EXPERIMENTAL INVESTIGATION ON SQUARE STEEL TUBED RC COLUMNS UNDER AXIAL COMPRESSION

This paper reports an experimental study on the behaviors and modes of failure of the square steel tubed RC columns subjected to concentrically axial load, applied directly to the RC core. The main variables were the compressive strength of the concrete, the wall thickness of the steel tube and the tie spacing. All square columns were 150 mm in width and 750 mm in height. A total of 36 specimens, including 24 tubed RC columns and 12 reference RC columns, were tested. It was found that the tubed RC columns have a ductile-like with strain hardening, elastic-perfectly plastic and strain-softening behavior. The mode of failure of the columns is in progressive mode with very large axial deformability. The wall thickness of the steel tube and the compressive strength of concrete are the major factors, influencing the behaviors, axial compressive capacity and modes of failure of the columns. Since the behaviors of the column are different from those of the CFT column, the ACI 318 design equation considerably overestimates the axial compressive capacity of the column. Finally, based on the results obtained from this study, the design equation for the tubed RC column was proposed.