Effect of Geometric Parameters on the Behavior of Concrete-Filled Steel Tubular Frames

Concrete-filled steel tubular (CFST) technology offers numerous structural benefits, including outstanding strength, fire resistance, and a considerable capacity for energy absorption. It has become crucial to investigate the ductility and stiffness of this type of structural system to gain an understanding of its capability to withstand external loads and prevent unexpected failure. This study provides insights into optimizing the design of CFST frames by offering a deeper understanding of how frame geometry affects their behavior. A finite element (FE) model was developed using specimen data from a previous study to analyze the behavior of the composite frame. The results of the FEA model were verified with the experimental data. An extensive analysis of the stress concentration in the CFST column, especially in the connecting portions, was conducted. Parametric studies were conducted to evaluate the impact of the axial load level, column length (L), and steel tube thickness (t) on the lateral stiffness and ductility behavior of CFST frames. For all frame models, no buckling occurred, and the failure mode was noticed after the formation of plastic hinges at the beam-column and base plate-column connections. The findings demonstrated that the lateral ductility of the CFST column improved with increasing L/D and D/t up to L/D equal to 15.53, at which point the development of lateral ductility was only slightly impacted by further increasing D/t. For all L/D ratios, the increase in skin thickness of the column tubes improved the stiffness of the frame; however, this improvement generally decreased noticeably as the L/D ratios increased. Increasing the length of the column with a small steel tube thickness (less than 2.67mm) insignificantly impacted the frame's ductility. On the other hand, increasing the column's length negatively impacted the frame's hardness in the case of a small steel tube thickness, i.e., less than 2.67mm.