Such structures may be composite structures, which may include or comprise flexible sheets of material such as shade cloth, canvas, or the like, which are, or are adapted to be used as awnings, umbrellas, tarpaulins or the like.

Shade cloth, as an example, has been known for many years. One form of shade cloth is manufactured by I. T. C. Of Asheville Inc., of Asheville, North Carolina, United States of America. It is a woven product, made from 100% polypropylene, and is available in various grades, from 63% shade to 95% shade.

For use as sun protection when growing crops, shade cloth may be mounted on a simple frame, by, for example, stretching the fabric over a wooden frame, and then one may tack, nail or staple the stretched fabric to the frame. I. T. C. of Asheville Inc. has a more sophisticated system in which shade cloth is secured to a sub-frame consisting of 41.3mm pipe, which sub-frame is secured by spring means to a main frame, such that when the sub-frame is loaded with ice or snow, the springs release, preventing structural damage to the framework. Such an arrangement is not suitable for other applications where it is desired to shade an area, particularly for shading or covering an area used by people.

These days, there is much use of flexible sheets of material as covering means for open areas, so that people may eat, drink and carry on other activities out of direct sunlight and/or protected from the rain. Such arrangements often use triangular sheets of material to simulate sails, and such sheets of material are held under tension by fixtures normally located at the corners of the sheets.

In order to support such"sails"above the ground, and in particular to cope with the forces required to hold the sails in tension, such arrangements necessarily must have large support posts sunk into the ground, often at an angle to the vertical. This can result in an unsightly proliferation of such posts, which also reduce the available space for activities beneath the cover, and add considerable cost to such a arrangement.

US-A-4,417,597 describes an awning structure in which a beam formed in two parts and joined by a joiner is coupled to an awning formed of shade cloth and canvas. The beam is deformed and connected to two poles. The deformation of the beam causes the awning to be placed under tension. However, upright support members also form part of the structure, and contribute to the tensioning of the awning and the placement of the beam under stress, and thus there is no self-contained structure disclosed, separate from the support members.

US-A-5,299,590 discloses a collapsible sun shade structure generally similar to a tent, in which structure a fabric cover is stretched over three interconnected flexible rods, the structure then being capable of being secured to the ground.

It is an object of this invention to provide an improved structure adapted to cover an area.

The invention provides a structure including a sheet of material attached to a frame, characterised in that said sheet is flexible and adapted to be placed under tension by said frame, in that said frame is constituted by at least one frame member, and in that all forces acting between said sheet and said or each frame member are contained within said structure.

The invention also provides a structure including a sheet and at least one frame member, characterised in that said or each frame member is relatively rigid but at least partially deformable, and in that said structure is self-contained as far as forces between said sheet and said at least one frame member are concerned, such that tensile forces in said sheet are balanced by the deformation of said or

each frame member.

Embodiments of the invention, which may be preferred, will be described in detail hereinafter with reference to the accompanying drawings, in which: Fig. 1 is a top plan view of one embodiment of a cover structure according to the present invention; Fig. 2 is a side elevation of the cover structure of Fig. 1, supported on posts; Fig. 3 is a side elevation of the supported cover structure of Fig. 2, from a position indicated by arrow 3 in Fig. 1; and Fig. 4 is a side elevation of the supported cover structure of Fig. 2, from a position indicated by arrow 4 in Fig. 1.

The cover structure 10 of Fig. 1 includes a sheet or"sail"12 of canvas or any other suitable sheet material such as shade cloth or any of the other synthetic materials available today, which sheet material is preferably flexible and may preferably be able to stretch to at least a limited degree when placed under tension, and has, before being placed under tension, a generally rectangular or square shape. Of course, the sheet 12 could be in any initial shape, such as that of a triangle, polygon or the like.

The other components of cover structure 10 are two relatively rigid but deformable frame members 14,16. In the embodiment of Fig. 1, each of the frame members 14,16 may be formed from lengths of 25.4mm square steel tube, but of course any suitable material may be used.

