Axial Compression Behaviour of Round-Ended Recycled Aggregate Concrete-Filled Steel Tube Stub Columns (RE-RACFST): Experiment, Numerical Modeling and Design

Round-ended recycled aggregate concrete-filled steel tube (RE-RACFST) column is an innovative composite member, which holds the advantage of round-ended concrete-filled steel tube (RE-CFST) and expands the application of RAC in structural members. This paper presents the testing and numerical investigation on the axial compression behaviour of RE-RACFSTs. A total of 18 stub columns were tested to determine the failure mode, axial load versus strain response, vertical and circumferential strains of the round-ended steel tube, and the confinement effect from external steel tube in different positions. The effects of cross-sectional aspect ratio, coarse recycled aggregate (CRA) replacement and steel ratio were analyzed. In general, the ductile behaviour of the specimens reduced with increasing aspect ratio and decreasing steel ratio. The confinement effect during the entire compression process was investigated based on the vertical and circumferential strains. Finite element (FE) models were then developed, and a constitutive model suitable for core RAC in RE-RACFST columns was proposed. Parametric analysis was then carried out to evaluate the effects of the aspect ratio, steel ratio, CRA replacement level, and material strength on the axial compression response. Finally, several existing design provisions for rectangular CFST and RAC-FST members were assessed the feasibility of their application in RE-RACFSTs by using the equivalent method.