Support leg for polytunnel structure

Abstract

A support leg subassembly 10 for a polytunnel structure that has hoops supported on legs and which enables easy replacement of the legs. The leg has a hub 20 comprising socket structures 40, 30 for co

Description

Field of the Invention The present invention relates to polytunnels, particularly to support legs for support hoops of polytunnels. More specifically, the invention relates a modular support leg assembly adaptable for different leg posts or hoop ends. Background A common form of polytunnel structure of the type used for cultivation of plants and crops comprises a series of pairs of support legs supporting an arched structure, or hoop, over which a cover material such as a polypropylene sheet is mounted to provide a generally semi-cylindrical or arched roof. Such polytunnel structures are usually arranged in generally parallel rows of tunnels, the hoops of adjacent tunnels sharing a common support leg with two attachment arms, such a support leg having a characterising forked shape or “Y”-shape comprised of an upright support leg and two arms, each arm supporting an end of a hoop. Whilst relatively uncommon, in the event of stress failure of a leg, it will be appreciated this can affect the stability of two tunnels. Upgrading or repairing of a single leg may require disassembly of a significant tunnel section and clearing of plants to permit access for machinery. The present invention seeks to provide an alternative leg design that at least partially addresses the aforementioned concerns. Summary of the Invention In accordance with a first aspect of the invention, there is provided a support leg subassembly as defined in claim 1, for a polytunnel structure of the type comprising hoops supported on legs, the support leg subassembly comprising a hub member, the hub member comprising a first socket structure for connection of a leg end and an arrangement of one or more second socket structures for connection of one or more hoop ends, wherein at least one socket structure is formed by assembly of a clamp member to the hub member. The invention relates to polytunnels of the type comprising arched sheet-supporting members, or hoops, the arched members being supported on both ends on an upright leg in the form of a post. The support leg subassembly is understood to be a subassembly for a support leg assembly. The support leg is a post member, such as a pipe element with optional anchoring leg such as a spike. Several types of support leg are known and the leg post members as such are not individually claimed in this specification. Conventional support legs may have two arms in the form of a forked end, each of the two arms to support the ends of respective adjacent hoops. The subassembly suggested herein is a modular hub arrangement comprising a hub member, in the form of a frame structure or support structure, for one or more socket structures. In a typical embodiment, the subassembly is thought to comprise three socket structures, one leg socket for attachment onto a support leg, and two hoop sockets for connection of hoop members. The provision of a hub member in modular form allows a hub member subassembly to be configured for different post geometries and / or hoop geometries. Likewise, a hub member subassembly may be provided with only a single hoop socket, for instance for a laterally installed post member that supports a single tunnel. In some embodiments, the hub member is formed from sheet material. The sheet material may be a metal sheet, composite material sheet, or other suitable structure. The sheet material may comprise reinforcing structures such as corrugations, ribs, angled portions, and the like. The sheet material may be flat. In some embodiments, the subassembly comprises two hub members formed from sheet material. The two hub members may be from the same material or each from a different material. The two hub members may sandwich, or partially sandwich, socket structures between them. In some embodiments, at least one hub member is formed by laser-cutting. A laser-cut structure may be characterised by the presence of laser cutting marks and / or by the absence of burr features associated with other forming processes. In some embodiments, one or more hub members are flat. The hub member may be a flat sheet component to which curved components such as clamp members are attached to form sockets. For instance, a socket may be formed by a cavity created between a concavely curved inner surface of a clamp member and a surface of the hub member. The hub member surface may be pre-shaped to comprise a concave portion, or may comprise a flat surface. In some embodiments, at least one socket structure comprises two clamp members attached to the hub member. A suggestion may in this disclosure is to provide a socket from a clamp member shaped to provide a periphery, or partial periphery, of a socket. As will be appreciated, the clamp