Structural behavior of partially confined circular CFST columns under lateral cyclic loading

The seismic performance of concrete-filled steel tubular (CFST) columns is severely influenced by the failure at the potential plastic hinge zone. This paper proposes a novel confinement technique at the potential plastic hinge region using an inner circular steel tube for the circular CFST columns named partially confined concrete-filled steel tubular (PCCFST) columns. This confinement technique strengthens the plastic hinge region, and hence, the overall structural performance of the columns is enhanced. To verify the effectiveness of the proposed technique, a total of 7 columns: 6 PCCFST and 1 counterpart CFST have been tested under lateral cyclic loadings while subjected to constant axial load. Failure mode, hysteretic behavior, flexural capacity, ductility, and energy dissipation ability of the PCCFST specimens were investigated by varying the diameter and height of the inner circular steel tube. It was seen that the height of the circular inner steel tube has an obvious effect on the cyclic performance of the columns. For the PCCFST columns considered, the maximum lateral strength, ductility, and energy dissipation ability were enhanced by a maximum of similar to 16 %, 24 %, and 14 %, respectively, when compared with the counterpart CFST column. A new design guideline has been proposed based on the Eurocode and limited experimental data obtained from the present study. A comparison between the experimentally determined maximum lateral strength and the proposed guideline has been made and is found to be in good agreement.