BAMBOO CONSTRUCTION ELEMENT

Abstract

The present invention relates to a construction element comprising a first and second bamboo layer and having a core layer interposed therebetween, wherein at least one of the first and second bamboo layers are fabricated with a residual stress. The present invention further relates to a method of manufacturing said construction element.

Claims

1. A construction element comprising at least a first and second bamboo layer and having a core layer interposed therebetween, characterised in that at least one of the first and second bamboo layers are fabricated with a residual stress.

2. A construction element according to claim 1, wherein the first and/or second bamboo layer(s) has a first surface that is in compression and a second surface that is in tension.

3. A construction element of according to claim 1, wherein the first and/or second layer(s) is biased against a pre-formed radius of curvature.

4. A construction element according to claim 1, wherein the first and/or second bamboo layer(s) is formed from a plurality of superposed bamboo sub-layers.

5. A construction element according to claim 4, wherein the sub-layers are formed of laminated bamboo or bamboo scrimber.

6. A construction element according to claim 4, wherein the plurality of sub-layers are arranged such that the bamboo fibres in each sub-layer are parallel to bamboo fibres in adjacent sub-layers.

7. A construction element according to claim 4, wherein the plurality of sub-layers are arranged such that the bamboo fibres in each sub-layer are arranged perpendicular to bamboo fibres in adjacent sub-layers.

8. A construction element according to claim 1, wherein each of the first and second bamboo layers are fabricated with residual stress.

9. A construction element according to claim 1, wherein the core layer comprises a laminated wood.

10. A construction element according to claim 9, wherein the core layer comprises cross-laminated wood.

11. A construction element according to claim 10, wherein the core layer comprises cross-laminated engineered bamboo and timber interlayers.

12. A construction element according to claim 1, wherein the core layer comprises at least one support member arranged perpendicular to the first and second bamboo layers and extending therebetween.

13. A construction element according to claim 12, wherein the at least one support member is connected to the first and second bamboo layers via a butt connection.

14. A construction element according to claim 12, wherein the first and second bamboo layer each comprise at least one groove configured to receive the at least one support member in a tongue-and-groove arrangement.

15. A construction element according to claim 12, wherein the core layer comprises a plurality of support members and optionally, a wood or insulation material between said support members.

16. A construction element according to claim 12, wherein the supporting member is a web.

17. A construction element according to claim 1, wherein the construction element is a truss, a wall panel, a floor panel, a column or pillar, or a beam, optionally, a sandwich beam, an I-beam or a double-web beam.

18. A method of manufacturing a construction element, comprising assembling a first and second bamboo layer with a core layer interposed therebetween, characterised in that at least one of the first and second bamboo layers are fabricated with a residual stress.

19. A method of according to claim 18, said assembling comprising: providing the first and second bamboo layer, wherein at least one of the first and second bamboo layers has a pre-formed radius of curvature; providing the core layer; and pressing the first and second bamboo layers and the core layer together such that the first and/or second bamboo layer(s) is substantially straightened against the pre-formed radius of curvature to induce the residual stress.

20. A method according to claim 19, wherein providing the first and second bamboo layer comprises the initial steps of: (i) providing a plurality of bamboo sub-layers; (ii) applying an adhesive to the sub-layers; (iii) pressing, and optionally heating, the sub-layers until the adhesive is cured to form the first bamboo layer having a pre-formed radius of curvature; and (iv) optionally, repeating steps (i) to (iii) to form the second bamboo layer.

21. A method according to claim 20, wherein the sub-layers are formed of laminated bamboo or bamboo scrimber.

22. A method according to claim 20, wherein the plurality of sub-layers are arranged such that the bamboo fibres in each sub-layer are parallel to bamboo fibres in adjacent sub-layers.

23. A method according to claim 20, wherein the plurality of sub-layers are arranged such that the bamboo fibres in each sub-layer are arranged perpendicular to bamboo fibres in adjacent sub-layers.

24. A method according to claim 18, further comprising forming tongue-and-groove channels in a surface of the first and second bamboo layers.

25. A method according to claim 18, wherein each of the first and second bamboo layers are fabricated with residual stress.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0049] The accompanying drawings illustrate presently exemplary embodiments of the disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain, by way of example, the principles of the disclosure.

