An experimental and numerical study of moisture transport and moisture-induced strain in fast-grown sitka spruce

The use of fast-grown timber in the manufacture of engineered wood products is increasing; however, the fast growth rate results in a low-density timber that is susceptible to significant swelling and shrinkage deformations under changing moisture content. The current study focuses on the characterisation of the moisture diffusion and swelling/shrinkage of fast-grown Sitka spruce and the prediction of the moisture-induced strain development in Sitka spruce glulam beams under variable humidity cycles. Moisture content evolution and swelling/shrinkage coefficients were measured and the longitudinal swelling/shrinkage was found to be significantly greater than for slow-grown timber. Sitka spruce glued-laminated beams were subjected to controlled relative humidity cycling for 52 weeks and the moisture distribution and moisture-induced strains were measured continuously. Coupled moisture-displacement numerical models, incorporating the experimentally measured material parameters were developed. The effect of the glue-line was found to have an insignificant effect on moisture transport, however, the material orientation greatly influenced the predicted moisture-induced strain. Accurately mapping the material orientation produced significantly better predictions of the experimental results over the 52-week period

An experimental and numerical study of moisture transport and moisture-induced strain in fast-grown sitka spruce

The use of fast-grown timber in the manufacture of engineered wood products is increasing; however, the fast growth rate results in a low-density timber that is susceptible to significant swelling and shrinkage deformations under changing moisture content. The current study focuses on the characterisation of the moisture diffusion and swelling/shrinkage of fast-grown Sitka spruce and the prediction of the moisture-induced strain development in Sitka spruce glulam beams under variable humidity cycles. Moisture content evolution and swelling/shrinkage coefficients were measured and the longitudinal swelling/shrinkage was found to be significantly greater than for slow-grown timber. Sitka spruce glued-laminated beams were subjected to controlled relative humidity cycling for 52 weeks and the moisture distribution and moisture-induced strains were measured continuously. Coupled moisture-displacement numerical models, incorporating the experimentally measured material parameters were developed. The effect of the glue-line was found to have an insignificant effect on moisture transport, however, the material orientation greatly influenced the predicted moisture-induced strain. Accurately mapping the material orientation produced significantly better predictions of the experimental results over the 52-week period

The influence of age on the timber properties and grading of Scots pine and larch in Ireland

Scots pine (Pinus sylvestris L.) and larch (Larix spp.) are two species that could contribute to diversifying Ireland’s timber supply. However, there is little knowledge about their properties as well as their variation with age. The aim of this study is to investigate the structural properties (modulus of elasticity, strength and density) of Irish-grown Scots pine and larch and the effect of cambial age on timber grading. Structural-sized pieces were used for this purpose, and the timber properties, knots and ring width were measured on 158 and 250 pieces of Scots pine and larch, respectively. Characteristic values of the properties and indicative yields for different strength classes were calculated. The age effect was assessed using an empirical approach, and a novel modelling approach that disaggregates the timber properties at the annual growth ring level. Yields above 90 per cent of C20 were achieved for Scots pine, whereas larch achieved a 100 per cent yield of C24 strength class. The effect of cambial age in the grading properties indicated that older boards increased the characteristic values of a timber population. In Scots pine, the empirical approach showed that the yields increased by up to 26 per cent when using pieces up to 50 years old compared with pieces up to 30 years old. In larch, the use of pieces up to 40 years old increased the yields by up to 16 per cent compared with using pieces up to 30 years old. The results of the modelling approach were consistent with the values obtained in the empirical analysis and can help to make informed decisions regarding rotation lengths for the production of structural timber. Our results found that cambial ages of 40 years in Scots pine produce high yields of structural timber, whereas 30 years are enough for larch

The Influence of Panel Lay-Up on the Characteristic Bending and Rolling Shear Strength of CLT

