Influence of timber density on the axial strength of joints made with glued-in steel rods: An experimental approach

Abstract Joints made with glued-in steel rods have many possibilities in the design of timber structures. They can be used for new buildings or for the rehabilitation of old structural elements damaged by the attack of biotic agents or humidity. Since the 1970s many studies have been carried out to characterize the strength of these joints when made with glued laminated timber (glulam). These studies hypothesize that the axial strength of joints made in glulam depends on some geometric parameters (anchorage length, steel rod diameter, adhesive thickness, etc.) as well as on timber density. For several years our research group has been studying the behavior of these joints when made in sawn timber, determining the influence of different geometric and material parameters on the axial strength of the glued-in steel rods. This work summarizes the experimental results of joints made in pieces of sawn timber of two species having different densities and mechanical properties. The experimental study was carried out for different geometric configurations: threaded steel rods of 10 and 12 mm diameter, epoxy adhesive of 1 mm thickness, and five anchorage lengths. The aim was to test the same specimen conditions for each timber species studied, tali and chestnut. The experimental results show that the axial strength of the joints does not increase linearly with timber density. This result contradicts many of the traditional design proposals suggested for joints made in glulam.