FIELD OF THE INVENTION

The present invention relates to an arched building structure and a method of constructing the same and relates particularly, but not exclusively, to such a building structure and construction method that employs lightweight pressed metal frame members.

The present invention was developed in response to the need to provide a large (over 30 metre) span building structure for use as an aircraft hangar. However, because of the simplicity

of the structure and the ease with which it can be erected it lends itself to many other applications involving large or smaller span structures such as, for example, greenhouses, undercover sports stadiums and exhibition centres. DISCUSSION OF PRIOR ART

In recent years, structural engineers have applied their skills to designing new structural forms and techniques to meet the structural needs of the twentieth century. The Strarch Building System is anAustralian system also developed to provide large span (up to 90 metres) building structures. The Strarch Building System is similar to our invention only in so far as construction takes place at ground level before the building is lifted, and in its final position it forms an arch shape. However, in the Strarch system the structure is typically lifted as one into place using hydraulic pre-stressing, (or induced compression) , of the bottom chord of each of the roof truss members, which causes the truss members to deflect upwards. Although this structure forms an arch shape in its final position, this arch terminates at a wall provided on each side to support the structure and does not extend down to the ground as in the present system. Examples of structures built in accordance with the Strarch Building System are described in Australian Patent Nos. 588421 and 588423.

The present building system is much simpler than the Strarch system as it uses simple beam frames rather than trusses to support the roof. More importantly, the structure according to the present invention gains its strength from its arch shape being anchored at the ends and not by the use of hydraulically induced compressions within the structure. Furthermore, our arched shape is not stressed into the structure but the frames are actually constructed in an arched configuration. The inclusion of a central pivotal connection in the preferred embodiment makes lifting exceptionally easy. SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided an arched building structure comprising: first and second elongate frames, each frame comprising a

plurality of rigid frame members fixed end to end in the shape of an arc, said first and second frames being adapted to be connected to each other at one end whereby, in use, said frames can be lifted and connected so that the connection forms a ridge of the building structure, and held in the lifted position by anchoring the free ends of the frames.

Typically said first and second frames are pivotally connected prior to lifting so that the pivotal connection forms said ridge of the building structure. Preferably each frame comprises a plurality of frame bays arranged to form frame segments, said arched building structure comprising a plurality of said frame segments constructed side by side and pivotally connected along said ridge.

The pivotal connection is preferably in the form of a pin joint between opposing frame members at the ridge. In its preferred form the building structure is a three pin arch frame structure being anchored to the ground at the free ends with pin joints. Preferably the structure is stiffened by columns provided adjacent the free ends of the frames. In the preferred embodiment each frame member comprises a lightweight pressed metal beam, and the frames are constructed with the frame members forming a double beam.

Preferably mounting means are provided on the ends of said frame members to enable the frame members to be fixed end to end. In the most preferred form of the invention the mounting means comprises a short length of L-shaped angle iron welded or rivetted to the end of the pressed metal beam.

According to another aspect of the present invention there is provided a method of constructing an arched building structure, the method comprising: joining a plurality of substantially rigid frame members end to end in the shape of an arc to form first and second elongate frames; lifting and connecting said frames to each other at one end so that the connection forms a ridge of the arched building struc ure; an , anchoring the free ends of the frames to hold the structure

in a lifted position.

Typically, said step of lifting and connecting comprises pivotally connecting said first and second frames at said one end prior to lifting both frames simultaneously so that the pivotal connection forms said ridge after lifting.

Preferably said step of joining involves fixing mounting means on the ends of said frame members, said mounting means providing an end face for the frame members.

The method of construction preferably further comprises the steps of: connecting a plurality of said frame members with purlins arranged transverse to the longitudinal direction of the frames; and, connecting diagonal bracing members to provide rigidity for said frames.

Preferably said step of lifting involves lifting a plurality of frame bays of said frame, said frame bays forming a frame segment, each segment being lifted separately to form said building structure. Preferably said step of lifting involves lifting the frames at the pivotal connection and/or applying a jacking force to one of the frames at its free end.

