Seismic behaviour of concrete-filled steel tubular columns with 100 % recycled coarse and fine aggregates: Experiments and modeling

Recycled aggregate concrete-filled steel tube (RACFST) is a sustainable solution for handling construction wastes by utilizing recycled aggregate concrete (RAC), saving natural aggregates, and not significantly reducing structural performance. Current investigations on the seismic behaviour of RACFSTs mainly focused on the RAC with only coarse aggregates replaced, lacking comprehensive investigations on the seismic behaviour of RACFSTs, especially for the RACFSTs with 100 % recycled coarse and fine aggregates. This study presents an investigation of the seismic behaviour of RACFST members under constant axial compression and cyclic lateral loads. The test variables are replacement ratios of recycled coarse and fine aggregates, axial load levels, and steel ratios. The cyclic test results are discussed carefully, including failure modes, hysteretic curves, ductility, energy dissipation capacities, and confinement mechanisms at plastic hinge regions. A simplified but efficient finite element modelling method is established and validated for the seismic behaviour of the RACFST members. Finally, the applicability of the existing design methods is examined for the combined compression-bending bearing capacities of RACFST members.