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

Abstract

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.

Further development of detail categories for bolt‐assemblies subjected to normal stress in steel constructions

“…A total of 411 fatigue tests are considered for which the forming (bolt threads rolled before or after heat treatment) and the surface condition (uncoated black, zinc flake, hot-dip galvanized) of all test specimens as well as the test conditions (including mean stress level) were available to the authors. This includes experimental data generated in [23][24][25][26][27][28]. In addition, five unpublished test series on HV bolts of nominal sizes M12 (hdg-HT and uncoated black), M20 (hdg-HT), M36 (hdg-NT) and M48 (hdg-NT) are presented.…”

Zur Ermüdungsfestigkeit großer Schrauben im Stahlbau unter Berücksichtigung von Herstell‐ und Randschichteinflüssen – Teil 2: Versuchsergebnisse und Bewertung

“…schlussgerollt) und der Oberflächenzustand (schwarz, Zink‐Lamelle, Feuerverzinkung) aller Prüflinge sowie die Versuchsbedingungen (Mittelspannungsniveau) für die Verfasser nachvollziehbar waren. Hierin sind zum Teil Versuchsdaten enthalten, die in früheren Arbeiten am Institut für Stahlbau der Universität Hannover [19, 20] und dem Fraunhofer‐Institut für Großstrukturen in der Produktionstechnik IGP (Fh‐IGP) [21–23] entstanden. Zusätzlich werden noch fünf unveröffentlichte Versuchsreihen an HV‐Schrauben der Nenngrößen M12 (tZn‐HT, vergütungsschwarz), M20 (tZn‐HT), M36 (tZn‐NT) und M48 (tZn‐NT) vorgestellt.…”

Experimental and numerical study on mechanical behavior of high-strength lockbolted friction grip connections

“…To date, no consensus has been reached regarding the design criterion of HSLFG joints, which hinders the application of HSLFG joints in steel bridges (Glienke et al, 2020a(Glienke et al, , 2020b. In general, the lockbolted joint can be designed as either slip-resistant or bearing-type, depending on different load-bearing patterns.…”

“…The results indicated that the pretension of lockbolt provided very limited friction force between aluminum alloy plates. Although the lockbolted connections, normally used for aluminum alloy plates, can be designed as bearing-type, some applications call for lockbolt use in slip-resistant connections, such as lattice towers for wind turbines in Germany (Glienke et al, 2020a(Glienke et al, , 2020b. Ebert et al (2017) experimentally compared the slip-resistant connections of both the high-strength bolts and bobtail lockbolts, which indicated that the tightening procedure for lockbolts is different from the high-strength bolts which adopt torque method.…”