PSI - Issue 70

Siddharth Deswal et al. / Procedia Structural Integrity 70 (2025) 350–357

352

3. Research Methodology The research employs a numerical simulation approach using FEA to evaluate and predict the mechanical performance of CFST columns under axial, uniaxial, and biaxial loading conditions. Two column configurations short (330 mm in length) and long (1850 mm in length) are analyzed to investigate the effect of column slenderness on performance. Both columns have identical cross-sectional dimensions, providing a controlled comparison of their behavior under various loading conditions. For this study, ABAQUS/CAE 6.14 was selected as the simulation platform due to its advanced capabilities in modeling nonlinear structural behaviors, complex contact interactions, and material models. The software is particularly suited for dynamic explicit analyses, which are necessary for simulating material and geometric nonlinearities under loading conditions. ABAQUS allows for accurate modeling of the interaction between the concrete core and steel tube in CFST columns, which is critical for understanding their combined response to external loads. The boundary conditions are applied to simulate realistic loading conditions. The bottom end of each column is fixed in all directions to prevent movement, while the top end is subjected to controlled displacement or velocity, depending on the loading type. For axial and bending loads, a velocity boundary of -1000 mm/s is applied in the axial direction. The simulation employs an explicit dynamic solver with a time step of 0.1 seconds, allowing for accurate representation of nonlinear material behavior and progressive failure modes. This setup ensures that the columns' response to the applied loads is captured effectively, including the critical aspects of material yielding and structural instability. The material properties for both the steel tube and the concrete core are defined as follows: For the steel tube, the density is 7.85 × 10⁻⁹ tonne/mm³, with a Young’s modulus of 200,000 MPa and Poisson’s ratio of 0.3. The yield stress is 400 MPa, and the u ltimate stress is 650 MPa at 0.18 plastic strain. For the concrete core, the density is 2.4 × 10⁻⁹ tonne/mm³, with a Young’s modulus of 25,600 MPa and Poisson’s ratio of 0.2. The concrete is modeled using the Drucker-Prager yield model, with parameters including an angle of friction of 20°, a dilation angle of 20°, a flow stress ratio of 0.8, and a flow potential eccentricity of 0.1. The yield stress for the concrete core is 28.18 MPa. These material properties were selected to accurately represent the behavior of the CFST column under different loading conditions in the analysis.

4. Results and Discussion 4.1 Short Column analysis

4.1.1 Axial Loading

Under axial loading, the stress distribution in the short column as shows in figure 1 the highest stress concentration occurring at the outermost fibers, with Von Mises stress values reaching a maximum of 135.8 MPa. The stress varies across the column's cross-section, following a linear gradient from compressive stress on one side to tensile stress on the other. The failure modes under axial loading include compression failure as shows in figure 2, which occurs due to excessive compressive stresses, tensile failure at the extreme fibers, and local buckling in thin-walled columns. The failure is triggered when the applied load exceeds the material’s yield strength. In terms of load-displacement behavior, the column exhibits linear behavior with a maximum applied load of 500 kN, resulting in a displacement of 0.22 mm. The column demonstrates high stiffness, with a calculated stiffness value of 2273 kN/mm, indicating strong resistance to deformation under the applied axial load.

4.1.2 Uniaxial Loading

Under uniaxial loading, the stress distribution as shown in figure 3 in the short column is asymmetrical, with a maximum stress of 67.92 MPa and a minimum of 0.146 MPa. One side experiences compression while the opposite side experiences tension, and the central axis remains a neutral zone with no stress. The failure modes as shown in figure 4 under uniaxial loading include cracking from tensile stresses, localized yielding, and buckling at critical sections, with extreme fibers being the most vulnerable. The load-displacement behavior reveals a maximum load of