Characterisation of the Long Bolts in Tension

Abstract The RFCS CONNECT4C European Research Project aims to enhance the adaptability and reusability of steel structures through the development of innovative joint configurations, in which long bolts play a critical role in load transfer mechanisms. Despite their growing use, long bolts lack thorough research and standardised design rules. This study presents an extensive experimental and analytical investigation into the tensile behaviour of long bolts to characterise their performance and validate existing design methodologies. A total of 66 tensile tests were conducted, examining the influence of key parameters, including four bolt diameters (M20, M24, M27, and M30), two bolt grades (8.8 and 10.9), surface finishes (black and galvanised), and configurations with single or double nuts. Experimental results are compared with the tensile resistance and stiffness predictions given in EN 1993‐1‐8, demonstrating that current design equations are applicable to long bolts. A material model for long bolts is proposed with constant values for strain hardening and ultimate strains according to the bolt grade. Finally, a reliability analysis conducted in accordance with Annex D of EN 1990 confirms the adequacy and safety of the existing formulations for use in design under tensile loading.