The Research On The Performance Of L-shaped Concrete Columns Confined By Stirrups Under Axial Repeated Loads

Special-shaped columns refer to under the condition of satisfying the structural strength and stiffness,using cross,T-shaped,L-shaped frame columns according to the room layout and the specific position of the columns.They are different from rectangular columns and circular columns,the column limbs are generally the same as the wall thickness,which solve the problem of column convex,expand the using space of the building,greatly improve the beauty of the building structure.Compared with the rectangular column and circular column,the seismic performance of special-shaped column structure is poor.In order to improve the strength and ductility of special-shaped column concrete,to avoid brittle failure when the earthquake happens,it is necessary to configure the appropriate stirrups in the special-shaped column,so that the core concrete is in the three-dimensional stress condition,to limit the core concrete lateral expansive deformation.At present,scholars have studied the theory of special-shaped concrete columns confined by stirrups under axial loads.And while in use,the special-shaped column structure will bear a variety of loads random or loading-unloading regularly repeated,the concrete must have a corresponding stress repeat.In this paper,the experimental study of L-shaped concrete columns with different stirrups under axial repeated loads is carried out,to analyze the strength and deformation capacity of L-shaped concrete columns confined by stirrups under axial repeated loads,which provides a reference for the nonlinear analysis and seismic performance analysis of L-shaped concrete columns,in order to analyze and design L-shaped column structures in a scientific and rational way.In this paper,axial repeated loads tests of 5 L-shaped columns confined by stirrups were carried out.The failure process and characteristics of L-shaped columns were presented.I analyzed the bearing capacity,strain development,deformation capacity and set up the formulas of ductility coefficient.The results showed that with the increasing of reinforcement characteristic value,the failure type was changed from oblique failure to longitudinal failure,the peak load and displacement of L-shaped columns increased,the descending segment of skeleton curves turned to be more flat,ductility became better,the calculated results of ductility coefficient were in good agreement with the experimental results.The restraint effect of stirrup on core concrete of L-shaped column was analyzed by using finite element software,the restraint mechanism was similar with axial load,and the expression between the compressive strength,peak strain of confined concrete and stirrup characteristic values,stirrup effective coefficient were established,the calculated results were in good agreement with the experimental results.And the calculation formula of axial compression bearing capacity of L-shaped columns was established.The calculated results were partial to security compared with the experimental results,it can be used to analyze the axial compression bearing capacity of L-shaped short columns confined by stirrups under axial repeated loads.I established the stress and strain envelope curve formula for confined concrete of L-shaped columns under axial repeated loads referring to the stress and strain mathematical model for confined concrete of L-shaped columns under axial loads,The calculated results are in good agreement with the experimental results.And analyzed the loading and unloading curve of confined concrete of L-shaped columns under axial repeated loads,the loading and unloading criteria was established,and the calculated results were in good agreement with the experimental results.It is shown that the loading and unloading curve equation proposed in this paper can well reflect the stress and strain curve of L-shaped confined concrete under axial repeated loads.