The objective of this study was to characterise the behaviour of cross laminated timber (CLT) panels and the influence of the panel lay-up on the failure strength. Three different panel configurations of thickness, 60 mm, 100 mm, and 120 mm, were loaded in the out-of-plane direction. The 60 mm and 120 mm panel configuration comprised three layers of equal thickness, and the intermediate 100 mm thick panel comprised five layers of equal thickness. The mean and characteristic bending and rolling shear strength of the panels were examined. The results show that the mean bending and rolling shear strength decrease with the panel thickness. The characteristic results have shown that there is an influence because of the number of boards within the panel. The characteristic bending strength values for the five-layer 100 mm thick panel were found to be higher than that of the three-layer 60 mm panel. The characteristic rolling shear values decreased in the five-layer panels, however, the increased number of layers subjected to the rolling shear results in a reduced variability in the rolling shear strength

The structural behaviour of compressed wood manufactured using fast-grown sitka spruce

An investigation was carried out to examine the potential to manufacture a compressed wood product from fast-grown Sitka spruce, using a process of thermo-mechanical compression to increase its strength and stiffness. The process involves subjecting timber to a thermal load followed by a compressive load to reduce its cross-section, increasing its density and improving its structural performance. In this study, the influence of the manufacturing parameters, specifically, the pressing time and compression ratio, are examined. These parameters have been evaluated based on the microscopic structure and bending strength from three-point bending tests. The results have demonstrated that there is significant potential to manufacture a compressed wood product with improved structural behaviour from fast grown timber.peer-reviewe

Evaluation of the mechanical behaviour of novel latticed LVL-webbed joists

The mechanical behaviour of a novel I-joist having a latticed Laminated Veneer Lumber (LVL) web is investigated. A total of 30 joists with C24 Grade flanges and latticed LVL webs were manufactured and tested to failure. Two joists depths of 241 mm and 305 mm are examined with flange sections of 60 x 50 mm2 and 65 x 55 mm2, respectively. Two different adhesive types are used to manufacture the LVL webs, namely, urea formaldehyde (UF) and phenol resorcinol formaldehyde (PRF). The failure behaviour was typically linear elastic to failure. The PRF adhesive performed best in moment shear capacities. Tests have shown that the use of latticed LVL-webbed I-Joists can outperform some commercially available I-joists of similar dimensions with the added advantage of having openings within the web to allow services pass through without affecting the structural integrity of the joist.This work has been carried out as part of the project entitled “Innovative I-Joist Products” (Project Code IP-2007-0453) funded by Enterprise Ireland and Grainger Sawmills under the Innovation Partnership program. The contribution of the technical staff of the College of Engineering and Informatics, NUI Galway, in particular, Peter Fahy, Colm Walsh and Gerard Hynes, is acknowledged. The authors would also like to acknowledge the contribution of project partners, Sean Moloney and Michael Bourke at the Wood Technology Centre, University of Limerick

An experimental and numerical study of moisture transport and moisture-induced strain in fast-grown sitka spruce

The use of fast-grown timber in the manufacture of engineered wood products is increasing; however, the fast growth rate results in a low-density timber that is susceptible to significant swelling and shrinkage deformations under changing moisture content. The current study focuses on the characterisation of the moisture diffusion and swelling/shrinkage of fast-grown Sitka spruce and the prediction of the moisture-induced strain development in Sitka spruce glulam beams under variable humidity cycles. Moisture content evolution and swelling/shrinkage coefficients were measured and the longitudinal swelling/shrinkage was found to be significantly greater than for slow-grown timber. Sitka spruce glued-laminated beams were subjected to controlled relative humidity cycling for 52 weeks and the moisture distribution and moisture-induced strains were measured continuously. Coupled moisture-displacement numerical models, incorporating the experimentally measured material parameters were developed. The effect of the glue-line was found to have an insignificant effect on moisture transport, however, the material orientation greatly influenced the predicted moisture-induced strain. Accurately mapping the material orientation produced significantly better predictions of the experimental results over the 52-week period. Keywords: Adsorption, desorption, finite element analysis, glued laminated timber, long-term moisture, long-term moisture transport, moisture diffusio