The cover structure 10 is self-contained, in that the elements 12,14 and 16 may be secured together such that all forces acting between the elements are contained within the structure 10, and therefore do not need to be resolved outside the structure 10. In addition, external forces applied to the structure 10

may be at least partly accommodated within the structure 10 by the temporary further deformation of the sheet or sail 12 and/or at least one of the frame members 14,16. That is, the structure may"flex"in order to accommodate external forces applied to it.

This is accomplished by the frame members 14,16 being bowed in different directions, as shown best in Fig. 2; one (16) is concave, and the other (14) is convex. The members 14,16 may be slightly pre-bent, or may simply be bent in the assembly phase of the structure 10. The two members cross at right angles in the preferred embodiment, but of course any suitable orientation may be used.

When the structure 10 is assembled, as will be described hereinafter, the two members 14,16 do not need to be secured together for structural reasons, although it may be desirable to do so for other reasons.

In the embodiment of Fig. 1, the corners 18,20,22,24 of the sheet or sail 12 are used to secure the sheet 12 to the members 14,16. Preferably, the corners 18,20,22,24 are not secured directly to the members 14,16, although that option may be chosen, but are attached to upstanding pins, posts or the like 19, 21,23 25, to space the corners from the members 14,16. The pins or posts may have a ring or loop at the upper end thereof, for attachment of the corners of the sheet 12.

Conventional means may be used to secure the corners 18,20,22,24 to the members 14,16. For example, rings or loops may be sewn or otherwise secured to the corners, and the rings or loops may in turn be secured to the aforementioned pins or posts. The corners may be provided with spring-loaded coupling members for releasably securing the sheet 12 to the members 14,16.

It has been found that three of the four corners 18,20,22,24 may be attached to respective ends of frame members 14,16 without any additional force being necessary. The final connection may require some force to establish the tensile stresses which in the final structure 10 are balanced between the stretched sheet 12 and the bowed members 14,16. Each member 14,16 could be seen to be

operating like the stave of a bow, while the sheet 12 acts like the string of the bow.

The shape of the structure 10 of Fig. 1 can best be seen from Figs. 2,3 and 4.

The differing bends of the frame members 14,16 impart an attractive shape to the structure 10 and to the stretched sheet or sail 12.

Of far greater importance is that as the forces within the structure 10 are fully resolved within that structure, in deploying the structure to shade or protect an area, one only has to take into consideration the weight of the structure 10, which in a prototype generally in accordance with the embodiment of Fig. 1 is not great, and any additional forces which may impinge upon the structure 10, such as forces exerted by wind, rain, sleet, snow and the like, which are not accommodated by the structure, by way of temporary further deformation thereof.

The structure 10 may be supported on any suitable manner. In Figs. 2,3 and 4, the structure 10 is supported by four twin-member posts 26,28,30,32, each of which supports a respective corner of structure 10. However, in theory the structure could be supported by a single post located beneath the intersection of frame members 14,16. Alternatively, the structure 10 could be supported by direct attachment to existing structures such as buildings. Another possibility is to suspend the structure by wires or the like. The post-supported embodiment could also use only three posts, with one side of the structure cantilevered.

Each cover structure 10 may be considered as a shade or cover module, and a number of such modules may be utilised to cover a particular area. Of course, the size of each structure could be varied, as well as the shape, and it may well be that a particular area could be covered by a single larger cover structure 10.

It can be seen that this invention provides an improved structure which may be used in construction, including building construction, and in one embodiment may provide a cover structure for providing protection from elements such as sun, rain, wind and the like. A structure in accordance with this invention could also

be used for sporting purposes, in that it could be used as a trampoline or the like. This could be accomplished by orienting both frame members so that they are curved in the same manner.

The entire contents of the specification and drawings of Australian provisional patent application no. PP8532, filed 8 February 1999, are hereby incorporated into the disclosure of this specification.

The claims form part of the disclosure of this specification.