Seismic behavior of thin-walled circular and stiffened square steel tubed-reinforced-concrete columns

Steel tubed-reinforced-concrete (TRC) columns have been gradually used in the construction of high-rise buildings recently because of their high axial load-carrying capacities and excellent seismic behavior. Existing studies about their seismic behavior were focused on columns with relatively thick tubes, i.e., diameter-to-thickness/width-to-thickness (D/t) ratios were below 100, while little is known about thin-walled TRC columns, especially for square TRC columns. Considering the infilled concrete of square TRC columns is non-uniformly and non-effectively confined, accordingly, stiffened square TRC columns are usually adopted in practice. Thus, two thin-walled circular TRC columns (D/t=120) and two stiffened square ones with diagonal stiffeners in plastic hinge regions (D/t=106) were tested under a constant axial compression combined with cyclic lateral loading. Both the circular and stiffened square TRC columns had the same cross sectional area, tube thickness, reinforcing bar ratio and column height. Flexural failure occurred for all the four specimens. Test results showed the strengths of the stiffened square TRC columns were a little higher in comparison to their circular counterparts; the ductility and energy dissipation capacities were excellent for both the stiffened and circular TRC columns, indicating very good confinement was gained from the yielded steel tubes of the plastic hinge regions at the peak loads. And shear stresses (35–90 MPa) in the sheared plates showed their moderate contribution of carrying lateral loads. Finally, cross sectional capacity analysis results demonstrated the method for TRC columns is acceptable for the stiffened square TRC columns.