Experimental behavior of circular concrete-filled steel tube stub columns

This paper presented an experimental study on the behavior of circular, concrete-filled, steel tube (CFT) stub columns with self-compacting concrete (SCC) and normal concrete (NC) concentrically loaded in compression to failure. Four measurement methods on the axial deformation of specimens were compared. Seventeen specimens were tested to investigate the effects of concrete strength, notched holes or slots, and different loading conditions on the ultimate capacity and the load–deformation behavior of the columns. The behavior of these stub columns in confinement was discussed.It is concluded that for the specimens with the entire section loaded, strain gauges with different dimensions could record the strains of the steel tubes, and electronic displacement transducers with certain gauge lengths could record the axial displacement. By using higher strength concrete, the specimens with the entire section loaded experienced a significant increase in the ultimate capacity, but their residual capacity after failure is almost constant. However, once the steel tube was notched, the axial compressive stiffness of specimens was reduced; in some cases the ultimate capacity was also reduced, and the steel tube acted more as a transverse confinement than an axial compression component. Eurocode 4 predicted a reasonable capacity for the unnotched CFT stub columns with both SCC and NC if the entire section of the specimen is loaded.