The step of anchoring preferably involves anchoring the free end of one frame or frame segment prior to lifting, and anchoring the free end of the other frame or frame segment after lifting.

According to another aspect of the present invention there is provided a frame member for a lift arch building system, the frame member comprising: a substantially rigid beam having a mounting means fixed to at least one end thereof, said mounting means providing an end face for the beam; said mounting means being fixed with said end face substantially transverse to the longitudinal direction of the beam whereby, in use, a plurality of said frame members can be joined end to end to form an arc-shaped frame.

Preferably said beam is a straight beam and said mounting means is fixed with said end face at an angle slightly off

perpendicular. Preferably said beam is a cold formed pressed metal standard section beam. In the prefered embodiment the standard section beam used for the frame members is a C section beam, and two of said C section beams may be joined adjacent to each other to form a double beam.

Preferably said mounting means comprises an L-shaped piece of angle iron welded or rivetted to the end of the C section beam.

BRIEF DESCRIPTION OF THE DRAWINGS In order to facilitate a better understanding of the nature of the invention, a preferred embodiment of the lift arch building system and construction method will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a preferred embodiment of an arched building structure according to the invention shown in perspective view;

Figure 2 is a plan view of the structure illustrated in Fig. 1; Figure 3 is a section view through the line A-A in Fig. 2;

Figure 4 illustrates a section of wall columns viewed in the direction of the arrow marked VIEW 1 in Fig. 3;

Figures 5 (a) and (b) are a side elevation and plan view respectively of a typical frame member connection at detail 2 in Fig. 2, and Figure 5 (c) is a section view through the line A-A in Fig. 5 (b) ;

Figures 6 (a) and (b) are a side elevation and plan view respectively of a typical pivotal connection at the ridge;

Figure 7 illustrates a typical fly brace connection; Figure 8 illustrates the configuration of two types of steel members employed in the embodiment of the building system , and includes a table of dimensions for the preferred sizes of each member;

Figure 9 (a) and (b) are a side elevation and a plan view respectively of typical base plate detail at 1 in Fig. 2;

Figures 10 (a) and (b) are a side elevation and end view respectively of a wall column detail at 3 in Fig. 4;

Figure 11 illustrates a preferred method of constructing the lift arch building structure;

Figure 13 is a side elevation of detail 5 in Fig. 12; Figures 14 (a) and (b) are a side elevation and plan view respectively of detail 4 in Fig. 12 and Figure 14 (c) is a section view through the line A-A in Fig. 14 (a) ;

Figures 15 (a) and (b) are a side elevation and plan view respectively of a typical frame member connection in an alternative embodiment, and Figure 15 (c) is a section view through the line B-B in Fig.15 (b) .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 illustrates in perspective view one embodiment of an arched building structure, in this case a large 40 metre span aircraft hangar, designed and constructed in accordance with the present invention. In the schematic representation of Fig. 1 it can be seen that the building structure comprises first and second elongate frames 10 and 12 respectively, each frame comprising a plurality of straight rigid frame members 14 fixed end to end in the shape of an arc. The first and second frames 10 and 12 are pivotally connected to each other at one end to form a ridge 16. The arched structure is held in the lifted position, as illustrated in Fig. 1, by anchoring the free ends 18 of the frames to the ground. In this embodiment, the frames 10 and 12 approximate circular arcs, but do not form a semi- circle when in the lifted position. Instead, the two frames 10 and 12 approximate the ideal parabolical arch shape when in their final lifted positions.

In Fig. 1 it can be seen that each of the frames 10 and 12 comprises fifteen frame bays preferably arranged in groups of three frame bays per frame segment. Each of the frames 10 and 12 comprises five frame segments constructed side by side and pivotally connected along the ridge 16 to the corresponding frame segments of the opposite frame to form the arched building structure. The arrangement of the frame segments can be seen more clearly in Fig. 2 which is a plan view of a slightly different building structure from that illustrated in Fig. 1.

