Loading performance of reinforced and recycled aggregate concrete-filled circular steel tube short column with different steel ratios

Abstract

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), RAC-filled 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 R-RACFSTs 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.