Structural, physical and mechanical changes of cement-bonded particleboards during sudden fluctuations in temperature and moisture

The paper presents research focused on behaviour of cement-bonded particleboards with modified composition during sudden changes of temperature and humidity. Four types of boards were made—one control and three modified ones. Finely ground limestone was used as a modifying component in binder. Secondary wood particles made from crushing cuttings of cement-bonded particleboards were used as chips substituent. Two sets of test specimens (1 set = 6 test specimens) were manufactured. The first set was stored in laboratory conditions. The second set was subjected to 10 cycles of sudden changes of temperature (− 20 °C to + 70 °C) and humidity in accordance with EN 321 (further in the paper referred to as “wet–frost–dry cycle”.) After each cycle, dimensions and mass of the test specimens as well as ultrasonic pulse velocity were determined. A detailed analysis of structural changes in boards during cycling was carried out by an optical microscope. After 10 wet–frost–dry cycles were completed, bending strength and modulus of elasticity in bending were determined. The analysis of test results implies a very good relation between change of ultrasonic pulse velocity and width of cracks in the area of interfacial zone between cement matrix and wood particles. This finding also corresponds with dimensional and volumetric changes of the boards. Dependence of bending strength and modulus of elasticity in bending on composition of boards is apparent. Positive influence of secondary spruce chips on dimensional changes of cement-bonded particleboards caused by sudden changes of temperature and humidity was proved. Finely ground limestone contributes to more resistant structure of boards which leads to improved bending properties. Adverse conditions had more considerable influence on bending strength (decrease by 21% to 26%) than on modulus of elasticity in bending (decrease by 12% to 19%).

An experimental study on changes in sound absorption capability of spruce (Picea sitchensis), Douglas fir (Pseudotsuga menziesii), and larch (Larix kaempferi) after microwave treatment

This study investigated changes in the sound absorption coefficients of three anatomical sections of cubed spruce (Picea sitchensis), Douglas fir (Pseudotsuga menziesii), and larch (Larix kaempferi) after microwave treatment. Microwave treatment at 1000 W and 2.4 GHz for 20 min increased the sound absorption coefficients (at 2000–5000 Hz) of spruce by 6.9% in the transverse section, 20.0% in the radial section, and 31.7% in the tangential section. The sound absorption coefficients of Douglas fir increased by 28.9% in the transverse section, 19.1% in the radial section, and 50.0% in the tangential section. Larch coefficients increased by 16.7% in the transverse section, 37.2% in the radial section, and 38.8% in the tangential section. The sound absorption coefficients of the softwoods differed according to species and anatomical plane after microwave treatment. It was concluded that changes in the measured sound absorption coefficient indicate alteration in the pore structure of wood, which can affect in turn wood permeability and impregnation. These data will be helpful for predicting the permeability and impregnation of wood after microwave treatment.

Research on seismic performance of traditional Chinese hall-style timber buildings in the Song and Yuan dynasties (960–1368 AD): a case study of the main hall of Baoguo Temple

The hall-style timber frame built in the Song and Yuan dynasties (960–1368 AD) is one of the most important structural prototypes of the traditional timber architecture in East Asia. The current research, through a typical case of the main hall of Baoguo Temple in Ningbo, China, aims to present an accurate and effective seismic performance evaluation method applicable to hall-style timber structures without time–cost expenditure. To obtain more realistic seismic response of hall-style timber frame, a simplified numerical model of the main hall of Baoguo Temple is established based on in situ measurements and low-cycle reversed loading tests results of mortise–tenon joints, moreover, nonlinear static pushover analysis has been performed to quantify the seismic performance levels under five loading conditions. The generalized force–deformation relationship of the timber plastic hinges is modified regarding to the moment–rotation curves of four special mortise–tenon joints. The seismic behaviour of global hall-style timber frame is evaluated through capacity spectrum method and verified by time history analysis, local failure mechanisms are evaluated by the occurrence sequence of plastic hinges. Finally, a performance-based assessment method adequate for the traditional hall-style timber architectures has been proposed with comparison to the current codes. The results have shown that the structural stiffness of the width-direction is less than that of the depth direction due to the asymmetrical configuration of the timber frame, and the building can maintain a stable state under large lateral displacement before collapsing. The inter-storey drift angles of the building under peak ground accelerations of 0.1 g, 0.2 g, and 0.3 g are less than the suggested ultimate values in the current local codes, however, the main hall represents to be more vulnerable to damage when suffer seismic action along the width-direction. This research can provide a reference for seismic performance evaluation and preventive conservation of ancient hall-style timber architectural heritage.

