Research On Seismic Performance Of Concrete Square Columns Constrained With Composite Spiral Stirrups

In the design of reinforced concrete structure,the stirrup can not only bear the shear force with the concrete,but also provide strong binding force to the core concrete,so that the bearing capacity and deformation capacity of the structure or component are improved.So the stirrups are especially important in the design of concrete structures.In the actual project,the bottom column of the frame structure is too large,resulting in excessive axial compression ratio,and the ductility is obviously reduced.It is prone to serious damage during the earthquake,which poses a great safety hazard to the entire building structure.The existing research shows that the spiral stirrups are obviously superior to the ordinary stirrups in improving the bearing capacity and deformation capacity of the column,which can effectively improve the seismic performance of the concrete columns.In actual engineering,most of them are square columns,which need to be equipped with circular composite spiral stirrups.At present,there are few studies on the seismic behavior of circular composite spiral stirrup columns at home and abroad,especially the lack of test support.Therefore,this paper has important theoretical research significance and engineering practical value for the study of seismic performance of composite spiral stirrup columns.In this paper,eight concrete square columns were subjected to low-cycle repeated loading tests.Two of them were comparative test pieces with common composite stirrups.Diamond composite stirrups and rectangular composite stirrups were respectively arranged,and the other six were equipped with composite spiral stirrups.Through the test,the failure process and failure mode of the circular composite spiral stirrup concrete square column under different axial compression ratios and hoop ratios are described.The test results show that the specimens have obvious bending failure and the failure mode is concrete shedding.There are many horizontal and oblique cracks.When the damage is serious,the concrete is crushed,the ordinary stirrups deform the outer drum,and the longitudinal reinforcement is bent.The hysteresis curve,skeleton curve,stiffness degradation,strength degradation and energy consumption of the column,ductility are analyzed.The results show that increasing the volumetric stirrup rate within a certain range can improve the bearing capacity and deformation capacity.The smaller the stirrup spacing,the stronger the lateral restraining force of the stirrup when the concrete expands and squeezes.However,the influence of the stirrup ratio is mainly reflected in the improvement of ductility,and has limited contribution to the improvement of bearing capacity;the increase of axial compression ratio can improve the bearing capacity and reduce the ductility,but the circular composite spiral stirrup can be used to test The part can maintain good ductility under the large axial pressure ratio.When the axial compression ratio exceeds the specification limit of 12%,the ductility coefficient can still reach 2.88;compared with the ordinary composite stirrup,the composite spiral stirrup can raise the bearing capacity,energy consumption and ductility,improve the initial stiffness and slow down the degradation of the strength and rigidity,which is very beneficial to the seismic resistance of the structure.At the same time,the ABAQUS analysis software was used to simulate the experiment,and the parameters were extended and analyzed.The effects of the longitudinal reinforcement ratio and the volumetric stirrup ratio on the seismic performance of the composite spiral stirrup square column were investigated.