WO2008009054A1

WO2008009054A1 - An apparatus for interconnecting structural elements

Info

Publication number: WO2008009054A1
Application number: PCT/AU2007/001000
Authority: WO
Inventors: Faris Albermani
Original assignee: Crc For Sustainable Tourism Pty Ltd
Priority date: 2006-07-18
Filing date: 2007-07-18
Publication date: 2008-01-24

Abstract

An apparatus (1) for interconnecting elongate structural elements, the apparatus including a hub (100) and at least two connecting members (200), each connecting member (200) having a support end (210) for supporting a respective structural element (320), and a hub end (220) pivotally mounted to the hub.

Description

An Apparatus For Interconnecting Structural Elements

Field of Invention

The present invention relates to an apparatus for interconnecting structural elements, and in particular to a joint system for connecting bamboo.

Background of Art

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

In the construction of structures, such as buildings or the like, there is often the requirement to construct a frame of the structure or scaffolding prior to adding other building elements such as bricks, tiles, or concrete. Often, materials such as wood or steel are used in constructing the frame or scaffolding.

Bamboo is traditionally used in rural housing and scaffolding in South East Asia and South America. Bamboo has numerous advantages as a building material. In particular, bamboo is often characterised as a renewable, biodegradable and energy efficient natural resource with a great potential as an environmentally sustainable building material. Furthermore, the rapid depletion of natural forests makes bamboo a viable alternative to timber as bamboo grows around 15-18 cm/day and reaches its full height in 4-6 months. Further still, bamboo can be harvested within 3-5 years of growth compared to 20-40 years for timber.

Additionally, bamboo has excellent strength to weight ratio compared to conventional materials such as timber, steel and concrete, and is comparable to steel in terms of strength and stiffness efficiency while the production energy required for bamboo (per m3) is only 0.1% of that required for steel. On average bamboo culms can reach 8-15m length, 5-12cm diameter with wall thickness 5- 10mm, a tensile strength around lOOMPa and compressive strength about one third the tensile. Notably, there are over 1000 species of bamboo and for certain species a tensile strength of 370MPa was reported.

However, one of the main obstacles for the commercial use of bamboo in construction is the lack of an engineered joint system suitable for bamboo. Bamboo has long been used as a building material for the construction of bamboo trusses and frames. Traditional methods require only simple tools, and rope type materials and/or dowels to construct bamboo joints through lashing or tying, while more modern connection systems often utilise additional materials, such as steel or timber in addition to bolting, gluing, or clamping, etc.

Traditional methods are categorised into four basic joint types, namely spliced joints, orthogonal joints, angled joints and through joints and while guidelines have been adopted to improve joint's mechanical performance (through minimising the use of holes, using seasoned culms, etc), safety (unpredictability) remains a major concern with using such connections. Moreover, traditional connecting methods provide limited stiffness and strength with large variations, and are hardly utilised to the advantage of bamboo's mechanical properties.

More modern connection systems for joining bamboo include the DANIDA, Duff, Spoer, Arce, ITCR Fukuoka, Gutierrez and Filled Joints, the Das Clamp, Herbert Shear Pin

Connector, and the Christoque Connection System. In general, while these techniques offer more reliable stiffness and strength than traditional bamboo joints, they present a variety of other problems. In particular, these connection methods require the making of holes in the bamboo for fastening purposes, and thus has actually impeded the bamboo culm to demonstrate its full carrying capacity. Bamboo is susceptible to cleavage as characterised by its low tangential stiffness, which is adversely facilitated when holes are present.

Although additional reinforcements can be placed on the external circumference of bamboo to strengthen its tangential stiffness, the long term effectiveness of these reinforcements are still unknown. Moreover, the lightweight advantage of bamboo culm is drawn back by the modern joint system which is mostly made up of conventional materials such as steel or timber or concrete or a combination of these. Inevitably this weighty joint utilises portions of the culm's capacity and lessens the bamboo's strength to support external applied loads.

This identifies a need for an apparatus for interconnecting structural elements which overcomes, or at least ameliorates, one or more of the problems inherent in the prior art, or provides an alternative to existing systems.

