IL30801A - Rigid tensioned frame structures - Google Patents

Description

o'ninai ο'π·»¾?ρ o"n-uoa D»33B Rigid teneioned frame structures TIMOTHY MICHAEL GILCHRIST C. 29028 the construction andjstabilisation of The present invention relates to/rigid tensioned roof supporting frame structures in which the roof is formed of plastics material or other flexible roofing membrane. More particularly, the invention is concerned_with_a greenhouse or like horticultural or agricultural building (hereinafter referred to collectively as a "greenhouse") in which the roof covering is a plastics material or similar flexible membrane.

It is well known to those conversant with the art and theory of stressed cable design, e.g. suspension bridges, that the stability of a tensioned structure may be achieved by the massive deadweight, which in itself is sufficient to resist all downward and upward movement due to wind pressures. Alternatively, in some structures stability may be achieved by a number of downward stressed cables firmly anchored to the ground, as in many hanger type or large tent buildings, by the use of two mutually contra-tensioned cables stretched between two or more main supporting rigid units, themselves tied to standard heavy ground . anchorages.

With particular reference to the erection of a stressed or tensioned structure for use in green-house development, none of the above systems are readily applicable since the most important aspects of a green-house structure, i.e. the angle of incidence of sunlight and the diffusion of light throughout the hours of daylight are not rigidly controlled and further the application of forced fan or natural ventilation ~ejt**e-.b- to one-ai-vth uf Llr¾~g,racrnd~a'rBft~o ~th^-¾tTTre't,tn,Tr; which is desirable in green-house constructions, is difficult to achieve. Additionally it is well known, in the art of green-house growing of vegetables and flowers, that the light transmission factor to the interior of the structure is directly related to the vertical depth of the The flexible roofing membrane - usually clear or translucent plastics material - is applied between layers of the aforesaid tensioned resilient members, in any sizes or shapes outlined by any selected pattern of structural members found most convenient for use with the minimum size of sheet membrane available commercially. In the case where the sheet membranes-are larger in width than the maximum width of a single supporting .flexible roofing unit or of unlimited length ther membrane may be fixed to the main longitudinal tensioned purlins only by any suitable method which eliminates the use of nailed battens, screws or clips. The flexible roofing fixing of the/membrane to the main longitudinal tensioned purlins should be such as to allow for removal and/or renewal of the plastics roofing membrane without interference with or damage to the supporting structure. If the membrane sheet thus fixed in position is to be adjoined transversely on structures of greater length than the membrane length available, this may be readily achieved by roll lapping adjacent sides of the two sheets together and fixing same in positinn by extra internal and external tensioned wires, ^rolled in lap, and held in position firmly by two main tensioned layers of resilient members. When the flexible ■plaotica roofing membrane is of a narrower width than a single supporting unit, it may be affixed diagonally or parallel between any two or greater number of supporting members which are fixed in position at a distance from each other, most appropriate to the width of plastics membrane used to form the roof and side covering of the structure. Further, any odd sizes of plastics membrane that lends itself to jointing by the simple process of pressure heat welding may be used to cover the structure and welded in situ to form a weatherproof joint, in any position on relation to the tensioned resilient members, purlins or other elements of the structure.

The rigid tensioned frame structure as described above ma be sheeted over its complete external surface with a single layer of flexible membrane. In the construction of greenhouses the provision of heat insulation is desirable. This is particularly important when plastics sheeting, which has a 10-15% greater heat loss than glass is used, as a roofing material. Consequently, th invention provides means for cladding the structure with two or more layers of flexible membrane.

