Seismic behavior of thin-walled square CFST columns with diagonal rib/circular liner stiffeners

This paper focuses on two novel enhancement schemes for thin-walled square concrete filled steel tubular (CFST) columns, i.e., diagonal rib stiffener and circular liner stiffener, with the advantages of sufficient confinement, easy fabrication, and flat outer surface. Seven thin-walled square CFST columns were tested under pseudo-static loading, considering the parameters of stiffener type, the width-to-thickness ratio of steel tube, and axial load ratio. The test results indicated that all the stiffened specimens showed excellent seismic performance with higher lateral resistance, better ductility, and greater energy dissipation than the unstiffened counterpart. The specimens with diagonal rib stiffeners effectively restricted the local buckling of the square steel tube but suffered a weld fracture between the tube plate and the diagonal rib at a large drift ratio. The circular liner stiffener could provide sufficient confinement to the core concrete. Even in the case of a high axial load ratio of 0.6, the circular liner stiffened specimen still showed a ductile behavior with the ultimate drift ratio (DR0.85) of 1/35 and the ductility coefficient (μ) of 4.3. The hysteretic behavior of the thin-walled square CFST columns with diagonal rib/circular liner stiffeners was predicted by both the FE model and the simplified theoretical model, in which the post-buckling strength of the thin-walled square steel tube and the confinement effect of the stiffeners are considered.