Summary of Invention In a first broad form, the present invention provides, an apparatus for interconnecting elongate structural elements, the apparatus including:

- a hub; and,

- at least two connecting members, each connecting member having a support end for supporting a respective structural element, and a hub end pivotally mounted to the hub.

Typically, the at least two connecting members are constrained to move in a plane.

Typically, each hub end is individually fixable to the hub.

Typically, the hub has two hub portions, each hub portion having a base portion, the hub portions abutting each other at their base portions.

Typically, the hub has a number of projecting members, the hub end of each connecting member being connected to a respective projecting member.

Typically, the projecting member and the connecting member are coupled together by a bolt.

Typically, the hub portions are moveable with respect to each other. Typically, each hub portion has a shaft, the hub portions being aligned such that a bolt passes through each shaft, thereby coupling the hub portions together.

Typically, the shaft is located at a centre of the hub portions.

Typically, each hub portion has a plurality of projecting members, the projecting members being disposed circumferentially around the centre of the hub.

Typically, the supporting end of the connecting means is a socket, the socket being able to receive the structural element.

Typically, the supporting end is cylindrical, the supporting end being able to receive a cylindrical structural element.

Typically, the socket has at least one groove extending around an inner surface.

Typically, the structural member is attached to the first connecting member by a grouting.

Typically, the structural element is bamboo.

Typically, the apparatus is made of any one or combination of: polymer of vinyl chloride; and,

- fibre reinforced polymer composite.

In a second broad form, the present invention provides an apparatus for interconnecting elongate structural elements, the apparatus including:

- a hub; and,

- at least two connecting members, each connecting member having a support end for supporting a respective structural element, and a hub end, each hub end being individually fixable to the hub. In a third broad form, there is provided, a hub for interconnecting elongate structural elements, the hub being connectable to at least two connecting members, each connecting member having a support end for supporting a respective elongate structural element, and a hub end, each hub end being individually fixable to the hub.

In a fourth broad form, there is provided a method of interconnecting elongate structural elements, the method including the steps of:

- coupling first and second structural elements to a support end of respective first and second connecting members; and, - connecting a hub end of the first and second connecting members to a hub.

Typically, the structural elements are bamboo, the method including cutting grooves at an end of the bamboo, prior to coupling the bamboo to the support end.

Typically, the method further includes adding glue into the cut grooves.

Brief Description of Figures

An example of the present invention will now be described with reference to the accompanying drawings, in which: - Fig. IA is a schematic side view of an example of a hub for interconnecting elongate structural elements;

Fig. IB is a schematic top view of the hub of Fig. IA;

Fig. 2A is a schematic side view of an example connecting member;

Fig. 2B is another schematic side view of the connecting member of Fig. 2 A; Fig. 2C is a schematic top view of the example connecting member of Fig. 2A;

Fig. 3 is a schematic side view of an example apparatus for connecting interconnecting elongate structural elements, including connecting members;

Fig. 4 is a schematic diagram of examples of various types of bamboo lattice structures;

Fig. 5 is a Von Mises stress contour plot of the hub of Fig. IA; Fig. 6 is a load-displacement response of the hub of Fig. IA;

Fig. 7 is an example response of a pull-out test on the connecting member of Fig. 2 A; Fig. 8 is a schematic top view of a module constructed including the apparatus of Fig 3; Fig. 9 is a schematic side view of the module of Fig. 8; Fig. 10 is an example load-deflection response of an example apparatus; and, Fig. 11 is a Von Mises stress contour plot for a support node of the module of Fig. 8.

Detailed Description of the Preferred Embodiments

An apparatus 1 for interconnecting elongate structural elements, is shown in Figures 1 to 3.

The apparatus 1 includes a hub 100, and at least two connecting members 200. Each connecting member 200 has a support end 210, for supporting a respective structural element 320, and a hub end 220, which is pivotally mounted to the hub 100.

