The effect of joint slope on bending strength of finger joint connection – case of poplar wood (Populus alba L.)

Abstract

Glued-laminated timber (glulam) is usually manufactured to order for architectural applications. It consists of two or more layers of lumber, called laminations, glued together, and can be produced as long as can be transported, due to finger joint connections, which are decisive elements of its strength. In this research, the effect of slope of the joint on bending strength of poplar (Populus alba L.) finger joint connection, bonded with polyvinyl adhesive, was studied. Modulus of rupture (MOR) and Modulus of elasticity (MOE) of joint perpendicular with strips edges, and 15° and 30° slope joints, referring to the first one direction, were measured, according to norms ISO 3133 and 3349. 24 samples for each type of joints, with dimensions 20x20x320 mm, were conditioned and tested by means of mechanical testing machine, in the Faculty of Forestry Sciences of Tirana. The MOR of perpendicular and 15° slope joints resulted almost the same, 36.75 N/mm2, while of 30° slope joint resulted 10% higher, 40.33 N/mm2. Modulus of elasticity wasn’t affected in a distinct manner by the slope angle of connection. For perpendicular joint it was 10152.12 N/mm2, while for 15° and 30° slope joints resulted 9944.91 and 10155.98 respectively. The research results obtained were discussed in order to analyze and evaluate the slope angle of finger jointing, which could affect its utilization potentials.