Model for predicting the axial strength of joints made with glued-in rods in sawn timber

Joints made with glued-in rods in sawn timber have been used for over 40 years in timber engineering, both for joint design in new constructions as well as in the repair of wood elements damaged by humidity or xylophage attack. One of the problems limiting the use of these types of joints is the absence of legislation regulating their sizing and design. Although EuroCode has given some proposals for estimating the load capacity of these joints, in practice, destructive testing must be performed for each specific case. Recent studies have offered design criteria and sizing restrictions, in most cases, for elements of glued laminated timber. Our research group has been studying the behavior of these joints in sawn timber for several years. The objective of this research is to determine the influence that different joint materials and geometric parameters have on their axial strength. A broad experimental study was performed on joints made with threaded steel rods glued with different types of adhesives and in different hardwood species. Over 400 specimens were tested with different geometric configurations, varying anchorage length, rod diameter and adhesive thickness. This paper presents a summary of the results obtained in the experimental analysis and proposes a model for predicting joint strength in sawn timber. Similarly, a comparative study of our design proposal is presented with the most recent equations for glued laminated timber connections.