It is to be understood that in comparison with orthodox metal or timber and glass structures, which at present generally form the artificial environment for growing of plants and vegetables, the plastics'membrane covered tensioned structure as described in this invention lends itself to all standard forms of both forced and natural systems of ventilating and heating. Ridge and side-wall vents, having inward and/or outward openings, may be incorporated in the plasticsjcovered structure with maximum efficiency. The plastics'covered greenhouse, according to the present invention, forms a sealed structure free from air leaks, such as occur between laps in glazing in metal and wood orthodox greenhouses and due to this particular attribute, the .sealed structure lends itself most efficiently to forced ventilation by motor driven fans, which are designed either to ventilate by forcing air into the greenhouse, the escape of the air being controlled by vents or louvers, or by the extraction of air from the interior of the structure, thereby causing air to flow from the external atmosphere into the greenhouse through the controller vents or through vents with plastics internal ducting positioned t the structure can be achieved by any of the well known heating systems used for horticultural purposes with improved efficienc^ The invention will hereinafter be described more particularly with reference to the accompanying drawings which illustrate, by way of example only, preferred embodiments thereo and wherein, Figure 1 is a perspective view of the roof and gable section of a single span greenhouse according to the invention, Figure 2 is a perspective view of a single span greenhouse having a construction different to that of Figure 1, Figure 3 is a diagrammatic plan of a single span greenhous having a gable construction corresponding to Figure 2 and a roof support structure corresponding to Figure 1, Figure 4 is a diagrammatic plan of a single span greenhous with a further alternative gable construction and showing the position of ridge opening ventilators, Figure 5 is a transverse cross-sectional view of the greenhouse illustrated diagrammatically in Figure 4? Figure 6 is a longitudinal elevation of the greenhouse illustrated in Figure A, Figure 7 to 14 inclusive are diagrammatic cross-sectional views of greenhouses having different span structures, Figure 15 is a cross-sectional elevation illustrating details of Figure 1, Figure 16 shows, in perspective, a detail of Figure 15, Figure 17 'is a diagrammatic representation of a method of securing a second layer of roofing membrane to a roof support member , Figure 18 is a diagrammatic perspective view illustrating the use of single pulleys attached to opposite structural elements through which single tensioned wires are threaded to form a contra-tensioned layer for support of a roof membrane. alternative systems of pulleys for tensioning of the top layers of resilient members for supporting of the roof membrane. ^ Figure 20 is a perspective view of a second tensioning system for use in tensioning the top layer of resilient members for supporting of the roof membrane.

Figure 21 is a cross-section of a greenhouse having a the removable layer of insulation material suspended from/roof.

Figure 22 is a longitudinal section of the greenhouse in Figure 21 with the insulation material in the partially removed position.

Figure 23 is a longitudinal section of the greenhouse in Figure 21 with the insulation material in the position of use .

Referring to the accompanying drawings , and initially to Figure 1 thereof, a greenhouse constructed in accordance with the present invention comprises concrete foundation members or elements (not shown) which are located below cultivation level in such a manner as to allow the structure to be readily removed to another site and/or to allow the soil to be cultivated with mechanical machinery. The concrete foundation elements support a series of tensioned trellis trusses which are located in spaced apart rows, each row containing three trusses 2, 2a, the central truss 2 a in each row being higher than the outer trusses 2 .

Extending from the upper extremity of each of the outer trusses 2 in each row of trusses and connected at the upper extremity of the central truss 2 a are stabilizing elements 3 while extending directly between the upper extremities of the outer trusses 2 in each row is a crop support member 4 the height and strength of which is determined by the weight and quantity of the crop to be grown in the greenhouse. The crop support member 4 is parallel to the ground and perpendicular to » each row is a strut 5 operatively connected between the upper extremities of each of the outer trusses 2 and between a tensi-ϋ foundation member (not shown) . The strut 5 may be tensioned by a turnbuckle 5a.

The rows of trellis trusses 2,2a, at each gable end of the structure, are additionally stabilized by struts 6, 6b operatively connected between the upper extremities of the trellis trusses 2 and ground anchorage units (not shown), the struts 6, 6b being tensioned by turnbuckles 6a. The gable end rows of trusses 2 support a main wire anchorage unit 7, which is additionally stabilized by struts 6d, operatively connected between the said main wire anchorage unit 7 and ground anchorage units (not shown) and tensioned by turnbuckles 6a.

Connected to the upper extremities of the trusses 2a in each row of trusses 2 is a purlin 11 which defines the apex of the structure, while connected between the upper extremities of the outer trusses 2 are a pair of. purlins 12 each of which is parallel to the other and to the purlin 11, the latter and the purlins 12 forming the main framework of the structure. Furthermore purlins 13 are connected between opposed wire anchorage units 7 and are located adjacent ground level.

