Analysis and comparison on the mechanical behaviors of original bolt-column (OBC) joint and improved bolt-column (IBC) joint

In this study, OBC joint is improved by incorporating one web, two flanges, and two additional bolts, putting forward a novel semi-rigid joint referred to as IBC joint. Finite element models of both OBC and IBC joints are established and the former is validated based on previous research. Subsequently, a total of 84 numerical models is utilized to investigate and compare the mechanical behaviors of OBC and IBC joints, taking into account different thicknesses of side plate and flange as wll as various loading conditions. The numerical results indicate that: (I) in comparison to OBC joints, the IBC joints exhibit significant enhancements in strong axis bending performance and axial tensile performance, including average enhancement ratios of 48%, 67%, 44%, and 19% in initial strong axis bending stiffness, ultimate strong axis bending moment, initial tensile stiffness and ultimate tension, respectively; (II) compared to OBC joints, the IBC joints demonstrate reduced capacity in axial torsional resistance and axial compressive performance, with mean decline ratios of 54%, 39%, 14%, and 7% in initial torsional stiffness, ultimate torque, initial compressive stiffness and ultimate compression, respectively; (III) OBC joints have better weak axis bending performance compared to IBC joints, but this gap decreases remarkably with increasing thicknesses of side plate and flange; (IV) the initial out-of-plane shear stiffness and ultimate out-of-plane shear of the IBC joint exhibit average enhancement of approximately 20% and 10%, respectively, when compared to those of the OBC joint; (V) regarding in-plane shear performance, the initial stiffness of IBC joints exceeds that of OBC joints by an average ratio of 61%, while IBC joints with flange thickness over 10 mm demonstrate significant improvement in ultimate capacity; (VI) The mechanical performance of OBC and IBC joints shows varying degrees of improvement with an increase in the thicknesses of side plate and flange.