EP2707554A1

EP2707554A1 - Truss

Info

Publication number: EP2707554A1
Application number: EP12713261.1A
Authority: EP
Inventors: John Christopher HOLT
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-03-10
Filing date: 2012-03-09
Publication date: 2014-03-19
Also published as: GB201104061D0; GB2488821B; GB2488821A; WO2012120310A1

Abstract

The invention relates to a truss (10) for a cage of a structural building panel. The truss (10) comprises elongate first and second support members (12, 14) defining longitudinal edge portions (16) of the truss (10), and a connecting element (18) which extends between the longitudinal edge portions (16) and which interconnects the first and second support members (12, 14). The first and second support members (12, 14) are adjacent to and in spaced parallel or substantially parallel relationship with each other. The invention also relates to the structural building panel (50a, 50b) itself. The structural building panel (50a, 50b) incorporates at least two said trusses (10), at least one insulation member (52) sandwiched between adjacent trusses (10), and at least one retaining member (56) for retaining the insulation member (52) in position. The structural building panel (50a, 50b) offers increased strength and rigidity over existing prefabricated building panels for the same dimensions and materials. An extended truss (100a, 100b) and extended structural building panel (150a, 150b) are also provided.

Description

Truss

The present invention relates to a truss, and more particularly but not necessarily exclusively to a truss for a cage of a structural building panel. The invention also relates to the structural building panels themselves, using such a truss.

It is known to construct buildings, such as houses and commercial and industrial buildings and structures, using prefabricated building panels. Such panels are formed off-site, ready for use as and when required. Typically, the panels are used in the floors, in the building walls, in the foundations and in the roof. A key reason why prefabricated building panels are widely used is that they help to reduce the time required on site for building construction.

Buildings are constructed by arranging the prefabricated building panels adjacent to one another on a foundation and then securing or anchoring the panels to the foundation. Once the floor, wall and roof panels have been erected, internal and external surfaces of the panels may be rendered to provide a finished surface.

The problem with this known prefabricated building panel is that it has a limited load bearing capacity and can therefore be unsuitable for the construction of multi- storey buildings without the use of additional supporting structure.

Furthermore, the known prefabricated panel is limited in terms of its width and insulation properties.

Additionally, at present in the building trade, there is a general industry move towards increasing the quantity and quality of insulation within new builds. For example, it has become desirable to increase the insulation thickness of external walls from around 40mm to around 240mm or more. However, to accommodate such significant increases, walls constructed with a single panel thickness often require an additional panel in order to retain sufficient structural rigidity. This not only significantly increases costs, but also produces a considerable increase in weight, making the panels much more difficult to handle.

It is an object of the present invention to provide a truss and/or a structural building panel which reduces or substantially obviates the above mentioned problems. In brief, it is the object of the invention to provide a structural building panel of improved load bearing capacity which meets the industry demands for improved heat insulation properties, and which also has a low manufacturing cost and a low weight. According to a first aspect of the invention, there is provided a truss for a cage of a structural building panel, said truss comprising elongate first and second support members defining longitudinal edge portions of the truss, the first and second support members being adjacent to and in spaced parallel or substantially parallel relationship with each other, and a connecting element which extends between the longitudinal edge portions and which interconnects the first and second support members.

The truss is advantageous due to the presence of the second support member within each edge portion of the truss. As can be expected, this increases the overall load bearing capacity of the truss. However, it is the proximity of the second support member to the first support member that provides the greatest benefit, as explained below.

If a conventional truss having only a pair of support members and a connecting element is oriented longitudinally vertically and placed in compression, the applied load is transmitted directly through the pair of support members and indirectly through the connecting element. The stress on the connecting element at the edge portions of the truss can be significant and under an excessive load, the connecting element tends to deform at the edge portions as the connecting element accommodates the load.

By including a second support member in each edge portion of the truss, the truss is strengthened in that region since the connection (e.g. spot weld) between the second support member and the connecting element prevents or significantly reduces the risk of the connecting element deforming. Thus the truss, as defined in the present invention, can accommodate a greater applied load before deformation occurs.

Since the maximum load that can be accommodated through the truss before deformation occurs is increased, the truss is especially useful in the construction of multi-storey buildings.

Preferable and/or optional features of the first aspect of the invention are set forth in dependent claims 2 to 18.

According to a second aspect of the invention, there is provided a structural building panel comprising at least one insulation member, at least two trusses in accordance with the first aspect of the invention, and at least one retaining member, wherein the trusses are arranged in substantially parallel planes and the insulation member is disposed intermediate the trusses, the retaining member interconnecting the said at least two trusses and extending substantially perpendicularly to the said at least two trusses for retaining the insulation member therebetween.