Curved stabilizing units 14 extend diagonally from an outer truss 2 in one row to an outer truss 2 on.the remote side of a spaced apart row of trusses 2.

At each side of the structure is a longitudinal* side board 15 of marine plywood, the upper edge of which is secured to the adjacent purlin 13 and the lower edge of which is embedded in the soil.

A curved base plate 16 is fixed to the ground below cultivation level and is utilized in association with the main wire anchorage unit 7 to form a frame for the gable end of the structure. plates 16 at each gable end of the building and extend through pulleys 22 on the main wire anchorage units 7 · Each wire 21 passes through a turnbuckle (not shown) located adjacent one of the base plates 16. Application of tension to each wire 21 through the intermediary of the associated turnbuckle ensures that the framework of the entire structure is rigid and capable of resisting wind loads.

Located over the longitudinal wires 21 is a flexible roofing membrane of plastic sheeting 23 and securing the plastic sheeting 23 in position are transverse wires 24 connected between the purlins 13» the wires 24 being also tensioned by turnbuckles 1. Transverse wires 24 also support the- * flexible roofing membrane 23 against wires 21 at the gable ends of the structure.

Between the/ struts 6b, and one of the struts 6d parallel thereto, there is connected a transverse strut 6c which defines a door to one gable end of the greenhouse. A further door may similarly be provided at the remote end of the structure.

Figures 2 and 3 show.- greenhouses similar, <but ncrte irlont wH^ to Figure 1. In the constructions illustrated in Figures 2 and 3* however, a pair of curved wire anchorage units 31 are positioned as shown so as to form equal angles, at each corner of a greenhouse construction.

Supporting the wire anchorage units 31 are purlins 11 , 12 borne by trellis trusses 2 , 2a identical to the correspondingly numbered trellis trusses shown in Figure 1. Additional purlins 12a bridge contiguous wire anchorage units 31 at each end of the structure, and render unnecessary struts corresponding to struts 6, 6a shown in the gable end of the structure to Figures 7 to 14 inclusive illustrate . various span structures incorporating the principles described with reference to Figures 1 to 6. The construction shown in Figures 7 to 14 inclusive are generally self-explanatory in the light of the foregoing description and demonstrate the manner in which single or multiple span greenhouses may be constructed.

For example, Figure 7 shows a cross-section of a simple structure involving the use of a pair of curved main anchorage units 7 at each extremity of the structure without the employment of internal trellis trusses. The construction of Figure 7 is normally employed only in minimum span structures.

Figures 7a, 7b and 7c show in diagrammatic form the three main wire anchorage systems described with reference to Figures 1, 3- and 4.

Figure 8 is a diagrammatic representation of a span structure, larger than those shown in Figures 7 , 7a, 7b and 7c, illustrating the use of trellis trusses and capable of supporting longitudinal purlins.. ' ' „.

Figure 9 shows diagrammatically a structure which has outer trusses 2 but no central truss.

The construction shown in Figure 10 is that of a medium span structure showin the location of longitudinal ,purlins supported by trellis trusses and having natural outwardly opening ridge ventilators of the kind described with reference to 40 I Figure 4 together with similar ventilators/on both sides thereof at ground level.

Figure 11 s a diagrammatic illustration of. a large span structure showing the use of two central trusses 2b in place of a single apex truss. This construction may incorporate crop In Figure 12 is shown a construction similar to that of Figure 11 but in which are incorporated outwardly and/or inwardly] opening ventilators.

Figure 13 is a diagrammatic view of a very large span structure of dimensions compatible with modern horticultural practice.

The construction shown in Figure 14 is similar to that illustrated in Figure 13 but contains natural outwardly opening ridge ventilators and natural inwardly and/or outwardly opening ventilators at ground level.

