Girma, Zerayohannes (PhD)Eseteselase, Berhanu2021-03-302023-11-112021-03-302023-11-112020-09http://etd.aau.edu.et/handle/12345678/25814This thesis presents the procedure to develop a new analytical model to define the axial capacity of concrete encased composite column by considering confinement effect on the core concrete from structural steel and transverse reinforcement. First a method to define the unconfined, partially confined, and highly confined concrete areas ware developed. To define this, arching action was assumed to act in the form of second-degree parabola with an initial tangent slope of 450. The arching action is expected to occur horizontally between longitudinal bars and the tips of structural steel flange and vertically between transverse reinforcement. Then a mathematical formulation was developed to define the lateral confining pressure from both transverse reinforcement and structural steel on the partially and highly confined concrete. By using the lateral confining pressure, the partially and highly confined compressive strength of concrete was determined. Finally by using the defined area of concrete and by their corresponding confined compressive strength, analytical model to define the axial compression resistance of concrete encased composite column was developed. And the analytical model is verified using eleven experimental concrete encased composite column results. It was showed that the analytical model have a good approximation with the experimental result. Parametric study was carried out to investigate how material and geometrical variables affect the confinement effectiveness in axial compression resistance of concrete encased composite columns. Compressive strength of concrete, yield strength of structural steel, and yield strength of transverse reinforcement ware selected as a material variables. Moreover, thickness of structural steel flange, width of structural steel flange, distribution of longitudinal reinforcement, and spacing of transverse reinforcement ware selected as a geometrical variables. From the result, it was observed that partially confined concrete highly affected by the transverse reinforcement spacing, compressive strength of concrete, and yield strength of transverse reinforcement. In addition, highly confined concrete highly affected by the compressive strength of concrete, transverse reinforcement spacing, and yield strength of structural steel. Additionally by developing a finite element model the effect of structural steel yield strength on the confinement effect is showed.en-USConcrete encased composite columnconfinement effectpartially confined concretehighly confined concreteThesis