The role of sapwood plasticity in the delamination phenomenon of repaired timber beams

For the repair of ancient wooden floors, the employment of steel plates glued by epoxy-adhesive into longitudinal grooves is a non-invasive technique which appears appropriate for the restoration of precious wooden beams. This technique requires particular attention to the delamination of the glued reinforcement due to the shear and normal stress concentration which occurs at the end of the repairing element. The peeling phenomenon is governed by the peak stress that depends on the capability of the sapwood to develop plastic strain. The aim of the present study is to evaluate the shear behaviour of the wood by means of a specific test focused on the plastic local resource of sapwood. Three small sapwood specimens were tested, providing an accurate shear-stress strain constitutive law which showed a significant plastic deformation. The experimental results were also adopted for nonlinear finite element analysis showing the importance of this plasticity on the delamination collapse of a repaired timber beam.