Adhesively bonded joints between spruce glulam and birch plywood for structural applications: experimental studies by using different adhesives and pressing methods

Due to the increasing interest in reducing the usage of metals in the construction sector, birch plywood has shown good potential in structural engineering and timber connections as a substitute for the more conventional slotted-in metal plate solutions. However, a proper way of bonding birch plywood with other timber parts that results in adequate connection strength has not been fully investigated. In this paper, experimental studies were carried out to investigate the proper workflow when manufacturing bonded connections made of birch plywood and spruce glulam beams. Tensile shear mechanical tests were then conducted on produced bonded joints to evaluate the bond strength. Three adhesives, i.e. melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and two-component polyurethane (2C PUR) were evaluated in dry and moist conditions. The influence of three pressing methods, i.e. (a) screw-gluing, (b) clamping by means of clamps, and (c) clamping by application of weight loads, on the bonding strength was investigated. The bonding strength was thereafter compared with the shear strength of spruce glulam and the wood failure percentage was also examined in this study.