Background to the Invention : The specification of European Patent Publication No. EP0237667 by one of the present co-applicants (Strarch) discloses a building formed of a series of parallel trusses interconnected by transverse purlins and clad with elongate corrugated sheeting. The trusses each include a pair of parallel and spaced apart upper and lower chords interconnected by diagonal web members. The lower chord is fabricated from a pair of tubes telescopically received within one another and through which high tension cables are threaded.

In construction the corrugated cladding is fixed to the transverse purlins and extends parallel to the trusses with adjacent ridges and grooves of the cladding running parallel to the trusses. The upper edge of the purlins are positioned at or near the neutral axis of the upper chord. Erection of the trusses is effected by tensioning of the high tension cables to provide shortening of the lower chord and arching of the trusses. The corrugated cladding intermediate the trusses and extending across the purlins is placed in pure bending only during this erection process.

The building of EP0237667 suffers from at least the following drawbacks: (i) the building is relatively complicated in construction having a large number of"components" ; and (ii) the trusses present a large number of internally exposed surfaces where dust and other contaminants may collect.

Summary of the Invention : According to one aspect of the present invention there is provided a structure comprising : a plurality of trusses being disposed generally parallel to one another and each including a top chord member and a bottom chord member interconnected by a plurality of web members, the bottom chord member being retractable and thus variable in length to effect displacement and reconfiguration of the truss; and a plurality of elongate cladding panels being connected transverse to the top and/or bottom chords and being configured to deflect sufficiently to accommodate said displacement of the truss.

Preferably the bottom chord member only is retractable to effect its shortening and bowing of the top chord member for arched displacement of the roof truss. More preferably the roof trusses each include one or more tendons operatively coupled to the bottom chord member wherein tensioning of said tendons results in retraction of the bottom chord member and arched displacement of the roof truss. Even more preferably the bottom chord member includes one or more telescopic fittings which permit retraction of the bottom chord member.

Preferably each of the elongate cladding panels is of a channel shaped cross-section including a web or pan and a pair of sidewalls. More preferably the cladding panel is generally trapezium-shaped and the pan includes one or more longitudinally extending strengthening ribs whilst the sidewalls are each provided with a plurality of transversely extending corrugations. Even more preferably each of the pair of sidewalls includes an inwardly and outwardly directed flange, respectively, at its free edge margin, said flanges being configured to interlock with a corresponding flange of an adjacent panel. Generally, the panels are each cold roll formed from strip steel.

Preferably the cladding panels deflect in a concertina manner to accommodate retraction of the bottom chord member and displacement of the truss. More preferably, during the concertina deflection of the cladding panels, the pair of sidewalls of the bottom panels are moved toward one another whereas the sidewalls of the top panels are moved away from one another. Even more preferably, during this concertina deflection of the bottom cladding panels, the pair of sidewalls are moved toward one another and the pan is deflected downward of the bottom chord member.

Preferably the structure includes a plurality of top and/or bottom fixing brackets being mounted to the top and/or bottom chord members, respectively, and configured to

provide fixing for the cladding panels. More preferably each of the top fixing brackets includes an upper mounting plate mounted to the top chord member and configured to fix to one of the pair of sidewalls of the cladding panels. Alternatively, the top fixing bracket includes an upper mounting plate mounted to the top chord member, and an upper affixture plate connected to the upper mounting plate and fixed to adjacent of the cladding panels. More preferably each of the bottom fixing brackets includes a lower mounting plate mounted to the bottom chord member and fixed to the cladding. Alternatively, the bottom fixing bracket includes a lower mounting plate mounted to the bottom chord member, and a lower cladding cleat connected to the lower mounting plate and fixed to one of the cladding panels.

Preferably the structure includes a plurality of top and/or bottom fixing cleats being mounted to the top and/or bottom chord members, respectively, and designed to provide fixing for respective upper and lower ends of the web members. More preferably each of said fixing cleats includes a fixing plate mounted to the top or bottom chord member and fixed to the web member.

Preferably the structure includes a plurality of pairs of support columns each of said pairs being fixed to opposing respective ends of one of the trusses. More preferably the pairs of columns are movable relative to one another to accommodate displacement of the truss.

