AU2009100554A4

AU2009100554A4 - Construction of Trusses for Roofs and Floors

Info

Publication number: AU2009100554A4
Application number: AU2009100554A
Authority: AU
Inventors: Graham Cooper; Bernard Kennelly; Afzal Laphir; Darren Onley
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2009-06-09
Filing date: 2009-06-09
Publication date: 2009-09-10
Anticipated expiration: 2017-06-09
Also published as: WO2010144261A1

Description

Regulation 3.2 AUSTRALIA Patents Act 1990 INNOVATION PATENT SPECIFICATION (ORIGINAL) Name of Applicant: Illinois Tool Works Inc. Address for Service: DAVIES COLLISON CAVE, Patent Attorneys, I Nicholson Street, Melbourne 3000, Victoria, Australia Innovation Patent specification for the invention entitled: "Construction of Trusses for Roofs and Floors" The following statement is a full description of this invention, including the best method of performing it known to us: P:\OPER\MRISpecifications\209\NNOVATION\30763664 107 doc-9/(6/2009 CONSTRUCTION OF TRUSSES FOR ROOFS AND FLOORS The present invention relates to trusses, and more particularly to trusses suitable for floors or as rafters in roofs. The invention has particular, though not exclusive, application to 5 parallel chord trusses. It is desirable to provide improvements in the construction of trusses suitable for floors or as rafters in roofs. 10 According to a first aspect of the present invention, there is provided a truss for a roof or floor, comprising: a pair of spaced apart chords, each chord comprising an elongate member having a web and substantially parallel flanges extending from the web; and web members extending between the chords, 15 wherein opposite ends of the web members are fastened to respective flanges of the elongate members. According to a second aspect of the present invention, there is provided a method of constructing a truss for a roof or floor, comprising: 20 providing a pair of elongate members to define respective chords of the truss, each elongate member having a web and generally parallel flanges extending from the web; and fastening opposite ends of the web members to respective flanges of the elongate members. 25 Preferably, the flanges extend from the respective webs in the same direction, whereby each elongate member comprises a channel member. In a preferred embodiment of the invention, the web and flanges define a generally U-shaped cross-section. In an alternative embodiment of the invention, the flanges may extend from the web in 30 opposite directions. In such an embodiment, the flanges and web may define a generally Z-shaped cross-section.

P:\OPER\M RF\Specifications\2(XmlNNOVATION\3107631 107 doc-/)06/2(009 -2 Preferably, the ends of the web members are received against outer faces of the flanges. Preferably, the elongate members are formed of metal. Preferably, the elongate members 5 are cold formed. In a preferred embodiment of the invention, the elongate members are rolled from metal sheeting. Preferably, the elongate members comprise light gauge or thin gauge section. 10 In a preferred embodiment of the invention, the elongate members are formed from steel. Preferably, the flanges have a base metal thickness of between 0.4 mm and 1.5 mm. More preferably, the flanges have a base metal thickness of between 0.6 mm and 1 .10 mm. Even more preferably, the flanges have a base metal thickness of between 0.7 mm and 1.0 mm. 15 Preferably, the webs have a base metal thickness of between 0.4 mm and 1.5 mm. More preferably, the webs have a base metal thickness of between 0.6 mm and 1.10 mm. Even more preferably, the webs have a base metal thickness of between 0.7 mm and 1.0 mm. 20 In another embodiment, the elongate members may be formed from another metal, such as, for example, aluminium. In that embodiment, the flanges and webs will preferably be of thicknesses which afford the truss comparable stiffness to that afforded by the steel elongate members described above. 25 Preferably, the web members are formed of metal. Preferably, the web members are cold formed. In a preferred embodiment of the invention, the web members are pressed from metal sheeting. Preferably, the web members comprise light gauge or thin gauge section. 30 P:\OPER\MRF\Spccications2I00\lNNOVATON\30763664 107 doc-9/62N9 -3 In a preferred embodiment of the invention, the web members are formed from steel. Preferably, the web members have a base metal thickness of between 0.4 mm and 1.5 mm. More preferably, the web members have a base metal thickness of between 0.6 mm and 1.10 mm. Even more preferably, the web members have a base metal thickness of between 5 0.7 mm and 1.0 mm. In another embodiment, the web members may be formed from another metal, such as, for example, aluminium. In that embodiment, the web members will preferably be of thicknesses which afford the truss comparable stiffness to that afforded by the steel web 10 members described above. In a preferred embodiment of the invention, the chords are arranged to be parallel. In a preferred embodiment of the invention, the opposite ends of the web members and the 15 respective flanges of the elongate members are clinched together to fasten them. It will be appreciated that, in this embodiment, the flanges and said opposite ends are of a thickness which permits the clinching. Advantageously, because each elongate member is an open section, each of the clinch connections between the web member ends and flanges may be able to be effected by inserting one of a die and punch of a clinching device through the 20 opening defined between the flanges of the respective elongate member such that the punch and die are arranged at opposite sides of the web member end and flange, then operating the clinching device. In an alternative preferred embodiment of the present invention, the opposite ends of the 25 web members and respective flanges of the elongate members are fixed to each other by fasteners received therethrough. The fasteners may be, for example, threaded fasteners, such as self-tapping screws, or rivets. Preferably, the flanges of one elongate member and the flanges of the other elongate 30 member are arranged to project towards each other.