member may be formed from a band of material, such as a metal sheet, comprising a concave region suitable for forming a socket structure or part of a socket structure. Two such clamp members may be combined in a clam-shell manner, such that the two concave regions complement each other for form a complete socket structure. In some embodiments, at least one socket structure comprises two clamp members comprising flange regions, the flange regions at least partially sandwiched between two hub members. The hub member may comprise one or more cut-out regions from which, or through which, the socket structures of the clamp members protrude. In some embodiments, at least one socket structure comprises two clamp members comprising flange regions, the flange regions attached to a hub member. The two clamp members may be attached to opposite faces of the same hub member. Likewise, the clamp members may be attached to each other to form a socket subassembly, and the socket subassembly may be attached to one side of the hub member. As in an aforementioned embodiment, the hub member may comprise one or more cutout regions from which, or through which, the socket structures of the clamp members protrude. In some embodiments, at least one socket structure comprises a single clamp member comprising a flange region, the flange region attached to a hub member. In some embodiments, the hub member and the clamp member comprise corresponding arrangements of mounting locations for connection to each other, wherein at least one of the hub member and the clamp member comprises two or more different arrangements of mounting locations, each different arrangement permitting connection of the clamp member to the hub member in a different orientation. For instance, a hub member may comprise a set of four mounting holes for a socket, and the flanges of the clamp member may be provided with two sets of four mounting holes, in the form of a first set and a second set angularly offset from each other. In this manner, the clamp member may be affixed to the hub member by aligning the four mounting holes either with the first set of the flange, or with the second set of the flange, resulting in a different angular orientation of the socket relative to the hub member. In some embodiments, the hub member comprises two second socket structures. The two second socket structures may be in-use upward-facing sockets. In this form, the hub member may be used to replace a pre-formed, conventional “Y” leg of two-arm form. In many embodiments, the second socket structures forming the sockets will be of the same shape. However, the invention permits the use of differently profiled sockets, e.g. if it is necessary to accommodate two hoops of different profile. In some embodiments, the hub member comprises one or more further attachment structures. The further attachment structures may be additional sockets and / or other attachment structures, such as hooks, hoops, rings, rail structures, support ledges or platforms, or other appropriate structures. The hub member may therefore provide a modularly adjustable structure for attachment of structures other than the polytunnel hoops, such as hooks for anchoring ropes, sockets for poles, ducts for cabling, guttering structures, and the like. The modular nature of the subassembly may permit replacing a hub member, for example a hub member for three sockets, with a replacement hub member, for example a replacement hub member for three sockets and integral anchoring rope hooks. In this manner, replacement allows a user to upgrade the subassembly. In some embodiments, the one or more further attachment structures are provided by a third arrangement of socket structures. In some embodiments, the support leg subassembly comprises a clamp member attached to each one of the socket structures, the attachment being of loosely preassembled form, to permit subsequent attachment of a post end and subsequent tightening. In some embodiments, the support leg subassembly comprises a leg post attached to the first socket structure and fastened by at least one clamp member. In accordance with a second aspect of the invention, there is provided a polytunnel structure comprising at least one support leg subassembly according to any one of the embodiments of the first aspect. In some embodiments, the polytunnel structure comprises an arrangement of support legs, comprising only one or a few of the support legs according to any one of the embodiments of the first aspect. In accordance with a third aspect of the invention, there is provided a method of retrofitting a support leg according to any one of the embodiments of the first aspect, comprising cutting a support leg of a tunnel structure to provide a support post with a free, cut post end, selecting a hub member and clamp member to fit onto the cut post end, and affixing the hub member and clamp member to the support post. As will be appreciated, the cutting of the