Experimental behaviour of circular concrete filled steel tube columns under lateral cyclic loading

This study experimentally explored the behaviour of 12 concrete filled steel tube (CFST) and steel tube columns subjected to lateral cyclic loading. The L/D ratio was 12.3 while D/t ratios were 45.4, 37.8 and 32.4, classifying these 12 specimens into 3 groups. Each group included 3 CFST and 1 steel tube columns and were tested to failure. The experimental results indicated that CFST specimens reached the state of 'collapse prevention' (drift 4%) prior to the occurrence of local buckling. Strength degradation of CFST specimens did not occur up to the failure by buckling. This showed the favourable characteristic of CFST columns in preventing collapse of structures subjected to earthquakes. The high energy absorption capability in the post collapse limit state was appropriate for dissipating energy in structures. Compared to steel tube columns, CFST columns delayed local buckling and prevented inward buckling. Consequently, CFST columns exhibited their outstanding seismic performance in terms of the increased ultimate resistance, capacity to sustain 2-3 additional load cycles and significantly higher drift. A simple and reasonably accurate model was proposed to predict the ultimate strength of CFST columns under lateral cyclic loading.