Abstract
The Improved Bolt-Column (IBC) joint is a kind of novel semi-rigid connections in spatial structures. By modifying the cone section of the bolt-column joint, the bending capacity of the joint is enhanced. However, in-depth research on its mechanical behavior under the combined action of bending moment and axial force remains limited. This study first investigates the failure modes and mechanical properties of IBC joints under eccentric loading. Moment-rotation curves and axial load-axial displacement curves under different plate thicknesses and eccentricities are obtained, and the stress distribution of the joints is analyzed using ABAQUS package. The results indicate that increases in both plate thickness and eccentricity result in greater initial stiffness and ultimate moment capacity of the joints. The critical eccentricity is identified as e = 200 mm; beyond this value, the mechanical behavior of the joints under eccentric loading becomes similar to that under pure bending. Furthermore, as the plate thickness increases, the failure mode gradually shifts from yielding of the conical section to yielding and fracture of the bolts. By analyzing the ultimate moments of four groups of joints with different plate thicknesses under eccentricities ranging from 10 to 200 mm, a predictive formula between eccentricity and ultimate moment is established. When the joints are subjected to combined axial force and bending moment, an increase in axial tension significantly reduces both the initial bending stiffness and the ultimate moment capacity. In contrast, an increase in axial compression also leads to a decrease in the ultimate moment capacity; however, the initial bending stiffness first decreases and then increases. A parametric analysis is conducted on the bending capacity of the joints under different magnitudes of axial force, and a formula is developed to quantify the influence of axial force on the bending capacity.
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