In Fig. 2 the arrangement of the frame segments 20, each

comprising three frame bays 22, can be clearly seen. Each of the frames 10 and 12 comprises three frame segments 20, the segments at both ends consisting of three end bays and the five internal frame bays making up the remaining frame segment 20 and two empty frame bays 21. When each of the frame segments 20 has been lifted into place the two empty frame bays 21 are filled by bridging the gap between frame segments with loose purlins 27. When the empty frame bays 21 are thus filled they become indistinguishable from the adjacent frame bays. The configuration of diagonal bracing members 24 and purlins 26 can also be clearly seen in Fig. 2. Each frame segment 20 is provided with a plurality of diagonal bracing members 24 extending diagonally across the centre frame bay, and a plurality of purlins 26 extending transversally across each frame segment. The combined effect of the purlins 26 and diagonal bracing members 24 is to give rigidity to the frame segments, whilst the purlins serve the double function of supporting the roof cladding material. In Fig. 2 it can be seen that both the end frame segments are provided with twice the number of purlins 26 as the internal frame segment. The additional purlins are provided to give increased strength to the end segments, which experience the most stress and strain due to increased wind turbulence at both ends of the building structure. The selection of three frame bays 22 per frame segment 20 is a matter of convenience only, as this number of frame bays was thought to be a convenient number which could be lifted in one segment without too much difficulty. Clearly, each frame segment may comprise any desired number of frame bays, indeed each complete frame 10 and 12 could be lifted in a single lifting operation, although this would greatly complicate the lifting operation which will be described in greater detail below.

Figure 3 is a section view taken through the line A-A in Fig. 2 and illustrates the arched shape of the building structure made possible by the joining of the straight frame members 14 end to end in the shape of an arc to form the first and second frames 10 and 12 respectively. The positions of the purlins 26 can also be clearly seen in Fig. 3. Also visible in Fig. 3 are the

positions of edge wall columns 28 adjacent the free ends 18 of the frames 10 and 12 respectively. The free ends 18 of the frames are anchored to the ground in concrete footings 30, to be described in greater detail below, and the edge wall columns 28 are likewise anchored on concrete footings and connected to the respective frames 10 and 12 adjacent a splice point, where two frame members 14 are fixed end to end.

Although the arched building structure is stable without the columns 28, their addition to the frames 10 and 12 further stiffens the structure and greatly improves its load carrying ability and deflection response. The connection of the column 28 to the frame member 14 will be described in greater detail below with reference to Fig. 10. Figure 4 illustrates a section of wall columns viewed in the direction of the arrow marked VIEW 1 in Fig. 3. Three rows of lap girts 32 are provided between each of the columns 28 together with diagonal bracing members 34 to form an internal edge wall for the building structure. The section of wall illustrated in Fig. 4 is that of three end bays, and the diagonal bracing members provide increased rigidity in the longitudinal direction in these sections. However, the wall sections for the internal bays do not require the diagonal bracing as these sections are not exposed to the same degree of stress and strain. The arrangement of a typical connection between two frame members fixed end to end will now be described in greater detail with reference to Fig. 5 (a) , (b) and (c) .

Figure 5 (a) is a side elevation of a splice point at detail 2 in Fig. 2. Fig. 5 (a) illustrates two mounting members 14 fixed end to end by means of mounting means 36 fixed to the ends thereof in such a manner that the mounting means 36 provides an end face for each member 14. In this embodiment mounting means 36 comprises a short length of L shaped angle iron welded to the end of frame member 14 substantially transverse to the longitudinal direction of the frame member, but at an angle slightly off perpendicular whereby, in use, several of the frame members 14 can be joined end to end using the mounting means 36 to form the arch shaped frame. In this embodiment the L shaped mounting means 36 are fixed to the ends of the members 14 at an

angle of 4.75° off perpendicular to the longitudinal direction of the frame members. However, clearly the angle of orientation of the mounting means 36 is dependant upon a number of factors, including the intended span and height of the building structure and the number and length of the frame members 14 to be employed in the structure. As can be clearly seen in Figs. 5(a) and (b) , the angle of 4.75° is determined by the position of cleats 37 welded to the top and bottom surfaces of the members 14. Holes 38 in the cleats 37 provide additional weld edges for fixing to the members 14. This method of fastening the angle iron mounting plates to the frame members 14 obviates the need to cut the ends of the members to the required angle.