P:\OPER\MFSpecifialtonst209\INNOVATION\307636(64 107.dc-9A)6/2(009 -4 Preferably, the elongate members comprise laterally inwardly disposed lips formed at ends of the flanges. Preferably, the lips comprise laterally inwardly extending portions which are substantially parallel to the webs of the elongate members and substantially perpendicular to the flanges of the elongate member. In one embodiment of the invention, 5 the lips further comprise edge portions which project perpendicular to the laterally inwardly extending portions. In one embodiment of the invention, each chord further comprises a further elongate member having a web and generally parallel flanges extending from the web, the further 10 elongate member of each chord being inverted relative to the elongate member of that chord and arranged such that its flanges overlap the flanges of the elongate member, whereby the elongate member and further elongate member define a box section. In that embodiment, the fastening elements are received through the overlapping flanges to fix the ends of the web members thereto. The fastening elements thus also fix the overlapping 15 flanges, and therefore the elongate members and further elongate members, together. Preferably, the elongate members and further elongate members are of the same cross-section. 20 In accordance with a preferred embodiment of the invention, the elongate members and further elongate members are configured such that interior faces of lips of the elongate members are received against exterior faces of the webs of the further elongate members, and/or vice versa, whereby the elongate member and further elongate member defining each box section are interlocked. 25 In a preferred embodiment of the present invention, the web members include a channel member disposed at an intermediate position between the ends of the truss ("the intermediate web member"), the intermediate web member having a web and substantially parallel flanges extending from the web, and being arranged such that the outer face of its 30 web lies in a plane which is perpendicular to the direction in which the truss extends for fixed receipt of a strongback thereagainst.

P30PER\MRF\Specifcaniom\2009\NNOVA TION\307636,64 107.doc-9/06/200)9 -5 The intermediate member may be formed from the same channel section as the channel members defining the chords. 5 According to a third aspect of the present invention, there is provided a truss for a roof or floor in accordance with said first aspect, wherein each elongate member comprises a closed hollow section member constructed from cold formed steel sheet material having a base metal thickness not exceeding 1.5 mm, each closed hollow section comprising parallel side walls which replace said flanges and a top wall and bottom wall either of 10 which replaces said web, the ends of the web members being fixed to respective side walls. According to a fourth aspect of the present invention, there is provided a method of constructing a truss for a roof or floor in accordance with said second aspect, wherein each elongate member comprises a closed hollow section member constructed from cold formed 15 steel sheet material having a base metal thickness not exceeding 1.5 mm, each closed hollow section comprising parallel side walls which replace said flanges and a top wall and bottom wall either of which replaces said web, comprising fastening the ends of the web members to respective side walls. 20 It will be appreciated that, where possible, the preferred features outlined above in connection with the first and second aspects of the present invention apply, mutatis mutandis, to the third and fourth aspects of the invention. Preferably, the top and bottom walls are flat, whereby the closed hollow section members 25 are square or rectangular hollow section members. According to a fifth aspect of the present invention, there is provided an arrangement of trusses as described above, each truss including said intermediate web member, wherein the trusses are arranged side-by-side such that the outer faces are substantially coplanar 30 and are interconnected by a strongback, the strongback comprising a channel member having a web which is fixed against each outer face.

