Bond Analysis of Timber Structures Strengthened with FRP Systems

Abstract: This study focuses on the adhesion analysis of glued joints between Norway Spruce and Carbon fibre reinforced polymer (CFRP) regarding timber reinforcement. An experimental programme was carried out on two different test series to evaluate the behaviour of timber‐CFRP bonded joints. ‘Pull‐Off’ tests were achieved to evaluate the strength of the adhesion connection between materials. Two strengthening techniques [externally bonded reinforcement (EBR), near‐surface mounted (NSM)] and several composite systems (laminate, sheets and textile) were analysed. Through ‘Four Point Bending’ tests, the adhesion behaviour of timber‐CFRP joints along the fibres direction was evaluated. Three trials were performed on models strengthened with different criteria (one EBR and two NSM series), each with three different bonding lengths. The maximum anchor strength of the composite, the effective bonding length between the materials, the medium shear strength developed along the interface and the maximum composite strain for the EBR and NSM reinforcements were obtained. The experimental results were compared with equivalent values from concrete‐CFRP joints found in literature. Furthermore, the theoretical model proposed in Fib Bulletin 14 was calibrated to predict the maximum anchor strength of the composite according to its bonding length. Finally, some recommendations are proposed for the design of timber structures reinforced with CFRP systems.