NONLINEAR INELASTIC ANALYSIS OF CONCRETE ENCASED STEEL STRUCTURES

Abstract

This dissertation presents an efficient numerical approach based on fiber element method to simulate the complete nonlinear inelastic behaviors of stub and slender concrete encased steel (CES) columns/beam-columns. The analysis scheme accommodates various important influences, i.e. materials and geometric nonlinearity, geometric imperfection, levels of concrete confinement, local buckling of structural steel and reinforcement bar. CES sections having H-, I-, and Cross-shaped steel with/without reinforcement bars were investigated. The developed approach is capable of tracing the complete structural performance such as load-lateral deflection curve, load-axial strain/shortening response, force-moment interaction diagram, and force-moment-curvature curve. An adaptive initial condition formulation with Müller numerical method has been developed to ensure the convergence solution. A total of 50 full-scale experimental tests of CES columns/beam-columns were used to validate the developed numerical approach. Good comparisons between the analysis and experimental tests have been achieved. A novel piecewise linear yield model of softening material properties underpinning CES sections have been proposed. Mathematical expressions for plasticity components were derived and validated with tests. The stepwise holonomic analysis approach has been adopted to trace the complete responses of structures with CES members. Both geometric and material nonlinearity were included in the analysis of CES structures. The proposed analysis method can predict CES structural behaviors with panoramas illustrations of plastic hinge. Structural retrofitting by means of typical steel bracings has been carried out. Some recommendations were given to select a suitable type of bracing configurations for the desired purpose.