|Title of Invention||
COMPOSITE FASTENER SYSTEMS FOR WOOD & BAMBOO STRUCTURAL APPLICATIONS
|Abstract||We claim: 1. Process for fabrication of wood-bamboo composites comprising an assembly of structural components wherein structural integrity is assured by virtue of stress lamination & creation of irregularities along the wood-bamboo interfaces with incorporation of macro & micro fibres, laminates and fillers for enhancing the shear resistance and tensile strength, wherein the structural components are prepared in steps comprising i. Selecting wood, bamboo materials based on design requirements with regard to strength and deformability; ii. Cutting and trimming of wood and bamboo to produce components including laminates of desired dimensions to satisfy the closeness of fits, iii. Creating designed irregularities such as indentation, serration, undulations maintaining fibre continuity; iv. Optionally treating the wood - bamboo interfaces with bamboo macro fibre and their like treated with resin admixed fillers: . Curing and seasoning after preservative treatment to ensure dimensional stability & finishing to the specified dimensions; further assembling the structural components in steps comprising: vi. Connecting the structural members by means such as, bolts, inserts, rods, U bolts, ties, wires, bands, strips to induce the normal stresses for effective stress lamination and tightening to induce pre-stress in the preferred directions in one or more stages; vii. Optionally incorporating resin coated macro/ micro, random / oriented fibres or fabric, reconstituted bamboo laminates at the wood-bamboo interfaces and / or at the extreme fibres of the cross-section of the members; viii.Optionally impregnating wood-bamboo with resins in the zones of tress concentration: ix. Optionally introducing punched or serrated metal plates at the wood-bamboo interfaces; x. Optionally installing fibre reinforced plastic bands / wire winding after pre-compression of the assembly|
|Full Text||FORM - 2
THE PATENTS ACT, 1970
(39 OF 1970)
(See Section 10; rule 13)
1 • TITLE OF INVENTION": "Composite Fastener Systerns;1»r Wood & Bamboo Structural Applications
2. a) Datye Krishna 'Ramchandra fa) having residence at Chaitraban, 1 Floor, - Han uman Cross Road No. 1, Vile-Parte East, Mumbal-400057 c) -an.. Indian National
The foiiowing specification panicuiariy describes the nature of the invention and the manner in which it is to be performed.
This invention relates to novel, cost-effective and easy to install wood-bamboo composite fastener systems to achieve desired strength and load transfer capacity with displacements restricted to stipulated limits, under all conditions of loading. Further, attachments and inserts, along with tension bolts and stress lamination devices of high strength corrosion resistant materials, with provision for retightening, to compensate dimensional changes are incorporated in the wood-bamboo composite fastener system.
Background of the Invention
There are two categories of wood engineering applications.
This first category is based on round wood poles of diameter of 100 mm -200 mm and length of 3-5m used as columns and piles and to construct space frames. A publication titled "Thin poles of round wood for structural engineering applications in building" by P. Huybers in Structural engineering review 1990, Delft University", p.p. 169-182 discloses the cost effective use of round poles for a variety of structures. For joinery, dowels with wire lacing tools are used. The wire-lacing tool does not allow cyclic tightening process to reduce residual deformation. However the advantage of this technique is the prospect of using short rotation forestry wood or coppice timber
Other publications that describe the use of joinery as applied to wood are 'Maximum strength of wire laced dowel joints for round wood" by Rogier Houtman et.al, in proceedings of the 5th World conference on Timber engineering, Montreux, Switzerland, Aug 17-20, 1998 Vol. 2, p.p. 161-176 ; The block Shear joint, a new joint for Round wood structures" by Erik W.P.SIuis et.al published in proceedings of the 5th World conference on Timber engineering, Montreux, Switzerland, Aug17-20,1998 p.p.268-275 & 500-OU7.
In the Indian situation, the availability of round wood in the above mentioned sizes is yet limited. Efforts have been made to extend the joinery techniques for fabrication with bamboo as its supply can be rapidly augmented with short rotation farm forestry. Bamboo has been used extensively in South America employing such joinery techniques. A comprehensive review of joinery of bamboo in its natural circular section is available in the INBAR report by Jules .A. Janssen (INBAR report- A review of techniques for joints is available in "Designing and Building with Bamboo " INBAR Technical report no. 20, Jules .A. Janssen,2000). Although techniques reported in the above mentioned reports, open up possibilities of large-scale use of bamboo as structural material, yet the range of applications is restricted by limited capacities of the members & joints.
It is therefore, necessary to focus attention on wood-bamboo composites to build up large sections for use as beams, columns, and members for a range of other major structural applications.
