Seismic behavior of large-size encased cross-section steel-reinforced high-strength concrete circular columns

Abstract

Steel-reinforced high-strength concrete (SRHSC) columns can resist large percentages of horizontal shear forces and axial loads, and are widely used in super high-rise buildings. To investigate the effects of the axial load ratio, steel ratio, and loading direction on the seismic performances of encased cross-section SRHSC circular columns, a low-cyclic loading test was conducted on four large-sized specimens, each with a diameter of 700 mm. The failure characteristics, hysteresis curves, bearing capacity, deformation, stiffness degradation, and energy dissipation were analyzed. The finite element software OpenSEES (based on fiber elements) was used to simulate the hysteretic curves of the test specimens, and the simulated results were in good agreement with the test results. The results indicate that all four specimens show bending-dominated damage characteristics. The axial load ratio has a significant influence on the peak load, ductility, and deformation capacity. By increasing the steel ratio, the stiffness degrades more slowly and the specimen shows a better seismic energy dissipation performance. The effect of steel ratio on the improvement of peak load is more evident under a low axial load. With increasing steel strength, there is no significant effect on the initial stiffness and ductility. The specimens with different loading directions have balanced seismic performance, therefore, the columns are suitable for structures in seismic regions. There is little difference between the results calculated by the code of China and Europe and the test results, but the results calculated by the code of China are in better agreement.