Research On Seismic Behavior Of Steel Fiber-reinforced Concrete Cross-shaped Column Confined With High-performance Stirrup

The reason why the special-shaped column(SSC)like T-shaped,L-shaped,zigzag and cross-shaped columns had great researchful significance and applied prospect was that the kinds of sectional column hold incomparable function with normal columns.However,the application of special-shaped column structure in high-rise or super-high-rise buildings is limited because of the defects discovered in the bottom column foot and beam-column joints of special-shaped column frame structure which are vulnerable and easily destroyed.Therefore,to improve the SSC strength and ductility,the steel fibers are mixed in 8 cross-shaped columns(CSC)with different-strength stirrups.The effect of high-strength stirrups and steel fibers on the seismic behavior of SSC under horizontal cyclic loading is systematically studied and analyzed,which will provide a researchful and experimental basis for promoting the development and application of SSC in practical projects.The contents of the study are as follows:(1)The failure characteristics of CSC under cyclic loading are observed and described.The bending failure of 8 specimens with good ductility is analyzed,which meets the requirements of seismic design in failure state and ductility.(2)The failure form,hysteretic property,skeleton curve,bearing capacity,lateral displacement,ductility,stiffness degradation,strength degradation,energy dissipation capacity of each specimen are mutually compared and analyzed.The results indicate that with the decrease of stirrup spacing,the horizontal bearing capacity of each specimen is remarkably increased,but the energy dissipation capacity and ductility of the specimens are sharp declined under the high axial compression ratio.Meanwhile,both high-performence stirrup and steel fiber can significantly enhance the seismic capability of each specimen,but the reinforcement effect of steel fiber is better than that of high strength stirrups.(3)Based on the comparisons and analysis of the above experimental results and the method of calculating the bearing capacity of rectangular members subjected to bending,a formula for calculating the bearing capacity of normal section of CSC under eccentric bending is proposed.The calculated results show that the flexural bearing capacity calculated by the proposed formula is in good agreement with the experimental datum subjected to little eccentric compression,but is smaller under large eccentric compression.(4)In view of the existing formulas for calculating the length of plastic hinges of rectangular concrete members and combining with the experimental results and numerical analysis,a formula applied to calculating the length of plastic hinges of steel-fiber reinforced concrete CSC with high-performence stirrup is presented.The length of plastic hinge calculated by this formula is in good agreement with the experimental results,which fully indicates that the geometric dimension,axial compression ratio,hoop eigenvalue and reinforcement eigenvalue of the members are the cardinal factors affecting the plastic hinge length of CSC.