Performance and calculations of recycled aggregate concrete-filled steel tubular (RACFST) short columns under axial compression

This paper describes a series of tests on steel tubular short columns of circular section filled with normal concrete (NA) and recycled aggregate concrete (RAC). Twenty-two specimens, including 11 small diameter of RAC-filled steel tubular (RACFST) columns named CA series and 11 larger diameter of RACFST columns called CB series, were tested to research the influence of variations in confinement index and replacement ratio of recycled coarse aggregate (RCA), from 0% to 100% with 10% increasing. The test results show that both types of RACFST columns and normal concrete-filled steel tubular (CFST) columns failed due to oblique shear pressure damage with a drum-like. Comparisons are made with predicted bearing capacities of RACFST columns using the existing theories, such as Unified Strengthen theory (I), Confinement theory (II) and Superposition theory (III). The equation for axial compression stress-strain curves of the whole process are proposed in this investigation for RACFST short columns, which can be directly used in theoretical and numerical analysis as well as practical engineering design and evaluation of RACFST structures.