Seismic behavior of ultra-high performance concrete long columns reinforced with high-strength steel

In this study, the cooperative working mechanism of high-strength steel and ultra-high performance concrete (UHPC) was investigated. Five UHPC columns were tested under reversed loading, including three UHPC columns reinforced with high-strength steel, one UHPC column reinforced with normal-strength steel and one UHPC column reinforce with normal-strength steel and confined by carbon fiber reinforced polymer (CFRP) sheet. The results show that all the columns failed in bending mode. High-strength reinforcement can restrain UHPC effectively and improve the initial stiffness, ductility and bearing capacity of the test columns. The larger stirrup spacing can result in earlier cracking and lower the bearing capacity of the test column. The CFRP sheet can provide effective confinement for the UHPC, which can improve the yield and ultimate displacement of the test columns. However, it has little contribution to the bearing capacity. A flexural model has been developed for the analysis of UHPC bending members, and the results from the model are in good agreement with the experiment data.