[0050] FIG. 1 is a schematic view of a construction element according to an embodiment of the invention;

[0051] FIG. 2 shows a first and second layer according to an embodiment of the invention;

[0052] FIG. 3 shows a first and second layer having tongue-and-groove channels according to an embodiment;

[0053] FIG. 4A is an expanded view of a first layer or second layer according to an embodiment of the invention in which the sub-layers are arranged in the same direction;

[0054] FIG. 4B is an expanded view of a first or second layer according to an embodiment of the invention in which the sub-layers are arranged perpendicular;

[0055] FIG. 5 is a schematic view of a construction element according to an embodiment of the invention in which the core layer comprises cross-laminated engineered bamboo and timber layers;

[0056] FIG. 6 is a schematic view of a construction element according to an embodiment of the invention in which the core layer comprises alternating layers of laminated bamboo and bamboo scrimber;

[0057] FIG. 7 is a schematic view of a construction element according to an embodiment of the invention having a core layer comprising timber and a plurality of support members connected to the first and second layers via butt connections.

[0058] FIG. 8 is an expanded view of the construction element shown in FIG. 7;

[0059] FIG. 9 is a schematic view of a construction element according to an embodiment of the invention having a core layer comprising timber and a plurality of support members connected to the first and second layers via tongue-and-groove connections.

[0060] FIG. 10 is an expanded view of the construction element shown in FIG. 9;

[0061] FIG. 11 is a schematic view of a construction element according to an embodiment of the invention having a core layer comprising laminated bamboo arranged between a plurality of support members connected to the first and second layers via butt connections;

[0062] FIG. 12 is an expanded view of the construction element shown in FIG. 11;

[0063] FIG. 13 is a schematic view of a construction element according to an embodiment of the invention having a core layer comprising laminated bamboo arranged between and a plurality of support members connected to the first and second layers via tongue-and-groove connections.

[0064] FIG. 14 is an expanded view of the construction element shown in FIG. 13;

[0065] FIG. 15 shows a schematic representation of a method of manufacturing a construction element according to one embodiment of the invention; and

[0066] FIG. 16 shows a schematic representation of an alternative method of manufacturing a construction element according to an embodiment of the invention.

DETAILED DESCRIPTION

[0067] The present invention provides a lightweight, high strength, multi-purpose construction element with flexible configurations to accommodate different engineering and architectural requirements, in particular, for long-span and tall building structures.

[0068] A construction element 10 according to one embodiment is shown in FIG. 1. The construction element 10 has a first layer 12, and second layer 14 and a core layer 16 interposed therebetween. In other words, the first and second layers 12, 14 are outer layers and the core layer 16 is a middle layer, sandwiched between the outer layers. Each layer is manufactured separately and can be customised for different end uses, as described in more detail below.

[0069] The first and second layers 12, 14 are formed of a plurality of superposed engineered bamboo sub-layers. For example, the engineered bamboo may be laminated bamboo or bamboo scrimber. The thickness of each sub-layer may independently selected and may range from 6 mm to 200 mm. Each of the first and second layers 12, 14 may be fabricated with a residual stress. In one embodiment, engineered bamboo strips are pressed and glued together in a curved mode to form each sub-layer of the first and second layers. In this way, the curvature of each sub-layer is adjustable to create a pre-configured radius of curvature. In the illustrated embodiment, the radius of curvature is the same for each sub-layer. However, it should be understood that in other embodiments the sub-layers may each have a different radius of curvature. Similarly, the sub-layers of the first bamboo layer may be formed with a different radius of curvature to the sub-layers of the second bamboo layer.

[0070] As best seen in FIG. 4, the plurality of sub-layers 12a-d are stacked on top of each other and pressed and glued together in their curved shape to form the first layer 12. The process is then repeated to form the second layer 14. The assembled first and second layers are shown in FIGS. 2 and 3. During assembly of the construction element 10, the first and second layers 12, 14 are pressed and flattened onto the core layer 16 while curing the glue or applying the mechanical fixings. In this way, a pre-stressed status is introduced to the construction element 10. The plurality of sub-layers 12a-d can be arranged such that the bamboo fibres in each sub-layer are parallel to bamboo fibres in adjacent sub-layers to produce a one-way pre-stressed member to create one-way pre-stressing (FIG. 4a). In other words, adjacent sub-layers curve in the same direction such that the curved edges of adjacent sub-layers are superimposed on top of one and other. Alternatively, the plurality of sub-layers 12a-d can be arranged such that the bamboo fibres in each sub-layer are arranged perpendicular to bamboo fibres in adjacent sub-layers to create two-way pre-stressing (FIG. 4b). In other words, adjacent sub-layers are arranged orthogonally such that the curved edges of adjacent sub-layers are perpendicular to one and other. The type of pre-stressing may be selected according to the engineering specifications based on the structural analysis and design.