P \OPER\MRF\Specifiarnons\29\INNOVATIONJUI76(%64 107 doc-)/1W2)t -6 The strongback may be formed from the same channel section as channel members defining the chords and/or intermediate members. 5 In a preferred embodiment of the invention, the strongback and intermediate members are clinched together to fasten them. In an alternative preferred embodiment of the present invention, the strongback and intermediate members are fixed to each other by fasteners received therethrough. The fasteners may be, for example, threaded fasteners, such as self-tapping screws, or rivets. 10 The present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a truss I constructed in accordance with a 15 preferred embodiment of the present invention; Figure 2 is a perspective view of an end section of the truss shown in Figure 1; Figure 3A is a perspective view of a pair of interconnected web members of the type used in the truss shown in Figure 1; Figure 3B is a perspective view of the two web members of Figure 3A separated; 20 Figure 4 is a perspective view showing clinch connections between a web member and chord in the truss of Figure 1; Figure 5 is a cross-sectional view showing one of the clinch connections illustrated in Figure 4; Figure 6 is a perspective view showing screw connections between a web and 25 chord of a truss, in accordance with an alternative preferred embodiment of the invention; Figure 7 is a cross-sectional view of a channel member used to form the chords in the trusses illustrated in the aforementioned drawings; Figure 8 is a cross-sectional view of a different channel member used to form the chords of a truss according to an alternative preferred embodiment of the invention; 30 Figure 9 is a cross-sectional view of a pair of channel members of the type shown in Figure 8 interengaged to form a chord of a truss according to a further alternative P30PER\MRISpecification~s\20)9\NNOVATION\0763( I( 107doc-9/06/2(0)9 -7 preferred embodiment of the invention; and Figure 10 is a perspective view of a pair of trusses interconnected by a strongback according to a preferred embodiment of the invention. 5 With reference to Figures 1 and 2, a truss 1 according to a first embodiment of the invention comprises a pair of spaced apart parallel steel chords 10 and a plurality of steel web members 20A, 20B arranged along both sides of the chords 10 to interconnect them. The chords 10 each comprise a light gauge channel member 11 which is rolled from a coil 10 of steel sheet and comprises a web 12 and parallel flanges 13 which extend from opposite sides of the web 12. In the present embodiment, the steel sheet has a base metal thickness (BMT) of 0.85 mm. The chords 10 and are arranged such that the webs 12 are outermost, as will be clear from 15 Figure 2. A chord 10 of the first embodiment is shown in section in Figure 7, from which it can be seen that, at the distal end of each flange 13, the sheet material is formed with a 900 bend, giving rise to a laterally inward lip 15. The lips 15 comprise laterally inwardly extending 20 portions 16, which, advantageously, afford stiffness to the channel sections, significantly increasing the rigidity of the truss I and thus the resistance of the channel sections to buckling, and, in turn, the truss's structural capacity. Each lip 15 is formed with 90' bend, whereby it further comprises a re-entrant edge portion or tip 17 which extends substantially parallel with each flange 13. The tip 17 affords the chord 10 greater rigidity in a plane 25 parallel with that of each flange 13. Arranged at each end of the truss I is an end web member 30 disposed either side of the chords 10. Each end web member 30 is a short length of C-section channel, which may be the same as that used for forming the chords 10 or of different section, and arranged to 30 extend perpendicular to direction in which the truss I extends such that its web at each end thereof is fixed against the respective flange 13 of the respective chord 10. The end web PI0PER\MRF\Specircations\2009\lNNOVATION\30763644117.doc-9/,/2M9 -8 members 30 may be fastened to the chords 10 by threaded fasteners, such as self-tapping screws (as shown), or by clinching each abutting flange-web pair. Clinching will be described in further detail later. 5 Disposed halfway along the truss I is a central web member 35 which, in addition to rendering the truss 1 relatively stiff mid-span, is configured for receiving strongback, as will be described later. The central web member 35 is also a short length of C-section channel that may be the same as that used for forming the chords 10 or of different section, and which is arranged to extend perpendicular to the direction in which the truss 1 extends. 10 Formed into the web of the member 35 at both ends thereof are cutouts, into which the respective chords 10 are received. The flanges of the member 35, which, owing to their thinness can be displaced outwardly if necessary to accommodate the chords therebetween, are fastened against the flanges 13 of the chords 10. Fastening may be effected by threaded fasteners, such as self-tapping screws (as shown), or by clinching the abutting 15 flanges in the same manner as described later. The web members 20A, 20B are formed by cutting, punching and pressing mild steel sheet, which may be the same sheet as that used to form the channel members 9 (and may thus have any of a range of BMTs, with the same considerations as to application being 20 applicable). Each web member is manufactured as part of a pair of web members 20 as shown in Figure 3A, one member of the pair being the mirror image of the other. The pair 20 is formed from a single piece of sheet steel, such that adjacent first end flanges 21 of the web members 20A and 20B are adjoined (see Figure 3A). Appropriate cuts 23 are made in the sheet material where the ends 21 join so that the web members 20A and 20B 25 can be separated by hand, by bending the join to break it. Each web member 20A, 20B further comprises a second end flange 22 and a spanning section 24 extending diagonally between the flanges 21 and 22, which extend parallel with each other in opposite directions from the spanning section 24 to be receivable against 30 flanges 13 of the respective chords 10 on the same side of the truss 1.

