Experimental Study on Multiple-Bolt Tension Joints

An experimental investigation on steel-to-timber joints arranged with multiple bolts was carried out, both in the case of load parallel and perpendicular to the timber grain. The joints were made with timber side members and steel main member; high strength bolts were used for fasteners. The experimental results allowed determining the stiffness in service, the slip at failure and the reference loads (proportional limit, yielding, ultimate). A decreasing ductility of joints was observed at the increase of the number of bolts. With the above characteristic loads the bolt effectiveness of multiple joint loaded parallel to grain was evaluated and compared with that obtained from some analytical predictions found in the literature. It was evidenced that the provisions of Eurocode N.5 provide values for the bolt effectiveness quite closer to experimental results. The results of joints loaded perpendicular to the grain were compared with some analytical predictions; significant differences were noted with all analytical predictions considered.