Axial compressive bearing capacity of short columns of reinforced recycled aggregate concrete-filled steel tubes

Xiamuxi Alifujiang; Shao Jinlan; Shi Lujiang

doi:10.16186/j.cnki.1673-9787.2023120060

Abstract：Objectives This study aims to mitigate the adverse effects caused by the inhomogeneity of re-cycled aggregate concrete and to promote full utilization of recycled coarse aggregate by developing a calcu-lation method for the bearing capacity of reinforced recycled aggregate concrete-filled steel tubes(R-RACFST).Methods Based on the unified theory approach,the study fully considered the dual restraining effects of the steel tubes and steel reinforcement on the core recycled concrete.It modified parameters such as the confinement coefficient in existing concrete constitutive models to derive a nonlinear numerical simu-lation model suitable for R-RACFST.After verifying the model's reliability with existing experimental data,a parameterized analysis was conducted on 90 model specimens obtained through orthogonal design consid-ering different steel tube wall thicknesses,longitudinal reinforcement diameters,and concrete strength grades,using the corrected hoop coefficient as a parameter.Results When other parameters remained un-changed,increasing the concrete strength and steel tube wall thickness led to increased ultimate compres-sive strength and enhanced post-peak plastic deformation capacity,whereas increasing the diameter of the longitudinal reinforcement had minimal effect.Based on these findings and considering the influence of the three parameters on bearing capacity,the study referenced the existing T/CECS625-2019 code's formula for short-column bearing capacity of recycled aggregate concrete-filled steel tubes,and proposed a new for-mula for calculating R-RACFST short-column bearing capacity based on the unified theory.To validate the reliability of the proposed formula,a comparative analysis was performed between experimental and calcu-lated values for 100 sets of existing tests and model specimens.Results showed that directly using the rein-forced concrete-filled steel tube formula from CECS408-2015 yielded an average ratio of 0.95 with a stan-dard deviation of 0.05 between experimental and calculated values.In contrast,the proposed R-RACFST formula resulted in an average ratio of 1.11 with a standard deviation of 0.06,indicating better agreement.Conclusions The formula proposed in this study for R-RACFST short-column bearing capacity is safe,reli-able,and applicable to engineering practice.