Figure 15 illustrates one preferred method whereby the flexible roofing membrane 23 may be secured to a longitudinal purlin 11. In a simple construction, the purlin 11 may be manufactured from a rectangular section of pressure preserved and waterproofed timber, two longitudinal portions of which are cut away to provide abutment members 1 for containing the flexible roofing membrane 23 as described hereinafter. cut away 11 Immediately below the/co-planar faces 42 of the purlin/on opposite sides of the projecting portion lib of the purlin 11 are provided spaced apart and axially parallel apertures 43 extending transversely through the purlin 11 for accommodating double headed bolts 44 each of which has a wing nut 45 on each end thereof. Between each wing nut 45 and the contiguous side of the purlin 11 is provided a flat steel washer or .pressure plate 46 so that, upon tightening of the wing nuts 45 * the steel washers 46 cause the abutment members 41 to press into and against the adjacent edges of the purlin 11. The abutment members 41 may be the same length ^ as the purlin 11, or may be cut into shorter sections, fixed independently by any required number of wing nuts 45 > for convenience in handling.

As shown in Figure 15 "the flexible membrane 23 on each side of the purlin 11 , is fully twisted around the appropriate abutment member 41 and firmly secured against the abutment member 41 by the steel washer 46, the area of contact between the steel washer 46 and the abutment member 41 being substantially airtight and watertight.

The purlin 11 is secured to a vertically disposed truss 2a by a bracket 51 shown separately in perspective in Figure 16.

The bracket 51 is secured to the purlin 11 and to the trellis truss 2a by means of a vertically disposed bolt 52. The bracket 51 has side wings 53 to which curved stabilizing units 14a are secured by bolts 55· It is necessary, at the apex of the structure, that the exterior surfaces of the purlin 11 (including the abutment members 41) and the stabilizing units 14a should be maintained in the same plane in order to allow to act firmly against each other and to avoid possible projecting portions of the ^unlift--i-i- abutment members 41 and stabilizing .protruding units 14a whflre-h-may prrbmt&v through the flexible membrane 23.

A channel shaped top rail 56 is bolted to the projecting portion lib of the purlin 11, which rail may be used as a support for a roof service gantry or like machine.

A second layer of roofing membrane 23a may be incorporated in the manner shown diagrammatxcally with reference to Figure 17· The layer 23a may serve to reduce the likelihood of failure of the primary roofing membrane 23, particularly at the connection point between a support member and the roofing membrane.

It is envisaged that alternative means may be employed to tension the wires supporting the flexible roofing membrane . The simplest and most convenient method is to use a plurality of wires as shown in Figures 1 and 2 and to tension each wire individually by providing a turnbuckle on each wire.

If desired, however, single turnbuckles on each wire may be avoided by use of the systems illustrated in Figures 18, 19 and 20.

Figure 18 shows the use of single pulleys 61 attached to a pair of purlins 12 and to/ / paortion of a wire anchorage unit 7 aid through which longitudinal wires 21 and transverse wires 24 are threaded to form a pair of contra-tensioned layers.

The transverse tensioning of wires 24 may be achieved by the use of an individual pulley attached to each wire 24 or by a selected number of pulleys 66 fixed to a longitudinal rigid unit 64 as shown in Figures 19 and 20. The wires 24 can be individually attached to the longitudinal unit 64 as shown in Figure 20 or a single wire may be threaded through a series of small holes 05 in the longitudinal unit 64 as shown in Figure 1 . The pulleys 66 are connected by a continuous wire or cable 02 to a series of pulleys 67 which are suitably attached to the rigid purlin 12 forming a tensioning system as shown ia the left hand side of Figures 19 and 20. An alternative tensioning system may be formed by the use of a double pulley 68 attached to purlins 12 in place of the single pulley 67, as illustrated in the right hand side of Figures 19 and 20.

Tensioning of the main longitudinal tensioned wires 21 may be achieved by the connection of pulleys and tensioning units to the main curved wire anchorage units 7 and the gable base plates 13 (reference Figures 1, 3, A, 5 and 6).

Where ground anchorage for wire tensioning is difficult to attain, a single continuous wire may be used for the main longitudinal tensioned wire 21 and hence forming both roof and gable end planes. For this method of construction, it is necessary to have the external trellis trusses 35 erected to form an oblique angle outward from the centre of the structure as described already with reference to Figures 4,5 and 6.

