الفهرس 
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Abstract
High-rise structures and bridges frequently use steel-concrete composite columns. Composite columns are more efficient and ductile than traditional reinforced concrete columns, although they are smaller and lighter. In this thesis, experimental and numerical studies were carried out to investigate the optimal distribution of the total steel area of the Concrete-Filled Hollow Steel Tube (CFHST) columns. The experimental program included 20 CFHST columns. Meanwhile, the numerical study comprises two phases: verification of experimental work using the nonlinear finite element software ANSYS 18.1 and a parametric study on the behaviors of 27 full-scale CFHST columns. The main variables of the experimental study and numerical studies were the distribution of the total steel cross-sectional area over the internal concrete core (steel reinforcement) and the external steel tube, the cross-sectional shape, the width-to-breadth ratio, the slenderness ratio, and the presence or absence of shear connectors. The experimental and numerical results indicated that, for a constant steel area, the presence of the internal steel reinforcements and the confinement action of the external steel tube together with the use of shear connectors enhanced the efficiency of the concrete core to resist higher values of ultimate loads, stiffness, and ductility for the CFHST columns. Furthermore, using equations from various codes, a comparative study was conducted between the experimental, theoretical, and analytical results.