Experimental Research on Seismic Behavior of +-shaped Columns Reinforced with High-strength Steel Bars under Cyclic Loading

500MPa steel bar is a new type of high-strength reinforcing bar applied in China. To investigate the feasibility of using this type of reinforcement in specially shaped column structure, six +-shaped column specimens varying in axial compression ratio and stirrup spacing were tested under cyclic loading. Behaviors in failure mode, shear crack width, bearing capacity, displacement ductility and energy dissipating capacity are studied to evaluate the seismic resistance performance of the columns. Test results show that 500 MPa steel bars can be effectively used as longitudinal reinforcement and provide more significant confinement to core concrete as transverse reinforcement. It is demonstrated by the observed results that expected oversize flexure-shear crack width can be prevented through an appropriate design procedure following the current building codes in China. Reducing stirrup spacing provides better performance in member ductility, crack behavior, cumulative damage and energy dissipation capacity, but has little influence on the bearing capacity; high axial load can offer advantages in bearing capacity, energy dissipating capacity and shear crack behavior, but reduce the member ductility. To predict the behavior of test specimens under cyclic loading, analytical model are implemented in program OpenSees using flexural fiber beam-column element with the consideration of the shear effect. Analytical results have an acceptable agreement with the test results.