This paper assesses the potential of grading of structural timber by use of in-plane buckling analysis combined with scanning, employing post processing of both ordinary photo images and images of wood surfaces illuminated by a large number of laser point sources. The results appear very promising in providing accurate predictions of structural strength. Finite element modelling is applied in the buckling analysis and obtained results are compared with experimental results from timber boards tested in accordance to the European standard EN 408 by four point bending tests.

In a previous research project, carried out during the years 2006-2008, the possibility to manufacture wet glued laminated beams using ungraded laminations of Norway spruce side boards was investigated with very promising results.

In the project presented in this report, the performance of the wet glued beams has been further investigated and developed as regards grading of side board laminations, bond line properties and lamination finger jointing. The possibility to use scanning equipment for measurement of fibre angles and prediction of strength and stiffness of boards and beams has been studied and the procedures for technical approval and CE marking have been probed into. Studies concerning market and economy for the beams and layouts for a pilot plant and a full capacity plant, respectively, for production of such beams have also been carried out.

The possibility to grade side boards in the wet state using axial dynamic excitation was investigated with a positive result. From such excitation, a board’s stiffness (modulus of elasticity) could be determined. Accordingly, grading criteria regarding axial stiffness, and knot size, was applied to grade side board laminations into two classes; outer and inner laminations. Strength and stiffness tests of beams manufactured from such graded laminations showed that the beams actually could challenge first rate glulam and LVL products available on the market.

Regarding beam shape and shape stability, cross section cupping may need further attention. Even if this deformation was small, it was still visible to the naked eye. The problem could probably be overcome if the beams are dried to a moisture content of 12-14% before planing.

Results of shear tests show that green glued bond lines can fulfil strength requirements for glulam. However, delamination requirements for service class 3 (outdoors) were not fully met. From small scale tensile testing of glued bonds it was concluded that green glued bonds with high density wood have the same tensile strength and fracture energy as dry glued bonds. For bonds with low density wood and/or small amount of adhesive, the tensile strength could be lower than for dry glued bonds, whereas the fracture energy was on a similar level.

Strength testing of wet and dry glued finger joints demonstrated that joints glued from high density wood was significantly stronger than low density joints and that there was no significant difference between the strength of green glued joints and joints glued after drying. From X-ray measurement it was shown that the glue penetration into the wood fibres is much deeper in a green glued joint than in a joint that is glued in the dried state.

From scanning algorithms developed within the scope of this project it is possible to obtain reasonably accurate predictions of grain-angle distributions on board surfaces as well as rather accurate descriptions of knot locations and of fibre-angle disturbances around knots. From scanning of board ends, cross section characteristics with respect to radial and tangential directions and of annual ring widths could also be determined. Finally, both board and beam stiffness were predicted from this data, with an accuracy that is comparable with the one obtained from well-reputed commercial grading systems.

The work presented in this paper deals with the use of green gluing (also known as wet gluing) as a mean to overcome the difficulties in making use of side boards for structural applications. By manufacturing laminated beams from unseasoned side boards several advantages are obtained. Beams were manufactured from side boards of approximately 25 mm thickness. The board width was 120 mm. The boards were glued together with a 1-component polyurethane adhesive to form a beam cross-section of approximately 120×315 mm2. After curing, the beams were split into two halves, each approximately 55 mm wide. These 55×315 mm2 beams were then dried in a conventional kiln dryer. Finally, the beams were planed to target size, 50×300 mm2. Tests performed included beam bending tests for strength and stiffness, tests of the shape stability of the beams, tests of the integrity of the adhesive bond lines (delamination) and tests on the strength and fracture energy of the adhesive bond lines. The main results obtained show that there is a potential for the production of green-glued laminated beams with good technical performance.

ABSTRACT: The paper assesses the potential of quality sorting of timber by use of modern scanning techniques, employing both fluorescent lighting and lighting from a large number of laser point sources. Tests were performed using wood-scanning equipment from one of its major manufactures. The results appear promising, especially in providing reasonably accurate predictions of grain-angle distributions on the wood surfaces, as well as rather accurate descriptions of knot locations and of fibre-angle disturbances around knots. A close characterization of end cross sections with respect to radial and tangential directions alike and of annual ring widths was also obtained. Characterization of the growth of annual rings in early to late wood was rather successful too. The techniques employed are illustrated by results of ongoing studies of both planed boards and of glued laminated beams.

The paper assesses the potential of quality sorting of timber by use of modern scanning techniques, employing both fluorescent lighting and lighting from a large number of laser point sources. Tests were performed using wood-scanning equipment from one of its major manufactures. The results appear promising, especially in providing reasonably accurate predictions of grain-angle distributions on the wood surfaces, as well as rather accurate descriptions of knot locations and of fibre-angle disturbances around knots. A close characterization of end cross sections with respect to radial and tangential directions alike and of annual ring widths was also obtained. Characterization of the growth of annual rings in early to late wood was rather successful too. The techniques employed are illustrated by results of ongoing studies of both planed boards and of glued laminated beams.

