Assessing the deformation energy of timber-to-timber inclined screw connections via computed tomography scan

Abstract

Inclined screws represent a typical connection solution for timber structures. They can provide higher capacity and stiffness due to the combined axial-shear interaction. This paper investigates the effect of engineering wood products choice (glued-laminated timber and cross-laminated timber), fibre inclination, friction, and interlayers on the capacity and deformation energy of timber-to-timber screwed connection with inclined screws. First, the authors carried out thirty push-out tests with inclined screws considering six structural configurations. Then, through X-ray computed tomography (CT) and threshold-based image segmentation, they assessed the deformed configuration of the screws to isolate the screw and timber contributions to the total deformation energy. The deformed shape of the connectors, fitted by a six-order polynomial, provides an estimate of the connection bending deformation assuming an elasto-plastic stress–strain constitutive for steel. By subtraction, the authors separately evaluated the role of timber embedment and steel deformation in the overall energy deformation in all the tested configurations. The experimental results revealed that most deformation energy comes from the screwed connection without interlayer, while the remaining can be attributed to timber plasticization. Conversely, the presence of the interlayer significantly unbalances such contribution, considerably reducing the role of timber plasticization.