[0071] The composition of the core layer 16 may be selected to meet the specifications of the engineering application. FIG. 5 shows an embodiment of the construction element 100, wherein the core layer 16 comprises a plurality of cross-laminated interlayers. In this example, the interlayers comprise a mixture of alternating layers of straight-engineered bamboo (i.e. laminated bamboo or bamboo scrimber) interlayers 18 and timber board interlayers 20, with each interlayer oriented perpendicular to adjacent layers. However, as would be appreciated by a person skilled in the art, the exact arrangement of the engineered bamboo and timber layers is flexible and able to accommodate different architectural and engineering specifications in complex constructions.

[0072] Alternatively, the core layer may comprise alternating layers of laminated bamboo interlayers 32 and bamboo scrimber interlayers 34, as shown in FIG. 6. In the example shown in FIG. 6, the first layer 12 and second layer 14 are formed from bamboo scrimber. In this way, a construction element is provided that is substantially or entirely formed from bamboo material, in particular, engineered bamboo. That is, the construction element of the present invention may be formed substantially free or completely free of wood products. Thus, a lightweight, high strength construction element may be provided that is made entirely from fast-growing and economical bamboo. Regardless of their composition, the interlayers of the core layer 16 may be bonded together by adhesive or mechanical fixings.

[0073] In FIGS. 7 and 8, a construction element 200 is shown having a core layer 16 comprising a plurality of support members 22. In the illustrated embodiment, the support member is a web, which may be formed from engineered bamboo or any other suitable material known in the art. In this embodiment, the web is bonded with first and second layers 12, 14 via butt connections 24. A simple butt connection may be advantageous as they are typically straightforward to manufacture. An alternative embodiment of the construction element 300 is shown in FIGS. 9 and 10, wherein a plurality of support members (i.e. a plurality of webs) are bonded to the first and second layers 12, 14 via tongue-and-groove connections 26. As shown in FIG. 3, the tongue-and-groove channels 28, if required, may be routed into the first and second layers 12, 14 before the construction element 300 is assembled. A tongue-and-groove connection provides a more secure connection at the expense of higher machining costs. However, the tongue-and-groove connections may be desired to prevent early failure at the connection and increase the overall strength across the whole construction element. In the example construction elements shown in FIGS. 7 to 10, the area between adjacent webs is infilled with a wood product 30, such as traditional timber or engineered timber lumber. The web and timber, or engineered timber, may be bonded by an adhesive or mechanical fixings or any other suitable means.

[0074] Alternatively, the area between adjacent webs may be infilled with engineered bamboo, such as laminated bamboo and/or bamboo scrimber. For example, FIGS. 11 to 14 show an example construction element having a core layer comprising laminated bamboo 36 arranged between a plurality of support members 22. In the example construction element 400 shown in FIGS. 11 and 12, the support members 22 are connected to the first and second layers 12, 14 via butt connections 24. FIGS. 13 and 14 show a similar example construction element 500 in which the construction element includes a core layer comprising laminated bamboo 36 arranged between a plurality of support members 22 that are connected to the first and second layers via tongue-and-groove connections 26. In these examples, the support members 22 may also be formed from engineered bamboo, such as bamboo scrimber, to provide a construction element that is substantially or entirely formed from bamboo material, in particular, engineered bamboo.

[0075] In the illustrated embodiments shown in FIGS. 7 to 14, the webs are equally spaced within the core layer 16. However, other suitable arrangements will be apparent to a person skilled in art. For example, the distribution of the support members 22 can be varied at different locations. The number of support members 22 may range from 1 to 160. However, any number of support members 22 may be used according to the particular architectural and engineering specification. The thickness of each support member may range from 10 mm to 300 mm. The centre-to-centre distance of the support member may be in the range of 100 mm to 4000 mm.

[0076] In some embodiments, it may not be necessary to include a wood or engineered bamboo material between support members, for example, if the external loading on the construction element is anticipated to be relatively low. In such embodiments, the spaces in-between the web may be left unfilled or infilled with insulation foam to improve the thermal performance of the structural member.

