Experimental study on seismic performance of bridge pier with new HRB650E high-strength steel bar

To facilitate the application of high-strength steel in reinforced concrete bridge structures, this study explores the seismic performance of full-scale HRB650E high-strength reinforced concrete bridge piers. Initially, monotonic tensile tests were conducted on HRB400 and HRB650E steel rebars with the same slenderness ratio to analyze the differences in their mechanical properties. Subsequently, quasi-static cyclic tests were carried out on four square full-scale RC bridge piers to examine the influence of new high-strength rebars, stirrup ratios, and axial load ratios on the seismic performance. Based on the experimental results, a hysteresis model suitable for HRB650E reinforced concrete columns was developed. The findings indicate that the HRB650E steel bar exhibited lower uniform elongation and fracture elongation compared to HRB400 steel bar. The displacement at which HRB650E piers reached crack damage was 36 % higher than that of HRB400 piers, and they also showed lower residual displacements at all load levels. The maximum lateral load capacity and the ductility coefficient of HRB650E piers increased significantly compared to HRB400 piers. While the initial secant stiffness of both types was comparable, HRB650E piers exhibited a slower rate of stiffness degradation, resulting in higher secant stiffness at the ultimate state. They also demonstrated 35 % higher cumulative energy dissipation at the ultimate state. When the stirrup ratio of HRB650E piers was increased from 1.1 % to 1.7 %, there was a slight reduction in residual displacement, a small increase of the yield strength, and a minor improvement in the maximum lateral load capacity. Furthermore, a higher stirrup ratio was observed to improve energy dissipation levels at all loading stages. Increasing the axial load ratio of HRB650E piers from 0.1 to 0.2 allowed the piers to withstand greater deformations at the same repairable ultimate state, with significant increases in yield strength, maximum lateral load capacity, initial secant stiffness, and secant stiffness at the ultimate state, but a small increase in the cumulative energy dissipation. The hysteresis model for HRB650E RC columns, based on experimental data, exhibited good computational accuracy.