The use of wood & bamboo for this purpose belongs to the second category of major wood engineering applications based on laminates & built up members
Present wood engineering practice for major applications is based on the use of laminates of 4 to 20 mm thickness to form glue or stress laminated members of large size upto 200 x 600 mm or more. These laminates are used in conjunction with built up members of cut wood in the range of 50-100mm to 150-300mm with lengths of 3-5m.Current engineering practice is described in standard publication such as "Wood engineering handbook", Forest Product Laboratory, USDA, 1956 and "Timber design and construction handbook", 1956 published by F.W. Dodge Corporation. New York, p.p.52-72.
"Glulam semi-Rigid Portal frames Composed of Hardwood Wedges & Metal Wares" by Kohei Komatsu & Kiyoshi Hosokawa, published in the proceedings of the 5th World conference on Timber engineering, Montreux, Switzerland Aug17-20, 1998 Vol.2, p.p. 246 -253 and "Mechanical performance of Fiberglass Reinforced Timber joints" by Chen Chi-Jen, published in proceedings of the 5th World conference on Timber engineering, Montreux, Switzerland, Aug17-20, 1998 Vol. 2 p.p. 500-507 disclose recent advances in wood engineering technology. Dan A. Tingley, wood science & Technology Institute, 1996 CERF Charles Pankow Award for Innovation winner, Washington DC and "Design, Testing and Erection of the Hiroshima Airport Bridge" by P.C.Gilham and Y.limura, published in the proceedings of the International Wood Engineering Conference, Louisiana, USA, Oct 28-31, 1996 Vol. 2 p.p. 2/209-2/216 convincingly establish the capability of engineered wood as material of adequate durability & structural strength to build large bridges and roof supports, ranging from 20 to 70 m span respectively.
In this category of applications, the raw material consists of high quality wood from natural forests or plantations with rotation period exceeding 20 years. Such material is not easily available in India. Another disadvantage is the high cost glue for lamination & large investments are required for processing & fabrication
An invention for cost effective manufacture of wood bamboo composites is disclosed in a co-pending patent application number 2345/RQ/2004 J8_t/MUM/2003, which is based on the dependable tensile strength of bamboo"" & their ready availability in sufficiently long lengths(3-5m).The invention overcomes the disadvantage of low inter-fiber bond of bamboo & uses stress-lamination techniques with designed interface irregularities to assemble members of required size (e.g100mm-600mm) with wood of 50 mm x 50mm of relatively short lengths. The invention also includes high strength bamboo micro and macro fiber laminates and resin blend of phenol and lignin liquor.
"Strength of Filled Bamboo Joint" by Morisco and Fitri Mardjono, published in the Proceedings of the Vth International Bamboo Workshop and the IVth International Bamboo Congress, Ubud, Bali, Indonesia, June 19-22, 1995 Vol. 3, INBAR Technical Report No. 8, p.p. 113-120 discloses that if no hollows are left, the performance of the joint improves however in this case hollow is filled by cement mortar which is subject to dimensional instability due to shrinkage/swelling of mortar/bamboo. In the present invention, split bamboo is used & normal stress on the surface of the filling is applied by use of fixtures such as band, bolts which makes retightening possible.
Fasteners of various types consisting of nails, spikes, bolts & special connectors such as split-ring connectors, tubular dowels, shear plates, toothed rings, spiked grids, clamping plates etc. are used in conventional wood engineering practices. Wood applications which require high-grade timber to fabricate structural assemblies such as beams, columns, trusses and other forms of built up sections are described in Timber design and construction handbook, 1956 published by F.W. Dodge Corporation. New York, p.p.52-72. Fasteners are required to resist forces acting on them while the deformation under load has to be restricted to meet design requirements.
The type of loading is a decisive factor in the choice of fastenings. For example, duration of load influences allowable loads while the duration of loading is determined by the use of structural component / type of fastening. Vibrations or reversal of loads tend to loosen some fastenings. Unless appropriately designed, some fasteners tend to loosen under such loading e.g. a tight fit is difficult to achieve in bolts. A line contact occurs in loose fitting bolts. This is also a cause of local high stresses and consequent increase in displacement of the joint and reduction in joint capacity. The stress concentration at the contact of the fastener with the hole in the wood-bamboo, causes splitting and lowers the bearing strength of wood and bamboo.
"The Concept of the Prestressed DVW (Densified Veneer Wood) Reinforced Joint with Expanded Tubes" is disclosed by Ad.J.M. Leijten in the Proceedings of International Wood Engineering conference, Louisiana,USA Oct 28-31,1996 Vol. 2 p.p. 2/295-299 ). These techniques require high cost materials as well as tools to achieve designed capacity and to limit deformation under the load.
