Tensile and Bending Strength of Birch and Beech Lamellas Finger Jointed with Conventional and Newly Developed Finger-Joint Profiles

In this study, the tensile and bending strength of birch and beech lamellas finger jointed with conventional (<i>Standard</i>) and newly developed finger-joint profiles (<i>New</i>) are presented. Polyurethane (PUR), Melamine-Urea-Formaldehyde (MUF) and Phenol-Resorcinol-Formaldehyde (PRF) adhesive systems were used to bond the finger joints. The objective of the <i>New</i> profiles was to reduce the stress concentrations within the finger joint by cutting the cross-grooved fingers perpendicular to the main orientation of the finger-joint profile. In the first trials of the development, larger cross-grooved fingers were cut with the aim to improve the stress distribution and to reinforce the finger joint by filling gaps in the finger joint with adhesive. As the study progressed, initial optimisations of the <i>New</i> profile were made. Smaller cross-grooved fingers were cut as it was assumed that they are beneficial for the manufacturing and integrity of the <i>New</i> profile. In combination with the MUF adhesive system, the <i>New</i> profile achieved the highest increase in the bending and tensile strengths compared to the <i>Standard</i> profile. In addition to the increased strength, other advantages such as reduced cracking in the finger joint were observed when using the <i>New</i> profile. The high strength and stiffness of hardwoods or other high-performance materials used in timber construction can probably be better exploited in combination with the <i>New</i> profile. Further tests will be carried out by considering different configurations of the <i>New</i> profile and different materials.