Figures IA and IB show the hub 100, which in this example has two hub portions 110, 120. Each hub portion 110, 120 has a base portion 111, 121 (respectively) and projecting members 112, 122 (respectively). In this example, the hub portions 110, 120 abut each other at their base portions 111, 121. Furthermore, each hub portion 110, 120 has a shaft 115, 114 where the hub portions 110, 120 are aligned to allow a bolt, or the like, to pass through the shaft 115, thereby coupling the hub portions 110, 120 together. The bolt 300 is held in place by a corresponding nut 301, to thereby hold the hub portions in position (as shown in Figure 3).

Notably, in this particular example, the shaft 115 is located substantially in the centre 114 of the hub 1. In any event, the bolting (or coupling) of the two hub portions 110, 120 together allows for the hub portions 110, 120 to be rotatable with respect to each other. In one example, the surfaces of the base portions 111, 121 may be profiled such as through the inclusion of cooperating grooves or the like, so that the hub portions can be retained in specific relative orientations. This can be used to help reduce the chance of unwanted relative rotation caused by forces on the hub portions 1 10, 120 in use.

In this example, the projecting members 112, 122 extend radially from the shaft and are spaced circumferentially around the centre 114 of the hub 1 (or the centre of respective hub portions 110, 120). Accordingly, the movement of the hub portions 110, 120, with respect to each other allows the projecting members 112, 122 to be arranged in various orientations with respect to each other. In one example, the projecting members 112 of one hub portion 110, are aligned at 45 degrees to the projecting members 122 of the hub portion 120.

In this particular example, each hub portion 110, 120 has four projections 112. However, it will be appreciated that this is for the purpose of example only and that in practice, the hub may only have two or more projections 112. Similarly, whilst two hub portions 110, 120 are shown in this example, a single integrated hub may be preferred in some situations.

In use, the projecting members 112, 122 are adapted to receive to the hub end 220 of a connecting member 200, in order to allow elongate structural elements 320 to be supported. An example connecting member 200 is shown in Figures 2A to 2C.

In this particular example, the connecting member 200 has a hub end 220 formed from two arms 220A, 220B, each having an orifice 221. The orifice 221 of the connecting member 200 can be aligned with a respective orifice 113 of the projecting members 112, 122. Once aligned, the orifices 221 and 113 can receive a bolt 310 (shown in Figure 3) or the like, which acts to connect or couple the hub end 220 of each connecting member 200 to a respective projecting member 112, 122. Accordingly, the connecting members 200 are constrained to move in a plane (or at least a range or orientations with respect to each other), and each hub end 220 can be individually fϊxable to the hub 100.

The connecting member 200 also has a support end 210, where the support end 210 includes a socket 211, with at least one groove 212 extending around an inner surface of the socket 211. The socket 211 is able to receive the structural element 320 (as shown in Figure 3).

In this particular example, the supporting end 210 is cylindrical, where the supporting end 210 is able to receive a cylindrical structural element 320. Furthermore the grooves 212 can be used to receive grouting, or the like in order to fix the structural element 320 within the socket 211.

In one particular example, the above-described apparatus 1 is particularly suitable for when the structural element 320 is bamboo. Additionally, in a further aspect, apparatus 1 is made of a vinyl chloride polymer.

It will be appreciated from the above-described apparatus, that by having the connecting members 200 being constrained to move in one plane, and being individually fixable to the hub 100, it can provide numerous advantages such as stability of the structural elements whilst joining numerous structural elements 320 to the same hub 100. Furthermore, by having the hub portions 110, 120 being moveable with respect to each other, an additional degree of movement is added for the connecting members 200. This allows the connecting members 200 to be fixable in a variety of orientations from the axis 130 and 303 as shown in Figure 3.

Furthermore, it will also be appreciated that the above-described apparatus is particularly suitable for injection moulding as the particular form of the apparatus limits the possibility of the formation of undercuts.

It will be appreciated that the above-described apparatus or joining system is particularly suitable for bamboo. The apparatus can be used for joining bamboo members to form an offset square-on-square double layer grid structure. The system can be light-weight, simple, efficient in fabrication and assembly, and is economically efficient. The joint is designed to transfer internal forces from connecting elements, and in one particular example, a maximum of eight bamboo members can meet at one joint. Furthermore, fastening by means of bolting, screwing or nailing directly to bamboo elements can be avoided.

