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The objective of this study was to assess the potential gains in log processing yield when integrating sawmill and engineered wood products manufacturing, a process which enables the use of random board widths and higher wane allowances than normal. The simulation was utilized and validated against real log sawing. The validation study showed that simulations consistently over-estimated the actual volume recovery by 2.1%. Simulation results showed that logs with smaller diameters returned higher recovery increases when adopting an increased wane strategy compared to large-diameter logs. When combining both increased wane and random width strategies, the recoveries were the highest. Using a weighted average of log classes (according to a common log size distribution in South African sawmills) an increased wane strategy returned higher recovery (11.0%) than a random width strategy (2.0%), but a combined strategy (13.0%) was the most efficient. The gains in volume recovery presented in this study showed that it is worthwhile to consider the integration of engineered products manufacturing in primary log processing using random widths strategy combined with higher wane allowance. For better use of the raw material, the maximum wane that engineered products can allow without compromising its strength and stiffness must be further investigated. [ABSTRACT FROM AUTHOR]

The structural use of wood from young trees requires gluing smaller timber pieces to form large elements. In young Eucalyptus timber of structural dimensions, knots do not significantly diminish the mechanical properties, yet their influence on wood adhesion has not been widely studied. Therefore, the aim of the study was to assess the influence of knots on the bond quality of face-glued wood from young E. grandis. Wood from seven-year-old E. grandis trees was tested in shear on the bond-line (polyurethane adhesive) using paired samples of knot-containing and clear wood samples. Knot features did not correlate with shear strength or wood failure percentage. Knot-containing samples had a lower percentage of wood failure (5.8%), but the same shear strength as clear wood samples. Below a wood density of 650 kg m−3, clear and knot-containing wood behaved similarly, but above this value, knots influenced wood adhesion negatively. By simulating glulam beams with high-density wood on the outer lamellas, it was possible to show that shear stress on those bond-lines is lower than the minimum shear strength observed on dense knot samples. Hence, lower adhesion caused by knots on denser wood probably does not represent a significant problem for glued laminated products from young Eucalyptus grandis trees. [ABSTRACT FROM AUTHOR]

Warping is a frequently encountered defect in wood products which is evaluated in different ways by various sawn timber product standards. However, there are weaknesses in the current evaluation methods especially when comparing warp in different board lengths. The objective of the work described in this paper was to develop a theoretical model of bow and spring based on pure bending theory and to evaluate the model experimentally. A warp index was developed that allows comparison of bow and spring in timber boards independent of the length. The theoretical model was evaluated in experimental trials with Eucalyptus grandis of board warping caused by growth stress release as well as board warping caused by differences in longitudinal shrinkage after drying. The model explained the warping phenomenon well and the errors between theoretical and observed data were, on average, very small. The warp index developed allows assessment of bow and spring in any length, and might be useful with segregating portions of lower distortions for modern production systems of finger-jointed lamellas for engineered wood products, as well as for assessing growth stress levels, sawmilling processes and timber seasoning techniques. [ABSTRACT FROM AUTHOR]

This study reviews, from a South African and developing world perspective, green building rating tools and life-cycle assessment methods with a focus on wood constructions. Based on existing studies, it seems as if the well documented environmental benefits of using wood is not sufficiently reflected in the green building rating systems reviewed. Although life-cycle-assessment is recognized as the best way to holistically evaluate the environmental impacts of a building, it is resource intensive, can be highly complex, and is dependent on the availability of accurate data. The life-cycle assessment research results on which green building rating tools were based, were mostly from colder, northern hemisphere developed countries. This might result in an over-emphasis on the operating energy requirements of buildings at the expense of embodied energy and the importance of material choices. We therefore conclude that there is a critical need for local life cycle assessment based research in South Africa and other developing countries on the environmental impacts of different building products and processes. [ABSTRACT FROM AUTHOR]

Key message: An increase in the stiffness of lumber with a decrease in initial tree spacing was confirmed forPinus patulaSchiede ex Schltdl. & Cham. The underlying properties of microfibril angle, wood density and knot frequency explained 71% of the variation in lumber stiffness. Tree spacing also influenced wood properties independent of radial growth rate. Context: Rapid growth rates and reduced harvesting ages of South African-grown pine plantations have caused a reduction in the stiffness of structural lumber, which accounts for about 75% of all sawn wood. Microfibril angle and wood density are known to influence wood stiffness, which may be manipulated by the growing space of trees. Aims: The objective of this study was to evaluate the effect of slower growth rates, caused by narrow tree spacing, on the suitability of Pinus patula Schiede ex Schltdl. & Cham. wood for structural lumber. Methods: An 18- and a 19-year-old spacing experiment with four levels of initial tree spacing (1.83 m × 1.83 m, 2.35 m × 2.35 m, 3.02 m × 3.02 m and 4.98 m × 4.98 m) were sampled. Linear and non-linear mixed-effects models were developed to examine the effect of tree spacing on the quality of wood and lumber as defined by the modulus of elasticity, modulus of rupture and knot frequency of 208 boards and the ring-level microfibril angle and wood density of 86 radial strips. Results: Wood and lumber quality improved with decreasing spacing, and only the narrowest spacing had lumber that conformed to the requirements of the lowest South African structural grade. Microfibril angle, wood density and knot frequency explained 71% of the variation of lumber stiffness. After accounting for ring width differences, there remained a significant effect of initial spacing on the parameters of models predicting microfibril angle and wood density. Conclusion: Wide initial spacing is discouraged if higher strength grades are desired for Pinus patula lumber. [ABSTRACT FROM AUTHOR]