Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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POLYTUNNEL STRUCTURE
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
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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
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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:
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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.
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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
5 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
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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
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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.
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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.
