This invention relates to a polytunnel structure, for example for use in aiding controlling the environmental conditions in which crops are grown, enhancing or optimising the growing conditions to enhance crop production, reduce insect damage and the like. However, the invention may also be employed in other applications.

One form of polytunnel structure in common use comprises a series of rows of upstanding legs, each of which is anchored to an underlying ground surface in a substantially vertical orientation. A series of cover support members are provided, each cover support member being supported, at one end, by one of the legs of one of the rows, and at its opposite end by a corresponding leg of an adjacent one of the rows. A cover, for example in the form of a flexible plastics material sheet, a net, a mesh or the like, extends over the cover support members and is anchored in position using ropes, straps or the like that extend over the cover and that are anchored, directly or indirectly, to the ground. The cover support members are typically of arcuate form, supporting the cover in such a manner that the cover adopts a substantially barrel-roof like profile. It will be appreciated, however, that this need not always be the case and the cover support members may be shaped such that the cover takes on a different shape if desired.

The cover support members typically take the form of lengths of a suitable steel material tube of circular cross-sectional shape, the tube having been bent to take on the desired arcuate form. The upper end of each leg is typically of bifurcated form, defining a pair of angled, upwardly extending projections of diameter slightly smaller than the inner diameter of the tube of the cover support members such that the end parts of the cover support members can receive the projections so that the cover support members are supported by the legs in a desired orientation.

In use, the loadings borne by the cover support members and legs in supporting the cover and in withstanding loads applied to the cover, for example as a result of high winds, can be significant, and the cover support members and legs are designed in such a manner that they are able to withstand these loads. By way of example, in order to ensure that the cover support members are able to bear the loads applied thereto, in use, the cover support members are typically formed from relatively thick walled tubes. However, the use of relatively thick walled tubes is disadvantageous in that it results in the loads having to be borne by the legs being increased, and in that the cover support members are of relatively costly form.

Furthermore, there is a tendency for the cover support members to sag under their own weight, in use, the end parts thereof rotating relative to the projections of the legs.

It is an object of the invention to provide a polytunnel structure in which at least some of the disadvantages associated with known polytunnel structures are reduced or overcome.

According to the present invention there is provided a polytunnel structure comprising a plurality of rows of leg members, and a plurality of cover support members, each cover support member being supported at one end by a leg of one of the rows, and at its opposite end by a corresponding leg of an adjacent one of the rows, wherein at least one of the cover support members is of tubular form of non-circular cross-sectional shape having a major axis and a minor axis, wherein, in use, the minor axis extends generally parallel to a ground surface upon which the polytunnel structure is used, and the major axis extends perpendicularly to the minor axis.

The major axis thus extends in a vertical direction or in a direction having a vertical component.

In use, the loads experienced by the cover support members of such a structure are predominantly in directions having a vertical component. By using cover support members of non-circular cross-sectional shape orientated as set out hereinbefore, cover support members of thinner wall thickness may be used without negatively impacting upon the load bearing capacity thereof in the directions in which most loads are experienced. Accordingly, weight and material cost savings can be made.

Whilst the cover support members could be of a range of cross-sectional shapes, for example they could be of elliptical shape or of rectangular shape, it is preferred for the cover support members to have a cross-sectional shape in the form of a pair of part circular regions spaced apart from one another by substantially straight sides.

In addition to achieving a reduction in weight without negatively impacting the load bearing capacity of the cover support members, the invention in advantageous in that where components are to be non-rotatably attached to the cover support members, relatively simple clips or clamps may be used to achieve this. The use of the non-circular cross-section material for the cover support members means that rotation of the clips of clamps relative thereto can be avoided without needing excessively high clamping loads to be used. The risk of damage to the cover support member through the application of such clamping loads is thus reduced.

Similarly, by the use of an appropriately, correspondingly designed leg, relative rotation or angular movement between the cover support member and the leg can be avoided. Accordingly, preferably each leg includes a projection of non-circular cross-sectional shape arranged to receive or be received by the end part of the associated support member.

The invention further relates to cover support members, legs, clamps and clips suitable for use in such a structure.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view illustrating a polytunnel structure in accordance with one embodiment of the invention;

Figure 2 is a view, to an enlarged scale, illustrating part of the polytunnel structure of the embodiment of Figure 1;

Figures 3a and 3b are views illustrating part of the polytunnel structure in greater detail;

Figures 4a and 4b illustrate two clip or clamp designs suitable for use with the polytunnel structure of Figure 1;

Figure 5 illustrates the application of the invention to another style of polytunnel structure; and

Figures 6a and 6b are views illustrating part of the structure of Figure 5.

Referring to Figures 1 to 4 of the accompanying drawings, a polytunnel structure 10 is illustrated that comprises a plurality of rows 10 of upstanding legs 12, each leg 12 being screwed or otherwise secured to the ground in a location in which a polytunnel structure 10 is desired, the legs 12 each extending generally vertically. Each leg 12 includes an upright 14 and a bifurcated support region 16 defining arms or projections 18 that are angled to the upright 14. As best shown in Figure 2, the projections 18 are of non-circular cross-sectional shape, in the arrangement shown being of a hollow tubular form. It will be appreciated, however, that the projections 18 could be of solid construction, if desired, and may be of other shapes than illustrated.

