Comparison of Seismic Performance of Steel-Reinforced Ultra-High-Strength Concrete Frames and Columns Under Cyclic Loads

To investigate the influence mechanism of axial compression ratio on the seismic performance of steel-reinforced ultra-high-strength concrete (SRUHSC) columns and frames, and to reveal the fundamental differences in seismic behavior between isolated columns and integral frames, comparative cyclic loading tests were carried out. Three sets of comparative experiments were designed for SRUHSC columns and frames under different axial compression ratios. Key seismic indicators, including failure mode, hysteresis curve, skeleton curve, stiffness degradation law, energy dissipation capacity, and ductility coefficient, were systematically analyze. Experimental results indicate that with an increase in the axial compression ratio, isolated SRUHSC columns primarily exhibit flexural failure, characterized by concrete crushing at the member ends and yielding of longitudinal reinforcement. In contrast, SRUHSC frames predominantly undergo flexure-shear-bond failure, accompanied by intensified bond-slip between the reinforcement and concrete in the joint regions and restricted development of plastic hinges at the beam ends.Comparative analysis reveals that, compared to isolated columns, the frame structure demonstrates a more pronounced advantage in overall seismic performance. Furthermore, an increase in the axial compression ratio affects the mechanical performance of both structural types: it accelerates the propagation rate and distribution range of cracks, leads to higher initial stiffness but faster stiffness degradation in the later stages, and substantially reduces both the ductility and energy dissipation coefficient of the structure, while also adversely affecting the ultimate load-bearing capacity. This study clarifies the differentiated roles of the axial compression ratio in the seismic performance of SRUHSC columns and frames, confirming that the seismic performance of a single column deteriorates when integrated into a frame structure. These findings provide critical experimental data and a theoretical foundation for the seismic design optimization and performance enhancement of SRUHSC structures.