Abstract:  In order to study mechanical properties of reinforced concrete protected concrete filled steel tubular (CFST) columns after fire, the finite element method was used to analyze the reduction amplitude of axial bearing capacity and axial stiffness. The axial bearing capacity and axial stiffness parametric analysis is discussed with experimental verified finite element model. The computing method of the residual axial bearing capacity and axial stiffness are obtained. The results show that: (1) Axial bearing capacity and axial stiffness of reinforced concrete protected CFST stub columns after fire decrease significantly. With the increase of heating time, reduction of axial stiffness is higher than that of axial bearing capacity; (2) Sectional core area ratio has significant influence on the reduced level of axial bearing capacity for reinforced concrete protected CFST stub columns after fire. Sectional core area ratio and steel tube ratio have significant influence on the reduced level of axial stiffness for reinforced concrete protected CFST stub columns after fire; (3) The simplified calculating method is able to predict the residual axial bearing capacity and axial stiffness of reinforced concrete protected CFST stub columns after fire. 

Key words: fire, concrete filled steel tubular column, axial bearing capacity, axial stiffness, simplified calculation method