Seismic performance of recycled aggregate concrete-filled steel tube columns

- The seismic performance of recycled concrete-filled steel tube columns is analysed.
- The damage degree of the columns is quantitatively described.
- A model of the damage degree based on three evaluation indices is proposed.
- The damage evaluation results truly reflect the failure condition of the structure.

In this study, low cyclic loading tests were performed on nine seamless steel tube columns filled with recycled aggregate concrete (RAC) and two steel tube columns filled with normal concrete to analyse their seismic performance and damage mechanism. The hysteresis behaviour, skeleton curve, ductility coefficient, stiffness degradation, and energy dissipation capacity of the steel tube columns were studied. The influence of the axial compressive ratio, steel strength, and steel thickness on the seismic performance of the steel tube columns was discussed. In addition, the failure mode and damage mechanism of the specimens were investigated; a skeleton curve-fitting formulation based on the Boltzmann mathematical model was proposed. A damage degree-based model was built for representing the damage degree quantitatively. The results indicate that the RAC-filled steel tube columns exhibit a full hysteresis loop, the equivalent coefficient of viscosity ranges from 0.402 to 0.572, and the coefficient of energy dissipation ranges from 2.617 to 3.595. The comparisons between the two types of steel tube columns indicate that the seismic performances of the RAC-filled steel tube columns are similar to those of the corresponding normal concrete-filled steel tube columns and that the RAC-filled steel tube columns even have appreciably better lateral bearing capacity, better ductility, and slightly lower energy dissipation ability at the same displacement level. These results consistently indicate that desirable seismic performance is achieved, and they serve as a potential reference for the structural design and application of RAC components in seismic areas.