In this preferred form of the invention, the main frame members 14 are lightweight pressed metal beams, manufactured in standard light gauge cold formed sections. The frame members 14 are C section beams with dimensions as listed in the Table 1 in Fig. 8 beside reference C25020. To date, in the structural engineering industry, the joining of light gauge cold formed sections with a connection which still enables the full strength of the section in bending to be developed, has not been considered a practical alternative. In the present building system, it has been found that fixing a short section of L shaped angle iron to the ends of the beams 14 allows the beams to be bolted or rivetted end to end in a relatively simple operation and still enables the main frame members 14 to develop their full strength. The L shaped mounting means 36 are welded or rivetted to the ends of the frame members with one face of the angle iron flush against the outside of the vertical face of the C section beam and the other perpendicular f ce of the angle iron providing an end face for the C section beam. The two frame members 14 may then be bolted together with four bolts provided through the bores as illustrated in Figs. 5 (a) and (c) .

Figure 5 (b) is a plan view of the splice or connection between the frame members 14, in which it can be seen that the frame design utilizes a double beam system (two beams adjacent to each other) . By utilizing a double beam system, the weight of the beam components can be kept down for the larger spans.

In Fig. 5 (b) the orientation of the four lengths of angle iron comprising mounting means 36, bolted together in a cross formation, is clearly visible. The two adjacent beams are bolted together by means of two bolts passing through bores provided in the mounting means 36, as illustrated in Fig. 5 (a) . When the two beams are bolted together adjacent to each other in the manner described, they effectively form a double beam having an I section as illustrated in Fig. 5 (c) .

Also illustrated in Figs. 5 (a) and (b) is the position of the purlin 26 and diagonal bracing member 24 adjacent the splice, at detail 2 in Fig. 2. Purlin 26 is a Z section beam, (reference Z10016 in the table of Fig. 8) , which is connected to the frame members 14 by means of an L shaped bracket 27 shown in broken outline in Fig. 5 (b) and in side elevation in Fig. 5 (a) . The diagonal bracing member 24 is a C section beam provided with a cleat 25 welded thereto and having its end cut to fit squarely on the frame member 14 adjacent the purlin 26, and which is bolted to the frame member 14 with a pair of bolts. It has been found that the frame members 14 can be manufactured in a reasonable length, (in this embodiment 4.1 metres in length), which reduces the number of splices and therefore reduces the need for an excessive amount of jointing. The arrangement of a typical pivotal connection between frame members 14 at the ridge 16 will now be described in detail with reference to Fig. 6. Figure 6 (a) illustrates a typical connection at the ridge in side elevation, in which the frame members 14 are each provided with mounting means 36 at their respective ends, similar to that illustrated in Fig. 5. The pivotal connection between the frame members 14 is provided in the form of a hinge connection comprising a T-shaped connecting member bolted to mounting means 36 on one of the frame members 14, and having a flange plate 40 protruding therefrom provided with a central hole for receiving a connecting pin. Flange plate 40 is received between two matching adjacent flange plates 42 bolted to the opposite mounting means 36 of the other frame member 14. The interleaved arrangement of the flange plates 40 and 42 can be more clearly seen in Figure 6 (b) , which is a plan view of a

typical pivotal connection between double beams formed by adjacent frame members bolted together in the manner previously described with reference to Fig. 5. All purlins, diagonal bracing members and fly brace members have been omitted from Figs. 6 (b) and (c) for clarity. The hinge pin passing through the flange plates 40 and 42 in Figs. 6 (a) and (b) is in the form of a bolt 44 provided with teflon washers to encourage free movement of the joint, and a finger tight nut and lock nut to hold the bolt in place. Once the frames are in the lifted position, the joint is locked together with short struts 45 to provide continuity at the ridge. Each strut 45 comprises two short lengths of angle iron with plates welded to each end, which are then fixed end to end with some packing 46 therebetween to span the distance between the mounting plates 36.