This construction is beneficial due to the presence of the earlier described trusses as part of the structural building panel. The trusses increase the load bearing capacity of the structural building panel whilst adding little to the overall weight. Furthermore, the secondary support members offer additional surface area onto and around which render or concrete can bond. By increasing the bond strength between the render or concrete and the structural building panel, the load bearing capacity of the structural building panel is yet further improved.

The insulation member improves the thermal insulation properties of the structural building panel, thereby contributing to a strong, lightweight and insulated prefabricated panel.

Preferable and/or optional features of the second aspect of the invention are set forth in dependent claim 20 and claim 21.

According to a third aspect of the invention, there is provided an extended truss comprising at least two trusses in accordance with the first aspect of the invention, the trusses being co-planar or substantially co-planar and arranged in a spaced parallel or substantially parallel relationship with each other, and at least one connecting means interconnecting the said at least two trusses.

The extended truss is suitable for receiving relatively wide compressive loads, and as such is particularly beneficial in structural building panels where the thickness of the insulation should be in a range of 100 to 300mm, or more. The extended truss dispenses with the need for an additional building panel in order to retain structural rigidity.

Preferable and/or optional features of the third aspect of the invention are set forth in dependent claim 23 and claim 24.

According to a fourth aspect of the invention, there is provided an extended structural building panel comprising at least two insulation members, at least two extended trusses in accordance with the third aspect of the invention, and at least one further retaining member, said at least two extended trusses being arranged in substantially parallel spaced apart planes, the insulation members each being disposed intermediate said at least two trusses, wherein the further retaining member is connected to and extends substantially perpendicularly between at least two extended trusses. The extended structural building panel is advantageous primarily since it can provide a thermal break between two co-planar trusses. The gap in between the trusses provides a space for a thermal insulator, which can either be air or alternative insulation material, thereby providing an opportunity for forming a thermal break. Since heat has to bridge the gap in order to escape from a building by making use of the enhanced structural building panel, heat loss is reduced. This feature is beneficial not only for the environment but also for the building owner / occupier whose heating bills will be correspondingly lower in the long term.

Notably, an extended structural building panel improves the standard insulation rating of a building.

Preferable and/or optional features of the fourth aspect of the invention are set forth in dependent claims 26 to 30.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

Figure 1 shows a side view of a first embodiment of a truss in accordance with the first aspect of the invention;

Figures 2a to 2c show a plan view of the first embodiment in three exemplary configurations, each arrangement having a first and a second support member together with a single connecting element;

Figures 3 a to 3c show a plan view of a second embodiment of a truss in accordance with the first aspect of the invention which incorporates a third support member in each longitudinal edge portion, and also two further exemplary arrangements of first, second and third support members and a connecting element;

Figure 4 shows a perspective view of a third embodiment of a truss in accordance with the first aspect of the invention, showing in particular a truss having first, second and third support members, a first connecting element and also a second connecting element;

Figures 5 a to 5c show a plan view of the third embodiment of the truss in three exemplary configurations, each arrangement having first and second support members with the first and second connecting elements;

Figures 6a to 6c show a plan view of the third embodiment of the truss with the third support member removed, showing three exemplary configurations, each arrangement having first and second support members together with first and second connecting elements;

Figure 7 shows a perspective view of a first embodiment of a structural building panel in accordance with the second aspect of the invention, which incorporates the truss of Figure 1;

Figure 8 shows a perspective view of a second embodiment of a structural building panel in accordance with the second aspect of the invention, which incorporates the truss of Figure 4;

Figure 9 shows a side view of a first embodiment of an extended truss in accordance with the third aspect of the invention;

Figure 10 shows a perspective view of a second embodiment of an extended truss in accordance with the third aspect of the invention;

Figure 11 shows a first embodiment of an extended structural building panel in accordance with the fourth aspect of the invention, which incorporates the extended truss of Figure 9; and

Figure 12 shows a second embodiment of an extended structural building panel in accordance with the fourth aspect of the invention which incorporates the extended truss of Figure 10.

Referring firstly to Figure 1, a first embodiment of a truss for a cage of a structural building panel truss is indicated generally at 10. The truss comprises elongate first and second support members 12, 14 which define longitudinal edge portions 16 of the truss 10, and a connecting element 18 which extends between the longitudinal edge portions 16 and interconnects the first and second support members 12, 14.

