the space between ribs 8 that is ultimately filled with 00 Sconcrete.

SOnce the assembly of figure 1 has been completed a layer of concrete may be deposited thereon to submerge the reinforcement and complete the manufacture of the composite beam.

The alternative reinforcing elements illustrated by figures 4 to 6 respectively may be made in a manner otherwise similar to that described in respect of element 11 but using a mandrel having a cross-section corresponding to the elliptical, square or triangular shapes of the helix cross-sections shown in those figures. It may be that the nature of desired supplementary reinforcement or other reasons may call for one or other of these discretionary alternative shapes, or any one of innumerable other possible cross-sections. However, other things being equal, the more conventional helix based on a right cylindrical surface is preferred if only because of the cost of the mandrels needed for other shapes and the fact that their use would require recurrent acceleration and deceleration of the feedstock being wound thereabout.

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.

9 ¢c It will be appreciated that variations and/or modifications may be made to o the parts previously described without departing from the spirit or ambit of the 00 invention.

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