Structural performance assessment and repair of carpentry joints

Abstract

Joints in traditional timber structures usually present notches where stresses are transferred by compression and, to some extent, by friction between the contact surfaces. There are many structures still in service today which employ a wide range of traditional notched joints with and without different metal parts, some introduced during construction and others added later as reinforcement, which can be reduced to a few common typologies. These traditional timber connections, even without any strengthening device, usually exhibit some moment-resisting capability, but common design methods are mainly focused in the transmission of compression internal forces and do not account for the presence of metal parts. Thus the common employment of steel stirrups, internal bolts or clamping devices in traditional connections can have unexpected consequences in the global performance of timber a structure, because while enhancing the joints’ strength they also modify their stiffness, failure mode and overall behaviour. As the assessment of ancient timber structures implies the evaluation of the mechanical properties of elements and joints, and since other research projects are narrowing the uncertainties around the determination of the members’ properties, the real behaviour of traditional timber joints has also to be addressed. The proposed presentation will discuss the relevant conclusions achieved in a research program, aimed at investigating the monotonic and cyclic behaviour of traditional timber joints, regarding their structural assessment, by identifying the effect of some key parameters, like geometry, detailing, damage and timber moisture content, and evaluating the effect of some strengthening techniques. These results allow understanding and predicting more accurately the behaviour of timber structures, which is crucial in every restoration or strengthening intervention.