AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant: BLUESCOPE STEEL LIMITED Invention Title: ROOF STRUCTURE BRACING The following statement is a full description of this invention, including the best method for performing it known to me/us: - 2 ROOF STRUCTURE BRACING This invention relates to roof structures for buildings and has particular application to roof 5 structures incorporating metal purlins to support a roof covering. The roof structures of modern buildings are commonly employ metal purlins which may be extended 10 transversely across rafters or otherwise supported on a building frame. Formed sheet metal sections for use as purlins are mass produced in various sizes and to varying profiles. Typically such sections may be formed to a C shaped profile or a generally Z-shaped profile, both of 15 these forms having upright webs and extending between upper and lower flanges. When laid with their connecting webs vertical such sections provide substantial stiffness against vertical bending. However the purlins must generally be braced against lateral deflection and 20 rotation by a bridging system incorporating bridging elements or braces extending between neighboring purlins. Typically the braces may be of channel shape and of smaller depth than the purlins. Insulation material may be laid between the purlins so as to be supported by the 25 braces either directly on the braces or via an insulation support structure such as a mesh or secondary purlins laid across the braces. Conventionally the purlin braces are longitudinally 30 aligned with mid-parts of the purlins so as to be located generally midway between the upper and lower faces of the purlins. By the present invention the braces may be offset downwardly from direct alignment with the mid parts of the purlins so as to be closer to the lower flanges of 35 the purlins then to the upper flanges of the purlins. This provides purlin strength enhancement by providing bracing to the unrestrained lower purlin flanges. It also 292661_1 (GHMatters)P88850AU.1 3/11111 - 3 enables direct laying of thicker and variable thickness insulation materials into the spaces between the purlins. According to one aspect the invention may provide a 5 brace structure for use in bracing purlins in a roof structure comprising an elongate brace member extending between a pair of elongate end brackets transverse to the brace member for connection to purlins, wherein the brace member is offset laterally away from direct alignment with 10 mid-parts of the end brackets so as to be closer to the ends of the brackets in the direction of the offset than to the other ends of the brackets. The brace structure may be integrally formed or 15 formed of a number of separate elements. The invention also extends to a roof structure comprising: a plurality of spaced purlins to support a roof 20 covering; and a plurality of purlin braces extending between neighbouring purlins to brace the purlins against lateral deflection; wherein the purlins have generally upright webs 25 extending between upper and lower purlin flanges, the braces are of lesser depth than the purlins and are located closer to the lower flanges of the purlins than to the upper flanges of the purlins. 30 The braces may be located immediately above the lower flanges of the purlins. The braces may be provided with elongate upright end brackets for connection to the upright webs of the 35 purlins and the braces may be located closer to lower ends of these brackets than to upper ends of the brackets. 29281_1 (GHMSItes) P88550.AU.1 3/11/11 - 4 The end brackets on the braces may be connected to mid-parts of upright webs of the purlins. The purlins may be of substantially channel shape 5 or alternatively they may be of substantially Z-shaped cross-section. Insulation material may be located between the purlins and supported by the braces either directly or 10 through an insulation support structure resting on the braces. The invention also extends to a brace structure for use in bracing purlins in a roof structure comprising an elongate brace member extending between a pair of elongate end is brackets transverse to the brace member for connection to purlins, wherein the brace member is offset laterally away from direct alignment with mid-parts of the end brackets so as to be closer to the ends of the brackets in the direction of the offset than to the other ends of the 20 brackets. The brace structure may be integrally formed or formed of a number of separate elements. 25 In order that the invention may be more fully explained particular embodiments will be described in detail with reference to the accompanying drawings in which Figure 1 illustrates diagrammatically a roof structure 30 constructed in accordance with the invention; Figure 2 illustrates one form of brace structure which may be incorporated in the roof structure; Figures 3 and 4 illustrate modified brace structure which may also be incorporated into the roof structure; 35 Figure 5 is a perspective view of the brace structure shown in Figure 2; Figure 6 illustrates how brace structure of the 292661_1 (GHMtters) PBM50.AU.1 3/11/11 -5 construction shown in Figures 2 and 5 are used to brace neighbouring purlins; Figure 7 illustrates an alternative form of brace structure; and 5 Figure 8 illustrates how brace structures of the construction shown in Figure 7 are used to brace neighbouring purlins. The roof structure illustrated in Figure 1 comprises a 10 series of Z section purlins 11 supporting a roof covering 12. Purlins 11 are spaced apart in parallel arrays to either side of roof ridge 13 and may be supported on rafters 14 or in some other manner on a steel building frame. Purlins 11 have generally upright webs 11a and 15 upper and lower flanges 11b, 11c respectively. The purlins may alternatively be formed of C sections in which they will also have upright webs extending between upper and lower flanges. Indeed the illustrated roof structure incorporates C section facia purlins as shown by the 20 purlin 15 in Figure 1 having an upright web 15a and upper and lower flanges 15b, 15c. A plurality of purlin braces 17 extend between neighbouring purlins 11 to brace the purlins against 25 lateral deflection. The braces are provided by brace structures the construction of which may be as shown in Figures 2, 5 and 6. Each brace structure 25 comprises a channel brace member 18 extending between a pair of elongate end brackets 19, 20 transverse to the channel 30 member 18 for connection to the purlins. The channel member 18 is offset away from direct alignment with mid parts of the end brackets 19, 20 so as to be located closer to the ends of the brackets in the direction of the offset than to the other ends of the bracket. More 35 particularly when the brace is installed the channel member is offset downwardly from the mid parts of the upright end brackets 19, 20 so as to be located closer to 2926W1_1 (GHMatters) P80850.AU. 3/11/11 - 6 the lower ends of those brackets than to their upper ends. The downward offset of the channel brace members is such that they are located closer to the lower flanges of the purlins than to the upper flanges of the purlins. The 5 channel members 18 may be offset downwardly to the maximum extent possible so as to be located immediately above the lower flanges of the purlins when the end brackets are connected to the purlins. 