Investigation On Concrete Filled Steel Tubes Columns with Collapse Performance with Varying End Conditions

Abstract

This research examines the collapse behavior of Concrete-Filled Steel Tube (CFST) columns with different end conditions using a nonlinear finite element method. Circular CFST samples with a diameter of 100 mm, a wall thickness of 4 mm and a length of 1250 mm, made with Mild Steel (fy = 250 MPa) and M30 grade concrete, were used. Four boundary conditions (Fixed–Free, pinned–Pinned, fixed Pinned and Fixed–Fixed) were analyzed under axial compression to study deformation behavior, strain distribution, stress concentration, and failure mechanism. ANSYS Workbench 2023 R2 was used to develop a model with the capability to simulate the nonlinearity of the material, the effect of confinement, geometry, localized buckling, and the behavior of CFST columns. The Fixed–Free condition showed the largest total deformation (3.554 mm) and the greatest von Mises stress (1145 MPa), which indicates a unstable condition at the restrained end, beyond the yield strength of steel. Increasing end condition restraint reduced total deformation, strain, and directed stress, resulting in the Fixed–Fixed boundary condition having the greatest collapse resisting capacity. From the results, it can be concluded that the boundary conditions of CFST columns have a strong influence on the structural stability and collapse. Also, current Indian Standard codes don’t have any provision for the design of CFST columns and thus stress the need for modeling end conditions in designing performance-based composite columns.