Seismic behaviour of SRC columns with high encased steel ratio

In recent years, steel reinforced concrete columns with encased steel ratios higher than 15% (HSR-SRC) have been utilized in many high-rise buildings as the key bearing components at the bottom floors. This paper investigated the hysteretic behaviour of the HSR-SRC columns. HSR-SRC columns with encased steel ratios above 15% exhibited excellent seismic performance and behave more like the short compact steel columns rather than the SRC columns with normal encased steel ratios. Although subjected to a high axial load ratio, HSR-SRC columns showed very mild degeneration of stiffness and resistance in the post-peak load range, granting the columns good energy dissipation capacity and high ductility. The moment resistance and total energy dissipation of the HSR-SRC columns were by and large directly proportional to the degree of the extensiveness of the encased steel section, so the flexural and hysteretic performance of the HSR-SRC columns can benefit from high shape distribution coefficient of the encased steel section. A finite-element modelling technique was developed allowing for the four levels of confinement on the concrete provided by the hoops and encased steel section. The modelling technique was able to accurately predict the hysteretic behaviour of the HSR-SRC columns. A new method was proposed to calculate the resistance of HSR-SRC columns based on the static theorem of the limit analysis and three possible stress distributions. The proposed method was validated against the collected experiment results and, with an average error of less than 5.8%, showed a much better accuracy than the Eurocode 4 provision.