Experiment On Seismic Performance Of Reinforced Concerte Columns Considering The Bucking Of Grade 600MPa Longitudinal Bars

At present,the research of HRB600 steel bars has just begun in China,and there is a lack of comprehensive and systematic research on the mechanical properties of components and structures.The seismic performance test of RC columns is especially scarce with HRB600 longitudinal reinforcement,which makes the relevant seismic performance design in specifications even blank.Under the action of earthquake,the buckling of the high-strength longitudinal bars in the plastic hinge region of RC columns leads to the decrease of the bearing capacity and even the failure of the structure.Therefore,this thesis studies the effect of longitudinal buckling on the damage mechanism and seismic performance of the column,and explores and analyzes the core area concrete expansion Correlation with the restraint of the protective layer concrete and the buckling of longitudinal bars.This thesis’ main research contents and conclusions are:(1)The low cycle loading test of 6 RC columns with 600 MPa longitudinal reinforcement was used to measure the buckling of the longitudinal reinforcement in the plastic hinge area and the lateral expansion deformation of the core concrete,which explore the law of mutual influence between the two.The test results show the two deformations are related.Before the buckling of the longitudinal reinforcement,the expansion and deformation of the core concrete effectively promote the buckling of the longitudinal reinforcement.After the longitudinal reinforcement is flexed,the longitudinal reinforcement is quickly detached from the contact state when the longitudinal reinforcement is compressed.When the longitudinal reinforcement is pulled back,the two contact again,The two always stay away when the longitudinal reinforcement is obvious buckling.(2)The author through recording the process of spalling and cracking of the cover concrete at the longitudinal reinforcement to analyze the correlation between them.The results show the trend of the buckling deformation curve increases after the peeling,it begins to buckle in 2 loading cycles,so the cover concrete plays a role in suppressing the buckling of the longitudinal reinforcement.(3)The author considers the effect of the different axial compression ratios and the ratios of length to diameter of longitudinal bars on the transverse expansion of the core concrete and the buckling of longitudinal bar.The result shows that the transverse expansion of the core concrete effectively promotes the buckling of longitudinal bar in the early stage of the test.The degree of buckling deformation decreases with the increase of the stirrup spacing;But in the later stage of the test,the buckling of the longitudinal bars is greater than the deformation of the core concrete,.The main cause of longitudinal buckling is compression of longitudinal ribs when the two remain detached.(4)The author consider the effect of the buckling of longitudinal bar and seismic performance with the different Longitudinal reinforcement aspect ratios and axial compression ratios.The results show the longitudinal bar flexion degree increases with the increase of the length-diameter ratio,and the displacement ductility of the specimen will gradually decrease.The buckling the longitudinal reinforcement decreases with increasing axial compression ratio,and the displacement ductility of the specimen becomes worse.(5)The results of this test are compared with the series of test results of the team’s400MPa and 500 MPa longitudinal RC columns.The auther not only analyze the buckling characteristics of the HRB600 longitudinal bars in the column,but also explore the influence of the longitudinal bars on the overall mechanical performance of the column.,The influence law of longitudinal bar buckling on column displacement ductility and bearing capacity degradation and interlayer displacement angle.