Effects of decay on the shear properties of nailed joints parallel and perpendicular to the grain

Information on the properties of nailed joints with decayed member is necessary to evaluate the remaining structural properties of timber constructions. In this study, loading tests were conducted on nailed joints parallel and perpendicular to the grain with decayed members, and the relationship between the decrease in shear properties and the loading direction to the grain was investigated. After the loading tests, the extent of decay of the specimens was evaluated by the penetration depth of Pilodyn and the decay depth, and these were compared with the shear properties of the nailed joints. The nailed joints with decay had a low load at the initial deformation, regardless of the loading direction to the grain. The initial stiffness, yield resistance, and maximum resistance of the nailed joints parallel to the grain were negatively correlated with the Pilodyn penetration depth, and those of the nailed joints perpendicular to the grain showed no significant correlation with the Pilodyn penetration depth at the 5% level. The initial stiffness, yield resistance, and maximum resistance of the nailed joints parallel to the grain tended to decrease with increasing decay depth, and those of the nailed joints perpendicular to the grain did not exhibit this tendency. The shear properties of the nailed joints significantly decreased at small decay depths.

Influence of juvenile and mature wood on anatomical and chemical properties of early and late wood from Chinese fir plantation

The proportion of juvenile wood affects the utilization of wood seriously, and the transition year of juvenile wood (JW) and mature wood (MW) plays a decisive role in the rotation and the modification of wood. To find out the demarcation of JW and MW, the tracheid length (TL) and microfibril angle (MFA) of early wood (EW) and late wood (LW) from four Chinese fir clones were measured by optical microscopy and X-ray diffraction. Then the data were analyzed by the k-means clustering method. The correlation and the differences among wood properties between JW and MW were compared. Results indicated that the LW showed better properties than that of EW, but the anatomical differences between EW and LW did not influence the demarcation of JW and MW. The cluster analysis of TL and MFA showed that the transition year was in the 16th year and the transition zone of EW and LW was different among clones. The MW has longer and wider tracheid, thicker cell walls, and smaller MFA. In terms of chemistry, MW had a higher content of holocellulose, α-cellulose, less content of extract, but no significant difference in lignin content compared with JW. The stabilization of chemical components was earlier than that of the anatomic properties. Correlation analysis showed that there were strong correlations between the chemical composition and anatomical characteristics in JW and MW. In general, compared with chemical components, anatomical indicators were more suitable for JW and MW demarcation. The differences and correlations between JW and MW properties provide a theoretical basis for wood rotation and planting.

Experimental study on flexural properties of timber columns with interior notches in traditional Japanese timber structures

In this study, the columns with interior notches in traditional Japanese timber frames were selected as the research object, and static bending tests were performed to investigate the effect of interior notches on the flexural properties of columns. First, the bending behaviors of columns under three-point and four-point load configurations were compared to obtain a suitable referenced strength of a column without notches. The reduction in the load-bearing capacity of columns with different types of interior notches in traditional Japanese timber structures was determined through experimental tests and statistical analysis. The results indicated that the mean bending strength of columns with three different notch types was consistent with those without notches, the continuous timber on both sides of the notch had a beneficial effect on maintaining a higher strength and reducing the stress intensity around the notch. The fracture position and the standard deviation of the bending strength were affected not only by the notch depth, but also by the notch width on the tensile side of the column.

The effects of cellulose nanofibers compounded in water-based undercoat paint on the discoloration and deterioration of painted wood products

