Axial compressive strength of concrete encased extended T-shaped steel composite columns with less reinforcement

A novel concrete encased extended T-shaped steel composite stub (ET-CES) column with less reinforcement for the prefabricated structure is proposed. Eight ET-CES columns, including one covered by concrete fireproof boards and two bare extended T-shaped steel stub columns, were tested under axial compression. Finite element analysis was also conducted. The effects of stirrup spacing, stirrup form, steel ratio, and concrete compressive strength on the axial compressive behaviour were studied. Furthermore, the failure modes, axial load-displacement curves, axial load-strain curves, and post-peak deformability of ET-CES columns were also investigated. The results demonstrated that the concrete cover with less reinforcement and a thin concrete encasement for the ET-CES column could still prevent steel skeleton instability under axial compression. Premature spalling of concrete cover might be prevented by installing fireproof boards, reducing stirrup spacing, and using closed stirrups. The steel ratio in ET-CES columns increasing from 8.1% to 10.4% had no effect on the maximum normalized resistance but could enhance the post-peak ductility and residual strength. The reduction of the concrete compressive strength of ET-CES columns from C50 to C30 could improve the maximum normalized resistance and residual strength. ET-CES columns had excellent post-peak deformability. Finally, an axial strength formula for ET-CES columns was proposed and validated.