The first and second support members 12, 14 are preferably rigid or substantially rigid struts of wire or cord, and may be or include metal, for example, steel. Typically, the first and second support members 12, 14 are made from a drawing process. It is envisaged that suitable alternative materials and manufacturing processes may be used, if available. The first and second support members 12, 14 are the main load bearing structural elements of the truss 10, through which most of any applied load are transmitted. The length of the first and second support members 12, 14 may be in a range of 100 to 6000mm. The first and second support members 12, 14 may have a circular lateral cross- section. In such an arrangement, the diameter of the first support member 12 may be the same or different to the diameter of the second support member 14. Preferably, the diameter of the first and/or second support member 12, 14 is in a range of 1 to 6mm. More preferably, the diameter of the first and/or second support member 12, 14 is in a range of 2 to 8mm. Although preferably circular, the lateral cross-section may be non-circular, such as square.

The outside distance between the first support members 12 in each longitudinal edge portion 16 is preferably in a range of 50 to 110mm. More preferably, the outside distance is in a range of 60 to 100mm. The inside distance between the second support members 14 in each longitudinal edge portion 16 is preferably in a range of 30 to 90mm. More preferably, the inside distance is in a range of 40 to 80mm.

The first and second support members 12, 14 are arranged adjacent to and in spaced parallel or substantially parallel relationship with each other. The spaced relationship is defined by a space or gap 20. The distance between the first and second support member 12, 14, i.e. the gap 20, in each edge portion 16 is preferably in the range of 5 to 10mm.

The purpose of the connecting element 18 is primarily to maintain or brace the longitudinal edge portions 16 at a fixed distance apart and to prevent or substantially reduce the risk of the first and second support members 12, 14 bending or deforming under an applied load.

The connecting element 18 is a preferably rigid and continuous wire or cord-like strut similar to the first and second support members 12, 14 and may be or include metal. The connecting element 18 may have a circular or non-circular lateral cross- section. Preferably, the diameter of the connecting element 18 is also in a range of 1 to 8mm. The cross-sectional area of the connecting element 18 may be the same or different to that of the first or second support members 12, 14.

Instead of being continuous, the connecting element 18 may be non-continuous and alternatively comprise a plurality of discrete struts. Such struts are made from lengths of rigid wire or cord, typically 30 to 120mm long. When a truss 10 is cut to size, there is a tendency for the struts of a non-continuous connecting member to spring out of position since they are under a certain amount of internal tension during cutting. Although this risk is reduced by having a second support member 14 as part of the truss, the risk is minimised by using a continuous connecting element.

The connecting element 18 preferably zig zags along the longitudinal extent of the truss 10. The connecting element 18 forms a series of triangles 22 with the first and second support members 12, 14. Preferably, the triangles 22 are equilateral triangles, but they may be isosceles or right-angled triangles instead.

Alternatively, if the connecting element 18 is a non-connecting member as described above, the individual struts may each pass diagonally from first support member 12 to second support member 14, or vice versa.

The connecting element 18 is connected to the first and second support members 12, 14 at or adjacent to each bend or apex 24 of the zig zag via a plurality of nodes 26. The nodes 26 help to rigidify the truss 10 and therefore provide an important role in the truss 10 resisting deformation under a non-uniform load. Each node 26 is preferably achieved through a spot weld. However, alternative types of fixing means may be used provided that a permanent connection is made. At least two of the nodes 26a, 26b may be formed by the connection of the connecting element 18 to the second support member 14 and at least one of the nodes 26c may be formed by the connection of the connecting element 18 to the first support member 12.

It is important that the space or gap 20 between adjacent first and second support members 12, 14 in each longitudinal edge portion 16 is minimal in order to prevent the connecting element 18 from buckling between the nodes 26 when the truss 10 is in compression. At the same time, the space should be sufficient to permit the establishment of discreet or distinct nodes 26.

As stated earlier, in compression, deformation of the connecting element 18 is most likely to occur at or in close proximity to each bend or apex 24 of each zig zag. By placing the nodes 26 at or very proximate each bend or apex 24, the truss's resistance to buckling is increased. Such positioning of the nodes 26 significantly increases the load bearing capability of the truss 10.

By having discreet nodes 26, the truss's rigidity is improved, thereby making the truss 10 more resistant to deformation especially under non-uniform loads, for example, during high winds or earthquakes.

The longitudinal edge portions 16 may be configured in many ways, for example, as shown in Figures 2a, 2b and 2c.