Thus, the apparatus described can work to utilise bamboo characteristics such as axial tension and compression capacity. It will be appreciated that the apparatus avoides the need for holes to be made in the bamboo thereby limiting the problem of cleavage. Additionally, in order to increase its low crushing strength, the ends of bamboo culm can be reinforced by increasing the cross-sectional area. The apparatus/joint system is flexible enough to accommodate the expected variations in bamboo diameter and cross-section shape. Furthermore, the apparatus can be made of PVC, which is a light material thereby avoiding the joint overtly adding to the weight of any resulting structure. Moreover, the apparatus is usually simple, generally inexpensive to mass produce, easy to assemble and offers generally predictable stiffness and strength.

Specific Examples

The following description is a specific example only. Persons skilled in the art would appreciate that many alternatives and modifications are possible, and are considered to fall within the scope the application.

Assessment of the Structural Characteristics of Two Bamboo Species:

As noted previously, bamboo is particularly suitable to be used as structural elements. Table 1 below shows the structural attributes of bamboo against conventional methods.

Table 1 Structural attributes of bamboo aaainst conventional materials

Two locally available bamboo species were sourced to evaluate their compression, bending and buckling capacities. The two species are Phyllostachy Bambusoides (PB) and Phyllostachy Pubescens (PP) commonly known as Mao Jue. The culms used were 3-6 years old, 50-65mm external diameter and over 1.5m length. A total of 28 specimens were prepared, 14 specimens of each type (PB and PP). For each type of bamboo, 8 compressive (stub), 3 bending (beam) and 3 buckling (column) tests were conducted. No attempt was made to determine the moister content of these culms but rather an estimate was made based on the bamboo's skin colour.

The PB has greener appearance than the PP which has a yellow-brown colour. Based on this it is assumed that the moisture content for PB is 15-30% while for PP is 5-20%. For each sample, three measurements of the external and internal diameters were made at each end and the cross-section area and moment of inertia were determined by averaging over the two ends of the sample. For the compression tests, a sample length of twice the external diameter of the culm and no less than a minimum of 75mm was used. For the bending test, a three point setup is used with a sample length of 1.2m with a Im simply supported span. For the hinge-hinge column buckling test a slenderness ration of around 70 was used for all the samples.

From these tests, average compression strength σ_c, bending elastic modulus, E_b, and buckling stress σ_b were obtained and are listed in Table 2, below.

Table 2 Compression, Biickling and bending Test Results σ_c

Bamboo type σb Eb

MPa MPa MPa PB 41. S 26.1 10052

PP 49.5 35.8 10173

Although both types of bamboo have a similar Eb, PP (Mao Jue) offers higher compression and buckling capacities, as noted from the bending, compression and buckling tests. Notably, under bending test the PB samples failed by splitting along the entire span starting from mid span while the PP samples failed by local crushing under the applied load. Table 3 below lists the results obtained recently by Chung et al in Hong Kong using Mao Jue (PP) bamboo.

Table 3 : Test Results from Chung et al [6]

Moisture Compressive Elasticity Modulus

Bamboo Content Strength Buckling Capacity Eb Species (Mpa)

(%) (Mpa) (GPa)

Mm Max Ave Mm Max Ave Mm Max Ave

< 5% 122 152 134 10 3 19 7 13 2

Phyllostachys Pubescens 5% - 30% 48 114 75 12 6 42 27 ($=67 6) 7 1 18 2 11 4

(Mao Jue)

> 30% 37 81 57 10 2 41 25 6 ($=72 5) 5 4 16 4 9 6

S= slendemess ratio

Given the inherent imperfections in bamboo as a natural material, the results obtained from the current testing (Table 2) are in good agreement with Chung et al results (5-30% moisture content, Table 3).

A PVC Joint for Bamboo The main obstacle for the use of bamboo in construction is the lack of engineered joint system suitable for bamboo. Joints have always been the least predictable part of the structure and for bamboo rudimentary jointing techniques, such as lashing, has been widely used. Jointing techniques that are based on drilling through the bamboo culm for fastening, generally reduce the bamboo's carrying capacity through cleavage failure. Techniques utilising timber plugs inserted or slotted into the bamboo culm suffer from culm splitting.