[0077] Once the core layer 16 is manufactured, the first and second layers 12, 14 may be bonded to opposite sides of the core layer, for example, by an adhesive or mechanical fixings (nails, screws, bolts, dowels, etc). Advantageously, openings for windows, doors and stairwells, can be cut out according to architectural specifications after the construction element has been assembled. Final finishes (not shown), such as wood panels, tiles, etc. can be fixed onto the outer surfaces.

[0078] Two exemplary methods of producing a sandwich beam in accordance with the present invention are now described with reference to FIGS. 15 and 16. However, others ways of assembling the construction element will be apparent to a person skilled in the art. For the purposes of clarity, the methods below are described in relation to a construction element in which only the first layer is pre-stressed. The method of superposition can be adopted to evaluate the summation of the overall structural response in instances where there are more than one pre-stressed layers.

[0079] In a first method, shown schematically in FIG. 15A, a curved engineering bamboo first layer is arranged such that the convex surface is adjacent to an outer surface of a core timber layer. The first layer is then pressed and glued onto the core timber layer. The pre-stressed condition is introduced during the pressing process as the first layer is straightened or substantially straightened against the outer surface of the core layer. When the press is released, the internal stresses remain inside the first layer and interact with the other parts of the construction element. A simplified analytical module is shown in FIG. 15B. As would be appreciated by a person skilled in the art, FIG. 15B is a simplification and approximation of the structural model.

[0080] In an alternative embodiment of the method shown in FIG. 16A, the curved engineering bamboo first layer is arranged such that the concave surface is adjacent to an outer surface of a core timber layer. That is, the first layer is fixed onto to the core timber layer at both ends. The first layer is then pressed and glued onto the core timber layer as described for the first method above. The difference in this method is that on top of the equivalent pre-stressed moment, a pre-stressed axil force is also induced during the pressing procedure. A simplified analytical module is shown in FIG. 16B. As would be appreciated by a person skilled in the art, FIG. 16B is a simplification and approximation of the structural model.

[0081] A sample solution for the structural analysis of bamboo-timber composite beam according to an embodiment of the claimed invention is shown below. For the purposes of clarity, the analysis below includes the assumption that only one bamboo layer is fabricated with residual stress. As would be understood by a person skilled in the art, the method of superposition can be adopted to evaluate the sum of the overall structural response where both the first and second bamboo layers are fabricated with residual stress.

[0082] In a simply supported beam with uniformly distributed load w applied on its entire span L, the maximum stress in the engineered bamboo layers may be defined as follow:

[00001]$\begin{array}{cc}{}_{\mathrm{xB}\max }=\frac{E_B}{\left[\mathrm{EI}\right]}\left(\frac{h_T}{2}+h_B\right)\left(\frac{w{L}^2}{8}-M_P\right)& \left(1\right)\end{array}$ [0083] the maximum stress in the timber layer may be defined as follows:

[00002]$\begin{array}{cc}{}_{\mathrm{xTmax}}=\frac{E_T}{\left[\mathrm{EI}\right]}\left(\frac{h_T}{2}\right)\left(\frac{w{L}^2}{8}-M_P\right)& \left(2\right)\end{array}$

[0084] In equations (1) and (2), [0085] [EI] is the homogenised equivalent bending stiffness of the bamboo-timber composite beam that can be derived from Euler-Bernoulli beam theory. [0086] E.sub.B is the Young's Modulus of the engineered bamboo [0087] E.sub.T is the Young's Modulus of the core layer [0088] h.sub.T is the thickness of the timber layer [0089] h.sub.B is the thickness of the engineering bamboo layers [0090] M.sub.P is the equivalent counteracting bending moment caused by the pre-stressing

[0091] As shown in equations (1) and (2), the negative contribution of M.sub.P reduces the magnitude of the maximum stress due to the pre-stressed effect.

[0092] Alternative methods for analysing the structural response would be apparent to a person skilled in the art.

EXAMPLES

[0093] The Modulus of Rupture (MOR) was measured for samples of a sandwich Bamboo-Timber beam (Example 1), an I-bone Composite Bamboo-Timber beam (Example 2) and a Traditional Glulam Beam (Comparative Example). In Examples 1 and 2, both the first and second bamboo layers are fabricated with a residual stress in accordance with an embodiment of the claimed invention. The sample were tested in the four-point bending and shear field test in accordance with BS EN 408:2010+A1:2012. As shown in Table 1, the combination of these two economical, fast-growing natural materials can achieve the same strength as hardwood glulam beam.

[0094] It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims.