Experimental Research On Seismic Behavior Of Concrete Shear Walls Confined By High-strength Reinforcement

In recent years,with the increasing height of the building,the increasing vertical loads are resisted by the shear walls at the bottom of the high-rise building.Under strong seismic loads,high-strength concrete shear walls of high axial compression ratio will be prone to happen the brittle failure,and the terminal hooks of stirrup will also open easily,which will make stirrups losing the confinement effect on concrete and longitudinal reinforcement.The results have shown that,using high-strength spiral stirrups in concrete columns could effectively constrain the concrete at the core area and the longitudinal reinforcement,and improve the seismic performance of the column,while avoiding the opening of terminal hooks of common monolithic hoops,saving steel,enhancing the construction efficiency.Thus,in order to improve the ductility of shear walls,high-strength spiral stirrups will be applied to the shear walls,and the seismic performance of this kind of shear walls under low-cyclic reversed loading will be studyed.In this paper,the high-strength steel(d=5mm)with the yield strength of 1100 MPa were used as the spiral stirrups and distribution reinforcements.A total of four concrete shear walls confined by high-strength reinforcement were prepared,and three of them were designed on the basis of two parameters: average constraining stress and reinforcement characteristic value,while the last one as comparison.The experiment of low-cyclic reversed loading about four specimens was done.The states of the cracks development and the failure process of all specimens was observed,and their failure modes were determined.According to the test datas,these indicators of seismic performance were analyzed,such as hysteretic curves,skeleton curves,ductility and deformation,energy dissipation capacity as well as the stiffness degradation etc.The results showed that:with the dense high-strength spiral stirrups in shear walls,the ductility,deformation and energy dissipation capacity were improved,while the rate of degradation of stiffness and strength being reduced,and the specimens’abilityies of continuing to bear loading and resist deformation under seismic loads were increased.Based on the test results,using the fitting method,a restoring force model being applicable to these specimens was established,including four-linear skeleton curve model,loading and unloading rules,and laws of stiffness degradation.This model was demonstrated to have good agreement with the experimental results,and could provide reference for the elasto-plastic time-history analysis of concrete shear walls confined by high-strength reinforcement.