P:\OPER\MRF\-Specifxicaons\2tXINNOVATION\k30763M64 107.doc-9/06/2Mx9 -9 The spanning section 24 is formed at both of its edges with respective stiffening ribs 25A, 25B. Ribs 25A, 25B extend substantially throughout the length of spanning section 24, and continue along respective edges of the flanges 21 and 22 respectively to stiffen the ends and also to define locating portions 26A and 26B which are receivable against inner 5 end portions 14 of the flanges 13 (see Figure 5) to locate the flanges 21, 22 correctly against the flanges 13. The spanning sections 24 are also formed with coining 29, which affords them further stiffness As can be seen in Figure 1, each side of the truss comprises a joined web member pair 20 10 adjacent each end and three joined web member pairs 20 arranged one after the other along a middle portion of the truss 1. Located between one end pair 20 and the middle pairs 20 is a web member 20B (which has been separated from the web member 20A with which it was joined). Correspondingly, located between the other end pair 20 and the middle pairs 20 is a web member 20A (which has likewise been separated from the member 20B 15 to which it was joined). It is to be appreciated that the web members 20A and 20B may be arranged in the truss in many different ways, as part of web member pairs 20 and/or individually. In the present embodiment, the flanges 21, 22 and flanges 13 are joined by clinch 20 connections 40 (see Figures 4 and 5). As will be known to a person skilled in the art, clinching is a method of mechanically fastening two sheets of material together by arranging them between a punch and die then advancing the punch such that the pressure thus exerted on the material causes it to flow into a cavity formed in the die to fix the sheets together. A well known clinching system is the proprietary "TOX" system, which is 25 well suited for fixing the web members to the chords in preferred embodiments of the present invention. In alternative embodiments, the flanges 21 and 22 are fastened against the flanges 13 by fastening elements received therethrough. In one such embodiment, illustrated in Figure 6, 30 the flanges 21, 22 and flanges 13 receive self-tapping screws 50 therethrough. In another embodiment, rivets may be used as the fastening elements.