In truss 10a of Figure 2a, the first and second support members 12, 14 are co-planar or substantially co-planar, and are disposed to one side of the connecting element 18. The second support members 14 are positioned in-board of the first support members 12. In truss 10b of Figure 2b, the planes of the first and second support members 12, 14 are separated by the connecting element 18 and thus placed on opposing sides thereof. In this arrangement, the first and second support members 12, 14 are in alignment with each other.

In truss 10c of Figure 2c, the first and second support members 12, 14 are adjacent to each other but off-set from each other, and are separated by the connecting element 18. Again, the second support members 14 are positioned in-board of the first support members 12.

Optionally, the longitudinal edge portions 16 may comprise two elongate third support members 28, the third support members 28 being disposed intermediate and in spaced parallel or substantially parallel relationship with the first and/or second support members 12, 14. Each third support member 28 is substantially the same as the first and second support members 12, 14, and therefore a detailed description is omitted.

The spacing between each third support member 28 and one or other of the first and second support members 12, 14 is defined by a further space or gap 30. The further space or gap 30 is preferably in the range of 5 to 10mm but may be less.

The third support members 28 may have the same or different cross-sectional area to the first and/or second support members 12, 14 and may have the same or different lateral cross- sectional shape.

As shown in Figures 3a, 3b and 3c, the connecting element 18 interconnects the first, second and third support members 12, 14, 28.

With regard to positioning, various configurations are possible, as shown in Figures 3a, 3b and 3c.

In truss lOd of Figure 3a, the connecting element 18 is disposed to one side of the first, second and third support members 12, 14, 28. In this arrangement, the second and third support members 14, 28 are positioned in-board of the first support members 12, and the third support members 28 in turn are positioned in-board of the second support members 14. Alternatively, the third support member 28 may be co-planar with one or other of the first and second support members 12, 14.

In truss lOe of Fig 3b, the first and second support members 12, 14 are in alignment with each other, separated by the connecting element 18. The third support members 28 are positioned in-board of the first and second support members 12, 14 on the same side of the connecting element 18 as the second support members 14.

In truss lOf of Fig 3c, again the first and second support members 12, 14 are in alignment with each other, and are separated by the connecting element 18. The third support members 28 are positioned in-board of the first and second support members 12, 14 on the same side of the connecting element 18 as the first support members 12. The third support members 28 are preferably connected to the connecting element 18 by a further plurality of nodes. The further plurality of nodes is similar to the nodes 26 described previously.

The presence of the third support members 28 is beneficial since the third support members 28 further increases the load bearing capacity of the truss.

Turning now to Figure 4, a third embodiment of a truss lOg may comprise a second connecting element 32. The second connecting element 32 is substantially the same as the first said connecting element 18, and therefore further detailed description is omitted.

Similarly to the first connecting element 18, the second connecting element 32 is connected to the first and second (and third support members 28, if present) support members 12, 14 at an additional plurality of nodes 34. The additional nodes 34 are similar to the nodes 26 described previously, but spaced from the nodes 26. The benefit of a second connecting element 32 is that its presence increases the nodal connections and therefore further improves the rigidity of the truss 10.

Preferably, the presence of the second connecting element 32 doubles the number of nodes in the truss lOg. However, the second connecting element 32 may increase the number of nodes in the truss lOg by any factor, for example triple, quadruple and so on. Similarly to the first connecting element 18, the second connecting element 32 may be a non-continuous connecting element. In such an arrangement, the struts preferably extend between first and second support members 12, 14 in an opposite direction to that of the first connecting element 18, with the combination of first and second connecting elements 18, 32 thereby forming a lattice arrangement.

At least one bracing element 35 may be used to help brace longitudinal edge portions 16 of the truss lOg and maintain them at a fixed distance apart. In this embodiment, the bracing element 35 is provided as a horizontal or substantial horizontal tie, which extends across and interconnects first, second and third support members 12, 14, 28. Each bracing element 35 is a preferably rigid and metal wire or cord-like strut.

Preferably, the bracing elements 35 are disposed at ends of the truss lOg, and at optionally any point therebetween. Each bracing elements 35 extends across and is connected to the truss lOg at at least the outer first support members 12. However, each bracing element 35 may be connected to each first support member 12 in each longitudinal edge portion 16 and/or each second support member 14 and/or third support member 28. Connection is achieved preferably by welding.

As indicated in Figures 5a, 5b and 5c, various configurations of the first and second support members 12, 14 and the first and second connecting elements 18, 32 of this third embodiment of the truss lOg are possible.

