Experimental Study On Mechanical Behavior Of Concrete Confined By Welded Fabric Bending Stirrup Cage Under Concentric Loading

Welded fabric products are now widely used in the field of architecture with advantages of the good quality, high work efficiency, energy conservation and environmental protection, etc. But its application forms are mainly used as the whole piece, however, the welded fabric into reinforcement cage is bend to replace stirrups in the concrete column has rarely been reported. According to conceptual analysis,with the variation of grid spacing, the longitudinal and transverse steel bars of reinforcement cage will perform the synergistic effect which can play an effective confinement to the core concrete and improve its mechanical properties. Therefore,the axial compression experiment research on the concrete column confined by the welded fabric bending reinforcement cage(WFBC) is proposed, which mainly include the following contents.Through comparison the test results of the twelve WFBC columns, the influence of parameters such as longitudinal bars of welded fabric, spacing, reinforcement ratio and configuration of stirrups on the mechanical properties of the core confined concrete are analyzed. Based on the test results, in order to consider the synergistic effect of welded steels on the mechanical properties of WFBC columns, the parameter of additional volume reinforcement rate is introduced. Upon verified, the results agree well with the experimental results.Based on the existing researches of concrete strength under multi-axial stress states, the Guo-Wang concrete five parameters failure criterion is used to establish the calculation formula of confined concrete peak stress. By comparison, the formula can not only be in good agreement with the test results, but also can be used to calculate the other literature, which can solve the poor applicability of the models established by the method of regression analysis.If the stirrup characteristic value is selected as the analysis variables will overestimate the actual constraint effect of core concrete confined by high-strength stirrups. In this paper, the confinement effect index is selected as the analysis variable,the calculation formulas of the peak and ductility strain of core confined concrete are established by regression analysis and verified by the experimental results. Moreover,the mean error of the calculated results of the formulas are smaller than other formulas which are proposed in the related articles.When the core confined concrete reach to the peak stress under the constraint of the high-strength stirrup, the stirrup may not reach to the yield strength. In this paper,the calculation formula of the stirrup stress at confined concrete peak stress is derived,according to the relational expression of the effective lateral restraint and stirrup strain.By comparing the experimental values, it show that the formula can not only be agree well with the test data, but also can solve the problems of the traditional loop iteration method by using analytical solution.Based on the uniaxial compression curve equations of concrete in the chinese code for design of concrete structures, the parameters which can control the ductility of the curve in descending part is introduced. The parameter calculation formula is given by using the method of the MATLAB program, and the calculated complete stress-strain curves are in good agreement with the experimental curves.Finally, the finite element software of the ANSYS is used to establish the nonlinear models of the WFBC columns by choosing proper material constitutive model, element type, etc. After verification, the effects on the mechanical properties of the WFBC columns by concrete strength, stirrup yield strength and section size are studied.