Document Type : Research Paper
Authors
1 Department of Biosystems, Faculty of New Technologies and Aerospace Engineering, Zirab campus, Shahid Beheshti University, Tehran, Iran.
2 Department of Biosystems, Faculty of New Technologies and Aerospace Engineering, Zirab campus, Shahid Beheshti University, Tehran, Iran
Abstract
Background and Objectives: Corner joints are among the most critical components of wooden structures and products, playing a decisive role in load transfer, structural stability, and durability. The mechanical performance of these joints is influenced by several factors, including joint type, board thickness, wood species, and bonding quality. An inappropriate selection of joint type or board thickness may result in stress concentration, reduced strength, excessive deformation, and premature structural failure. Despite the widespread use of traditional and engineered wood joints in the wood and furniture industries, comprehensive experimental information regarding the combined effects of joint type and board thickness on the shear strength of corner joints, particularly in fir wood, is limited. Therefore, the present study aimed to investigate the effects of joint type and board thickness on the shear strength of fir wood corner joints in order to identify the most suitable combination in terms of mechanical performance and provide guidance for improving the design and safety of wooden structures.
Materials and Methods: Fir wood was used as the raw material in this study. Five joint types, namely butt joint, mortise-and-tenon joint, dowel joint, half-lap joint, and dovetail joint, were evaluated. Wooden boards were prepared at six thickness levels (1.0, 1.5, 2.0, 2.5, 3.0, and 4.0 cm), and the required joints were fabricated from these boards. Three replicates were considered for each combination of joint type and thickness. A total of 90 specimens were prepared using polyvinyl acetate (PVAc) adhesive. After the adhesive curing period, the specimens were subjected to shear testing, and the failure load of each specimen was recorded as the shear strength indicator. The experimental data were analyzed using SPSS software through two-way analysis of variance (ANOVA) to evaluate the individual effects of joint type and board thickness, as well as their interaction on the shear strength of the corner joints. Statistical significance was ascertained at P < 0.05.
Results: The statistical analysis indicated that the developed model exhibited a satisfactory fit and that the investigated variables accounted for a substantial proportion of the variation in shear strength. The effects of board thickness, joint type, and their interaction on the shear strength of the corner joints were all statistically significant (P < 0.05). The results demonstrated that the butt, mortise-and-tenon, dowel, half-lap, and dovetail joints exhibited significantly different mechanical behaviors and shear strength values. Furthermore, increasing board thickness generally enhanced the shear strength of the joints; however, the magnitude of this improvement varied depending on the joint type. These findings indicate that joint type and board thickness jointly determine the load-bearing capacity and ultimate shear strength of wooden corner joints and should not be considered independently in joint design.
Conclusion: The results demonstrated that the shear strength of fir wood corner joints was significantly affected by joint type, board thickness, and the interaction between these two factors. Significant differences in mechanical performance were observed among the butt, mortise-and-tenon, dowel, half-lap, and dovetail joints. Increasing board thickness generally improved the shear strength of the joints, although the extent of improvement depended on the joint configuration. Therefore, the selection of an appropriate joint type should always be made in accordance with the board thickness to maximize load-bearing capacity, structural strength, and durability. The findings of this study provide useful guidance for the selection and design of wood joints in the wood products, furniture, and timber construction industries and may contribute to the optimization of their mechanical performance.
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