Experimental and theoretical investigations of recycled self-compacting concrete filled steel tubular columns subjected to axial compression

Axial loading tests were conducted on fifteen Recycled Self-Compacting Concrete Filled Steel Tubular (RSCCFST) columns to investigate the influence of the replacement ratio of the Recycled Aggregate (RA), concrete strength grade and diameter-to-thickness ratio of the steel tube on the mechanical behaviors of the RSCCFST columns. The failure mode, bearing capacity, axial load-deformation relation, ultimate strains, stiffness and stress-strain relationship were presented and analyzed. The results showed that the buckling failure and obvious drum-like bending in the middle of the columns were observed. The bearing capacity, ultimate stress and strain declined with the improvement of the replacement ratio of RA or diameter-to-thickness ratio of the steel tube, while raised with the increase in the concrete strength grade. Increasing the replacement ratio of RA and diameter-to-thickness ratio of the steel tube would amplify the strain growth rate and axial ultimate deformation, and promote the specimens enter the elastic-plastic stage in advance, while the increase in the concrete strength grade led to the opposite effect. The stiffness degradation rate raised as the increment of the replacement ratio of RA, diameter-tothickness ratio of the steel tube or concrete strength grade. According to the experimental investigation and limit equilibrium theory, the prediction formula for the bearing capacity of the RSCCFST columns were derived. Then the models for predicting the ultimate strains, stiffness and stress-strain relationship of the RSCCFST columns were proposed, respectively. The comparisons between the predicted and experimental values demonstrated that the proposed formulae had high accuracy. (C) 2020 Elsevier Ltd. All rights reserved.