As shown in Figure 2, the cross-sectional shape of each projection 18 conveniently takes the form of a pair of part circular regions 18a, 18b interconnected by straight regions 18c, 18d. The structure 10 further comprises a series of cover support members 20. Each cover support member 20 is of arcuate form, being constructed from a tubular steel or the like material that is bent to take on the desired arcuate form. Each support member 20 is supported, at one end thereof, by one of the legs 12 of one of the rows 10, and at the opposite end thereof by a corresponding leg 12 of an adjacent one of the rows 10. The end parts of the cover support members 20 are supported by the leg members 12 by being slid over respective ones of the projections 18. Alternatively, they could be designed to be received by the leg members 12.

As best shown in Figure 3, each cover support member 20 takes the form of a length of a tubular steel or the like material that is bent or otherwise formed to take on the desired arcuate form. The tubular material is of non-circular cross-sectional shape, defining a major axis 22 and a minor axis 24, the material being of substantially the same cross-sectional shape as the projections 18, but of slightly larger dimensions so as to allow the introduction of the projections 18 into the ends of the support members 20. The cross-sectional shape of each cover support member 20 thus conveniently takes the form of a pair of part circular regions 20a, 20b interconnected by straight regions 20c, 20d.

The orientation of the cover support members 20 is such that, throughout the length of each cover support member, the minor axis 24 extends generally horizontally, substantially parallel to the ground surface upon which the polytunnel structure 10 is constructed. The major axis 22 extends perpendicularly to the minor axis 24. The arcuate form of the cover support members 20 results in the orientation of the major axis 22 varying along the length of the cover support member. Despite this variation in orientation, throughout the length of the cover support member 20 the major axis 22 extends either vertically or in directions having a vertical component.

The cover support members 20 together carry a cover 26, for example of flexible plastics material sheet, net, mesh or the like, the arcuate shaping of the cover support members 20 resulting in the cover 26 adopting a barrel-roof like form. Ropes, straps or the like (not shown) extend over the cover and are anchored to the ground or to the legs 12 to secure the cover 26 in position.

It will be appreciated that the cross-sectional shape of the cover support members 20 is such that the cover support members 20 are better able to withstand loads applied, for example, to the curved faces 20a, 20b thereof than to loads applied to the flat faces 20c, 20d thereof. Consequently, the cover support members 20 can bear significant loads arising from side winds incident upon the cover 26. These loadings can be borne even if the cover support members 20 are of thinner walled form than is normally the case. The use of non- circular cross-section cover support members 20 thus enables weight savings and material cost savings to be made whilst maintaining a desired load bearing capacity, or enables an increased load bearing capacity to be achieved without increasing the weight of the cover support members 20.

By designing the projections 18 so as to have substantially the same cross-sectional shape as the cover support members 20, it will be appreciated that upon assembly the cover support members 20 will automatically adopt an orientation in which they extend perpendicularly to the rows 10 of legs 12. Assembly of the polytunnel structure may thus be simplified.

Furthermore, as the cover support members 20 and projections 18 are substantially non- rotatably fitted to one another, the relative rotation therebetween that often occurs with traditional polytunnel structures having cover support members of circular cross-sectional shape as a result of the tendency of the cover support members to rotate and sag under their own weight is resisted. The polytunnel structure is thus of enhanced structural rigidity.

There are many situations in which it is desired to clamp or otherwise secure fittings to the cover support members 20, and for the fittings to be secured in such a manner that they are unable to rotate or move angularly relative to the cover support members 20. By using cover support members 20 of non-circular cross-section as illustrated, clamps or clips 28, 30 (see Figures 4a and 4b) may be used that are specifically designed for use with cover support members 20 of non-circular cross-sectional shape, the cooperation between the clamps or clips 28, 30 and the cover support members 20 being such that angular movement therebetween is resisted even when the clamping load applied between the clamps or clips 28, 30 and the cover support members 20 is relatively small. Accordingly, fittings may be non-rotatably fixed to the cover support members 20 without requiring the application of excessively large clamping loads that could result in damage to the cover support members 20.

In the arrangement shown in Figures 1 to 4, a series of polytunnel structures may be erected side-by-side, certain of the legs 12 supporting ends of the cover support members 20 of two adjacent ones of the tunnel structures. However, the invention is not restricted to such use and may be employed with a standalone tunnel structure, for example as shown in Figure 5. Such structures are often used in climates in which significant snow loadings may be experienced, and so the use of cover support members 20 of non-circular cross-sectional shape, arranged to enhance the ability of the tunnel structure to withstand loadings applied to the cover, such as by the presence of snow thereon or due to strong side winds or the like, is beneficial. As shown in Figures 6a and 6b, each leg 12 of such an arrangement preferably includes a lower part 12a of circular cross-sectional shape arranged to be driven into the ground, the lower part 12a carrying a screw formation 12b. The leg 12 further comprises an upper part 12c of non-circular cross-sectional shape arranged to be received within an end part of the associated cover support member 20. Between the parts 12a, 12c is located a flange 12d with which a tool can be engaged to allow the leg 12 to be driven for rotation to drive the leg 12 into the ground, that serves to provide a guide to show when the leg 12 has been driven into the ground by a suitable distance, and to carry hooks 12e whereby ropes or the like used to secure the cover in position may be anchored. The positions of the hooks 12e may be chosen in such a fashion as to enable control over the spacing of parts of the ropes or the like from the axes of the legs 12, for example to allow movement of a roller vent tube when parts of the tunnel structure are vented. It will be appreciated that an arrangement of this type benefits from many of the advantages described hereinbefore with reference to Figures 1 to 4.

Whilst one embodiment of the invention is described hereinbefore with reference to the accompanying drawings, it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.