Liang 2009
A performance-based analysis (PBA) technique based on fiber element formulations for the nonlinear analysis and performance-based design of thin-walled concrete-filled steel tubular beam-columns with local buckling effects. Analysis was verified against experimental data from other authors. The PBA technique was also used in a parametric study of thin-walled CFT beam-columns.
Analytical Study
Geometric imperfections, residual stresses and strain hardening of steel tubes and confined concrete models are considered in the PBA technique. Initial local buckling and effective strength/width formulas are incorporated in the PBA program to account for local buckling effects. The progressive local buckling of a thin-walled steel tube filled with concrete is simulated by gradually redistributing normal stresses within the steel tube walls. Performance indices are proposed to quantify the section, axial ductility and curvature ductility performance of thin walled CFT beam-columns under axial load and biaxial bending. Efficient secant algorithms are developed to iterate the depth and orientation of the neutral axis in a thin-walled CFT beam-column section to satisfy equilibrium conditions. The analysis algorithms for thin-walled CFT beam-columns under axial load and uni- and biaxial bending are presented. The PBA program can efficiently generate axial load-strain curves, moment-curvature curves and axial load-moment strength interaction diagrams for thin-walled CFT beam-columns under biaxial loads. The proposed PBA technique allows the designer to analyze and design thin-walled CFT beam-column made of compact or non-compact steel tubes with any strength grades and normal and high-strength concrete.
The PBA technique was compared with experimental data taken from other studies for verification. The technique predicted stiffness, strength, and ductility performance of thin-walled CFT beam-columns very well. Algorithms developed were found to be highly efficient in dealing with progressive local buckling in thin walled CFT beam-columns.
Effects of local buckling, depth to thickness (D/t) ratio, concrete compressive strengths, steel yield strengths, and axial load levels on thin walled CFT beam-columns was examined in a parametric study utilizing the PBA technique. Increasing the D/t ratio reduced the section axial performance, axial ductility, flexural stiffness and strength, curvature ductility, and section interaction performance. Increasing the concrete compressive strength increased the axial load an moment capacities of thin-walled CFT beam-columns but decreased their section axial performance, axial ductility, and section interaction performance. The increase in axial load capacities is more significant than the increase in moment capacities. Increasing the steel yield strength of the steel tubes increases the section axial performance, axial and flexural strengths and section interaction performance. In addition, the increase in the axial load capacities is more significant than the increase in the moment capacities. Increasing the steel yield strength of the steel tubes increases the section axial performance, axial and flexural strengths, bending moment capacities, and section interaction performance of thin walled CFT beam-columns but generally reduced their axial ductility. The flexural stiffness, strength, and curvature ductility of thin walled CFT beam-columns are reduced by increasing the axial load levels.