According to another aspect of the invention there is provided a method of constructing a structure as disclosed in the preceding aspect of the invention, said method involving varying the length of the bottom and/or top chord members to effect displacement and reconfiguration of the truss whilst the cladding panels deflect sufficiently to accommodate said displacement of the truss.

Generally the structure is a roof structure.

Brief Description of the Drawings : In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a roof structure and a method of constructing the roof structure will now be described, by way of example only, with reference to the accompanying drawings in which: Figures 1 and 2 are schematic representations of a roof structure together with bottom and top cladding, respectively, showing the construction and progressive erection of the roof structure; and

Figure 3 illustrates fixing details pertaining to top and bottom chord members, cladding panels and the diagonal webs of the roof trusses of the roof structure of Figure 1 and 2.

Detailed Description of the Preferred Embodiment: As best shown in Figures 1 and 2 there is a structure in the form of a roof structure 10 comprising a plurality of roof trusses such as 12 being arranged generally parallel to and laterally spaced from one another, and a plurality of top and/or bottom cladding panels such as 14A/B and 16A/B, respectively. Each of the trusses such as 12 includes a top chord member 18 and a bottom chord member 20 interconnected by a plurality of web members such as 22A/B. The web members such as 22A/B are oriented diagonal to the top and bottom chord members 18 and 20 and form a zigzag configuration therebetween.

Each of the roof trusses 12 in this embodiment includes the bottom chord 20 which is variable in length. The variation in length is provided by a plurality of longitudinally spaced apart telescopic fittings (not shown) included in the bottom chord member 20 which thus permits retraction of the bottom chord member 20. This retraction of the bottom chord member 20 effects displacement and reconfiguration of the roof truss 12 which progressively arches upwards as depicted in Figures 1 and 2. The telescopic retraction of the bottom chord member 20 is provided by way of one or more tendons (not depicted) which extend internally of the bottom chord member 20 and on tensioning of the tendons the bottom chord member 20 retracts and in this example effects arching of the roof truss 12 and the overall roof structure 10. The specific construction and componentry of this example of the reconfigurable roof truss is disclosed in Australian Patent No's 535636, 588421,588423, and 594056 by the co-applicant Strarch Industries Pty Ltd. The disclosure of these patents are included herein by way of reference.

Importantly, the roof structure 10 includes the top and bottom roof cladding panels such as 14A/B and 16A/B which deflect during erection of the roof structure 10 to accommodate the displacement of each of the roof trusses such as 12 and in this example retraction of the bottom chord member 20. As shown in Figure 1 the elongate cladding panels 14A/B and 16A/B of this example are of a channel shaped cross-section including a web or pan 24 and a pair of sidewalls 26A/B. The cladding panel such as 16A is generally trapezium-shaped and the pan 24 includes a pair of longitudinally extending strengthening ribs (not designated) and the sidewalls 26A/B are each provided with a plurality of transversely extending corrugations (not shown). Each of the pair of sidewalls such as

26A/B includes an inwardly and an outwardly directed flange (not designated), respectively, located at its free edge margin. These flanges are configured to interlock to permit connection of adjacent panels such as 16A/B.

The cladding panels 14A/B and 16A/B are generally cold roll formed from strip steel and the process and apparatus for forming the panels together with a disclosure of the panels themselves are described in International Patent Application No's PCT/AU98/00175 and PCT/AU98/00517 both invented by the co-applicant Wade Hilton Blazley. The disclosure of these international patent applications is considered to be included herein by way of reference.

As shown in the enlarged representations of Figures 1 and 2 the deflectable cladding panels such as 14A/B and 16A/B permit retraction of the bottom chord 20 and thus erection of the truss 12 and the roof structure 10. The top and bottom cladding panels 14A/B and 16A/B deflect in a concertina manner to accommodate shortening and retraction of the bottom chord member 20 and bowing or arching of the top chord member 18. The bottom cladding panels 16A/B of Figure 1 are deflected during erection wherein the opposing pair of sidewalls such as 26A/B and in particular the free edge margins of these sidewalls are moved toward one another and as a result the pan 24 is ever so slightly deflected downward of the bottom chord member 20. The top cladding panels 14A/B of Figure 2 are deflected wherein opposing sidewalls are to a lesser extent shifted away from one another. This deflection of the roof panels 14A/B and 16A/B is shown by the enlarged views of Figures 1 and 2 in the intermediate and erected positions. The hidden detail of Figures 1 and 2 depict the original position of the roof cladding whereas the solid detail depicts the deflected or final position of the cladding.