In truss lOg of Figure 5a, the first, second and third support members 12, 14, 28 are co- planar and all sandwiched between the first and second connecting members 18, 32. The second support members 14 are positioned out-board of the third support members 28, and in turn the first support members 12 are positioned out-board of the second support members 14.

In truss lOh of Figure 5b, the first support members 12 are sandwiched between the first and second connecting members 18, 32, whilst the second and third support members 14, 28 are disposed to one side of the first connecting element 18. The third support members 28 are positioned in-board of the second support members 14.

In truss lOi of Figure 5c, the first and third support members 12, 28 are sandwiched between the first and second connecting members 18, 32, whilst the second support members 14 are disposed to one side of the first connecting element 18. The third support members 28 are positioned in-board of the first support members 12.

Similarly, various configurations of the first and second support members 12, 14 with the first and second connecting elements 18, 32 are envisaged, for example, as shown in Figures 6a, 6b and 6c.

Truss lOj of Figure 6a shows only the first and second support members 12, 14 intermediate the first and second connecting elements 18, 32. The second support members 14 are positioned in-board of the first support members 12.

In truss 10k of Fig 6b, the first and second support members 12, 14 are in alignment with each other, and are separated by the connecting element 18. The first support members 12 are sandwiched between the first and second connecting elements 18, 32. In truss 101 of Fig 6c, the first and second support members 12, 14 are off- set from each other, and are separated by the connecting element 18. The second support members 14 are positioned in-board of the first support members 12.

The second and third support members 14, 28 each on their own merit render the truss 10 stronger than heretobefore possible. This means that the cross-sectional areas of the first, second and/or third support members 12, 14, 28 and/or first and second connecting members 18, 32 can be reduced as appropriate without reasonably compromising the strength of the truss 10. This reduces the manufacturing cost of the truss 10.

In Figure 7, a first embodiment of a structural building panel is indicated generally at 50a. The structural building panel comprises a plurality of insulation members 52 and a plurality of trusses 10. Features in common with the first aspect of the invention are denoted by the same reference numerals, for example, component parts of truss 10 are indicated.

In this embodiment, each truss 10 has first and second support members 12, 14 and a single connecting member 18, though any combination of first, second and third support members 12, 14, 28 together with first and second connecting elements 18, 32 are envisaged, such as those arrangements described previously. For example, Figure 8 shows a second embodiment of the structural building panel 50b, which comprises first, second and third support members 12, 14, 28 and first and second connecting elements 18, 32.

One insulation member 52 is disposed intermediate each pair of adjacent trusses 10. Preferably, the material of the insulation member 52 provides good thermal insulation. The insulation member 52 may be or may include a low density material, for example polystyrene, or more preferably expanded polystyrene. Polyurethane foam may be used instead. Polyurethane foam is a better insulator than polystyrene but it is less environmentally friendly than polystyrene.

Optionally, the insulation member 52 takes the form of a rectangular block. Exemplary dimensions of the insulation member 52 are: 2400mm (length) x 40mm (width) x 50mm (depth). Selection of the depth is important to the extent that it permits the insulation member 52 to be fitted between adjacent trusses 10, i.e. the depth of the insulation member 52 must be the same or less than the spacing between adjacent trusses 10.

With reference to Figures 7 and 8, each truss 10 (or lOg in Fig 8) is arranged adjacent to another truss 10 in parallel or substantially parallel spaced apart planes. A plurality of vertically spaced elongate retaining or strapping members 56 extends perpendicularly to the trusses 10 to interconnect the trusses 10 typically via the first support members 12 at the longitudinal edge portions 16. The plurality of trusses 10 and plurality of retaining members 56 together form a wire framework or cage in which the plurality of insulation members 52 are housed. The retaining members 56 help to keep the insulation members 52 in position between adjacent trusses 10.

It is advantageous if there is a clearance between the insulation members 52 and the cage once assembled together, as described in more detail below.

The retaining members 56 also maintain the trusses 10 at a fixed or substantially fixed distance apart. A typical spacing between adjacent trusses 10 is in a range of 40 to 60mm, and more preferably the spacing is approximately 50mm. The retaining members 56 are positioned at regular intervals along the longitudinal extent of the truss 10, typically every 50mm.

Each retaining member 56 is a preferably rigid wire or cord-like strut, and may be or include metal. Each retaining member 56 may have a circular or non-circular lateral cross- section. The diameter of each retaining member 56 may be in a range of 1 to 6mm. However, the retaining members 56 may be planar and provided as, for example, a continuous sheet or alternatively a mesh, which extends along or around at least a portion of the structural building panel 50a, 50b.