The pivotal connections illustrated in Fig. 6 allow virtually unhindered movement in the plane of the flange plates 40 and 42, (parallel to the longitudinal direction of the frame members 14) , but allow virtually no movement in the axial direction of the hinge pin connecting bolt 44. Also illustrated in Fig. 6 (a) is an expandable flashing member 48 fabricated from light gauge resilient sheet metal, and formed to clip onto the facing edges of the cladding material 50 fastened to the purlins 26 on the frame members 14. Figure 7 illustrates a typical fly brace connection between a frame member 14 and purlin 26. A fly brace member 54 is bolted to the purlin 26 at one end, and to the internal vertical face of the C section frame member 14 at the other end. The adjacent frame members 14, forming a double beam, are provided with packers 56 welded to the external face of the C section through which a bore is provided to receive the bolt connecting the purlin 54 to the frame members. The packers 56 help to maintain a 20mm gap between the adjacent frame members of the double beam illustrated in Fig. 7. Fly braces are provided at every purlin for internal bays and every second purlin line for the end bays. In Fig. 7 it can be seen how the purlins 26 extend beyond the respective frame members 14 to overlap at the points where they

are connected to the frame members of the double beam. A lap joint is readily achieved with the Z section purlins and helps to increase the strength of the frame.

Anchoring of the free ends of the frames 10 and 12 in Fig. 2 will now be described in more detail with reference to Figs. 9 and 10.

Figure 9 (a) is a side elevation of a typical base plate connection, of the kind employed at detail 1 in Fig. 2. The base plate connection comprises a base plate member 60 bolted to a concrete footing (not shown) provided at ground level. Frame member 14 is provided with a 3mm thick stiffening plate, shown in broken outline in Fig. 9 (a) , and welded to the inside of the C section beam. The free end of frame member 14 and the stiffening plate is provided with two holes 62 and 64 extending therethrough. Hole 62 is used during the lifting operation of the frame segments to be described in greater detail below with reference to Figs. 11 to 14. Hole 64 is provided for connecting frame member 14 to the base plate member 60. Base plate member 60 is made of 12mm thick steel plate and is received between the adjacent frame members 14 of the double beam. A single bolt with teflon washers and finger tight nut and lock nut is received through hole 64 to provide a pin connection between the frame members 14 and base plate member 60, (similar to the pivotal connection at the ridge 16 illustrated in Fig. 6) , which effectively anchors the free end of the frame members to the base plate 61. The base plate 61 is made of 16mm thick steel plate and is bolted to the concrete footing using four heavy duty anchor bolts.

In this embodiment of the building structure the footing for the base plates is made of reinforced concrete poured into a trench extending the length of the building and being 0.7m deep and 1.6m wide. Similarly, the footing for the edge wall columns 28 is reinforced concrete poured into a trench extending the length of the building and being 0.6m wide by 0.6m deep. With smaller portable structures, the footings may be provided by alternative means, such as containers for holding water or sand ballast to anchor the structure under wind loadings. The

connection of the frame members 14 to the wall columns 28 will now be described with reference to Fig. 10.