If necessary or desirable in order to provide continuous support to the upper and lower surfaces of the roofing membrane, the invention provides in addition to the two main tensioned wires 21 and 24 described above, a plurality of secondary wires. When the main longitudinal tensioned wires 21 have been fixed in position a lower transverse stabilizing wire may be fixed at right angles to the main longitudinal tensioned wire 21, between the longitudina?. puvlins 12 and 13· The function of this layer of transverse stabilizing wires is to support the roofing membrane between the parallel lines of the main longitudinal tensioned wires 21 against the contra pressure of the main transverse tensioned wires 24. This lower transverse stabilizing wire is preferably tensioned sufficiently to prevent sag in the plastic membrane between the main longitudinal tensioned wires 21. After the vcufing membra has been placed on top of this net an upper stabilizing wire similar to the lower stabilizing wire may be laid longitudinally so as to press the roofing membrane down to the main longitudina tensioned wires 21. To obtain this pressure it is preferable to apply tension to the upper stabilizing wires.

It will be appreciated that these stabilising wires and the main tensioned wires form what is in effect a reticulate underlay and a reticulate overlay, with the roofing membrane sandwiched between them. The developed plan of the underlay and the overlay is in each case a grid formed by two crossing arrays of wires. It should be noted that these extra sets of §¾a ia§ing wires would not be §een in tlii aeeefflpiHying o a¾l i,^ as the transverse stabilising wires and the longitudinal stabilisin wires coincide with the main transverse and -2 tensioned wires 24 and the main longitudinal tensioned wires 21 respectively.

It is well known to those conversant with the use of inflatable structures, particularly those constructed from plastic sheeting, that the risk of deflation and subsequent damage to crops caused by either accidental damage to the plastic sheeting or deterioration, is high. Therefore, this invention provides a slidable net beneath the roof which can be pulled across the whole interior of the building in the event of roof collapse and so protect the crops from damage until the roof is repaired.

To improve the heat insulation properties of the construction an alternative construction envisages double glazing the structure. This is achieved by a double layer of roofing membrane which is fixed to the structure in the same manner as described above. This double layer of roofing membrane forms, when in position, a plurality of sealed envelopes between the crossing apertures formed by the/coirfcra-feonoioncd wires 21 and 24. Air under pressure is introduced between the layers of roofing membrane. The air pressure forces the two layers apart in each mesh opening forming an insulated roof. Similarly it is also possible to reverse the process, evacuate the air space and hence ensure that the double layer of membrane operates as a single layer.

By a~ utilisation of the main features of the roofing construction as described above, it is possible to obtain various other methods of double glazing for the roof surface. To the external curved roof surface there is fixed and sealed between the roofing members a second layer of suitable material such as plastic£*sheeting. A light net of wire or other suitable material is fixed and tensioned, if required, on top of this layer of material. In the sealed space between this layer, of material and the roofing membrane air is forced at a low pressure by a suitably adapted fan to inflate and separate the two layers of the materials and hence provide double glazing.

An alternative embodiment envisa es the sus ension of a suitably tensioned net from the internal roof surface and the fixing and sealing of a second layer of suitable material such as plastic sheeting to the interior of the roofing members. The evacuation of air by a fan from the sealed space between this sheeting and the roofing membrane forces the lower sheeting against the net which prevents contact between the two layers and hence a suitable double, glazing system is formed.

It will be appreciated that the disadvantage of using the methods of heat insulation as hereinbefore described is that the light penetration is reduced, during daylight hours, by the extra layer of roofing membrane or other material. Accordingly an alternative embodiment envisages the suspension from the roof of one or more easily removable layers of insulation material.

Referring to Figs. 21, 22 and 23 there is provided a plurality of longitudinal tensioned steel wires 69 fixed to the bottom portions of the curved stabilizing units 14 said wires 69 stretching the complete length of the structure beneath the layer* of """†ra nmi iiiiinl flexible elements namely the longitudinal wires 21 and transverse wires 24. Two layers 70 of insulation material are slidably suspended by means of eyelets 74> of known construction, from the wires 69 one end of each layer 70 being connected to one of the curved stabilising units and other end i of each layer 0 being connected to a buffer element 71 slidably mounted on the wires 69. Each buffer element 71 has. a front face' 75 constructed from a resilient material such as foam rubber. To each buffer element 71 there is connected two control wires 72 and 73 each of which is operatively connected to an electric ; motor (not shown).

