The German technical approval (Z-14.4-591) for Huck Bobtail lockbolts covering diameters M12-M36 has been extended by Germanys highest building authority DIBt (Deutsches Institut für Bautechnik) for a further five years.
The approval gives Bobtail lockbolts the verification of ‘static load-bearing capacity and fatigue strength’ in the context of Eurocode 3 for applications in construction. The extension of the approval means Bobtail lockbolts can be used in areas regulated by the building authorities as a replacement for non-preloaded structural bolting assemblies (acc. to EN 15048) or high-strength structural bolting assemblies for preloading (acc. to EN 14399). The values published can also be used in many other applications, including rail, commercial vehicles, lattice towers or wind turbines.
The updated rules for design and execution enable structural engineers to take further advantage of lockbolt technology in steel construction: the update contains some important changes for the fatigue verifications, enabling the higher fatigue strength to be applied regardless of the diameter of the fastener.
In addition to the load-bearing capacities, which are superior to that of a threaded bolt, BobTail offers other advantages, such as the low scatter when applying the preload force, the non-detachable connection, vibration resistance and high fatigue strength. Bobtail lockbolts are also characterized by the fact that they are mechanically maintenance-free (no re-tightening required) and are easy, quick and quiet to install.
Fatigue strength studies on the Bobtail lockbolts go back more than 10 years and continue to be carried out in the test laboratories of recognized Fraunhofer-Institute IGP, Rostock and University of Applied Sciences, Wismar, Germany.