Joints in bamboo &wood (including round timber poles) members used in structural applications have been a major problem. Connectors in the prior art, also do not give reliable load transfer in small wood and bamboo due to poor inter-viber bond and cracking, brooming, splitting which occur at the contact with b amboo. Additional provisions are necessary for small wood and bamboo applications subjected to crushing and brooming of the fibers and splitting in the zcnes of stress concentration even under normal loads
It has been a long-standing need in wood engineering and bamboo applications to develop high performance fastener system to achieve tight fit without stress concentration thereby mitigating crushing and splitting of wood and bamboo and controlling the deformation. Further the fasteners system should be capable of being fabricated and installed without the use^special and costly equipments. Such high performance yet economical fastener system would overcome the limitations of conventional fasteners such as bolts, nails, shear plates, split rings, clamping plates and wedges and have desired capacity considerably higher than the conventional fasteners. The high performance fastener system would perform satisfactorily in bamboo and common grades of small wood, which are susceptible to crushing, cracking and splitting at the holes, notches, near knots and other defects. Use of high-grade timber produced in the main forests would be avoided as far as possible.
Summary of the invention
The main object of the invention is to provide novel, cost effective and easy to assemble high performance wood-bamboo composite fastener systems to achieve desired strength and load transfer capacity while restricting displacement to the stipulated value at the working load, for various types of loads, including impact, vibratory and reversible loads and all environmental / field conditions, such as earthquake, cyclones, cyclic drying and wetting, etc.
Another object of the invention is to provide composite fasteners that combine the benefit of higher strength of steel, metals / fiber reinforced plastics and the compressibility of bamboo/wood.
Another object of the invention is to use above mentioned materials having specified strength-deformation properties appropriate for the applications and functions
Another object of the invention is to enhance joint capacity in order to effectively utilise structural capability of materials produced in short rotation forestry, like bamboo and small wood in a cost effective manner to enlarge the scope of applications.
Another object of the invention is to achieve high performance of the fasteners using two or more materials in combination such as hard and densified wood, high strength bamboo and fiber laminates, high strength corrosion resistant metal alloys, stainless steel, HDG steel, fiber reinforced plastics, etc.
Yet another object of the invention is to provide fasteners, that have provisions for retightenina and can be installed by conventional tools used for wood and bamboo fabrication and assembly.
Another object of the invention is to develop fasteners that enhance interface shear resistance, overcome adverse effects of stress concentration / poor inter fibre bond in bamboo and wood and arrest cracks resulting from defects in the wood and bamboo.
Yet another object of the invention is to provide durable fasteners of hollow tubes of corrosion resistant metals and achieve adequate shear and flexural resistance by using the split tubes in conjunction with inserts of hardwood, bamboo laminates to arrest brooming or splitting failure at zones of stress concentration in bamboo and small wood.
Yet another object of the invention is to provide fasteners with tight-fit and high capacity for installation in the pre-bored and optionally pre-compressed holes or slots.
Yet another object of the invention is to utilize wedges or diamond shaped inserts of bamboo / natural fiber laminates and fiber reinforced plastic mouldings to arrest brooming or splitting failure at zones of stress concentration in bamboo and small wood.
Yet another object of the invention is to use tension bolts and other devices to improve the performance by virtue of stress lamination effects and confining stresses for enhancing the bearing capacity
Yet another object of the invention is to provide composite fasteners for engineered wood or bamboo structures thereby extending their use in diverse forms such as arches, shells, pipes, cylinders, beams, rafters, trusses, columns, struts, ties and posts applied to construction of buildings, bridges, culverts, structural framework, towers for wind mills and rope ways, structural framework for solar thermal energy generation equipment, etc and joints in the assembly of reinforcement & their connection with facings in reinforced soil applications for river training, bank protection, landslide control, approach embankments and abutment walls for bridges, raising of flood protection embankment etc.; wood / bamboo gabions for coffer dams, storage structures and overflow diversion weirs;
Brief Description of the Drawings
Figure 1 shows different forms of the fasteners.
Figure 2 shows wedge shaped composite dowels with stress lamination bolts.
Figure 3 shows a complete assembly of cylindrical dowels, inserts of high strength bamboo laminates, tension bolts with washers in over size holes and stress lamination bands.
Detailed description of the invention
The invention consists of a composite system of fasteners of various forms and materials to facilitate use of wood and bamboo and their composites to fabricate and assemble structural members for various engineering applications.
The performance requirements, with regard to strength, load transfer capacity with specified deformations, can be achieved only when the wood-bamboo composite fastener system is adopted by using designed irregularities, along with stress lamination devices and dowels, inserts, bolts/bands for inducing confinement. Individual components such as composite wedges used in isolation in the prior art cannot guarantee the performance.