P 30PER\MRF\Speeex:itionsU 9\INNOVA TION\07r,3(,6 107 doc-9.6/2(09 - 10 Channel members having various cross-sectional configurations may be used to form the chords of the truss without departing from the invention. One such channel 11', which defines an alternative truss chord 10', is shown in section in Figure 8, the channel having a 5 flat web 12' and flanges 13', and a BMT of 0.75 mm. The flanges 21, 22 are fixed against the flanges 13' by clinching and/or fastening elements as described above. At the distal end of each flange 13', the sheet material is formed with a single 90* bend such that it forms a laterally inward lip 15', which, similar to lip 15, comprises a laterally inwardly projecting portion 16, affording stiffness to the respective channel section in the same way 10 as the lip 15, but which is not configured with a re-entrant tip 16 and is thus straight, rather than L-shaped. One of the flanges 13' is deeper than the other such that the lips 15' are offset, permitting two channel members of the type shown to interlock with each other (see Figure 9) to form 15 a chord 10" of the truss, in accordance with a further preferred embodiment of the invention. Specifically, one channel member 11' is inverted and laterally offset slightly with respect to the other such that the shorter flange of each channel 11' is received against the inside face of the longer flange 13' of the other channel member 11'. The lip 15' of each deeper flange 13' is thus received against the exterior face of the web 12' on the other 20 channel member 11', whereby the two channel members 11' are retainably interlocked. Fastening elements, such as self-tapping screws or rivets, are received through the flanges 21, 22 and overlapping flanges 13' to join the former to the latter. Advantageously, the mode of connection between the webs and chords in the preferred 25 embodiments, which does not involve welding, is such that the truss can be constructed simply and quickly. In particular, using channel members, instead of, for example, rectangular hollow section members, for the truss chords can reduce material costs without significantly reducing chord rigidity/strength. Moreover, in the case of the embodiments in which the flanges 21, 22 and flanges 13 are clinched together, the opening defined 30 between the flanges 13 conveniently allows the die of the clinching tool to be inserted into the interior of the channel and received against the inner wall of the flange 13 whilst the P:\OPER\MNRfASpecraifiatioA2(M\INNOVATION\30763664117.doc-9/06/21XN9 - 11 punch of the clinching tool is received against the outer face of the flange 21/22, so that clinching can be effected. Figure 10 shows two adjacent trusses 1 within an arrangement of several parallel trusses in 5 a floor or roof application, in accordance with a preferred embodiment of the invention. In the arrangement, the central web members 35 of all of the trusses are interconnected by a strongback 60. The strongback 60 is also, advantageously, formed by a length of the channel (which may be the channel section 11 from which the chords 10 and end web members 30 are formed or a different, perhaps stronger, section). The web of the 10 strongback 60 is fixed against the webs of each of the central web members 35, which are all arranged in a plane. Advantageously, the strongback 60 may, owing to its also being an open section, be fastened to the flanges 13 by clinching, as described above. Alternatively, it may be fastened by threaded fasteners, such as self-tapping screws, or rivets, as also described above. The end web members 30 of the trusses in the arrangement may also be 15 interconnected by strongbacks 60, in exactly the same manner. Whilst the channel members in each of the described embodiments have a generally C- or U-shaped cross-section, alternative cross-sections are possible in other embodiments of the invention, such as M-shaped cross-sections. 20 In alternative embodiments, the webs and/or chords may be formed from another material having suitable strength and rigidity for the application concerned. The other material may be another metal, for example aluminium. 25 In other embodiments of the invention, the chords may be arranged so as to be not parallel; for example, they may be generally divergent in one direction along the length of the truss. The chords in the preferred embodiments have significantly better straightness and cross sectional size tolerances than timber chords, whereby they can be more easily prefabricated 30 and give rise to greater precision and uniformity in truss profile. In particular, greater precision can be achieved not only in the arrangement of surfaces to which the flooring or P:\OPER\M RF\Specurinom2lxm9lNNOVATIOWuu76366,4 l7.doc-9/06/21X19 - 12 ceiling is to be fixed, but also in the arrangement of chords, allowing for the screw holes to be punched and positioned very accurately in the chords and/or web members, whereby, in the case of factory prefabrication, the need to use jigging, which is generally required in the case of timber chorded trusses, may be eliminated, and, in the case of on-site 5 fabrication, assembly may be carried out to very tight tolerances using simple equipment, such as a power screwdriver. Moreover, compared to timber chorded trusses, the "all steel" trusses of the preferred embodiments are lighter and therefore more easily and quickly handled, both in the 10 manufacturing process and on site during installation. A further advantage of neither the chords nor web members being formed of timber is that permanent termite resistance is ensured. 15 While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described 20 exemplary embodiments. For example, whilst the channel members in each of the described embodiments have a generally C- or U-shaped cross-section, alternative cross-sections are possible in other embodiments of the invention, such as M-shaped cross-sections. 25 Moreover, in alternative embodiments, the webs and/or chords may be formed from another material, particularly another metal, having suitable strength and rigidity for the application concerned. The other material may be another metal, for example aluminium.

P:\OPER\M~RF\Specifiaions\2109\lNNOVATIONu0763664 )To7do-9/6/209 - 13 Also, in other embodiments of the invention, the chords may be arranged so as to be not parallel; for example, they may be generally divergent in one direction along the length of the truss. 5 In the described embodiments, the steel sheet has a base metal thickness (BMT) of 0.75 mm or 0.85 mm. However, other values of BMT are possible, in particular 0.95 mm. More generally, it is envisaged that BMT values as low as 0.4 mm, for light duty applications, and 1.5 mm, for heavy duty applications, could be suitable, though a range of 0.6 mm to 1.1 mm may be more practicable, and a range of between 0.7 mm to 1.0 mm 10 more practicable still. In another embodiment of the invention, the chords may each instead be formed of hollow section, such as square or rectangular hollow section constructed by cold forming steel sheet material having a base metal thickness not exceeding 1.5 mm, the side walls of that 15 section replacing the flanges, and one of the top and bottom walls of that section replacing the web. Typically, such a section is formed by joining two channel members, produced by cold forming, by electric resistance (ER) welding the flange toes of one member to the flange toes of the other. 20 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 25 The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A truss for a roof or floor, comprising: a pair of spaced apart chords, each chord comprising an elongate member having a 5 web and substantially parallel flanges extending from the web; and web members extending between the chords, wherein opposite ends of the web members are fastened to respective flanges of the elongate members. 10