Cellulose nanofibers (CNFs) have many potentials as filler to improve the properties of the other materials. We have developed the novel paints containing CNFs, and which controlled the discoloration of wood products. To clarify the discoloration mechanism of wood panels using an undercoat paint containing CNFs, prepared by an integrated process from Cryptomeria japonica, the composites and films made of CNFs and acryl resin that was a raw material for the paints were prepared. Observation of the surface of the CNFs/acryl resin composite film by atomic force microscopy showed that the fibers and the resin were uniformly mixed. The composite film prevented light transmittance in the ultraviolet (UV) light region, as well as oxygen gas permeation. The permeability coefficient of the oxygen gas decreased to 60% with the addition of 1.5 wt% of CNFs to the acryl resin. The addition of CNFs also increased the breaking stress by approximately 1.5 times compared with the acryl resin film. Electron spin resonance (ESR) analysis after UV irradiation resulted in the lowest radical formation of a piece of wood wrapped in the CNFs/acryl resin composite compared with the acryl-coated specimen and the wood as it was. Therefore, the CNFs composite film shielded the UV rays and oxygen more effectively than the original acryl resin, making it difficult for these factors to reach the wood’s surface, and thus, perhaps suppressing the generation of radicals from the wood. These actions would suppress the production of coloring substances caused by the radicals, resulting in the suppression of discoloration. Furthermore, the increase in the film’s strength by the addition of CNFs would have enhanced the stability of overall the paints with a CNF-containing undercoat. These effects might have contributed not only to the prevention of discoloration but also to the prevention of the occurrence of minute cracks caused by various weather deterioration factors.

Anatomy and cell wall ultrastructure of sunflower stalk rind

The anatomy and ultrastructure of sunflower stalk rind are closely related to its conversion and utilization. We studied systematically the anatomy and ultrastructure of the stalk rind using light, scanning electron, transmission electron and fluorescence microscopy. The results showed that the stalk rind consisted of phloem fibers (PF), xylem fibers (XF), vessel elements (V), ground parenchyma cells (GPC), axial parenchyma cells (APC), xylem ray parenchyma cells (XRPC), and pith ray parenchyma cells (PRPC). These cell walls were divided into the middle lamella, primary wall, and secondary wall (S). It was found that the S of PF, XF and V was further divided into three layers (S1–S3), while the S of APC, GPC, XRPC and PRPC showed a non-layered cell wall organization or differentiated two (S1, S2) to seven layers (S1–S7). Our research revealed the plasmodesmata characteristics in the pit membranes (PMs) between parenchyma cells (inter-GPCs, inter-XRPCs, and inter-PRPCs). The morphology of the plasmodesmata varied with the types of parenchyma cells. The thickness and diameter of PMs between the cells (inter-Vs, V–XF, V–APC, and V–XRPC) were greater than that of PMs between parenchyma cells. The cell corners among parenchyma cells were intercellular space. The lignification degree of vessels was higher than that of parenchyma cells and fibers. The results will provide useful insights into the biological structure, conversion and utilization of sunflower stalk rind.

Experimental investigations into the mechanical performance of glulam dowel-type connections with either bolts or screws as fasteners

Dowel-type connections are the most common connections in glulam structures. Bolts are often used as fasteners for dowel-type connections. However, the clearance between the bolts and the pre-drilled bolt holes leads to low rotational stiffness and insufficient moment-resisting capacity. To achieve better mechanical performance, screws can be used as alternative fasteners for dowel-type connections. In this paper, monotonic and cyclic loading tests were conducted on glulam dowel-type connections with either bolts or screws as fasteners. The failure modes, moment-resisting capacity, ductility ratio, stiffness degradation, and equivalent viscous damping ratio of the specimens were analyzed and reported. Results showed that compared with traditional bolted connections, the screwed connections had larger moment-resisting capacity and better ductility. The hysteretic loops of the screwed connections were plumper, and the pinching effect was gentler compared to those of traditional bolted connections.

The mechanical properties and thermal conductivity of bamboo with freeze–thaw treatment

The aim of this research was to investigate the effect of freeze–thaw treatment on bamboo with different initial moisture content (water-saturated, air-dried and oven-dried). Bamboo (Phyllostachys pubescens) were treated with two freeze treatments and its microstructure, chemical composition, mechanical properties and thermal conductivity were characterized by field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), mechanical testing machine and thermal conductivity tester, respectively. The results showed that the freeze–thaw treatment had little influence on the microstructure of bamboo, the chemical composition content and the cellulose crystalline structure of bamboo were also not altered. The crystallinity index was found to increase with the increase of initial moisture content. The bending strength and elastic modulus of the treated bamboo increased, the extent of the increase was dependent on the initial moisture content and the freezing temperature. The thermal conductivity of the treated bamboo increased remarkably, which might be possibly determined by the cellulose crystallinity, moisture content, and density of bamboo.