Seismic behavior of recycled concrete columns reinforced with ultra-high-strength steel bars

This paper investigates the seismic behavior of concrete members incorporating recycled coarse aggregates. Tests were carried out on three full-scale specimens with a 600 mm side length. The main parameters include axial load ratio (ALR) and the employment of CFRP external confinement and spiraled groove ultra-high-strength steel bars (UHSSBs) with a nominal yield strength of 1400 MPa. Lateral cyclic displacement and co-existing axial load were applied to specimens. After describing the experiment results and observations, an iterative method was proposed to investigate the relationship between reinforcement slip and reinforcement stress. Based on the iterative method, the lateral capacity and displacement of members reinforced with UHSSBs were discussed. The recycled coarse aggregate concrete columns employed both the CFRP jacket and the UHSSBs can maintain positive lateral stiffness under a 4% drift and have less residual drifts compared with that of the traditional ductile column. Besides, the increase of ALR gives rise to higher residual drift. The method proposed here is capable of predicting the experimental yield loading capacity and the yield drift.