In operation, when it is desired to draw the layers 70 of insulation material beneath the roof structure, the control wires 73 are drawn across the structure by means of the electric motors (not shown) until the facing buffer elements 71 are in contact, the resilient materials of their front faces 75 forming joint a substantially airtight poirvfe. The control wires 72 are used to draw the insulation material in the opposite direction. Referring to Fig. 23 it will be noted that in the closed position the layer of insulation material forms a series of concave sections hence eliminating any longitudinal stress on the insulation material and allowing drops of condensation which may occur as the surrounding atmosphere cools, to fall from the interior of the roofing membrane and run off to the lower edge of the structure where the water may be drawn off by suitable means.

It is envisaged that suitable control means such as a photoelectric call may be utilised to control the electric motors (not shown) used to draw the control wires 72 and 73 across the structure. The insulation material is drawn across the structure when the incident light is below a desired minimum, while the insulation material is removed when the incident light is sufficient for horicultural purposes .

It will be appreciated that more than one layer of insulation material and longitudinal tensioned steel wires, similar to those hereinbefore described, may be used.t Alternatively two or more layers of insulation material may be suspended from one layer of longitudinal tensioned steel wires in such a manner that in the operative position the layers form a series of suspended envelopes.

Where "short day" culture is required, as in flower bloom timing the insulation layer may comprise a layer of opaque material which may be drawn across the structure during some of ο '"Jjojeio o timber panolo or ohingloo fixed to a wire grid etc.

Claims (2)

1. J W 30801-2 WHAT I CLAIM IS; 1. A curved roof structure comprising one or more layers of flexible roofing membrane supported by and secured between two or more layers of tensioned flexible elements, each layer comprising a plurality of tensioned flexible elements laid transversely across so as to bear against a further plurality tensioned flexible elements.
2. 2. A roof structure according to Claim 1, in which the 26.10.67 flexible elements are constituted by wires, cables or cords. 10 3. A roof structure according to Claim 1 or 2, in which the flexible roofing membrane is a layer of one or more sheecs 4. A roof struc¾¾cr¾^ according to any of claims 1 to 3, supported by a pair of spaced apart curved anchorage units 15 or membrane each of which is disposed in a plane vnich is substantially perpendicular to the ground. 5. A roof structure according to any preceding claim which is substantially convex and is carried by a supporting framework of widely spaced curved anchorage units the structure being 20 provided with a roof covering in the form of an impervious membrane of flexible sheet plastics material, s ndwiched between a reticulate underlay and a reticulate overlay, each of which is constituted by flexible elements which span the building structure and are tensioned from edge to edge over the support¬ 25 ing framework; the developed plan of the underlay and overlay being in each case a grid formed by two crossing arrays of flexible elements each array comprising a number of substantially parallel rows of flexible elements and means for adjusting individually or collectively, the tension of flexible 30 elements or group of flexible elements in either of the array. 6. A roof structure according to claim 4 or 5 in which the curved anchorage units or members are supported by tensioned trellis trusses located in and perpendicular to the ground. 7. A roof structure according to Claims 4 or 5 in which one 35 or more stabilizing purlins are disposed parallel to the ground and between said curved anchorage units. 20. A greenhouse substantially as hereinbefore described 15 with reference to, and as illustrated in, any one or more of Figures 1 to 6 of the accompanying drawings. 2.1. Span structures substantially as described with reference to Figures 7 to" 14 of the accompanying drawings, for _use in a roof structure as claimed in any one of claims 1 to 16. 20 22. A method of securing a flexible membrane to a purlin in the construction of a roof structure according to any one of .10.6! the claims 8 to 15, said method being substantially as hereinbefore described with reference to, and as illustrated in, Fi#"ures 16 or 17 of the accompanying drawings. 23. 25 A method of tensioning flexible membrane supporting wire elements in the construction of a roof structure as claimed in any one of the preceding claims, -said method being substantially as hereinbefore described with reference to and as illustrated in Figures 18 to 20 of the accompanying 30 drawings. r the A licants