The investigation of the affecting factors on withdrawal resistance of the wooden biscuit joints

The aim of this study is to investigate withdrawal resistance of T-shaped joints made of wooden biscuits. Biscuit joints which also called plate joints are usually constructed from compressed solid beech wood. Biscuits in the joints take up the moisture from water-based glues and resulted swelling at the slot leads to appropriate and strong joint. The variables of this study were the species of joint members including beech (Fagus orientalis) and fir (Abies alba), biscuit size of 10 and 20 (1 biscuits per joint) and type of glue including Polyvinyl acetate (PVAc), Polyurethane (PU) and Urea formaldehyde (UF). After constructing the specimens, withdrawal resistance test of biscuits was carried out. The results showed that the effects of independent variables namely, the species of joint members and the type of glue on the withdrawal resistance of biscuit joints was significant in the 1% level, but the independent effect of biscuit size was not significant. Also the results showed that the withdrawal resistance of the joints made with beech species was higher than fir. The polyurethane adhesive exhibited the best performance in comparison with the other adhesives. Finally, the best performance of the joints made with biscuit (beech, biscuit size 10 and polyurethane glue) was compared with the wooden dowel joints, which former showed the higher withdrawal resistance.