Adhesive multi-bulbs: A novel anchoring system using threaded steel rods glued into wood

Joints created from threaded steel rods glued into wood using epoxy could provide an interesting advantage for the construction of wooden structures. This article presents a novel anchoring system developed to increase the load capacity of a joint. This innovation utilises multiple widenings or bulbs along the length of the bore, which are filled with epoxy adhesives. These widenings increase the resistant surface of the wood against shear stress, which translates into a significant increase in the ultimate load value. This improved load capacity allows the use of high performance steels, maintaining a ductile failure mode in the joint. This article details the drill bit design for implementing the multi-bulbs and presents the results of experiments comparing the load values of the new system with those obtained using a straight anchor.