Experimental research on seismic performance of steel fiber-reinforced recycled concrete-filled circular steel tube columns

Abstract

To study the seismic performance of steel fiber-reinforced recycled concrete-filled steel tube (SRACFST) columns, 14 circular specimens with different replacement rates (Rp) of recycled coarse aggregate (RCA), volume fractions (Vf) of steel fiber, axial compression ratios (n), steel tube thickness (t), and concrete strengths were tested to failure under constant axial and lateral cyclic loads. All the specimens exhibited a similar typical compression bending failure mode. Subsequently, the effect of different parameters on the various seismic characteristics in terms of the lateral load-displacement (P−Δ) hysteresis curve, skeleton curve, ductility, stiffness degradation, strength degradation and energy dissipation were obtained and studied comprehensively. The results indicated that the addition of steel fiber to core concrete can effectively compensate for the marginal negative influence of the defects of recycled aggregate concrete (RAC). Furthermore, the lateral bearing capacity, ductility, and energy dissipation capacity were improved as the steel fiber fraction increased. An increase in the thickness of the steel tube resulted in a remarkable improvement in the overall seismic behaviour. However, a higher axial compression ratio resulted in inferior seismic performance, particularly in terms of the deformation capacity and ductility. The bearing capacity and energy dissipation improved as the concrete strength increased. However, the ductility, stiffness stability, and strength stability weakened. The equivalent viscous damping index corresponding near failure attained 0.281–0.414, and the ductility was higher than 3.0. This demonstrated that the SRACFST columns could be used in load-bearing structures in seismic regions. The Code AIJ-2001 was recommended to calculate the compression bending bearing capacity of SRACFST columns under cyclic seismic loading, with an expansion index of 1.15 for calculation accuracy. Further, the fiber modelling (FM) method was established to predict the skeleton curves. The calculated results matched the experimental results well, and this indicated the relevance of this method for further elastoplastic analysis of SRACFST columns during earthquakes.