Experimental and numerical studies were conducted to clarify the influencing law of steel ratio on the mechanical properties of reinforced and recycled aggregate concrete (RAC)-filled circular steel tube short columns (R-RACFST) with 100% recycled coarse aggregate (RCA) replacement. Concrete-filled steel tube (CFST), RACfilled steel tube (RACFST) and R-RACFST test series were designed using five different wall-thicknesses of steel tube with two replicates for each wall-thickness. Based on the test, the influencing law of steel ratio on the failure, loading performances and ductility was analyzed, and the improving effect of reinforcement on the behavior of R-RACFSTs was confirmed, and the finite element (FE) model was developed, and the FE simulations were then performed considering the coupling effect between the wall-thickness of steel tube, reinforcement and strength of RAC. The strength prediction equations of CFSTs from codes such as T/CECS 625, GBT51446-2021, GB50936-2014, ANSI/AISC A360-16, AIJ, Eurocode 4 and AS/NZS 5100.6 were studied and their applicability to RACFSTs was confirmed. Meanwhile, novel equations for predicting the strength of R-RACFSTs were proposed and verified. The results demonstrate that: R-RACFST makes it possible to fill RAC with 100% RCA; when combined with an appropriate amount of reinforcement, R-RACFSTs with thinner steel tube performs as well or better than RACFSTs with thicker steel tube; reasonable ranges of steel ratio and confinement index for RRACFSTs are recommended as 6.2%-12.8% and 0.78 - 1.53, respectively; the proposed equations are accurate and reliable, and can be applied to design the load bearing capacity of axially loaded R-RACFSTs.