Various forms of fasteners e.g. circular, rectangular wedges, diamond shaped inserts, split sleeve etc. are used in the invention with stress lamination devices, bands, wires and tension bolts to improve bearing strength and resistance to indentation and splitting/ brooming. Metal plates with serrations & indentations are used in combination with the stress lamination bolts or bands to transfer the load from the individual member to another. The plates are also bent and shaped to bond with the diamond shaped inserts. Consequently high capacity, low deformation under long-term loading, reduced creep and ability to withstand stress repetition and reversal are achieved.
The invention aims at overcoming the limitations of bamboo arising from poor inter fiber bond and tendency of brooming and splitting at locations subjected to stress concentration, resulting from transfer of loads from one member to other or from one part of the member to other portions as required to perform the structural function.
By use of composite fastener systems, structural components and their assemblies can perform the desired functions as struts, ties, beams, etc.
Monolithic action of the assembly and shear resistance of the members and joints is realised through stress lamination achieved by use of steel rods / bolts with nuts and washers or bands, assembly of wires etc. The loads are transferred through the inserts and dowels by bearing, or by gripping action of serrated plates or friction at the interface.
By use of various devices, the designed load transfer capacity is achieved with the designed margin of safety with reference to yield or failure. The deformations resulting from the load transfer are limited to the design levels by precompression of the dowels and wedges.
The geometry and the forms chosen are such as to ensure that loss of shear resistance due to dimensional changes is prevented. This is achieved through a combined action of stress lamination bolts and designed irregularities, like serrations, undulations, etc.
The capacity of bolts or dowels to transfer the loads by bearing is enhanced by virtue of the confining stress induced by the action of stress lamination devices consisting of bolts, bands, etc. Further improvement in bearing capacity is achieved by providing metal plates or by insertion of laminates in critical zones subjected to high bearing stress. The wedges and split sleeves are tightened to ensure that load transfer is achieved with displacement limited to allowable \ alues as per design requirements.
Figure 1 shows foims of fasteners for making composite wood bamboo assembly. The numbered parts are as follows:
Hard wood wedges (1) for getting a,tight fit of the split tube dowel in wood and bamboo and expanding the split metal tube (3). A bamboo laminate insert (2) installed in the wood to give a good bearing surface for the split tube dowel. A type of hard wood wedge dowel (4) strengthened by metal wedges (5) on both bearing surfaces. A diamond shaped insert (6) .A variant of the diamond shaped insert (7). Another variant of the diamond shaped insert, with strengthening metal plates bent around the periphery (8). A metal dowel with threaded ends (9), over which nuts can be tightened to induce normal stress.
Figure 2 shows composite dowels and tension bolts inducing stress lamination. U bolts (1) are used for inducing normal stress on the irregularities / undulations (3) created at the interfaces of wood and split bamboo (4). A nail plate (5) is pressed down by a washer plate (6) in the flattened region by the U-bolt (1). A high strength bamboo fiber laminate dowel (2) is used for connecting split bamboo (4) to the wood. A variant of the wedge dowel, is a hardwood wedge dowel strengthened by a metal plate bent around its periphery (7). Another variant is a high strength bamboo fiber laminate wedge dowel (8). In another variant of the wedge dowel, a vertical bolt is introduced (9).
Figure 3 shows composite assemblies of wood and bamboo using dowels, inserts, tension bolts and stress lamination bands. The figure shows a method of connection of half split bamboo (1) to wood (2) through hardwood inserts (4). Stress lamination is achieved through bands / wire loops (3). The loops / bands are tensioned by tightening of the transverse bolts (7) which press onto the plates (5) welded to the loops/bands (3). A split circular tube dowel (10) consisting of the split metal tube (9) and the wedging wood pieces (8). A serrated nail plate (6) is fixed to top surface of bamboo by means of nails and screws.
The present invention makes use of wedge shaped dowels to transfer load from bamboo to wood. The problem of poor inter-fiber bond is overcome by applying confining stress using bands, tension bolts, wire etc. So also interface shear is mobilized by designed irregularities such as indentation, undulation, serration, & using inserts of high strength woods reinforced by metal plates or fiber reinforced plastics (FRP).
Presence of confining bolts and designed irregularities results in reduced space for making wood-to-wood connections. This entails use of special fasteners for transferring load from wood to wood e.g. tubular dowels are usually preferred over bolts for vibratory, reversible, and impact loading.
High strength low compressibility fiber lami late inserts are used to mobilize specified dowel strengths with deformations limited to designed requirements which can be as small as 1 mm at working lo ad.
