Joints with lockbolts in steel structures - Part 2: Design and execution

Many mechanical joints in steel structures use conventional bolts. Nevertheless, this proven joining technology has some significant disadvantages. These basically include the high levels of scatter during application of the assembly preload using the torque-controlled tightening process, the risk of loosening during cyclic loads due to transverse displacement of the components and the low fatigue resistance under axial loading. Lockbolt technology was invented as long ago as the 1930s and mainly used for the aviation and space industry because of its evident advantages. This joining technology has been constantly further developed in response to the most diverse demands from sectors such as aviation, commercial vehicles, rail vehicles, agricultural machinery, defence technology and steel structures. The application of lockbolt technology, which is primarily used in mechanical engineering, was in most cases based on individual studies, since no consistent rules and guidelines were available for the design and execution of lockbolt connections in steel structures. Within the scope of several public research projects funded by the AiF (German Federation of Industrial Research Associations) and conducted by the iGF (Industrial Collective Research) organization as well as through approval investigations, the Fraunhofer Institute for Large Structures in Production Engineering (IGP) has successively developed the necessary design rules according to the EN 1993 standard (Eurocode 3) for use in structural connections. These design rules will be presented within the context of this article in order to make the benefits of this joining technology available to other users. In addition, insights into the use of technical approvals will be presented together with some current applications.