Figure 10 (a) provides a side elevation of the top end of a typical wall column 28 at detail 3 in Fig. 4. Each edge wall column 28 comprises two C section beams 68 joined together to form a double beam. The column 28 is connected to the frame member 14 by a connecting plate 70 which is bolted between the beams 68 at the top end of column 28 and to the frame member 14 adjacent the splice. Purlin 26 on frame member 14 supports a roof cladding material, in this case SPANDECK HI-TEN in 700, and a lap girt 32 connected to the column 28 by means of a cleat 74, supports a wall cladding material 72. Figure 10 (b) illustrates the position of the lap girt 32 on the wall column 28, and also illustrates the position of the diagonal bracing members 34 which are provided between the columns of the end bays as illustrated in Fig. 4. The preferred method of constructing the lift arch building structure of the invention will now be described with reference to Figs. 11 to 14.

Figure 11 is a section view of the building structure similar to Fig. 3, showing the structure in various stages of construction. In the method illustrated in Fig. 11, an internal propping system is used to lift the frame segments in the initial stages of construction. In this preferred method the building is divided into three lifting segments as previously described. Each frame segment may be lifted into its final position by either lifting internally or externally , or by jacking or winching the bases of the frames together, or a combination of both, (as in the following described method) , as is common for larger structures. External lifting of the building segments may be performed by a crane, in which case the crane must continue to support the lifting segment at the pivotal connection along the ridge, until jacking has proceeded to remove all the load from the crane. The lifting of the lightweight frames in segments, typically three frame bays per segment, to its final position has eliminated the need for expensive hydraulic systems normally expected to be required to lift a building of this size into place.

Each lifting segment is preferably constructed from the central pin outwards, by connecting the frame members end to end and joining with purlins and diagonal bracing members in the manner described with reference to Fig. 5, while the central pin is supported by the internal propping system in a lowered position. When the full span of each frame segment 10 and 12 has been completed, (in this embodiment comprising 6 frame members joined end to end) , the building structure will be in its lowered position as illustrated in Fig. 11. The free end of frame segment 12 is pivotally connected to the base plate members 60, whilst the free end of the frame segment 10 rests on skate beams 80 supported by footings 82 as shown in the left hand side of Fig. 11. A jacking or winching arrangement is provided to pull the free end of the frame segment 10 along the skate beams 80 towards the base plate member 60, following the lifting operation performed by the internal propping system. When the internal propping system has lifted the pivotal connection to a height of approximately 6.2m, as illustrated in Fig. 11, the structure is lifted the remainder of the way by a jacking arrangement. Prior to lifting, the roof cladding material can also be fastened to the frame segments at ground level which greatly simplifies the method of construction. Although lifting with the internal propping system is preferably performed at the pivotal connection, such lifting can also be performed at any other suitable location on the frames. The jacking arrangement at both ends of a typical lifting segment will now be described with reference to Fig. 12.

Figure 12 is a plan view of a typical jacking arrangement for a frame segment. The free ends of the frame members 14 of the frame segment are pivotally connected to a strong beam 84 which is slidably supported on the skate beams 80. Two 5 tonne capacity wire ropes 86 are connected to the strong beam and extend to a jack and pulley arrangement anchored to the footings of the building structure. The pulleys allow 2.5 tonne capacity jacks to be employed to provide the pulling force applied to the strong beam to help lift the frame segment, and to temporarily hold it in its final position.

Figure's 14 (a) and (b) illustrate the connection of the wire rope to strong beam 84 using a shackle 87. The shackles 87 connect to the strong beam 84 at the location of a pair of skates 88 which ride on the skate beams 80. Figures 14 (a) and (c) illustrate the configuration of the skate 88 which facilitates sliding movement of the strong beam supporting the frame segment 10 as it is being lifted to its final position. When the strong beam has been pulled the full length of the skate beams 80, the free end of the frame segment 10 is almost in its final position, as illustrated in Fig. 13. Figure 13 is a side elevation of detail 5 in Fig. 12.

