Abstract
This study investigated the effects of threaded bolt fasteners on the initial and final stiffness of bolted joints in special steel modular construction. A comprehensive set of 246 specimens, including 4, 7.6, and 12 mm thick plates with 20 and 30 mm diameter bolts and different end spacings, were tested. The results revealed that connections with threaded bolts exhibited lower initial stiffness compared to pure shaft connections. This study introduced a novel formula that significantly improved simulation results for bolted joints, surpassing previous modeling approaches. Following the American Society for Testing and Materials (ASTM) definition, the "elastic" stiffness values obtained from the laboratory tests were compared with those of Eurocode provisions. Additionally, ad hoc formulas were proposed for the stiffness of shank, lap connection with partially threaded, and fully threaded bolts. These results offer valuable insights for enhancing the stiffness of bolted shear connections.