In one example, the above-described joint system is made of PVC (Polyvinyl Chloride) and is comprised of two parts, a joint hub and connectors. The joint hub encompasses top and bottom parts with an M20 bolt which connects the two together. Both pieces have a circular base plate and four rectangular vertical plates sitting on the top. One end of the connector is cylindrical that encase the bamboo open end. Strong MEGAPOXY glue is grouted between the bamboo and the PVC connector. The other end of the connector has a u-shape arrangement which fits into one of the rectangular vertical plates of the joint hub and is fastened by M 16 bolt. Notably, conventional structural steel bolts can be used, although it is intended that lighter PVC bolts may be used in the future. Furthermore, it will be appreciated by persons skilled in the art that other forms of material such as Fibre Reinforced Polymer Composite (FRP), can also be used.

A Finite Element Method (Strand 7) was used to proportion the present joint. A 3D solid model of the joint was generated and meshed using Hexa-20 and Wedge- 15 iso-parametric brick elements.

Various loadings and boundary conditions were applied to the joint. A comparison of stiffness obtained under the different loading and boundary conditions for the hub (one part only) are; 12.632 kN/mm for compression, 7.02 kN/mm for tension and 0.8 kN/mm for bending. For the connector, 13.542 kN/mm was obtained for tension.

It is recommended that 5mm wide by 3mm deep grooves are made at 20mm apart and starting at 20mm from each end of the bamboo member are cut into the ends of the bamboo prior to connecting the bamboo to the PVC connector. Cutting grooves maximises the strength of the MEGAPOXY glue to avoid slippage of the bamboo from the connector. Once the lattice system is in place it is recommended that the connectors remain attached to the bamboo. The lattice system can be dismantled by removing the connectors from the joint hub. The system can then be reassembled by reconnecting connectors (attached to the bamboo) back to the joint hub. Examples of various types of bamboo lattice structures that can be created are shown in Figure 4.

The apparatus or joint system described is suitable for the construction of bamboo double layer grid. To maintain the lightweight nature of a bamboo structure, PVC (Polyvinyl Chloride) was selected as a suitable material for the joint. The joint design is based on preserving the good tensile and compression strength of bamboo culms without adversely affecting them through cleavage or splitting failure. The above-described apparatus or joint system can allow some flexibility in the configuration of the double layer grid assembly, keeping in mind the inherent imperfection in the bamboo culms.

In particular, the joint can accommodate up to 8 members, is composed of a joint hub and up to 8 cylindrical connectors. The joint hub itself is composed of two identical parts that are connected together by 20mm diameter bolt. This allows the joint to be used for different configurations and can accommodate the expected imperfections in the assembly. The ends of the bamboo culms are encased inside the cylindrical connector with a megapoxy grouting material filling the gap between the bamboo and the PVC wall.

The spatial aspects of the joint were determined based on geometric requirements and finite element analysis using PVC material properties. Three coupon tests were conducted on the PVC material which gave tensile yield strength of 45 MPa and Elasticity modulus of 3000 MPa. Figure 5 shows Von Mises stress contour plot of the joint under one of the loading conditions, a 12 kN compression load case, used in the design. As can be seen from this figure, the stress in most of the joint is maintained at an acceptable level below the 45MPa capacity of the PVC material used.

In this particular example, the joint was fabricated by machining using CAM and usual structural steel bolts. It is envisaged that for practical applications the joint can be produced economically using mould injection and a special PVC bolts can be used instead of the steel ones. Proof testing of the prototype joint was also conducted. Six joint hub samples were tested under compression, tension and bending (two tests each) The joint hub component failed under 24 kN load in compression, 9 kN load in tension and 3 kN load in bending.

Figure 6 shows a typical load-displacement response of the joint hub obtained from the compression test together with the prediction from linear finite element analysis. Similarly a pull-out test was conducted on the cylindrical connector as shown in Figure 7. Two techniques were used here, the first was that the bamboo member was inserted into the cylindrical connector and grouted. In the second technique, the two ends of the bamboo member were roughened using sandpaper and three grooves were made at each end before inserting into the cylindrical connector and grouting. Each groove is 5mm wide and 3mm deep, the grooves were made at 20mm apart and starting at 20mm from each end of the bamboo member.