In Fig. 13, it can be seen how the frame member 14 in its initial position, as shown in broken outline, is pivotally connected to the strong beam 84 by a pin connection through hole 62 of the frame member. When the strong beam 84 reaches its final position, the hole 64 aligns with the corresponding hole in the vertical base plate member 60 mounted on the base plate 61. Frame member 14 is connected to the base plate members 60 by means of bolts as previously described with reference to Fig. 9. Once the frame segment has been anchored to the footings 30, the tension on the wire ropes 86 can be released. Preferably, the wall columns 28 and bracing members are fixed in place prior to releasing the structure. According to the preferred method of construction, a three bay frame segment is not lifted into position until the next adjacent three bay segment has also been constructed on the ground.

From the above description of a preferred embodiment of the lift arch system, it will be apparent that the arched building structure is basically a three pin arch frame structure, (having a simple pin type connection for the bases and at the top) , which can be erected on the ground and either lifted or hand winched into place in segments. The central pin greatly reduces the stresses imposed upon the structure during the lifting operations, and this assists in keeping the beams lightweight. This type of arch structure has not been commonly utilized due to the perceived construction difficulties associated with this shape, even though it has proven to be very economical in terms

of reduced material and labor costs.

The preferred constructionmethod for this type of structure has totally removed the difficulties with traditional construction procedures. The lightweight nature of all components used in the structure has also permitted the frames to be easily erected by two men on the ground, without the need for mechanical assistance by cranes, etc. The lightweight, simple construction of the frames permits even large clear span buildings (up to 55m) to be manufactured in kit form, or as transportable and demountable structures. The construction method permits a temporary building to be easily lowered back to the ground, where it can be bolted for transport of the lightweight components. To facilitate the transport requirements of demountable structures a modified arrangement has been designed to permit a PVC or canvas roof cladding to be used, which can be easily placed and removed on the ground and rolled up for transport.

Figure 15 illustrates an alternative arrangement of a typical main frame member connection for PVC or canvas covering. The connection of the frame members 14 is basically the same as that illustrated in Fig. 5 except that mounting means 36 has been provided with a central cut out portion 38, as illustrated in Fig. 15 (c) to provide a recess through which a guide 90 can extend along the inner wall of the C section beams of the frame members 14. Guides 90 are adapted to receive an edge bead provided on the PVC or canvas cladding material, which is provided in sheets having a width dimension corresponding to the width of each frame bay. The roof cladding material sheets can be drawn over each frame bay with their longitudinal edges slidably received in the guides 90, and can be partly supported by bracing members 92 shown in Fig. 15 (b) , which are connected to the frame members 14 by angle cleats 94 as illustrated in Fig. 15 (d) . The angle cleats and bracing members have been omitted from Figs. 15 (a) and (c) for clarity. The lift arch building structure and construction method of the present invention has totally removed the difficulties associated with the construction of traditional pinned arched

structures and results in a final structural form capable of high load carrying ability and minimal deflection response. This efficient structural form has also permitted the use of lightweight frame members with a capacity to cover very large spans. It will be apparent to those skilled in the structural engineering arts that many variations and modifications may be made to the lift arch building system, other than those already described, without departing from the essential inventive concepts. For example, variations of the system for different span configurations can be developed, and high tensile steel fabricated beam sections can be employed for the frame members for buildings with spans over 55m, where lightweight cold formed standard sections may not be practical. Furthermore, whilst the preferred frame members are straight beams, the frame members may themselves be fabricated in an arc shape or curved configuration to form the arc shaped frames when joined end to end.

In the above described preferred method of construction, the two frames 10 and 12 or frame segments are pivotally connected prior to lifting and then lifted simultaneously in a single lifting and jacking operation. However, it is also possible to lift each frame or frame segment separately and then connect the two frames or frame segments at the ridge in the lifted position. However, this latter method is obviously less advantageous than the described preferred method. In addition, in the described embodiment frame members 14 are bolted together using bolts passed through bores provided in the mounting means 36. However, the frame members 14 can also be joined end to end by rivetting, using large, (for example, 16mm), rivets. Indeed, it is envisaged that rivets be used everywhere that bolts or welding is employed in the above described embodiments of the arched building structure, thus further simplifying the method of construction.

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