Haiqing Ren

Cell wall structure and formation of maturing fibres of moso bamboo (Phyllostachys pubescens) increase buckling resistance.

The mechanical stability of the culms of monocotyledonous bamboos is highly attributed to the proper embedding of the stiff fibre caps of the vascular bundles into the soft parenchymatous matrix. Owing to lack of a vascular cambium, bamboos show no secondary thickening growth that impedes geometrical adaptations to mechanical loads and increases the necessity of structural optimization at the material level. Here, we investigate the fine structure and mechanical properties of fibres within a maturing vascular bundle of moso bamboo, Phyllostachys pubescens, with a high spatial resolution. The fibre cell walls were found to show almost axially oriented cellulose fibrils, and the stiffness and hardness of the central part of the cell wall remained basically consistent for the fibres at different regions across the fibre cap. A stiffness gradient across the fibre cap is developed by differential cell wall thickening which affects tissue density and thereby axial tissue stiffness in the different regions of the cap. The almost axially oriented cellulose fibrils in the fibre walls maximize the longitudinal elastic modulus of the fibres and their lignification increases the transverse rigidity. This is interpreted as a structural and mechanical optimization that contributes to the high buckling resistance of the slender bamboo culms.

Effect of stand and tree attributes on growth and wood quality characteristics from a spacing trial with Populus xiaohei

The effect of stand density (1000 stems/ha, 500 stems/ha and 250 stems/ha) on tree growth and wood quality characteristics was studied in a 27-year-old plantation species of Populus xiaohei in China. Results indicated that stand density had significant effects on tree radial growth and crown size, and the lowest stand density produced trees with the largest stem taper. In terms of wood quality characteristics, there was no significant effect of stand density on either wood basic density or fiber length. However, significant differences were found between different stand densities for wood mechanical properties. A positive relationship between modulus of elasticity, compression strength and stand density was observed, while the highest modulus of rupture was recorded at a moderate density of 500 stems/ha. Stand density was responsible for highly significant effects on both juvenile wood and wet heartwood basal areas in individual trees, and there was an obvious tendency towards increasing juvenile wood and wet heartwood basal areas with decreasing stand density. In addition, the relationships between wood quality characteristics and tree and stand characteristics were also examined. Some wood quality characteristics, namely mechanical properties and juvenile wood and wet heartwood basal areas, were quantified successfully in relation to selected tree characteristics using a regression approach with various degrees of goodness of fit. Based on comprehensive consideration of various factors, such as wood quality, tree growth, and establishment cost, results from this study suggest that a density of 500 stems/ha is optimum for wood production.RésuméCe travail analyse les effets de la densité de plantation (1000 tiges/ha, 500 tiges/ha and 250 tiges/ha) sur la croissance et la qualité du bois dans une plantation chinoise de Populus xiaohei âgée de 27 ans. Les résultats montrent (i) que la densité de plantation affecte significativement la croissance radiale et la dimension des houppiers et (ii) que la densité la plus faible conduit à des arbres ayant le défilement le plus important. Par contre, il n’y a aucun effet de la densité de plantation sur la densité du bois ou sur la longueur des fibres. Cependant, il existe des différences significatives entre traitements pour les propriétés mécaniques. Nous avons observé une corrélation positive entre le module d’élasticité, la résistance en compression et la densité de plantation tandis que le module de rupture le plus élevé a été obtenu pour la densité de plantation intermédiaire de 500 tiges/ha. La densité de plantation est responsable des effets les plus significatifs sur les surfaces terrières de bois juvénile et de cœur humide qui augmentent lorsque la densité de plantation diminue. Nous avons également analysé les relations entre la qualité des bois et les caractéristiques des arbres et des peuplements. Certaines propriétés du bois comme les propriétés mécaniques et les surfaces terrières de bois juvénile et de cœur humide ont été quantifiées avec succès par l’utilisation de régressions multiples. À partir de ces résultats il a été possible de prendre en compte différents facteurs tels que la qualité des bois, la croissance et le coût d’installation des différentes densités de plantation et de montrer que la densité de plantation de 500 tiges/ha est optimale pour la production de bois.