end of the support leg will shorten the leg. The hub member may be provided with clamp members that provide a socket structure of sufficient length to accommodate the shorter leg, if necessary. In accordance with a fourth aspect of the invention, there is provided a method of retrofitting a support leg according to any one of the embodiments of the first aspect, comprising cutting a hoop end of a tunnel structure to provide a hoop beam with a free, cut hoop end, selecting a hub member and clamp member to fit onto the cut hoop end, and affixing the hub member and clamp member to the hoop beam. As will be appreciated, the cutting of the end of the hoop end will shorten the hoop. The hub member may be provided with clamp members that provide a socket structure of sufficient length to accommodate the shorter hoop, if necessary. In accordance with a fifth aspect of the invention, there is provided a method of installing a polytunnel structure on undulating land, wherein the undulating land comprises an incline along a hoop end-to-end distance, the method comprising installing a series of support legs comprising a leg and a hub member according to any one of the embodiments of the first aspect, and affixing a clamp member to the hub member such that the socket structure is oriented at an angle that accommodates or offsets, respectively, the topological incline. The method may utilise embodiments of the first aspect to provide socket structures fixed to the hub members at different angles, so as to better conform to undulations of the ground underneath. In some embodiments, the method comprises installing at least two pairs of legs to accommodate different angles of inclination. In accordance with a sixth aspect of the invention, there is provided a polytunnel installation covering an area of undulating land. Embodiments of the first aspect allow the hoop end of a polytunnel installation to be attached to the hoop-supporting leg at different angles. Due to the individual attachment of each clamp member to the hub member, each hoop end may be attached at a different angle. This facilitates the installation of polytunnels on undulating areas of land, using the same shape and length of hoop. As will be appreciated, a small hill or ditch formation in otherwise even land may have previously rendered an area less suitable for polytunnel installations. By way of the present invention, it is believed that polytunnels will be more readily installed in uneven, undulating regions of land. In some embodiments, the polytunnel installation comprises a hoop end-to-end orientation across undulations. This allows polytunnels to be oriented with regard to a preferred sun exposure, reducing the need to fit a polytunnel footprint to even regions of land. Any one or more of the embodiments disclosed in relation with the first, second, third, fourth, fifth and sixth aspect may be combined with any one or more of the embodiments of the respective one or more other aspects. For example, any one or more embodiments of the polytunnel installation of the sixth aspect may comprise one or more support leg assemblies as defined in the embodiments of the first aspect, such as support legs with first and second socket structures attached to the hub such that polytunnel arches may connect to the support leg assembly at different angles. Description of the Figures Exemplary embodiments of the invention will now be described with reference to the Figures, in which: Figure 1 is a schematic illustration of a polytunnel arrangement; Figure 2 is a front view of a prior art polytunnel support leg; Figure 3 is an isometric view of a support leg subassembly; Figures 4 to 6 are isometric views of components of a support leg subassembly; Figure 7 is an exploded view of components of a support leg subassembly; Figure 8 is an isometric view of an assembly of the Figure 7 components; Figure 9 is a front view illustrating a component for a support leg subassembly; Figure 10 is a front view of a support leg subassembly; Figures 11 and 12 are views illustrating each a different support leg configuration; Figures 13 to 15 show a component and exemplary assembly of another embodiment; Figure 16 is a sequence of exemplary steps of a replacement method; Figure 17 is a sequence of exemplary steps of a method of installing a support leg; and Figure 18 is a schematic illustration of another polytunnel arrangement. Description Figure 1 is a simplified schematic illustration of a polytunnel installation 100 that is comprised of rows of tunnels formed by support legs 10 supporting hoops 102, the hoops 102 providing a support scaffold for a cover sheet 104. To provide an illustration of scale, the space between two support legs 10 spanned by a hoop 102 may be in the region of six to twelve metres, and the length of each tunnel may be in the region of several tens or around hundred metres. Figure 2 is a front view of a prior art support leg 1 comprising a post 3 