Performance of recycled aggregate concrete-filled high-strength steel tubes under axial compression, tension and torsion

This paper reports the performance of recycled aggregate concrete-filled high-strength steel tubes (RAC-FHST) under axial compression, tension and torsion. A total of 50 specimens, including 22 compressive specimens, 16 tensile ones and 12 torsional ones, were tested. The main parameters varied in the tests were the sectional type, the steel yield strength and the replacement ratio of recycled coarse aggregate (RCA). Analysis on the full-range load-deformation response, the typical failure modes, the ultimate strength, the passive confinement effect and the influence of key parameters were conducted. Results reveal that the use of RCA affected the failure modes especially when subjected to tension or torsion. Meanwhile, the performance of RAC-FHST is improved due to the excellent confinement effect of high-strength steel tube. The finite element modelling method was used to investigate the mechanical property and the effects of important parameters. Simplified models for the calculation of ultimate compressive, tensile and torsional strengths of RAC-FHST were proposed. Based on reliability analysis, the effects of the steel yield strength, the concrete strength and the confinement factor on the reliability index of RAC-FHST were evaluated.