2. A truss according to any one of the preceding claims, wherein the elongate members are formed of steel.

3. A truss according to claim 2, wherein the webs and flanges have a base metal thickness of between 0.4 mm and 1.5 mm. 15

4. A truss according to any one of the preceding claims, wherein the web members are formed of steel.

5. A truss according to claim 4, wherein the web members have a base metal 20 thickness of between 0.4 mm and 1.5 mm.

6. A truss according to any one of the preceding claims, wherein the opposite ends of the web members and the respective flanges of the elongate members are clinched together. 25

7. A truss according to any one of claims 1 to 5, wherein the opposite ends of the web members and respective flanges of the elongate members are fixed to each other by fasteners received therethrough. 30

8. A truss according to claim 7, wherein the flanges of each elongate member extend from the web in the same direction, and each chord further comprises a further elongate P:\OPER\MRF\Spccaficati~ons\209\INNOVATION\30761('A lo7doc-"us2009 - 15 member having a web and generally parallel flanges extending from the web in the same direction, the further elongate member of each chord being inverted relative to said elongate member of that chord and arranged such that its flanges overlap the flanges of the said elongate member, whereby the elongate member and the further elongate member 5 define a box section, and wherein the fastening elements are received through the overlapping flanges to fix the ends of the web members thereto.

9. A truss according to any one of the preceding claims, wherein the elongate members comprise lips formed at ends of the flanges, the lips comprising laterally 10 extending portions which project substantially perpendicular to the flanges of the elongate member.

10. A truss according to claim 9 as appended to 8, wherein the elongate members and further elongate members are configured such that interior faces of lips of the elongate 15 members are received against exterior faces of the webs of the further elongate members, and/or vice versa, whereby the elongate member and further elongate member defining each box section are interlocked.

11. A truss according to any one of claims I to 7, wherein each elongate member 20 comprises a closed hollow section member constructed from cold formed steel sheet material having a base metal thickness not exceeding 1.5 mm, each closed hollow section comprising parallel side walls which replace said flanges and a top wall and bottom wall either of which replaces said web, the ends of the web members being fixed to respective side walls. 25

12. A truss according to any one of the preceding claims, wherein the web members include a channel member disposed at an intermediate position between the ends of the truss ("the intermediate web member"), the intermediate web member having a web and substantially parallel flanges extending from the web, and being arranged such that the 30 outer face of its web lies in a plane which is perpendicular to the direction in which the truss extends for fixed receipt of a strongback thereagainst. r P:\OPER\MR FSpecifiaions\200)9\lNNOVATION\3076366.4 107.doc.9/06/209 - 16

13. An arrangement of trusses, each truss according to claim 12, wherein the trusses are arranged side-by-side such that the outer faces are substantially coplanar and are interconnected by a strongback, the strongback comprising a channel member having a web which is fixed against each outer face. 5

14. A method of constructing a truss for a roof or floor, comprising: providing a pair of channel members to define respective chords of the truss, each channel member having a web and generally parallel flanges extending from the web; and fastening opposite ends of the web members to flanges of the channel members. 10

15. A method according to claim 14, comprising clinching the opposite ends of the web members and the respective flanges of the channel members together to fasten them.

16. A method according to claim 15, wherein each of the clinch connections between 15 the web member ends and flanges is effected by inserting one of a die and punch of a clinching device through an opening defined between the flanges of the respective elongate member such that the punch and die are arranged at opposite sides of the web member end and flange, then operating the clinching device. 20

17. A method according to claim 16 wherein each elongate member comprises a closed hollow section member constructed from cold formed steel sheet material having a base metal thickness not exceeding 1.5 mm, each closed hollow section comprising parallel side walls which replace said flanges and a top wall and bottom wall either of which replaces said web, comprising fastening the ends of the web members to respective side walls.