Mechanical Behavior And Seismic Design Of RC Columns-Joints Confined With High-Strength Stirrups

Adopting high-strength reinforcement as the lateral ties in the reinforced concrete columns could enhance the confined effect of high strength concrete. The high-strength lateral reinforcement could overcome the brittleness of concrete and improve the aseismic performance of structure, meanwhile, the consumption of reinforcement and pollution in the producing process would be reduced. The research in this thesis has great significance in the aspect of promotion and application of high-strength concrete and high-strength reinforcement. By means of experimental study, theory analysis and numerical simulation, the compressive property and mechanism of high strength concrete confined with high-strength lateral ties, the design method of lateral ties in concrete columns and the seismic performance of concrete joint will be investigated respectively in this paper. The mainly contents are as follows:The stress strain curves of concrete confined with high-strength ties was obtained through concentric loading test. Based on the test results, the influences of the tie volume ratio, the confinement effectiveness coefficient and concrete strength on the tie stress and the characteristics of strength and deformation are analysed. A confined concrete model was developed on the basis of existed model, which is suitable to varirous confined level.The damge paramenter of different confined concrete model was evaluated.The relationship between confining index, axial compressive ratio and ductility was established through simulating the ductility of concrete column confined with high-strength lateral ties. The design method of lateral ties was proposed based on displacement ductility. The rationality of the design equation was verified by means of comparing with test result, meaning while the calculating result was comparing with design code equations. At last, a ductility evaluating process was performed on concrete column, which satisfied the rule of Chinese concrete design code.Five RC beam-column joint specimens were tested under low cyclic reversed loading. The failure pattern, hysteretic behavior, energy dissipation,shear behavior and stress magnitude of high-strength stirrups were studied. The influence of stirrup yield strength, the volume ratio of stirrup, and stirrup configuration on the shear bearing capacity, ductility, shear deformation and energy dissipation of specimens were analyzed. Increasing stirrup yield strength has limited enhanced effect on bearing capacity of specimens, but the ductility, energy dissipation of specimens and restricted effect of shear deformation in joint core are improved effectively. Baed on existed RC joint model, a modified strut model was proposed, which considering strut transferring mechanism and shearing of lateral ties. The joint shear model and fiber model in Opensee programe was empolied to analyze the mechanic behavior of high-strength reinforcement concrete joint, the effect of concrete strength and axial compressive ratio on the mechanic behavior of RC beam-column joint was discussed. Based on a modified strut model and design equation,a shear capatcity equation of RC beam-column joint confined with high-strength lateral ties equation was proposed.