providing an anchoring region to be inserted, or drilled, into ground. The post 3 is provided at its in-use upper end with a Y-shaped support structure 5 comprising two arms 7a, 7b. The Y-shaped support structure 5 may be attached on the post 3 or may be welded onto the post 3. Each of the two arms 7a, 7b comprises a cross-section corresponding to a cross section of a hoop member, such as a hoop 102, for connection of hoop members to the arms 7a, 7b. Specifically, the outer diameter or perimeter of the two arms 7a, 7b is smaller than an inner diameter perimeter of the hoops to be supported by the arms, to allow hoops to be slotted onto the arms 7a, 7b. Figure 3 shows a support leg assembly 10, comprising a post 12, two beam ends 14a, 14b, and a hub member 20. The hub member 20 is provided with two socket structures 30 and a socket structure 40. The hub member 20 and the socket structures 30, 40 constitute a support leg subassembly. Individual components will be described with reference to Figures 4 to 15. Figure 4 shows an isometric view of a hub member 20, here in the form of a body 22 of sheet metal material. The body 22 is, here, of generally triangular periphery comprising two opposite flats 21. The body 22 comprises three recessed regions, comprising a first pair of recesses 24a, 24b for hoops and a recess 26 for a leg. Each of the recesses 24a, 24b, 26 is of generally rectangular shape, comprising two parallel lateral edges extending into the body 22 towards its centre, and an inner edge constituting the inner end of each recess. The recesses 24a, 24b comprise each an inner edge 25a, 25b, respectively. The recess 26 comprises an inner edge 26. While other shapes and geometries may be used, the arrangement and dimensions of the recesses 24a, 24b, and 26 correspond, here, roughly to the arrangement, in section, of the ends of the post 12 and the beam ends 14a, 14b expected in a polytunnel installation. Each of the recesses 24a, 24b and 26 comprises an arrangement of holes 29a, 29b, 29c, each constituting a mounting location. In this embodiment, each recess is surrounded by four holes, recess 24a by four holes 29a, recess 24b by four holes 29b, and recess 26 by four holes 29c. The member may have a different number of holes per recess. Between the first pair of recesses 24a, 24b, opposite the recess 26, the body 22 comprises a free region 28. The free region 28 is, in this illustration, constituted by an edge of the body 22. In some embodiments, the free region 28 may be provided with a connector or further (fourth) recess. The further recess may comprise mounting locations for attachment of a further socket (not shown). Figure 5 shows an isometric view of a component of a clamp member 30 for a hoop end, here in the form of a formed body 32, comprising a channel region 34 in the form of a recessed flattened halfpipe flanked on either side by lateral wings 36 each generally planar and shaped to provide a flange region. Within the flange region, the body 32 comprises an arrangement of holes 39, constituting mounting locations. In this example, the clamp member 30 comprises eight holes 39 that will be described below with reference to Figure 9. Four of the holes 39 correspond in shape to an arrangement of the holes 29a and / or 29b. Figure 6 shows an isometric view of another component, of a clamp member 40 for an end of a support post, here in the form of a formed body 42, comprising a channel region 44, similar to the clamp member 30, in the form of a halfpipe, flanked on either side by lateral wings 46 each generally planar and shaped to provide a flange region. The flange region comprises an arrangement of, here, four holes 49, constituting mounting locations. The clamp members 40 and 30 are symmetric along the centre axis of their respective channel regions 34, 44, the centre axis therefore constituting a mirror axis of each component. Furthermore, both the clamp members 40 and 30 are also symmetric around an axis perpendicular to the centre axis. As such, the clamp members 40 and 30 have bi-fold symmetry. The holes 39, 49 are distributed symmetrically relative to a mirror axis of the first clamp member 40 and the second clamp member 30. While a symmetric arrangement is not necessarily a requirement of all embodiments, the symmetric layout allows the components to be matched with a like component, the concave sides of the channel regions 34, 44, respectively, facing each other to form a hollow channel, and the flats of the flange regions abutting each other. Figure 7 shows an exploded view of components making up a hub member subassembly 10 relative to two hoop ends 14a, 14b and a support post 12. In this embodiment, a subassembly comprises two hub members 20a, 20b, and for each hub member 20a, 20b a first clamp member 40a, 40b and a pair of second clamp members 30a, 30b. The clamp members 40a, 40b are each dimensioned such that their channel regions 44 protrude between the lateral edges of