Seismic Performance Of Reinforced Concrete Columns Confined With Two Layers Of Stirrups

In seismic design,reinforced concrete columns are detailed to behave in a ductile manner to absorb and dissipate the energy transmitted from the earthquake.The performance of concrete,including strength and ductility,can be improved by the confinement of stirrups.The effectiveness of confining steel primarily depends on the volume of concrete that can be confined and the distribution of confining pressure.The deformation capacity of reinforced concrete columns has been studied by many researchers to investigate the effect of the amount,arrangement and spacing of confining reinforcement.In order to make further investigation on the performance of reinforced concrete columns confined with stirrup.Six reinforcement concrete columns with two layers of stirrups were tested under cyclic lateral loading with a constant axial load.(1)According to the cyclic horizontal loading test,The failure process of concrete columns with two layers of stirrups is described.All specimens were destroyed at the bottom of the column,and all of them were flexural failure.Satisfied with the requirement of ductile destruction in seismic design.(2)Loading-displacement hysteretic curves,together with the skeleton curves,lateral load carrying capacity,ductility,strength and stiffness degradation and energy dissipation were analyzed and studied.All specimens showed good seismic performance,Lateral load carrying capacity of circular section column is lower than that of square section column,but showed a higher ductility.(3)The main influencing factors on the plastic hinge length of the reinforcement concrete columns were discussed and a new equation for the plastic hinge length of reinforcement concrete columns confined with two layers of stirrups was proposed on regression analysis and test results.It is concluded that the equivalent plastic hinge length mainly depending on the axial load,span-to-depth ratio and the properties of longitudinal and transverse reinforcement.(4)Based on analytical and experiment results,approaches were developed for predicting the yielding,maximum and failure loads,as well as corresponding deformations.And then according to three feature points,a simplified method was proposed to describe the backbone curve of restoring force model for reinforcement concrete columns confined with two layers of stirrups.And the simplified model is in good agreement with the experimental results...