Experimental Investigation On Axially Compressive Behavior Of Composite Spiral High-strength Concrete Columns Confined By High-strength Reinforcing Wires

High seismic intensity makes high performance vertical structural members become necessity of concrete structure.Using High strength stirrups to restrain high strength concrete can effectively reduce the section size of frame column and avoid the shear failure of columns under strong earthquake.Double-confinement stirrups using high strength steel with higher yield strength,which are composed of conventional rectangular stirrups and circular spiral stirrups,can improve the strength and axial compressive strain of core concrete.Particularly,the deformability of structural members is distinctly enhanced by the double confinement.This paper makes a research on axial compressive behavior of high-strength concrete columns confined doubly by high-strength reinforcing wires,and purposes calculation and design method of it,which can promote concrete structure constructing more reasonably in high seismic intensity zone.Based on previous experimental investigation of double-confinement concrete columns under eccentric loading and low cyclic reversed loading,a total of 11 concrete columns were tested under axial loading with different volumetric ratio of stirrups and strength of concrete stirrups.According to the results of experiments,the typical fracture model and compressive failure mode of constraint column are summarized and the study analyzed the peak bearing capacity and deformability of these columns under different conditions.By the relationship of the two types of wires between load and strain,it is found that “double-confinement” effect comes from two aspects: the core spiral stirrups and the surrounding rectangular stirrups.The former maintains lateral confinement at the core of concrete columns under high stress level;the latter,other parts of columns,simultaneously restaining lateral expansion of core concrete.It can effectively prevent delamination of concrete between wires and the break of high-strength wires before structural failure.Calculation formula for volumetric ratio of composite spiral stirrups is proposed to establish the foundation for quantitative analysis of lateral restraint forces of the double stirrups.The stress reduction coefficient of spiral stirrups is fitted to determine the value of real stress of high-strength stirrups when the short columns reach the peak bearing capacity.Combining with “double-confinement” mechanism of composite spiral stirrups,this study derived the formula for the bearing capacity of concrete columns with highstrength composite spiral stirrups under axial loading.The mechanics condition of the concrete column confined by high strength composite spiral stirrups under axial compression is analyzed.Through the method of Mann-Kendall,the abrupt change point of the column's state parameters was determined,so that the failure load of confined concrete column is obtained.It showed the sudden change in mechanics of each column by state schema graph.By comparing the failure load of different specimens,the effects of compressive strength of concrete,strength of stirrups and volumetric ratio of stirrups on confinement effect were investigated.Experimental data was extended by numerical function to draw a section nephogram,which can reflect the trend of section stress change in column visually.At last,through the simulation with FEM software ABAQUS,parameters analysis is performed,giving a further verification of the confinement effect.