INFLUENCE OF KNOTS ON STRAIN DISTRIBUTIONS IN GLUED LAMINATED TIMBER BEAMS

Glued laminated timber (GLT) beams are engineered wood products made by gluing finger-jointed timber boards to create structural elements for various construction applications. The mechanical properties of GLT beams depend significantly on the mechanical properties of the timber boards and local defects, such as knots. This paper examines the influence of knots on the mechanical behavior, particularly strain distributions of GLT beams. In total 22 GLT beams, each five meters long, were tested in four-point bending. Strain distributions were measured in the constant bending moment region of the beams using a digital image correlation method. The effects of growth irregularities, finger joints, and particularly knots, as well as their interaction within bonded lamellae, on the longitudinal and transversal strain distributions, were investigated. The results show that knots induce significant strain concentration in longitudinal and transversal defects on the mechanical behavior of large-scale GLT beams.