As shown in Figure 7, the test sample without grooves failed by slippage between the bamboo and the PVC connector. This took place at 13 kN. The test sample with grooves failed at the bolt hole of the PVC connector without any noticeable slippage. The failure load was 19 kN. It is clear that the insertion of grooves at the two ends of the bamboo member results in higher strength (about 150% increases) and stiffness (170% increases). This approach was adopted in the fabrication of the double layer grid, as described in the following section.

Double Layer Grid (DLG) Module The PVC joint described in the previous section was used to assemble an offset square-on- square module of bamboo DLG. Mao Jue (PP) bamboo described is used. The module is 2.6x2.6m in plane and 0.9m deep as shown in Figures 8 and 9.

The module is composed of 32 bamboo members with an average length of 1.15m each and 13 PVC joints. Each joint has a number of connectors that vary from 3 to 8 connectors depending on the location of the joint in the grid. Each member was inserted into the connectors and grouted first. The grout was allowed to cure for 24 hours. Following that the grid was assembled. The assembly was carried out by one person and it took only 30 minutes to complete with all bolts being snug tight. The total weight of the assembled DLG is about 100kg only. Following the assembly, the grid was supported at four corner supports shown as A, B, C and D in Figures 8.

At support A, all degrees of freedom were restrained while supports B, C and D allow free in-plane translation and free rotation about the vertical axis. Thirteen members were instrumented with strain gauges, two gauges were used for each member and placed on opposite sides and located at the member's mid-length. These members are labelled Xl to Xl 3 in Figure 8. Two members were selected in the top layer (X 12 and X 13), five web members (X5-X7, X9 and XI l) and six members in the bottom layer (X1-X4, X8 and XlO).

The displacements were monitored at four nodes, these nodes are shown in Figure 8 as N5, Nl 1, Nl 3 and D. N5 is the central node in the bottom layer, Nl 1 and Nl 3 are corner nodes in the top layer and node D is corner support at the bottom layer. A rigid frame was placed inside the grid and used as a base for the displacement measurements, similarly a rigid cross frame was placed on the top layer to transfer the applied load to the top four nodes. A uniform load was incrementally applied on the top layer of the grid. The loading was applied using a timber pallet loaded with concrete mix bags with a total weight of 10 kN (equivalent to 5.92 kPa applied on the top layer of the grid).

The load was applied in six increments, following each load increment, the average strain in each of the thirteen members and the displacements at the four instrumented nodes were recorded. The loading of the grid from zero loads to 10 kN was completed in about 15 minutes, the load was kept on the grid for 3 minutes then was removed. No visible damage or excessive deformation was observed.

Table 4 below gives the measured axial forces in each of the thirteen members indicated in Figure 9 when the total applied load on the grid is 10 kN. As can be seen, the highest compression is close to 3.5kN in member X-7 (web member) and the highest tension force is close to 1.8 kN in member X-2 (bottom layer). Elastic geometric nonlinear analysis of the grid was also conducted and the predicted results were compared to the ones obtained from an experiment conducted by NIDA, the Nonlinear Integrated Design and Analysis of Steel Frames, Department of Civil and Structural engineering, Hong Kong Polytechnic University, Hong Kong. This comparison is shown in Table 4. Table 4: Comparison of member axial forces obtained from experiment and nonlinear analysis (Negative is compression)

or the bamboo members, the properties shown in Table 5 below were used in the analysis.

Table 5: Average properties of the bamboo members used in the double layer grid

These properties are based on the average properties obtained for the 32 members used in the grid. Due to the inherent imperfections in the bamboo, a 3% member geometric imperfection was assumed in the nonlinear analysis.

Figure 10 shows the load-deflection response of the DLG, the vertical deflection at node N5 (central node at the bottom layer) is shown in this figure. The nonlinear analysis prediction is in good agreement with the experimental response. The grid response is quite stiff with a total deflection of only 2.5mm under the 1OkN applied load. Using the member forces obtained form the nonlinear analysis under 1OkN applied load, finite element analysis of different joints in the DLG was carried out to assess the stresses within the PVC joints.

