Screws with continuous threads in timber connections

Screws, bolts and dowels loaded perpendicular to the fastener axis are all dowel-type fasteners, whose load-carrying capacity in timber-to-timber connections may be determined based on Johansen ́s yield theory (Johansen, 1949). The ultimate load of joints with dowel-type fasteners loaded perpendicular to the fastener axis is limited by the embedding strength of the timber members and the bending capacity of the fasteners. Exploiting the withdrawal capacity of long screws with continuous threads leads to increased load-carrying capacities and hence more economic connections. In order to avoid bending of screws they are not placed perpendicular to the interface between the members to be connected but arranged under an angle of about 45°. The load is then transferred by a truss-like system where the screw is loaded in tension and the contact surface between the members in compression. The paper presents a comparison between the test results of connections with inclined screws and fasteners loaded perpendicular to their axis and shows a number of opportunities for connections with inclined screws.