AU2008101288A4 - An improved Z section structural member - Google Patents

Abstract

The present invention relates to Z section structural members or purlins, configured so that they have higher buckling capacity than conventional Z section structural members. The Z section structural members have upper and lower flange 5 portions of predetermined width, each flange portion having a recess extending along longitudinal edges thereof, for providing additional strength to the structural member and for facilitating mounting of roof sheets there above.

Description

13727AUDIV ORIGINAL Complete Specification Applicant: Fielders Australia Pty Ltd Title: An improved Z section structural member Address for Service: LESICAR PERRIN, 49 Wright Street, Adelaide, South Australia 5000, Australia The following statement is a full description of this invention, including the best method of performing it known to melus: 2 An improved Z section structural member FIELD OF THE INVENTION The present invention relates to a Z section structural member and, in particular. to a structural member having a Z shaped cross section for use as a load 5 bearing element, for example, as a load bearing purlin in a roofing structure. BACKGROUND OF THE INVENTION Load bearing roof supporting elements are generally referred to as purlins and are longitudinally located in a roof frame. Such purlins typically have a Z shaped cross section in metal roofing systems and comprise a central web with two oppositely 10 directed parallel flanges extending from the ends of the central web. The Z section purlins are constructed from cold formed steel and are configured to be overlapped or nestled within one another so as to create a continuous beam arrangement. Z section structural members are formed with a lip at the outermost edge of the oppositely directed parallel flanges. The two lips are designed to add strength to 15 the Z section member and are directed substantially parallel to the central web. Also, to ensure that the purlins can be nestled together, one flange is typically narrower than the other. Improvements have been made to basic Z section structural members by attempting to increase their local, flexural-torsional, and distortional buckling 20 capacities under different load conditions. For example, it has been found that overall strength can be increased with the addition of a return to the lip in the flange portions of the structural members. Even these new structures suffer shortcomings though. For example, when using lip returns, the width of the flange portions need to be shortened to maintain the 25 required structural rigidity. This may not be desirable in some building situations. Further, in modifying the conventional design of the Z section member so as to increase its buckling capacity, other considerations are overlooked, such as the ease at which cladding material can be connected to the structure during use.

It is therefore an object of the present invention to overcome some of the aforementioned problems or at least provide the public with a useful alternative. It is a still further object of the present invention to provide a Z section structural member having improved flexural rigidity. 5 It is a yet further object of the present invention to provide a Z section structural member having improved flexural rigidity and which facilitates mounting of cladding elements to flange portions thereof SUMMARY OF THE INVENTION Therefore in one form of the invention there is proposed an elongate structural 10 member, including: a substantially upright web portion; and two oppositely directed flanges projecting outwardly from the ends of the web portion, each of said flanges including a first stiffening recess proximate the edge between the flange and the upright web portion, and a second stiffening recess at an 15 outer edge thereof, whereby each flange and associated first and second recesses are shaped to facilitate nesting of a first structural member and a second inverted structural member. The use of recesses and, in particular, having recesses located along the edges of each flange, increases the buckling capacity of the structural members. 20 Furthermore, in having a flat central region on the flange, as opposed to having a central recess, each flange is able to better accommodate a roofing cladding element. The stiffening recesses therefore contribute to increasing the strength characteristics of the structural member, as well as facilitating construction using such structural members. 25 Preferably each flange further includes a strengthening lip. In preference the lip of the upper flange extends perpendicularly downwardly from said outer edge, and the lip of the lower flange extends perpendicularly upwardly from said outer edge.

