Stop-Splayed Scarf-Joint Reinforcement with Timber Pegs Behaviour

Abstract

Restoring ancient timber structures often involves cutting or reinforcing stop-splayed scarf-joints in beams or truss-rods. Steel nails, bolts and plates or adhesive resins and rods are commonly used, however these jointing technologies cause some disadvantages, such as moisture between steel and timber surfaces, hard reversibility of the intervention and a questionable aesthetic output in uncovered structures. The employment of timber pegs, inserted perpendicular to the grain, could be an efficient solution and is already preferred in some applications. Since no design rules for traditional timber joints or for timber pegged connections are given by European codes, investigations on scarf joint behaviour before and after reinforcement are needed aiming to reliable design procedures. In this study, the role of the fastener inside this tension resisting carpentry joint and its contribution in yield strength and stiffness have been investigated. Specific attention has been addressed to stiffness, which is positively influenced by the insertion of timber pegs. Three samples of fir scarf-joints have been tested, a total of eight specimens, with different configurations: without fasteners, with timber pegs and with steel pins. The different failure modes under tension load of the samples and their rheological behaviour have been studied and compared to trace force distribution between the resisting elements, that is the ash key and the added fasteners.