Steel tube dowels are used with * inserts of densified wood veneer with surface reinforcement of glass fibre. The present invention is an improvement, which obviates the need for special tools and expand dowel & precompress the densified wood veneer. The dowel system uses split metal tubes with hard wood wedges and inserts of bamboo laminates to achieve capacity & reduce the deformation while reducing the cost & using simple tools.
A composite fastener of this invention is an improvement over conventional fasteners comprising wedges or dowels of wood and bamboo of low strength. The invention combines the benefit of higher strength of steel or other metals and fiberglass and the compressibility of wood, which ensure closeness of fit. In the case of composite fastener the operations are significantly simplified as the pre-compression of the hole is done only in the wood component of the member.
By using bamboo / fiber laminate of high strength of this invention, improved capacity is achieved without pre-compression of the holes in the bamboo fiber laminate inserts. In contrast to the conventional mechanical fasteners, the composite fastener systems of this invention, installed in the pre-bored holes with a tight fit, ensure relatively high bearing capacity without brooming or splitting failure, particularly in the zones of stress concentration.
Incorporation of tension bolt on either side of the dowel adds to the capacity by mobilizing interface friction, and increases the bearing capacity of the wood or bamboo by bolt-induced confining stress. The composite fastener combines action of several resisting mechanisms apart from increasing the strength achieved by virtue of the strength of the steel or the fiber reinforced plastic added to the low cost easy to install wedges of wood or bamboo fiber laminates. The composite fasteners of this invention are amenable to installation in the stress-laminated members where the bolts or bands used for stress lamination enhance the resistance to cracking. Further the interface friction and shear resistance helps to add to the capacity. Individually the components such as wedge shaped dowels, diamond shaped inserts & stress lamination without design irregularity does nor ensure that load transfer capacity is achieved with deformation limited to values specified in the design.
The invention has the benefits of various mechanisms used in combination, such as bearing of the fasteners on the surface of tight fitting holes and stress lamination achieved by use of tension bolts. Use of oversized holes for tension bolts minimizes the adverse effects of stress concentration and crushing at the line contact of the bolts. The tension bolts induce normal stresses in the potential slippage plane thereby enhancing the interface shear resistance. Such confining stress also improves the resistance to indentation on the surfaces of the holes where the fasteners are installed.
The dowel of this invention can be installed using simple tools similar to those used for installing conventional wood and bamboo dowels and wedges. The
split sleeve and wooden wedges allow lateral expansion to ensure a tight fit in the hole.
High strength bamboo /fiber laminate used as insert or attachment provides higher strength, lower compressibility thereby eliminating the need to precompress the portion of the hole where the high strength laminate is provided. Thus the operations for the final assembly can be simplified.
Crack formation due to defects in the wood is arrested where ever the surfaces of wood is bonded with fiber-reinforced piastic or high strength bamboo /fiber laminates. Surfaces of holes are coated with fiberglass or suitable adhesive. In addition, bamboo can be impregnated with suitable resin to prevent splitting or cracking or brooming or local failure by indentation.
Durability of the construction is ensured by using composite dowels of hollow tubes of corrosion resistant metal, mouldings of wedge shape or other shapes of high strength bamboo fiber laminate, fiber reinforced plastic etc. The fastener may be used with advantage for joints, splices & connections of high capacity wood /bamboo composite members. Fasteners would ensure monolithic action for reinforcement of wood /bamboo composites attached externally to concrete or brick masonry.
Prior art reported in "Design, Testing and Analysis of Bamboo-wood-concrete composite Beams by the Society for Advancement of Renewable Materials and Energy Technology (SARMET), March 2001 submitted to the International Network for Bamboo ana Rattan (INBAR), discloses that, the deformation caused by presence o: the hollow in the bamboo culms compromises the efficacy of stress lamination.
In this invention use of wood filler of appropriate grade size and geometry, to fill the hollow of split bamboo is obligatory to ensure that deformation during tightening does not compromise the stress lamination benefits. The invention also uses tension bolts and precompression devices, which are located optimally and placed in the appropriate direction so that the designed confining and normal stress level is realised at the critical zones.
The fasteners disclosed in this invention extend the range of applications of the wood bamboo composites for various uses as described below:
> Beams, rafters, trusses, columns, posts applied to construction of buildings, bridges & industrial structures.
> Joints of reinforcement & junction with facings in reinforced soil application for river training, bank protection, landslide control, approach embankments and abutment walls for bridges, raising of flood protection embankment etc.
> Wood /bamboo gabions for coffer dams storage reservoirs, overflow diversion weirs etc.
