Fellah, F.Seridi, A.Othmani, N.2015-06-112015-06-112015-06-112261236Xhttps://dspace.univ-boumerdes.dz123456789/1678published by EDP Sciences.The purpose of this paper is the determination of flexural stiffness EIx and EIy of a concrete filled rectangular cross section of a composite steel column, under biaxial bending (N, Mx and M y). The rigidities will be estimated from a theoretical approach using a finite element analysis (element bar with 4 degrees of freedom), based on the equilibrium conditions at mid-span using the moment-curvature relationships (M-Φ) of the deformed element by applying the following equation: EI=M/Φ. The material behavior is the one adopted by Eurocode 2 and 3, respectively, for concrete and steel. To validate the theoretical approach used, two comparisons were made: one comparing the rigidities given by the moment-curvature relations versus those calculated by the Eurocode 4, and a second comparison between failure loads of two columns scale one with those tested in the laboratory [2]. Based on the results obtained, we may conclude that the theoretical approach used in this study and the models of behavior of materials are suitable for such problemsfrCivil engineeringDegrees of freedom (mechanics)Rigidity4 degrees of freedomEquilibrium conditionsFlexural stiffnessMaterial behaviorMoment-curvature relationArticle