Ductility of fully encased composite columns used to obviate soft storey mechanisms in reinforced concrete frames

This paper presents a non linear finite element numerical modelling of reinforced concrete and fully encased composite columns. The model is a multi fibres beam 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 against the experimental results, a parametric study is performed. The main objective is to obtain the full moment-rotation behaviour of the columns under different level of axial forces and with different resistance of concrete, and to deduce ductility and rotation capacity of the composite sections.