The use of cross-laminated structural timber elementsis becoming increasingly popular. The number of layersvaries normally from three upwards. The structural performanceof five-layer cross-laminated timber elements was investigated.The five layers consisted of 19mm thick boards,laid successively at right angles to each other and gluedtogether with PU-adhesive, layers 1, 3 and 5 lying in onedirection and layers 2 and 4 in the other. The stiffness andstrength of four cross-laminated timber elements (4955mmlong, 1250mm wide and 96mm thick) were studied duringin-plane bending. Two of the elements were first partitionedinto two parts that were reconnected in two different waysprior to testing. The influence of the way in which the crosslaminatedtimber elements were reconnected was studied,the behaviour observed being compared with the test resultsfor the unpartitioned specimens with respect to both strengthand stiffness. The experimental tests performed showed thecross-laminated timber elements to possess a high degree ofstiffness and strength. There was also found to be a markeddifference in behaviour between the two different ways inwhich the elements were connected to each other. One of thetwo connecting methods studied, being of less good designbut earlier frequently used in Sweden, showed as expectedpoor structural performance, whereas the other one appliedas a safer alternative performed well.

The purpose of this project was to investigate the possibilities to manufacture wet-glued laminated beams for load bearing applications from Norway spruce side board lamellae and by that achieve products that are difficult to obtain from the centre yield of a log and also contribute to increased profitability in the sawmill industry.

Properties such as shape stability, strength and stiffness of wet glued beams with crosssectional dimensions 50×300 mm2 and lengths 4850 and 5200 mm were analysed and compared with corresponding dry glued products. The results obtained are very promising. espite the fact that the beams were produced from a batch of unsorted boards, the performed tests showed that the product has the necessary qualities to be competitive in relation to both glued laminated timber of grade L40 and structural strength graded timber of grade C35. Requirements concerning limitations for geometrical characteristics as expressed in a proposal for a new harmonised glulam standard are also met.

The bond line of the wet glued beams was analysed regarding mechanical properties such as fracture energy, local strength and wood failure percentage after cyclic boiling and drying treatments. The results showed that the bonds are able to comply with requirements concerning bond lines to be used in indoor as well as outdoor constructions for structural pplications.

To be able to improve the quality of boards for use as lamellae in wet glued beams, a method for scanning the slope of grain and disturbance of grain on board surfaces was also further developed and implemented.

Projektets syfte har varit att undersöka möjligheterna att använda sidobräder av gran för tillverkning av våtlimmade balkar för byggmarknaden och därigenom erhålla produkter som dels är svåra att få fram ur centrumutbyte, dels kan bidra till förbättrad lönsamhet i sågverksindustrin.

Formstabilitet, hållfasthet och styvhet för våtlimmade balkar med tvärsnittsdimensionen 50×300 mm2 och längderna 4850 resp. 5200 mm har undersökts och jämförts med motsvarande torrlimmade produkter. De resultat som framkommit är mycket lovande. Trots att balkarna tillverkats av ett osorterat sortiment bräder visar genomförda provningar att produkten har goda förutsättningar att kunna konkurrera med såväl limträ i klass L40 som konstruktionsvirke i klass K35. Dessutom uppfylls de krav på måttavvikelser som ställs i det föreliggande (juni 2008) förslaget till ny harmoniserad standard för limträ.

Balkarnas våtlimmade limfogar har undersökts med avseende på tekniska egenskaper som brottenergi, korttidshållfasthet och risk för delaminering. Delamineringsprovning innebär att limfogen först utsätts för upprepade uppfuktningar och uttorkningar t.ex. genom kokning eller autoklavbehandling, varefter man mäter hur stor andel av limfogen som släppt. Resultaten visar att fogarna kan uppfylla de krav som ställs på limfogar för användning såväl inom- som utomhus i lastbärande konstruktioner.

För att i framtiden kunna sortera fram ett bättre sortiment sidobräder för tillverkning av balkar har en metod för skanning av fibervinkel och snedfibrighet på brädytor vidareutvecklats och implementerats.

A nonlinear model for analysing heat and moisture flow in wood during drying below the fiber saturation point is presented. The model used considers wood at a macro level without taking the various moisture transports mechanisms at the microscopic level into account. Based on the finite-element method, a coupled system of equations resulting from the adopted heat and moisture transfer equations is established and an iterative scheme is proposed. The numerical procedure is verified by a test example. In a two-dimensional analysis, the influence of the coupling on the combined heat and moisture transfer is studied for a board subjected to a typical kiln-drying condition. How well the results agree with those obtained by introducing a commonly applied simplification is discussed.