> Towers for wind mills and ropeways, structural supports for solar equipment for renewable process heat generation.
The hard wood used in this invention is selected from materials that are reasonably free of defects such as knots and cracks, with shear strength of about 100 to 150 kg/cm2, modulus of elasticity of about 1 to 2 x 105 Kg/ cm2 and flexural strength of about 500 to 800 Kg/ cm2.
The bamboo used are selected from those exhibiting shear strength of about 20 kg/cm2 to 40 kg/cm2, modulus of elasticity of about 1 to 2 x 105 kg/cm2 and tensile strength of about 1000 kg/cm2 to 1500 kg/cm2.
The high strength bamboo fiber laminate used are selected from those exhibiting shear strength of about 100 Kg/cm2 to 300 kg/ cm2, modulus of elasticity of 1 to about 3 x 105 Kg/ cm2 and tensile strength of 1200 to about 2000 Kg/ cm2
The stainless and other steel used in the dowel are selected from materials with shear strength of about 1500 to 3000 kg/ cm2, modulus of elasticity of about 2 to 3 x 106 Kg/ cm2 and tensile strength of about 3000 to 10,000 Kg/ cm2
The fiber reinforced plastics are selected from materials of shear strength of about 200 to 1000 kg/ cm2, modulus of elasticity of about 1 to 5 x 105 Kg/ cm2, and tensile strength of about 1000 to 5000 Kg/ cm2
Thus in a preferred embodiment of the present invention
i. Structural components of wood and bamboo are cut to required size and
length and dimensions are matched, ii. Irregularities are made on the surfaces by cutting and/or pressing to
create the undulations, serrations or indentations, iii. Holes and slots of the required size and shape are made at the specified
locations to accommodate the dowels, inserts and bolts, while ensuring
that the desired tolerances are satisfied, iv. Inserts of diamond shape, of wood, bamboo fiber laminates and metal
are introduced for shear transfer across the interfaces, v. Dowels of circular, elliptical or rectangular cross section are installed vi. Wedges are driven to ensure tight fit of the dowels, vii. Holes in the wood and bamboo, for accommodating split sleeve "dowels,
are precompressed. viii. U-bolts, tension bolts, threaded dowels or rods with or without washers
are installed and tensioned to induce confining stress in bearing zones of
dowels and inserts tc improve bearing capacity, ix. U-bolts, rods, Wire bops, bands, straps are installed and tensioned by
availing of an arrangement of plates and bolts, to induce normal stress
for stress lamination.
x. The bolts, wire loops, bands, straps are retightehed after specified service period to compensate for any dimensional changes.
In another embodiment, dowels of circular, elliptical or a combination of rectangular, diamond and semi-circular shapes and constituted of solid steel or hard wood or high strength bamboo fiber laminates are used.
In another embodiment, in lieu of solid dowels of various shapes, split tube dowels of high strength non-corrosive material like stainless steel, along with wedges of compressible materials are installed.
In another embodiment, the metal dowel may have threaded ends to so as to make a bolt and nut assembly.
In another embodiment, inserts of high strength bamboo fiber laminates used in combination with dowels are attached to the wood in the zones subject to stress concentration.
In another embodiment the wedges are precompressed by tightening the nuts or the threaded dowel, and a washer is used to press the wedge. There after, the projecting part of the wedge is cut off to make it flush with the top surface of the wood. Then the washer can be reintroduced and nut tightened to the desired extent
In another embodiment, screws are used as a means of expansion of the wood part of the split tube dowel.
In another embodiment, metal plates are attached to reinforce wedges, inserts or dowels of hard wood or bamboo fiber laminates.
In another embodiment, metal plates with serration, indentation are attached to the bamboo using wires, nails, screws for enhancing the load transfer by shear and so also for arresting crack formation.
In another embodiment, wire windings are used around serrated plates to achieve gripping action and improve shear resistance.
In another embodiment, the metal plate attached to the bamboo is bonded to the counterpart plate attached to the diamond inserts.
In another embodiment, to restrict deformntion, hole in the wood is precompressed and there after the cut is ma ie in the wood to install the bamboo fiber laminate insert.
In another embodiment additional holes are drilled after the making the assembly to install tension bolts with washers to enhance indentation resistance of the material constituting the structural members.
In another embodiment holes in the laminates as well as the assembly are reamed to make a continuous surface.
In another embodiment, inner surfaces of the holes are coated with high strength adhesive with or without admixture of high strength fibers.
In another embodiment, a layer of high strength, resin bonded, fiber reinforced plastic, is attached to the surface of the wood or bamboo, to arrest cracking in the vicinity of holes and zones of stress concentration.