The retaining members 56 are preferably mounted to the trusses 10 at a plurality of positions using fixing means 58. Each retaining member 56 may be connected to every other truss 10. However, alternative interval spacing may be considered, for example, a connection between each retaining member 56 and every truss 10, or, a connection between each retaining member 56 and every third truss 10. Preferably, the fixing means 58 is a spot weld. Alternatively, the fixing means 58 may include a loop provided on one or more of the first support members 12, through which the retaining member 56 passes, thereby securing the retaining member 56 to the truss 10.

To form the structural building panel 50a, 50b, the trusses 10, lOg and insulation members 52 are assembled together in an alternating sequence. If desired, the insulation members 52 are connected together during assembly using joining means. Such joining means may be or include an adhesive. The retaining members 56 are then connected to the trusses 10.

With the structural building panel 50a, 50b in situ on site, a concrete and/or plaster render 60 is applied to opposing faces of the structural building panel 50a, 50b. The render 60 is not necessary to add strength to the wire cage but can do so if required. The render 60 bonds to the first and second support members 12, 14 and also to the retaining members 56. Since it is intended that there is a clearance between at least an outwardly facing portion of the insulation member 52 and the wire cage, the render 60 is able to enter the confines of the cage and bond to and around the primary and secondary support members 12, 14 and the strapping members 56 from within the cage as well as outside of the cage. The bonding helps to improve the overall load bearing capacity of the structural building panel 50a, 50b compared to existing structural building panels, since the surface area available for bonding is increased.

The render 60 typically comprises a weatherproofing mix of Portland cement, aggregates and sand. Alternatives, such as gypsum plaster, are commonly used for rendering internal surfaces. The layer of cement or plaster 60 encases the mesh cage on both sides of the core producing a strong and rigid structure when dry. If desired, various waterproofing, anti-fungal and fibre reinforcing agents may be applied to the rendering mixture or the dried surface. Internal and external surfaces are defined in this context as such relative to the constructed building.

For the same overall dimensions and materials, the second embodiment of the structural building panel 50b has a higher load bearing capacity than the first embodiment 50a. Turning now to Figures 9 and 10, first and second embodiments of an extended truss are indicated generally at 100a and 100b respectively. The extended trusses 100a, 100b comprise a pair of co-planar trusses, each truss being substantially as described earlier with reference to 10 and lOg respectively. However, any of the previously described trusses 10a to 101 may be used. Parts in common with the first and second aspects of the invention are denoted by the same reference numerals. A gap 102 separates the two trusses 100a (or 100b in Fig 10) and the trusses 100a are in a parallel or substantially parallel relationship with each other. The gap 102 is preferably in a range of 60 to 100mm, and is more preferably approximately 60mm. At least one connecting means 104 maintains the trusses 100a, 100b in position relative to one another. In the embodiment of Figure 9, the connecting means 104 is provided as a horizontal or substantially horizontal tie 106, which extends across the gap 102 midway along the longitudinal extent of the trusses 10. However, additional ties 106 may be provided, for example, at the ends of the trusses lOg, as indicated in Figure 10, and optionally at any point therebetween, depending on the length of the trusses lOg. Each tie 106 is a preferably rigid and metal wire or cord-like strut.

Each tie 106 extends across and is connected to the pair of trusses 10 at at least the outer first support members 12. However, each tie 106 may be connected to each first support member 12 in each longitudinal edge portion 16 and/or each second support member 14 (and/or third support member 28, if present). Connection is achieved preferably by welding.

The tie(s) 106 may be dispensed with and alternative connecting means are envisaged, as will become apparent later.

The extended truss 100a, 100b is particularly beneficial where a greater increase in strength or truss width is required. For example, the extended truss 100a, 100b is especially useful for use in building panels where a width of 300mm or more is required. Such building panels are particularly advantageous in the use of multi-storey buildings.

Referring to Figures 11 and 12, first and second embodiments of an extended structural building panel are indicated generally at 150a and 150b respectively. The extended structural building panel 150a, 150b comprises a plurality of insulation members 52 and a plurality of extended trusses 100a, 100b. Each extended truss 100a, 100b can be made up of any combination of trusses 10a to 101, and extended trusses 100a and 100b are used in the following description for example only. Features in common with earlier aspects of the invention are denoted by the same reference numerals.

