Axial compressive behaviour and design calculations on recycled aggregate concrete-filled steel tubular (RAC-FST) stub columns

This paper introduces a series of axial compressive tests on 32 recycled aggregate concrete-filled steel tubular (RAC-FST) stub columns. Apart from the cross-section type, the confinement factor and the replacement ratio of recycled coarse aggregate (RCA) are chosen as the main variables to investigate the passive confinement effect of RAC-FST. Analysis of the typical failure modes, the full-range response, the passive confinement effect, the ultimate strength and the effect of RCA replacement ratio are successively carried out. It is suggested that the confinement factor determines the development pattern of the load-strain curves, while the use of RCA has influence on the ultimate strength, the elastic modulus, the critical strain and the transverse deformation coefficient of specimens. The critical confinement factor for circular specimens is determined. A stress-strain model of RAC in RAC-FST is proposed and verified through finite element analysis based on a database of test results presented in this paper and previous literatures. Parametric analysis is carried out and simplified calculation model is proposed. Based on reliability analysis, partial factors for the axial compressive strength of RAC-FST stub columns are calibrated.