a recess 26, while their lateral wings 46 overlap with portions of the flat 21, such that the holes 29c register with the holes 49. Likewise, the clamp members 30a, 30b are each dimensioned such that their channel regions 34 protrude between the lateral edges of the respective recesses 24a, 24b, while the lateral wings 36 overlap with portions of the flat 21 and at least four of the holes 39 register with the four holes 24a and 24b, respectively. As illustrated in Figures 7 and 8, the components may be arranged such that three pairs of socket structures sit between two hub members 20a, 20b, in a sandwiched manner. Each pair of socket structures may be held together by fasteners 18 such as bolt and nut arrangements, to effectively clamp the support post 12 and the hoop ends 14a, 14b within the socket structures. While the illustration of Figure 7 suggests the use of pairs of components, some embodiments may utilise a single hub member 20 onto which clamp members are mounted. The clamp members 30, 40 may be affixed to two opposite sides of the hub member 20. The clamp members 30, 40 may be mounted to each other before being mounted, as a pre-assembled socket, to one side of a hub member. Although not shown in the drawings, a hub member may be provided with an integrally formed clamp member portion, to form a circumferential socket structure by attachment of a single clamp member. In a simple variant, the or each hub member is flat, a flat surface portion of the hub member providing a clamp portion. During an installation procedure, fasteners 18 may be supplied in a loose manner to facilitate positioning and insertion of post ends, before the subassembly 10 is tightened. The subassembly provides a relatively stable configuration, because the free end of the support post 12 may bear against one or two inner edges 27. Likewise, in the illustrated arrangement, the channel regions 44 may also bear against the inner edges 27, depending on dimensions of the clamp member 40 relative to the recess 26. Furthermore, the ends of the hoop members 14a, 14b may in a similar manner bear against one or two inner edges 25a, 25b, respectively. Figure 9 shows a front view of the body 32 to depict the layout of the holes 39. A first set of holes 39a is arranged at corners of a first square, illustrated by dotted lines, angularly offset in one direction relative to the (45 degree) diagonal lines of the body 32. A second set of holes 39b is arranged at corners of a second square, angularly offset in a direction opposite to the first square relative to the (45 degree) diagonal lines, illustrated by dashed lines. The eight holes 39a, 39b are arranged with bi-fold symmetry, such that two clamp members 30 may be used as pair and attached in an angularly offset manner to a set of holes 29a or 29b, as illustrated in Figure 10. Referring to Figures 11 and 12, the clamp member 30 may be arranged in a first angular orientation relative to the sockets 24a, 24b, as illustrated in a hub member subassembly 10a in Figure 11, or in a second angular orientation relative to the sockets 24a, 24b, as illustrated in a hub member subassembly 10b in Figure 12. In the subassembly 10a, the first angular orientation of the components 30, illustrated in Figure 11, provides an included angle of 68.5 degrees between two hoop members 14a, 14b. In the subassembly 10b, the clamp members 30 are assembled in a second angular orientation that provides an included angle of 90 degrees between two hoop members 14a, 14b. As will be appreciated, in this manner the same components of a subassembly may be used with hoops of different curvature, and / or hoops for different tunnel widths. Likewise, while Figures 11 and 12 both show symmetric arrangements, the invention is not so limited and one side of the hub member 10 may comprise a socket at a steeper angle that the other side of the hub member 10. The alternative arrangements of holes, or mounting locations, may be provided on the clamp members and / or on the hub member 20. The socket cross section is determined by the shaping of the channel regions 34, 44, respectively. For instance, in the illustrated example, the support post 12 has a cylindrical geometry and the clamp members 40 comprise a semi-cylindric channel region 44 to for a socket for the support post 12. The clamp member 30 may comprise a flattened semi-cylindric channel region 34 to form a socket for hoop members 14a, 14b with obround cross-section. As such, the hub member 20 may be used with a range of support post and hoop member cross sections, which increases the versatility of the proposed arrangement for a wide range of polytunnel systems. In this manner, the clamp members may be formed corresponding to any shape of hoop member or other component to be supported. While the exploded view of Figure 7 is provided mainly to illustrate the relationship of different components, it also indicates the possibility of assembling the components