4 Preferably the lip of the upper flange terminates in a perpendicular lip return directed towards the web portion, and the lip of the lower flange terminates in a substantially C shaped projection also directed towards the web portion. In preference said web portion includes at least one stiffening recess extending 5 at least partially along its length. In preference said structural member is an extruded length of cold roll formed steel. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part 10 of this specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings: Figure 1 illustrates an end view of a Z section structural member in accordance with the present invention 15 Figure 2 illustrates a top view of the Z section structural member of Figure 1; Figure 3 illustrates a side view of the Z section structural member of Figure 1; Figure 4 illustrates an end cross-sectional view of the Z section 20 structural member of Figure 1; Figure 5 illustrates an end cross-sectional view of a first Z section structural member, and a second Z section structural member which is inverted and nested inside the first Z section structural member in accordance with the present invention; 25 Figure 6 illustrates a perspective view of the nested first and second Z section structural members of Figure 5; 5 Figure 7 illustrates a perspective view of the Z section structural member of Figure 1 including corrugated roof sheeting mounted thereabove. DESCRIPTION OF THE PREFERRED EMBODIMENTS 5 The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Figures 1-4 show, from different views, a purlin or roof system structural 10 member 10 in accordance with the present invention. The purlin is preferably cold formed from roll reduced steel to form a Z shape. Although the purlin of the present invention is intended for use in roofing, the invention is not intended to be limited to such use. The structural member 10 includes a substantially central web 12 with two 15 oppositely directed parallel flanges or flange portions or components 14 and 16. The flanges 14 and 16 extend outwardly and substantially perpendicularly from the ends of the central web 12. Flange 14 is adapted to be narrower than flange 16 to enable flange 16 to accommodate the flange 14 of a second purlin. This allows the ends of the two adjacent purlins to be nestled to form a longer beam, as shown in Figures 5-6. 20 In a preferred embodiment, the height of the purlin 10 is approximately 350mm, flange portion 14 is approximately 116.5mm, and flange portion 16 is approximately 119.5mm, allowing at least a few millimetres to accommodate the flange 14 of a further purlin 10. The skilled addressee would realise that every second purlin in- a plurality of nestled purlins forming a continuous beam would need to be 25 inverted. In addition, the upper and lower flanges 14 and 16 of the purlin 10 have a lip 18 and 20 respectively, extending from the ends of each flange. The upper lip 18 includes a lip return 22 extending perpendicularly from the lip 20 and directed towards the central web 12. Alternatively, the lower lip 20 terminates in a C shaped 6 lip projection 24, which is also directed towards the central web 12, enabling easier insertion and removal of two nestled Z sectioned purl ins 10. Those skilled in the art would realise that when one purlin is nestled within another purlin, the adjacent lip returns 22 and lip projections 24 of respective purlins 5 do not contact or interfere with one other, as is clearly shown in Figure 5. The lip projections 18 and 20 serve to provide additional strength to the purlin as mentioned in the preamble of the invention. The purlin 10 also includes a number of strengthening recesses. For example, in order to strengthen the central web 12 and allow for a longer structural member, 10 there is a longitudinal recess 26 extending along the middle of the central web 12. Those skilled in the art would realise that when two purlins are nestled together, as described above, the recesses 26 face one another, as shown in Figure 5, and form a longitudinally extending channel 28 therebetween. Two longitudinally extending stiffening recesses 30 and 32, and 34 and 36, are 15 also present on flange components 14 and 16 respectively. Each recess extends along a longitudinal edge of the flange components, that is, recess 30 extends along the outer edge of flange 14, recess 32 extends along the opposite edge adjacent the central web 12, and likewise, recess 36 extends along the outer edge of flange 16, and recess 36 extends along the opposite edge adjacent the central web 12. This recess 20 arrangement: 1) contributes to improving the flexural rigidity of the structural member, including increasing its local, distortional and flexural torsional buckling capacity; 2) enables the purlins to be made wider than hitherto known purlins 25 having lip components, because of the way in which nestled recesses of adjacent purlins interact; 3) facilitates mounting of roof sheeting 38 above the structural member because the flange portion 14 or 16 (whichever is at the top) provides a flat surface to which roof sheeting 38 may be easily 30 attached, as shown in Figure 7.

7 The skilled addressee would realise the difficulty in mounting the roof sheeting to the purlins if there was a recess at or near the centre of the flange components. In having the recesses on opposed edges of the flanges 14 and 16, a flat central surface is provided on each of the flanges which facilitates mounting of the 5 roof sheeting 38 thereto. For example, when using bolts 40 as shown in Figure 7, the skilled addressee would realise the case at which the bolts 40 can be screwed through the troughs in the corrugated sheeting 38, and the upper flange portion 14, to thereby secure the sheeting 38. A person skilled in the art would now appreciate the benefits of the present 10 invention. The Z shaped structural members embodied herein are configured so that they are more structurally robust than conventional structural members known to the Applicant: The strategically located stiffening recesses and lip returns contribute to increasing the buckling capacity of the structural members, whilst allowing for traditional purlin widths to be used. Furthermore, the recesses do not interfere in the 15 nestling of two structural members, and the position of the recesses facilitates mounting of cladding onto the structural member. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred 20 embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus. In any claims that follow and in the summary of the invention, except where 25 the context requires otherwise due to express language or necessary implication, the word "comprising" is used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

Claims (7)

1. An elongate structural member, including: a substantially upright web portion; and 5 two oppositely directed flanges projecting outwardly from the ends of the web portion, each of said flanges including a first stiffening recess proximate the edge between the flange and the upright web portion, and a second stiffening recess at an outer edge thereof, whereby each flange and associated first and second recesses are shaped to facilitate nesting of a first structural member and 10 a second inverted structural member.

2. An elongate structural member as in claim I wherein each flange further includes a strengthening lip.

3. An elongate structural member as in claim 2 wherein the lip of the upper flange extends perpendicularly downwardly from said outer edge, and the lip 15 of the lower flange extends perpendicularly upwardly from said outer edge.

4. An elongate structural member as in claim 3 wherein the lip of the upper flange terminates in a perpendicular lip return directed towards the web portion, and the lip of the lower flange terminates in a substantially C shaped projection also directed towards the web portion. 20

5. An elongate structural member as in any one of the above claims wherein said web portion includes at least one stiffening recess extending at least partially along its length.

6. An elongate structural member as in any one of the above claims wherein said structural member is an extruded length of cold roll formed steel. 25

7. An elongate structural member substantially as hereinbefore described with reference to Figures 1-7.