In another embodiment fasteners are strengthened by coating with fiber-reinforced plastic to envelope the fastener or by fixing the metals split sleeve to the fastener.
In another embodiment, steel, hard wood and bamboo laminate wedges may be used.
In another embodiment the wedge may be of hard and densified wood coated with a layer of fiber-reinforced plastic of appropriate thickness or alternatively the bamboo fiber laminate is coatad with a layer of fiber-reinforced plastic of appropriate thickness.
In another embodiment, strips of high strength outer part of bamboo are used to fill gaps between adjacent bamboo segments, used for assembling a member.
In another embodiment, strips of high strength outer part of bamboo are twisted into high tenacity ropes.
In another embodiment, steel wires or fibers impregnated by resin are used as windings in the assembly of strips.
In another embodiment, filler/ reinforcing strip of high tenacity material (FRP, carbon / glass fibre) is introduced at the interface of bamboo segments.
In another embodiment, high tenacity material (FRP, carbon / glass fibre) is used for making stress lamination bands.
In another embodiment, bands are constituted of hand wound, high strength natural fibers with or without resin impregnation and subsequently the bands are tightened by using screws or bolts.
In another embodiment, serrated plates are attached to the bamboo using nails, optionally to improve the interface shear transfer.
In another embodiment, split tube dowels with hardwood, bamboo inserts are used for shear transfer between the serrated plates.
In another embodiment, thin walled high strength bamboo segments are assembled in a suitable arrangement to limit the inter-space size.
In another embodiment, twisted bamboo strips, wires, FRP, etc. are used to fill the inter-space of the thin walled high strength bamboo segments.
In another embodiment fasteners would ensure monolithic action for reinforcement of wood / bamboo composites attached externally to concrete or brick masonry.
In another embodiment, diamond shaped inserts and tension bolts are used to stress laminate the assembly of wood strips and thin walled high strength bamboo segments
In another embodiment of the invention greater confining stress can be induced at the interface of the split bamboo and wood by use of bands or bolts in a transverse direction, with reference to the interfaces of the wood laminates constituting the web of the beam or likewise in other structural forms.
In another embodiment, bolts or wire loops, bands, straps are retightened after subjecting the member to wetting and drying cycles to compensate for any dimensional changes.
In another embodiment, retightening in cyclic manner can be done, with variation in the induced confining stress in the desired sequence and value to minimise residual deformation.
Following non-limiting examples illustrate applications of the composite joinery system of this invention.
Wood bamboo composite exhibited in Example-1 is typically an axial force resisting member applied to construction of trusses. The assembly consists split bamboo segments with fillers (2) attached to wood (3) using a threaded steel dowel (1). High strength bamboo fiber laminate inserts (4) are placed at the interface of wood (3) and bamboo (2) to enhance the bearing capacity. Hardwood wedges (5) are then fitted on either side of the steel dowel (1) to
give a tight fit . A thin metal plate (6) is connected to the top surface of the bamboo (2) and enables transfer of load from the steel dowel (1) to the outer hard skin of the bamboo. This form / module can be easily built up, using transverse bolts or dowels, into members of a wide range of capacities. Applications include, space frame member, stanchions, tower-legs, etc.
The wood bamboo composite assembly shown in Example-2 is designed to serve as a tower-leg. The member consists of thin bamboo strips (1) arranged one over another with adequate hardwood / wood filler (3) inserted in the hollows. These strips (1) are connected to the wood (2) by diamond shaped inserts (4) which bear on the wedges (5) which in turn bear on the high strength bamboo fiber laminate wedge dowels (6) or the threaded steel dowels (7), which transfer the load from the bamboo strips (1) to the wood (2) by bearing. Metal strips (8) with adequate holes / slots for bolts / dowels are used to distribute the confining stress developed by the bolts / dowels, uniformly over the surface of the assembly. Intermittently serrated plates (10) are introduced at the interfaces of bamboo and wood to enhance the transfer of shear.
