Experimental Studies On The Effect Of Hoops On Seismic Behavior Of Reinforced Concrete Columns

The performance of concrete, including strength and ductility ,can be improved by the comfinement of stirrups. Increasing the number of stirrups in the end of reinforced concrete columns ,the confinement of concrete in the area of plastic hinge will be hardened and the seismic behavior of the column will be improved greatly. Though the study on the seismic behavior of reinforced concrete column which comfinement by the hoops has been done widely in and abroad, there is much difference between the provisions, which guide the design of the hoops in the end of columns bearing earthquake, in codes of different country. In order to spread the using of high-strength reinforcement, based on the works have done, the author did a study on the seismic behavior of the reinforced concrete columns with lateral hoops and 500MPa steel as longitudinal bar.Five reinforcement concrete columns with different stirrup were tested under the reversed cyclic lateral loads. All the longitudinal bars in the specimens were made up of HRB500 bars, and the stirrups in the columns were designed as the first class of the aseismic structure in Code for Design of Concrete Structures of China. The author analysed the effect of the lateral reinforcement's strength, diameter and space on the columns'seismic behavior, including the interstory drift, the deflection ductility, the stiffness degradation and the energy exhausting behavior.It was proved that the influence of factors of hoops was great on the seismic behavior and little on the bearing capacity of the columns. Hoop characteristic value determined by these factors have a positive correlation with the seismic behavior, that means that the larger the hoop characteristic value, the better the behavior. The columns with longitudinal bars made up of HRB500 bars has a nice deformability but bad deflection ductility, and is basically meet the requirements of earthquake-resistance. The author point that the columns design as the present Code for Design of Concrete Structures may not safe enough under the seismic load.Finite-element simulate analysis was done based on the experimental investigation. Since that the analysis had a good result, it was used on simulate columns which has different axial compression ratios and hoop characteristic values. The equation used to calculate deflection ductility of columns was obtained, which based on the axial compression ratio and hoop characteristic value of a column. The deflection ductility calculating by this equation are almost equal to or a little smaller than the experimental ones. This equation can be used in design or study work.