Graduate Research

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Browsing Graduate Research by Subject "Forest Engineering"

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    Effect of butt joints on flexural properties of nail laminated timber
    (University of New Brunswick, 2019) Ma, Tianying; Gong, Meng
    Nail laminated timber (NLT) is manufactured using dimension lumber laminations, stacked on edges, and fastened with nails, to create large flat structural components that are widely used for constructing timber bridge decks in North America. Butt joints usually exist due to the length limits of lumber, leading to concerns about the decrease of structural performance of NLT. This project was undergone to understand the impact of butt joints on flexural properties of NLT and investigate the methods for reinforcing the NLT containing butt joints. To reach this goal, four-point bending tests were performed on 7 types of 3-layer NLT specimens, 1 without butt joints as reference, 3 with butt joints and 3 with butt joints reinforced with nails. It was found that the effective stiffness (𝐸𝐼𝑒𝑓𝑓) and load capacity (𝑃𝑝𝑒𝑎𝑘) of 3-layer NLT specimens with butt joints, in comparison to those without butt joints, could be reduced up to 64% and 71%, respectively. The reduction in 𝐸𝐼𝑒𝑓𝑓 of NLT specimens with a certain 1-in-3 frequency pattern of butt joints was found to be 34%, which proved the applicability of the stiffness reduction factor in current CSA S6 standards. It was found that the nailing reinforcement was an effective approach to recover the 𝐸𝐼𝑒𝑓𝑓 and 𝑃𝑝𝑒𝑎𝑘 of NLT specimens with a certain 1-in-3 frequency pattern of butt joints by 21% and 38%, respectively. This approach could be used to make NLT with butt joints, but more research is required. Keywords: Effective stiffness, Load capacity, Nail laminated timber, Nailing reinforcement
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    Effect of elevated temperature on the bond strength of wood block shear specimens
    (University of New Brunswick, 2022-09) Qi, Jianan; Gong, Meng
    This report examined the effect of elevated temperature on the shear strength of wood block shear specimens bonded using two types of adhesives. The adhesives used were phenol formaldehyde (PF) and polyurethane (PUR). Each type had two recipes, SPF and CPF for surface and core layers of oriented strand boards, and 1-component (1-PUR) and 2- component (2-PUR) for PUR. The species of wood used was sugar maple (Acer saccharinum) of an average air-dry density of 0.739g/cm3. Four groups of block shear specimens were made, and four temperature levels were employed, 20°C, 80°C, 150°C, and 200°C. Each group had 11 replicates, generating a total of 176 specimens tested. It was found that (1) The shear strength of all PF specimens linearly decreased as the temperature increased from 20°C to 200°C, with CPF decreasing by 51.4%, and SPF decreasing by 65.9%. There was also a decline in the shear strength of PURs specimens in a non-linear way as the temperature increased from 20°C to 200°C. The most significant decrease in shear strength was observed to be 89.6% and 53.7% for 1-PUR and for 2-PUR, respectively. (2) In the block shear tests, the highest peak loads differed among groups with 13,879 N for 1-PUR, 29,588 N for 2-PUR, 30,011 N for CPF, and 27,103 N for SPF. (3) In 200°C, 1-PUR and 2-PUR had higher coefficients of variation of more than 50%, 58% and 53% for 1-PUR and 2-PUR, respectively. At 200°C, the stability of PF adhesive was higher than that of PUR. 2-PUR performed much better than 1-PUR at all levels of temperature used. (4) CPF and SPF did not show remarkable difference in bond strength, which was because the Tg of PF was about 200°C, being higher than that used in this study. (5) The shear strength of groups 1-PUR and 2-PUR did not have a significant difference when the temperature being 150°C and over since PUR had a Tg of around 80°C. (6) In the block shear test, the percentages of wood failure at maximum load were 58.72%, 35.70%, and 47.92% for groups 2-PUR, CPF and SPF, respectively. The group SPF recorded the highest wood failure percentage of 61.40% at 80°C. (7) The percentages of wood failure of group 2-PUR were 58.72%, 53.26%, 37.54%, and 25.58% at the temperatures of 20°C, 80°C, 150°C, and to 200°C, respectively. The percentage of wood failure decreased as the temperature increased. It could be recommended to conduct the tests at a temperature of higher than 200°C for PF-bonded specimens and a temperature of 100°C, 120°C, and 180°C for PUR-bonded specimens with an aim to gather more first-hand information about how the elevated temperature impacts the block shear strength. Key words: adhesive, elevated temperature, block shear test, shear strength, percentage wood failure
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    Mechanical performance of timber connection made by wood welding technique
    (University of New Brunswick, 2022-08) Wang, Xiaoyu; Gong, Meng
    A new type of timber connection is developed using the wood friction welding technique, which is a non-adhesive gluing process. During this process, heat is needed to melt the wood material in the course of pressing one wood piece to another via linear vibration or rotation. The objective of this study was to investigate the mechanical performance of timber connections made via the rotation welding. The spruce-pine-fir (S-P-F) lumber was used to fabricate the members, and the sugar maple (Acer saccharum) was used to make the dowels with a diameter of 19mm (3/4"). The bolts were used to make the timber connections as well as for comparison purpose. Two loading directions (parallel (PA) and perpendicular (PE)) and three connection types (push-in dowel (P), welding dowel (W), and bolted (B)), were considered in the design of experiment. There were two (2) groups of three (3) sets each. Each set had six (6) replicates, making a total of 36 specimens. Each joint specimen was performed on a universal mechanical testing machine. It was found that (1) The peak load and initial stiffness of set PA-B were 33kN and 5kN/mm, which were about 135% larger than and 45% less than set PA-W. The peak load and initial stiffness of set PA-P were 14% and 50% larger than that of set PA-W. (2) The yield loads for sets PA-P and PA-W were almost the same, being 13kN, which were about 150% lower than that of set PA-B. (3) The ductility and energy accumulated of set PA-B were about 30% less than and 140% larger than set PA-W. (4) The average peak load and initial stiffness of group PA were about 25% and 27% greater than those of group PE.(5) Johansen Theory was found to be conservative in derivation of engineering design values of wood dowelled and metal bolted joints. (6) The failure of wood doweled joint specimens was the fracture of the dowels, and the failure of bolted joint specimens was the crushing of member wood. (7) The mechanical properties of welded joints were similar to those of push-in joints. (8) The welding process did not generate cracks, minimizing stress concentrations, in wood members, in comparison to push-in process. It has great potential in fabrication of dowel-laminated wood products and repair/reinforcement of laminated beams. As for the future work, application of welding techniques should be explored during the manufacturing and construction of timber products and buildings, such as reinforcing glued laminated wood with notches. Key words: wood welding, timber joints, peak load, initial stiffness, yield load, ductility, energy dissipation, European Yield Model.