Each extended truss 100a, 100b is positioned adjacent to one another in substantially parallel spaced apart planes. Two insulation members 52 are provided between each pair of parallel extended trusses 100a, 100b, the two insulation members 52 being separated in the same plane by gap 152 which is the same or substantially the same sized gap as the gap 102 in each extended truss 100a, 100b.

A further plurality of retaining members 154 extends in a plane substantially perpendicular to the extended trusses 100a, 100b and is connected to every other extended truss 100a, 100b. The retaining members 154 may be connected to each extended truss 100a, 100b or every third extended truss 100a, 100b. The retaining members 154 are substantially the same as retaining members described earlier with reference to retaining members 56, and so further detailed description is omitted.

In a similar manner to the structural building panel 50a, 50b described previously, the retaining members 154 and extended trusses 100a, 100b together substantially form a cage in which the insulation members 52 are retained.

A gap filler member 156 may be provided in the gap 152 between each pair of co-planar trusses 100a, 100b. The gap filler member 156 may be adhered to adjacent insulation members 52 using joining means for enhanced strength at the core of the extended structural building panel 150a, 150b. The joining means may be or include adhesive. The gap filler member 156 can be used to improve the insulation value or rating of the final extended structural building panel 150a, 150b. Typically, the gap filler member 156 is or includes polystyrene and preferably expanded polystyrene. Again, polyurethane foam may be used instead.

It should be noted that the gap filler member 156 is not essential and may be omitted. If a gap filler member 156 is utilised, the horizontal tie 106 described earlier may be omitted and instead the connecting means 104 takes the form of adhesive used to adhere one or more adjacent insulation members 52 to the gap filler member 156, thereby interconnecting the extended trusses 100a, 100b. The connecting means 104 may be or include adhesive, or one or more clips. Alternative connecting means 104 may include a plurality of protrusions (e.g. spikes) extending from at least a portion of the extended truss 100a, 100b for engagement with at least the insulation members 52.

Without a gap filler member 156, the gap 152 simply contains air and as such is an air gap. Air is known to be a reasonable thermal insulator. With an air gap, at least one tie 106 is required to couple two co-planar trusses 10a together in the same plane. The tie 106 acts as a heat conductor and thus it is desirable to minimise the size of the tie 106 when possible. The air gap is advantageous since it provides a cavity that is potentially useful for storing and concealing conduit, especially conduit for carrying electrical wiring.

Conduit may additionally or alternatively pass between the outwardly facing portion of each insulation member 52 and the wire cage prior to rendering. In such an arrangement, it is envisaged that at least one of the retaining members 154 is provided adjacent the gap 152, running along an inner portion of the extended truss 100a, 100b. The insulation member 52 abuts the at least one retaining member 154, thereby leaving a space adjacent the outwardly facing portion of the insulation member 52 for receiving conduit.

The gap 152 between co-planar trusses 10a and their corresponding insulation members 52 acts as a thermal break whether it is filled with a gap filler member 156 or, more cheaply, with air. A complete thermal break can be achieved by omission of the interconnecting tie 106. The thermal break significantly reduces the quantity of heat loss through the extended structural building panel 150a, 150b.

The truss, extended truss, structural building panels and extended structural building panels described herein are advantageous since they significantly improve on the load bearing capacity of existing trusses and prefabricated panels. The prefabricated panels described herein are suitable for use in the construction of multi-storey buildings.

Furthermore, use of such panels results in buildings with improved energy ratings, with consequential clear cost benefits for the building owner/occupiers. Notably, the panels are environmentally friendly as less heat is lost from the buildings to the environment. The buildings panels are simple and cost effective to manufacture. Moreover, the panels can be easily handled on and off site and can be readily cut to size, as required.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A truss (10) for a cage of a structural building panel (50a, 50b), said truss (10) comprising elongate first and second support members (12, 14) defining longitudinal edge portions (16) of the truss (10), the first and second support members (12, 14) being adjacent to and in spaced parallel or substantially parallel relationship with each other, and a connecting element (18) which extends between the longitudinal edge portions (16) and which interconnects the first and second support members (12, 14).

2. A truss (10) as claimed in claim 1, in which the first and second support members (12, 14) of each longitudinal edge portion (16) are co-planar and disposed to one side of the connecting element (18).

3. A truss (10) as claimed in claim 1, in which the first and second support members (12, 14) of each longitudinal edge portion (16) are disposed on opposing sides of the connecting element (18).

4. A truss (10) as claimed in claim 3, in which the first and second support members (12, 14) are off-set from each other.

