The overall objective of this study is to develop fast, simple and accurate numericalrnanalysis tool to investigate the non-linear inelastic response of circular CFT columns andrnbeam-columns subjected to eccentric compressive loading. This thesis presents arnsystematic development of new numerical models for the nonlinear inelastic analysis ofrncircular CFT columns and slender beam-columns. In the proposed numerical model, therninelastic behavior of column cross-sections is simulated using the accurate fiber elementrnmethod. Accurate constitutive laws for confined concrete are implemented in the models.rnThe effects of steel tube local buckling are taken into account in the models. Axial loadmoment-curvaturernrelationshipsrncomputedrnfromrnthernfiberrnanalysisrnofrnsectionsrnarernusedrninrnrnthernrncolumn stability analysis to determine equilibrium states. Efficient computationalrnalgorithms based on Secantâ€™s method are developed to obtain nonlinear solutions.rnAnalysis procedures are proposed for predicting load-deflection and axial load-momentrninteraction curves for circular CFT columns and slender beam-columns under eccentricrncompression. The numerical model was used to develop fast, easy and user-friendly MSrnExcel spreadsheet analysis tool using visual basic programmed Macros to enhance thernapplicability of the study. A total of more than 200 experimental tests of circularrnconcrete-filled steel tube columns and beam-columns have been used to validate therndeveloped numerical approach by comparing the maximum load capacity, axial loadaxialrnrnstrain/shortening, and axial load- deflection response curves. The developed toolrnwas utilized to undertake extensive parametric studies on the fundamental behavior ofrncircular CFT slender columns covering a wide range of parameters. The proposedrnnumerical approach is capable of tracing the complete circular CFT columnsrnperformance including the challenging post-peak inelastic softening response. Despiternrich features of the proposed numerical scheme, the computational time is highlyrnefficient and suitable for practical design and analysis of circular concrete-filled steelrntube columns and beam-columns using the tool. Good agreements between the numericalrnresults with experiments have proved that the proposed numerical scheme is veryrnefficient for predicting both the maximum load capacity and the axial load - deflectionrnresponse of the stub and slender circular concrete-filled steel tube composite columnsrnand beam-columns. The numerical model analysis has successfully captured the axialrnload-strain and axial load-deflection response along with important features.