[en] This paper presents results ofanumerical study onreinforced concrete and fully encased composite columns designed according to the “Inerd” concept aiming at obviating the soft storey mechanism in frames subjected to earthquake. The model uses fibre beam elements with mono-axial non linear material laws for concrete, steel and reinforcing steel. The crushing of concrete in compression and the cracking in tension are taken into account. The steel behaviour is elastic-plastic with strain hardening. After calibration of the model against experimental results, a parametric study is performed. The main objective is to generate the cyclic moment-rotation curves of the columns under different level of axial forces and with different proper-ties of concrete and then to deduce ductility and rotation capacity of the composite sections from these curves.