Figure 1 1 shows Von Mises stress contour plot for support node D at the total applied load. It is clear from this figure that the stress within the joint is kept within acceptable limit within 50% of the PVC material capacity (45MPa).

Accordingly, the PVC joint system can be used in practice for constructing lightweight medium-span bamboo DLG structures with excellent structural and aesthetic aspects. Thus, there has been described, an apparatus for interconnecting structural elements.

Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions, and alterations can be made by one of ordinary skill in the art without departing from the scope of the present invention. Notably, although the above-described apparatus is particularly suitable for bamboo, it will be appreciated that the system can be used for any other structural elements.

Claims

CLAIMS:

1) An apparatus for interconnecting elongate structural elements, the apparatus including: a) a hub; and, b) at least two connecting members, each connecting member having a support end for supporting a respective structural element, and a hub end pivotally mounted to the hub.

2) The apparatus of claim 1 , wherein the at least two connecting members are constrained to move in a plane.

3) The apparatus of any one of claims 1 or 3, wherein each hub end is individually fixable to the hub.

4) The apparatus of any one of claims 1 to 3, wherein the hub has two hub portions, each hub portion having a base portion, the hub portions abutting each other at their base portions.

5) The apparatus of claim 4, wherein the hub portions are moveable with respect to each other.

6) The apparatus of any one of claims 1 to 5, wherein the hub has a number of projecting members, the hub end of each connecting member being connected to a respective projecting member.

7) The apparatus of claim 6, wherein the projecting member and the connecting member are coupled together by a bolt.

8) The apparatus of claim 4, wherein each hub portion has a shaft, the hub portions being aligned such that a bolt passes through each shaft, thereby coupling the hub portions together.

9) The apparatus of claim 8, wherein the shaft is located at a centre of the hub portions. 10) The apparatus of claim 9, wherein each hub portion has a plurality of projecting members, the projecting members being disposed circumferentially around a centre of the hub. 11) The apparatus of any one of claims 1 to 10, wherein the supporting end of the connecting means is a socket, the socket being able to receive the structural element. 12) The apparatus of any one of claims 1 to 11, wherein the supporting end is cylindrical, the supporting end being able to receive a cylindrical structural element. 13) The apparatus of claim 11 , wherein the socket has at least one groove extending around an inner surface.

14) The apparatus of any one of claims 1 to 13, wherein the structural member is attached to the first connecting member by grouting.

15) The apparatus of claim 14, wherein glue is grouted between the structural member and the first connecting member.

16) The apparatus of any one of claims 1 to 15, wherein the structural element is bamboo.

17) The apparatus of any one of claims 1 to 16, wherein the apparatus is made of any one or combination of: a) polymer of vinyl chloride; and, b) fibre reinforced polymer composite.

18) The apparatus of any one of claims 1 to 17, wherein the apparatus is made by injection moulding. 19) An apparatus for interconnecting elongate structural elements, the apparatus including: a) a hub; and, b) at least two connecting members, each connecting member having a support end for supporting a respective structural element, and a hub end, each hub end being individually fixable to the hub. 20) The apparatus of claim 19, wherein the apparatus is the apparatus according to any one of claims 1 to 18.

2I) A hub for interconnecting elongate structural elements, the hub being connectable to at least two connecting members, each connecting member having a support end for supporting a respective elongate structural element, and a hub end, each hub end being individually fixable to the hub.

22) A method of interconnecting elongate structural elements, the method including the steps of: a) coupling first and second structural elements to a support end of respective first and second connecting members; and, b) connecting a hub end of the first and second connecting members to a hub. 23) The method of claim 22, wherein the structural elements are bamboo, the method including cutting grooves at an end of the bamboo, prior to coupling the bamboo to the support end.

24) The method of claim 23, wherein the method further includes adding glue into the cut grooves.

25) The method of any one of claims 22 to 24, wherein the method includes using apparatus according to any one of claims 1 to 20.