Figure 3 on the left hand side shows the fixing detail for the bottom chord 20 whereas the right hand side illustrates the fixing detail for the top chord 18. The uppermost representations illustrate one embodiment of the fixing detail whereas the lowermost drawings depict an alternative embodiment. The fixing brackets 30 and 32 of the top and bottom chords 18 and 20, respectively, are in this example welded to said respective chord member and configured to provide fixing for the respective cladding panel. The top fixing bracket 30 is in the form of a mounting plate 34 welded at an acute angle (matching that of the sidewall of the upper cladding panels 14A/B) and bolted to the sidewall (not designated) of the panel such as 14A. The bottom fixing bracket 32 includes a lower mounting plate 34 welded to either one or both of the pair of bottom chord members 20

and bolted or otherwise screw fastened to interlocking flanges (not designated) of adjacent bottom cladding panels such as 16A/B.

In the alternative form of the top chord 18 fixing detail the bracket 30'includes an upper mounting plate 34'welded substantially at right angles to the top chord member 18, and an upper fixture plate 36'welded to the mounting plate 30'and bolted or otherwise screw fastened to adjacent of the roof cladding panels 14A/B. In the alternative form of the bottom chord 20 fixing detail the bottom fixing bracket 32'includes a pair of lower mounting plates 38'welded to or otherwise coupled to the pair of lower chord members 20, and a pair of lower cladding cleats such as 40'bolted or otherwise fixed to both the mounting plate 38'and the adjacent bottom cladding panels 16A/B.

As best shown in Figure 3 the roof structure also includes a plurality of top and bottom fixing cleats 42 and 44, respectively. The top fixing cleats 42 include a fixing plate 46 welded to an underside of the top chord member 18 and generally aligned with the diagonal web member such as 22A to which it is to be fixed. The bottom fixing cleat 44 includes a bottom fixing plate 48 welded to a T-shaped coupling element 50 which in turn is welded to the pair of bottom chord members 20. The bottom fixing plate 48 is generally aligned with the diagonal web member such as 22A to which it is to be fixed. The web members such as 22A/B are at their opposing ends flattened so as to permit screw fastening or other means of fixing to the top and bottom cleats 42 and 44.

The general steps involved in construction and erection of the preceding roof structure 10 will now be described wherein: (i) the roof structure 10 is assembled in its horizontal configuration on a temporary scaffold support structure 15 with the top and/or bottom cladding panels such as 14A/B and/or 16A/B being fixed to the respective top and bottom chord members 18 and 20 of the various pre-assembled roof trusses such as 12; (ii) the bottom chord member 20 of each of the trusses 12 is retracted, in this example by tensioning the corresponding tendons of the bottom chord member, to provide arching of the roof truss 12 as shown in the intermediate position; and (iii) the bottom chord member is further retracted whereupon the roof truss 12 is arched into the erected position and the roof structure is essentially complete.

The construction and erection of the roof structure 10 together with the top and/or bottom cladding panels 18/20 of this embodiment is made possible by way of the deflection of said panels. The cladding panels 14A/B and 16A/B concertina to accommodate retraction of the bottom chord member 20 and the resultant reconfiguration of the roof truss 12. The top and/or bottom fixing cleats 42/44 are in this example designed to deflect or bend to allow the angular shift in the web members such as 22A/B during erection of the truss 12.

Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the art that the described structure and its method of construction have at least the following advantages: (i) the roof structure including the trusses and top and/or bottom cladding panels may be assembled in the horizontal position at or near ground level which reduces safety requirements associated with risks of falling from elevated structures; (ii) the roof structure including the transverse cladding panels may not require purlins and thus there is a reduction in cost and weight of the structure; and (iii) the structure, and in particular a roof structure, lends itself to a variety of applications where for example the truss or roof framework structure is to be concealed.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, the specific construction and fabrication of the roof truss may vary provided it can be reconfigured as broadly defined. The cladding panels need not be of the described configuration but rather any shape which will deflect to accommodate reconfiguration of the roof trusses is acceptable.

All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

It is to be understood that a reference herein to a prior art document does not constitute an admission that the document forms part of the common general knowledge in the art in Australia or in any other country.