Stiffness of Prosthetic Repairs for Historic Timber Beams

Glued connections are often used as reinforcements or repairs of decayed parts in historic timber frames. Those timber frames are most of the time statically indeterminate structures, meaning that the ratios of stiffness between different members and joints of the structure are related to distribution of stresses within the structure. Hence, a poor repair, i.e. a too stiff or at the contrary a too flexible intervention may change dangerously the distribution of stresses within the structure, induce cracks and damage the whole structure. However, there are still no guidelines on how to evaluate the stiffness of glued connections and therefore, on how to predict the impact of these interventions on the force distribution in the timber frame. This paper focuses on glued-in rods, and uses finite element models to predict and compare the stiffness of glued-in rods in different configurations of repairing connections. This study shows sensitively different axial stiffness between those configurations: they may indeed vary in the ratio of one to two for the same strength. This highlights the importance of predicting the stiffness of glued-in rod connections to be able to make recommendations for the configuration which best respects the original structure.