5. A truss (10) as claimed in any one of the claims, in which two elongate third support members (28) are disposed intermediate and in spaced parallel or substantially spaced parallel relationship with the longitudinal edge portions (16), the connecting element (18) interconnecting the first, second and third support members (28).

6. A truss (10) as claimed in claim 5 when dependent on claim 2, in which the third support member (28) is disposed on an opposite side of the connecting element (18) to the first and second support members (12, 14).

7. A truss (10) as claimed in claim 5, in which the third support member (28) is co- planar with at least one of the first and second support members (12, 14).

8. A truss (10) as claimed in any one of the preceding claims, in which a second connecting element (32) extends between the longitudinal edge portions (16) and which also interconnects the first and second support members (12, 14).

9. A truss (10) as claimed in claim 8, in which at least one of the first and second support members (12, 14) is disposed intermediate the first and second connecting elements (18, 32).

10. A truss (10) as claimed in claim 8, in which the third support member (28) is disposed intermediate the first and second connecting elements (18, 32).

11. A truss (10) as claimed in any one of the preceding claims, in which the first connecting element (18) zig zags along the longitudinal extent of the truss (10).

12. A truss (10) as claimed in any one of the preceding claims, in which the first connecting element (18) is continuous.

13. A truss (10) as claimed in claim 8, in which the second connecting element (32) zig zags along the longitudinal extent of the truss (10).

14. A truss (10) as claimed in claim 8, in which the second connecting element (32) is continuous.

15. A truss (10) as claimed in claim 14, in which the diameter of any two or more of the first, second and third support members (12, 14, 28) are different.

16. A truss (10) as claimed in claim 14, in which the diameter of any two or more of the first, second and third support members (12, 14, 28) are or are substantially the same.

17. A truss (10) as claimed in any one of the preceding claims, in which the first connecting element (18) forms a plurality of triangles with the first and second support members (12, 14).

18. A truss (10) as claimed in claim 8, in which the second connecting element (32) forms a plurality of triangles with the first and second support members (12, 14).

19. A structural building panel (50a, 50b) comprising at least one insulation member (52), at least two trusses (10) as claimed in any one of claims 1 to 18, and at least one retaining member, wherein the trusses (10) are arranged in substantially parallel planes and the insulation member (52) is disposed intermediate the trusses (10), the retaining member (56) interconnecting the said at least two trusses (10) and extending substantially perpendicularly to said at least truss (10) for retaining the insulation member (52) therebetween.

20. A structural building panel (50a, 50b) as claimed in claim 19, in which a plurality of insulations members (52), trusses (10) and retaining members (56) are provided.

21. A structural building panel (50a, 50b) as claimed in claim 20, in which at least two of the said insulation members (52) are joined together using joining means.

22. An extended truss (100a, 100b) comprising at least two trusses (10) as claimed in any one of claims 1 to 18, the trusses (10) being co-planar or substantially co- planar and arranged in a spaced parallel or substantially parallel relationship with each other, and at least one connecting means (104) interconnecting the said at least two trusses (10).

23. An extended truss (100a, 100b) as claimed in claim 22, in which two connecting means (104) are disposed at opposing ends of the extended truss.

24. An extended truss (100a, 100b) as claimed in claim 22 or claim 23, in which a plurality of said connecting means (104) is provided, each connecting means being a tie member (106) which extends across the trusses (10) and which is connected to each truss (10) at at least two positions.

25. An extended structural building panel (150a, 150b) comprising at least two insulation members (52), at least two extended trusses (100a, 100b) as claimed in any one of claims 22 to 24, and at least one further retaining member (154), said extended trusses (100a, 100b) being arranged in substantially parallel planes, the insulation members (52) each being disposed in a respective said extended truss (100a, 100b), wherein the further retaining member (154) is connected to and extends substantially perpendicularly between the said at least two extended trusses (100a, 100b).

26. An extended structural building panel (150a, 150b) as claimed in claim 25, in which at least one of the insulation members (52) is or includes polystyrene.

27. An extended structural building panel (150a, 150b) as claimed in claim 25 or claim 26, in which the spaced relationship between said extended trusses (100a, 100b) is defined by a gap (102), said gap (102) providing a thermal break between extended trusses (100a, 100b).

28. An extended structural building panel (150a, 150b) as claimed claim 27, in which a gap filler member (156) is provided in the gap (102).

29. An extended structural building panel (150a, 150b) as claimed in claim 28, in which the gap filler member (156) is connected to at least one of the insulation members (52) using further joining means.

30. An extended structural building panel (150a, 150b) as claimed in claim 39, in which the further joining means include adhesive.