onsite, and specifically when a post member and hoop members are already installed. As such, the system disclosed herein is thought to be particularly practical for upgrades, retrofitting, and / or repairs of existing polytunnel installations. Figures 13, 14, and 15 show an alternative support leg subassembly, comprising a hub member 120 formed from flat sheet material. The hub member 120 has a similar peripheral contour as the hub member 20, including a flat region 121. Instead of cutout recesses 24a, 24b, 26, the hub member 120 comprises surface regions 124a, 124b, 126 that each provide a clamp region, wherein each clamp region is a portion of the flat region 121. Each surface region 124a, 124b, 126 is surrounded by an arrangement of, here, four holes 129a, 129b, 129c, respectively. As illustrated in Figures 14 and 15, a clamp member 130 may be mounted to the hub member 120 to form a socket. The clamp member 130 is generally similar to the clamp member 30, comprising however a deeper channel region to allow it to accommodate a post end when abutted against a flat surface. The clamp member 130 comprises, like the clamp member 30, a first arrangement of four mounting locations 39a and a second arrangement of four mounting locations 39b. The first arrangement of mounting locations 39a and the second arrangement of mounting locations 39b correspond to the layout described in Figure 9 and so the detailed description is not repeated. In Figure 14, the clamp members 130 are attached via the second arrangement of mounting locations 39b (indicated by four thick circles) to the respective holes 129a, 129b, to form a support leg subassembly 120a. In Figure 15, the clamp members 130 are attached via the first arrangement of mounting locations 39a (indicated by four thick circles) to the respective holes 129a, 129b, to form a support leg subassembly 120b. Thereby, the clamp members 130 are connected to the hub member 120 in a different orientation in the subassemblies 120a and 120b. Similar to Figures 11 and 12, the same clamp members 130 can be used to provide different included angles between two hoop members (hoop members no illustrated in Figures 14 and 15). The hub member 120 may be provided with a further clamp member 140, corresponding to the clamp member 40, and shaped to accommodate an end of a leg post. While the clamp members 30, 130 illustrate a first arrangement of mounting locations that is angularly offset relative to the second arrangement of mounting locations, the clamp members may comprise other arrangements that are laterally offset. Figure 16 illustrates steps of a method of replacing an existing polytunnel support member, e.g. for upgrading or repairing. For instance, a polytunnel member may have bent under stress during wind loads. While a broken polytunnel member is a relatively rare occurrence, the repair of conventional polytunnels can be time-consuming, requiring access for heavy machinery and corresponding clearance of crops and equipment usually located in the polytunnel. While rare, when a break occurs, this is typically in the region of a Y-shaped member where stress points may be located. The method 50 comprises a step 52 of identifying one or more polytunnel members requiring replacement, e.g. for repair of upgrade purposes. In step 54, a portion of the polytunnel member, i.e. a hoop end or post end, is cut and removed. As will be appreciated, the cut end may be relatively close to a Y-shaped member, such that the hoop end or post end is only shortened by a small amount. The cut end of the polytunnel member is understood to be a free end. Depending on the design of the Y-shaped member, several connections are cut, to provide several free ends, e.g. three free ends of two adjacent hoop members and of a leg post. In step 56, a hub member subassembly is provided with socket structures corresponding to the free ends. In step 58, the free ends are connected to the subassembly. As will be appreciated, steps 56 and 58 may be carried out in a combined step. Due to the shell structure of the socket subcomponents, one “half’ of the hub member subassembly may be used to attach the leg and hoop members to the hub member subassembly, before closing the subassembly by attachment of the other “half” of the hub member subassemblies or socket structures, as the case may be. Alternatively, or in addition, one clamp member of a socket structure may be attached to a surface clamp region of a hub member. In this manner, a single polytunnel member may be replaced within an existing polytunnel installation. The method 50 may, likewise, be used for upgrading an existing sub-assembly of the invention, e.g. to provide a further socket or support structure for another component. Free hoop ends may be supported by temporary support leg structures during the replacement procedure. A replacement assembly for a cut, shortened member may require a longer socket structure. The invention is thought to be useful