Behaviour and design resistance of long bolts in tension

Long bolts, also known as bi-directional bolts, have multiple applications in structural engineering, particularly as an instrumental part of the adaptability and reusability of steel members. Despite that, the long bolt design is not properly covered by current standards. This paper describes an experimental and analytical study to characterize the long bolts in tension for their inclusion in the component method precluded by Eurocode 3. The study is part of a wider campaign (including the behaviour in shear, preloading, and relaxation of the bolts) developed in the framework of the European Research Project CONNECT4C. The study shows that the current design expressions for bolt resistance and stiffness can be used for long bolts in tension, regardless of bolt material or finishing surface. A bolt material model is proposed for possible inclusion in steel design standards. Finally, it is also recommended to adopt double nuts in long bolts to avoid premature thread stripping. • Experimental and analytical investigation of long bolts under tensile forces to support their inclusion in EN 1993–1-8. • Evaluation of tensile resistance and stiffness of long bolts. • Development of a bolt material model for 8.8 and 10.9 class bolts. • Reliability analysis performed following Annex D of EN 1990 to assess the γ M2 safety factor.