10 The purlins are provided at regular intervals along their length with punched holes 30 to facilitate rapid connection of the purlin braces. In the structure illustrated in Figure 1 the three purlins between the innermost purlin adjacent the ridge and the facia purlin 1 are interconnected by braces 11 of the construction illustrated in Figures 2, 5 and 6. In this construction one of the end brackets 19 is provided with a pair of longitudinally projecting vertically spaced tabs 21 perforated by holes 22 whereas the other end bracket 20 is 20 provided with laterally a pair of vertically spaced laterally projecting hooks 23. The braces are installed by inserting the tabs 21 of bracket 19 through a pair of the punched purlin holes 30 and then engaging the hooks 23 of the next installed brace into the holes 22 of the tabs 25 21 after they have been inserted through the punched purlin holes in the respective purlin web. Hooks 23 are initially engaged with the new brace generally at right angles to the previously installed brace and then swinging the new brace into alignment with the previously installed 30 brace to firmly connect the two braces to the purlin between them. In view of this kind of connection the end bracket 19 with the tabs 21 may be termed a female bracket and the bracket 20 with the hooks 23 may be termed a male bracket and the standard brace may be termed a male-female 35 brace or strut. Two modified forms of brace structures are provided 292861_1 (GHMatters) P88850.AU. 3/11/11 -7 for connection to the first purlin adjacent the ridge at the beginning of a brace installed sequence and to the facia purlin at the end of the installation sequence. The first modified brace structure, which may be termed a 5 female bolted brace 25F, is illustrated in Figure 3 and the second modified brace structure, which may termed a bolted male brace 25M, is illustrated in Figure 4. The bolted female brace 25F has a female end bracket 19 with projecting tabs 21. However there are no projecting hooks 10 at the other end of the brace and the end bracket simply has holes to allow the end bracket to be bolted to the innermost purlin adjacent the roof bridge and to be also connected to a threaded rod bridging 24 as shown in Figure 1. Modified brace 25M as illustrated in Figure 4 has a 15 male end bracket 20 with projecting hooks 23 but at the other end it has a plain end bracket with holes for bolting to a facia purlin. The illustrated braces enable rapid connection of 20 braces between the roofing purlins. An installation sequence begins by bolting a bolted female brace 25F to a ridge purlin. The tabs 21 of the bolted female brace are then inserted through purlin holes 30 of the neighbouring purlin and these are connected to the hooks 23 of a 25 standard male-female brace. Following the roof line the installation continues with male-female braces being successively fitted between neighbouring purlins until a male bolted brace 25M is required to attach the facia purlin to complete the bridging installation. 30 Because the brace channels are offset downwardly from alignment with the mid parts of the purlin webs to the maximum extent possible to allow the braces to sit immediately above the lower flanges of the purlins, the 35 depth of the spaces 24 between the braces and the roof covering 13 is maximised or enhanced to enable installation of thick insulation. The insulation may be 292001.1 (GHMatter) P8850.AU.A 3/11/11 - 8 supported directly on the braces 11 or it may be laid onto an insulation supporting structure extended across the braces. The supporting structure could be a mesh or grid structure or a series of secondary insulation supporting 5 purlins laid transversely across the braces. The downward offset of the purlin braces also improves the structural performance of the purlins by bracing the purlins closer to the unrestrained lower purlin flanges. The offset also increases the air gap within the roof structure and 10 enables thermal and moisture barriers to be installed with confidence. Figures 6 and 7 illustrate a further modified form of brace structure which may be incorporated into a roof 15 structure in accordance with the invention. This structure comprises a channel shaped brace member 31 and end brackets 32, 33. End bracket 32 is provided with a pair of hooks 34 and end bracket 33 is angled relative to brace member 31 and provided with a pair of hooks 35 which 20 are of larger size than the hooks 34 of the other end bracket 32. As shown in Figure 7 braces of this formation are installed by firstly inserting the smaller hook members 33 of one brace structure through a pair of punched purlin holes and then fitting the larger hooks 35 25 of the next installed brace structure over the smaller hooks 34 after they have been inserted through the punched holes. The angling of the end bracket 33 with the larger hooks 35 enables those hooks to be initially engaged by positioning the new brace generally at right angles to the 30 previously installed brace and then swinging the new brace into alignment with the previously installed brace to firmly connect the two braces to the purlin between them. The illustrated roof construction and brace 35 structures have been advanced by way of example only and many variations are possible. For example channel shaped braces are commonly used in roofing structures but it 292681_1 (GHMatter) P8865OAU.1 3/11111 -9 would be possible to substitute angle, rod, or tube or members of other shapes. The shape of the purlins could also be modified and the end brackets of the brace structures could be varied to suit varying installation 5 needs. Instead of offsetting the brace members downwardly on the brace end brackets the purlins could be provided with pre-formed holes located toward their lower flanges for location of the braces in the downwardly offset positions. It is to be understood that many such 10 variations will fall within the scope of the appended claims. 2926881_1 (GHMatlers) P8SO.AU.1 3/11/11