not only for enabling the use of hoop members of different curvature and length. It may further facilitate, and for practical purposes enable, the installation of polytunnel arrangement on undulating ground. Figure 17 illustrates steps of a method 60 of installing a polytunnel arrangement on undulating ground. In step 62, an undulating area of land is selected for a polytunnel installation. The area may be suitable for a desired type of crop, fruit and soft fruit, however might be relatively uneven so as to hitherto have been unsuitable for a polytunnel installation requiring flat ground. In step 64, a polytunnel arrangement is installed using hub member subassemblies comprising socket members extending at different angles, the angles corresponding to the angles at which a hoop member attaches to the hub member. For instance, the hub member subassemblies may comprise socket members of the type described with reference to Figures 9 to 15, although that is not necessarily a requirement of every embodiment. In an optional step 66, one or more of the socket structures of the hub member subassemblies are adjusted and / or exchanged for more suitable hub member subassemblies. Figure 18 illustrates a polytunnel arrangement 100a installed on undulating ground 101. The polytunnel arrangement 100a may have been installed using the method 60. The polytunnel arrangement 100a comprises a plurality of support leg assemblies 10c that are assembled with their respective socket structures extending at different angles, to support hoops 102a at different angles. For instance, the socket structures may be oriented such that they follow, or offset, respectively, the angle of include of ground underneath. The individual components of the hub member subassemblies and the posts 12 used in the polytunnel arrangement 100a may be the same components throughout the arrangement 100a, or may be the same in at least a majority of the support leg assemblies 10c. As will be appreciated, the use of the same type of component facilitates logistics and storage for both installation and servicing. The components of a hub member subassembly may be affixed to another by fasteners, such as bolt-and-nut arrangements. In variants of the invention, the fasteners may be provided by bolt-and-wingnut arrangement, self-tapping threaded fasteners, by clips and / or clamps. While the illustrated embodiments show two hub members of identical shape, two hub members may be of complementary design to allow sliding engagement, and or by a hinged arrangement that allows two hub member halves to open in a clam-shell manner. While it is thought that hub members of flat-bodied sheet material form combine several advantages such as ease of storage and transportation, manufacture and versatility, the invention is not necessarily so limited. The hub members may be formed with reinforcing structures such as ribs, corrugations, and the like. Likewise, the invention is not necessarily limited to sheet material components and may comprise hub members of different material and / or design. In a similar manner, while the use of clamp members of shaped sheet material form, arranged in pairs to form a socket, is believed to combine several advantages such as versatility, ease of handling and modularity, the invention may use other socket components, either instead of the illustrated examples, or in combination with one or more of the illustrated examples. Components of a sub-assembly may be provided in loosely pre-assembled form, e.g. comprising two hub members 20, three socket structures each comprising a pair of clamp members, and fasteners 18. However, this is not necessarily a requirement of all embodiments. While each socket structure and clamp component is illustrated with an arrangement of four holes per recess, any suitable number of mounting locations may be used. Instead of or in addition to holes or slots, the mounting locations might comprise complementarily engaging rail structures for sliding engagement, clips or helping-hand structure or clamping means, and the like. The socket structures may be pre-assembled as single-component socket structure, and / or formed as a unitary component. Likewise, in some scenarios an assembly procedure may comprise attaching clamp components onto an end of a hoop or support leg before attaching the clamp components, as a socket structure, to the hub member. The hub member has been described with three sockets and one or more optional sockets. However, the invention is not so limited, and the hub member may incorporate any number of recesses, and / or any number of surface regions to provide a clamp region, for use with any number of socket members, if desired. Whilst the principle of the invention has been illustrated using exemplary embodiments, it will be understood that the invention is not so limited, and that the invention may be embodied by other variants defined within the scope of the appended claims.

