Use of ultra-high-strength bars for seismic performance of rectangular high-strength concrete frame columns

The application of high-strength concrete (HSC) in high-rise structures is becoming an increasingly used practice. In order to improve the ductility of HSC, many studies are conducted worldwide. In this paper, the effect of ultra-high-strength reinforcement on the seismic behaviour of HSC columns is investigated through numerical analysis and experiments. The results of the numerical analysis are compared with the experimental results. The comparison shows that the numerical analysis results agree very well with the experiments. The results also show that the flexural behaviour of the columns can be effectively improved by use of mixed ultra-high-strength steel bars with a yield strength above 1000 MPa and normal-strength steel bars for the longitudinal reinforcement. Moreover, the test also shows that the ductility of HSC columns, which are reinforced by an ultra-strength stirrup rebar, is better than that of a column which is confined by the normal reinforcement, especially in the case of high-strength concrete columns with compression strength above C60. Finally, an experiential formula for the ductility, which is related to the yield strength of ultra-high-strength steel bars, was derived on the basic of test data and numerical analysis results.