Effects of Temperature on the Compressive Strength Parallel to the Grain of Bamboo Scrimbe

The objective of this study was to investigate the compressive strength parallel to the grain of bamboo scrimber during and after exposure to various temperatures, in a range from 20 to 225 °C. These data were used to provide a basis for the evaluation of the fire performance of bamboo structures. A total of 152 specimens, assembled as group “during-fire” and “post-fire”, were tested during and after exposure to high temperatures. The experimental results indicated that there were significant differences in compressive properties between the “during-fire” and “post-fire” groups. At one temperature level, the compressive strength and modulus of elasticity of the “post-fire” group were significantly higher than those properties of the “during fire” group, but the ductility coefficient was reversed. FTIR analysis results showed that 175 °C was a key turning point, at which thermal decomposition occurred in the cellulose of the bamboo and phenolic resin.

Detection of complex vascular system in bamboo node by X-ray mu CT imaging technique

Abstract Bamboo is one of the world’s fastest growing plants. They reach a final height of 15–40 m during a period of 40–120 days. The full height is reached by intercalary growth of each node. However, it is very difficult to detect the complex vascular system in a bamboo node using traditional methods. X-ray computed microtomography (μCT) is a noninvasive novel approach to the three-dimensional (3D) visualization and quantification of biological structures. In the present article, μCT has been applied to provide insights into the internal structure of bamboo node, where three branches are connected. The picture obtained could hardly be obtained by any other means. The bamboo nodal characteristics of three transverse and axial sections are presented. The complex 3D network of vascular bundles has been directly obtained for the first time.

Experimental and Statistical Evaluation of the Size Effect on the Bending Strength of Dimension Lumber of Northeast China Larch

This study investigated the size effect on the bending strength (modulus of rupture—MOR) of dimension lumber of Northeast China larch (Larix gmelinii); providing a basis for the further application in light wood frame construction. Experimental and statistical evaluations were conducted on the bending strength. A total of 2409 full-size dimension lumber samples were tested by static bending tests; which included three different sizes: 2 × 3; 2 × 4; and 2 × 6. Results indicate that the size has a significant effect on the MOR. Both the chi-square (χ2) and Kolmogorov-Smirnov (K-S) test results show that the lognormal distribution generally fits to the MOR better than to the normal distribution. Additionally; the effects of partial safety factor (γR) and live-to-dead load ratio (ρ) were studied by reliability analysis. Reliability analysis results indicate that the reliability index increases nonlinearly with the decrease of γR and the rise of ρ. Finally; the design value of bending strength and its adjusting factor of size effect of 2 × 3; 2 × 4; and 2 × 6 larch dimension lumber were obtained according to the Chinese National Standards’ requirements of the reliability index.

Distribution of wet heartwood in stems of Populus xiaohei from a spacing trial

Abstract The development of wet heartwood was studied in relation to different tree spacings (2×5 m, 4×5 m, 4×10 m) in a 28-year-old Populus xiaohei T.S. Hwang et Liang in China. Stem discs of 5 cm thickness were taken every 2 m from the stump to the top (including the 1.3 m height), and wet heartwood area was measured for each section. Results indicated that wet heartwood was present in all sample trees, and represented a substantial part of the stem, accounting for nearly 62.0%, 56.0% and 65.2% of tree stem volume, respectively, for spacings 2×5 m, 4×5 m and 4×10 m. Wet heartwood tapered towards the top of the tree, closely following the stem wood profile. This vertical distribution pattern of wet heartwood was scarcely influenced by spacing. However, wider spacing resulted in larger wet heartwood area and volume, and the production of wet heartwood was positively and significantly correlated with tree diameter. Estimation of wet heartwood volume from external tree characteristics was possible using various regression models with fairly high coefficients of determination ranging from 0.87 to 0.92.

Development and investigation of a hybrid built-up column made of small diameter logs originating from juvenile trees

Small diameter logs from juvenile trees are heavily produced during the management of artificial forests around the world. As a kind of plentiful and inexpensive natural resource, the potential was not fully explored. So far the small diameter logs are mainly used as raw materials for products other than building materials. To utilize these small diameter logs originating from juvenile trees as structural members into wood construction, a kind of hybrid built-up column was developed and the performance was investigated experimentally and theoretically. It was found that column had good load-carrying capacity. To apply the developed member in wood construction, the prediction method of the column was proposed. The effective slenderness ratio which took the shear deformations due to the bending of limbs and slip of nail connections between U-shaped nails and limbs into consideration was derived based on mechanics theory. The proposed prediction method was found to have good accuracy in predicting the load-carrying capacity of the hybrid built-up column. This paper can promote the structural application of the small diameter logs originating from juvenile trees.