Claims

1. A support leg subassembly for a polytunnel structure of the type comprising hoops supported on legs, the support leg subassembly comprising a hub member, the hub member comprising a first socket structure for connection of a leg end and an arrangement of one or more second socket structures for connection of one or more hoop ends, wherein at least one socket structure is provided by a clamp member on the hub member.

2. The support leg subassembly according to claim 1, wherein the hub member is formed from sheet material.

3. The support leg subassembly according to claim 1, wherein the subassembly comprises two hub members formed from sheet material.

4. The support leg subassembly according to claim 2 or 3, wherein at least one hub member is formed by laser-cutting.

5. The support leg subassembly according to any one of the preceding claims, wherein one or more hub members are flat.

6. The support leg subassembly according to any one of the preceding claims, wherein at least one socket structure comprises two clamp members attached to the hub member.

7. The support leg subassembly according to claim 6, wherein at least one socket structure comprises two clamp members comprising flange regions, the flange regions at least partially sandwiched between two hub members.

8. The support leg subassembly according to claim 6 or 7, wherein at least one socket structure comprises two clamp members comprising flange regions, the flange regions attached to a hub member.

9. The support leg subassembly according to any one of the preceding claims, wherein at least one socket structure comprises a single clamp member comprising a flange region, the flange region attached to a hub member.

10. The support leg subassembly according to any one of the preceding claims, wherein the hub member and the clamp member comprise corresponding arrangements of mounting locations for connection to each other, wherein at least one of the hub member and the clamp member comprises two or more different arrangements of mounting locations, each different arrangement permitting connection of the clamp member to the hub member in a different orientation.

11. The support leg subassembly according to any one of the preceding claims, wherein the hub member comprises two second socket structures.

12. The support leg subassembly according to any one of the preceding claims, wherein the hub member comprises one or more further attachment structures.

13. The support leg subassembly according to claim 12, wherein the one or more further attachment structures are provided by a third arrangement of socket structures.

14. The support leg subassembly according to any one of the preceding claims, comprising a clamp member attached to each one of the socket structures, the attachment being of loosely pre-assembled form, to permit subsequent attachment of a post end and subsequent tightening.

15. The support leg subassembly according to any one of the preceding claims, comprising a leg post attached to the first socket structure and fastened by at least one clamp member.

16. A polytunnel structure comprising at least one support leg subassembly according to any one of the preceding claims.

17. The polytunnel structure according to claim 16, comprising an arrangement of support legs, comprising only one or a few of the support legs according to any one of claims 1 to 15.

18. A method of retrofitting a support leg according to any one of claims 1 to 15, comprising cutting a support leg of a tunnel structure to provide a support post with a free, cut post end, selecting a hub member and clamp member to fit onto the cut post end, and affixing the hub member and clamp member to the support post.

19. A method of retrofitting a support leg according to any one of claims 1 to 15, comprising cutting a hoop end of a tunnel structure to provide a hoop beam with a free, cut hoop end, selecting a hub member and clamp member to fit onto the cut hoop end, and affixing the hub member and clamp member to the hoop beam.

20. A method of installing a polytunnel structure on undulating land, wherein the undulating land comprises an incline along a hoop end-to-end distance, the method comprising installing a series of support legs comprising a leg and a hub member according to any one of claims 1 to 15, and affixing a clamp member to the hub member such that the socket structure is oriented at an angle that accommodates or offsets, respectively, the topological incline.

21. A method according to claim 20, comprising installing at least two pairs of legs to accommodate different angles of inclination.

22. A polytunnel installation covering an area of undulating land.

23. The polytunnel installation according to claim 22, comprising a hoop end-to-end orientation across undulations.

24. The polytunnel installation according to claims 22 or 23, comprising one or more support leg assemblies according to any one of claims 1 to 15.

25. The polytunnel installation according to claim 24, comprising at least two support leg assemblies, wherein the first socket structure and the one or more second socket structures are attached to the hub attached to the hub such that polytunnel arches may connect to the support leg assembly at different angles.

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