1. Process for fabrication of wood-bamboo composites comprising an assembly of structural components wherein structural integrity is assured by virtue of stress lamination & creation of irregularities along the wood-bamboo interfaces with incorporation of macro & micro fibres, laminates and fillers for enhancing the shear resistance and tensile strength,
wherein the structural components are prepared in steps comprising
i. Selecting wood, bamboo materials based on design requirements with
regard to strength and deformability; ii. Cutting and trimming of wood and bamboo to produce components
including laminates of desired dimensions to satisfy the closeness of
fits, iii. Creating designed irregularities such as indentation, serration,
undulations maintaining fibre continuity;
iv. Optionally treating the wood - bamboo interfaces with bamboo macro
fibre and their like treated with resin admixed fillers:
v. Curing and seasoning after preservative treatment to ensure
dimensional stability & finishing to the specified dimensions; further assembling the structural components in steps comprising:
vi. Connecting the structural members by means such as, bolts, inserts, rods, U bolts, ties, wires, bands, strips to induce the normal stresses for effective stress lamination and tightening to induce pre-stress in the preferred directions in one or more stages;
vii. Optionally incorporating resin coated macro/ micro, random / oriented fibres or fabric, reconstituted bamboo laminates at the wood-bamboo interfaces and / or at the extreme fibres of the cross-section of the members;
viii.Optionally impregnating wood-bamboo with resins in the zones of stress concentration:
ix. Optionally introducing punched or serrated metal plates at the wood-bamboo interfaces;
x. Optionally installing fibre reinforced plastic bands / wire winding after pre-compression of the assembly.
2. Process for construction of wood-bamboo composites as claimed in claim 1, wherein the rods, bolts and U-bolts are selected from steel of various grades including stainless steel and high modulus, high strength corrosion resistant metals and inserts of corrosion resistant metals or high performance plastics.
3. Process for construction of wood-bamboo composites as claimed in claim 1, wherein the bands are selected from metal, fiber glass, natural or synthetic fibers coated with adhesives to provide effective stress lamination.
4. Process for construction of wood-bamboo composites as claimed in claim 1, wherein strips of resin bonded reconstituted bamboo laminates provide effective stress lamination.
5. Process for construction of wood-bamboo composites as claimed in claim 1 wherein the macro & micro fibers are resin bonded and used in combination with cross fibers of high tensile strength and elastic modulus.
6. Process for construction of wood-bamboo composites as claimed in claim 1 wherein, cracks are arrested in wood-bamboo composites through interlocking action achieved by suitable geometry of the wood-bamboo interface.
7. Process for construction of wood-bamboo composites as claimed in claim 1, wherein the design irregularities in the form of undulations/ serrations with amplitude & spacing in the range of about 10% to 30% of the thickness of the laminate, wherein the strips & cut wood sections are generally within
about 0.5 to about 1.5 % of the length of the rod, U bolt or strip with spacing of about 5 to 15times that of the amplitude.
8. Process for construction of wood-bamboo composites as claimed in claims 1 & 7, wherein indentation is continuous and parallel to the axis of the component.
9. Process for construction of wood-bamboo composites as claimed in claim 1, wherein the fillers are selected from those of compressive strength exceeding 100Mpa and Young' modulus greater than 105 Mpa and high internal friction, preferably crushed quartz sand.
10. Process for construction of wood-bamboo composites as claimed in claims 1-2, wherein resin treated high strength bamboo laminae & natural fiber monofilaments are placed at the interface of wood-bamboo to improve shear resistance and to control cracking of wood.
11. Process for construction of wood-bamboo composites as claimed in claims 1-2, wherein high strength glues are used in critical heavily stressed zones.
12. Process for construction of wood-bamboo composites as claimed in claims 1, 4-5 wherein the resin, preferably phenolic is blended with materials selected from lignin liquor, cashew nut shell oil, marking nuts e.g. (bhilawa) and other resins such as polyurethane based on castor oil and their like.
13. Process for construction of wood-bamboo composites as claimed in claims 1-2, wherein the wood or bamboo are strengthened by impregnation of resin & by densification used separately or in combination.
14. A wood-bamboo composite comprising reconstituted bamboo (RCB)
laminates fabricated, with bamboo sized into thin strips typically 2-3 mm
thick and 15-20 mm wide followed by resin treatment, and assembled with
cross bands and pressed to provide a built up section of 6 sq. cm exhibiting minimum tensile strength of 100 N/mm2-
15. A wood-bamboo composite comprising twisted chords upto 6mm diameter, of high strength outer skin of bamboo separated in long lengths and assembled with de-structured bamboo pith, treated with resin and cross bands of twisted bamboo skin or glass fiber, the assembly pressed and cured to produce RCB laminate with minimum tensile strength of 120 N/mm .
16. Wood-bamboo composites prepared by the process of the invention as claimed in claims 1-13.
Dated : 24TH day of March 2005
V. N. Gore (Applicant)
|Indian Patent Application Number||829/MUM/2003|
|PG Journal Number||41/2008|
|Date of Filing||19-Aug-2003|
|Name of Patentee||DATYE KRISHNA RAMCHANDRA|
|Applicant Address||1ST FLOOR, HANUMAN CROSS ROAD NO. 1, VILE PARLE EAST, MUMBAI,|
|PCT International Classification Number||B 27 M 3/28|
|PCT International Application Number||N/A|
|PCT International Filing date|