| Earthquake damage and experimental studies have shown that the damage of reinforced concrete columns is generally mainly concentrated in the end plastic hinge area.The buckling of longitudinal bars within the stirrup spacing is an important nonlinear force characteristic.In addition to degrading the strength of the reinforcement,the buckling also causes the column’s longitudinal reinforcement produces a concentration of plastic strain,which reduces the low-cycle fatigue life of the longitudinal reinforcement and affects the seismic performance of the frame column.In recent years,domestic scholars have completed a lot of seismic performance tests of high-strength reinforced concrete members,but researchers have not paid enough attention to the difference in the mechanical properties of steel bars with different yield strengths.In reinforced concrete structures,steel bars mainly bear tensile force,so they paid more attention to tensile strength,and the difference between compression performance and tensile performance is often ignored.Therefore,the buckling performance of domestic steel bars with different yield strength is studied,and a material constitutive model that can accurately predict the buckling performance of the column longitudinal reinforcement under monotonic compression is established,and the low cycle fatigue life can accurately calculate the damage degree of the buckling longitudinal reinforcement,and the model is very important for the reasonable evaluation of the seismic performance of reinforced concrete columns.In this paper,36 steel bar specimens with different yield strengths and length-diameter ratios were subjected to monotonic compression,unequal tension and compression,and equal tension and compression cyclic loading tests with consideration of buckling.During the test,the vertical displacement of the buckling section of each specimen and the lateral displacement of the weak axis and the strong axis at the midpoint were collected,and the average stress-average strain curve of the steel bar specimens and the transverse displacement of the midpoint of the buckling section were obtained.curve.Based on the cyclic loading test data,the inapplicability of the existing fatigue model to domestic steel bars was verified,and the traditional fatigue life model proposed by Coffin and Manson(hereinafter referred to as the C-M model)was revised,and it was obtained that it is suitable for domestic steel bars and can reasonably consider the longevity.A modified model of the influence of diameter ratio and yield strength on the fatigue life of buckled steel bars.Based on the results of the monotonic compression buckling test,the influence of the buckling performance of domestic steel bars was analyzed from the aspect ratio and yield strength,and then the original material model proposed by Dhakal and Maekawa suitable for buckling steel bars(hereinafter referred to as D-M The monotonous compression skeleton line of the model)was modified,and a modified D-M model suitable for domestic steel bars and able to consider the effect of buckling through the aspect ratio and yield strength was obtained.The research results show that the buckling performance of steel under monotonic compression is mainly affected by the aspect ratio and yield strength.The larger the aspect ratio of the steel,the earlier the buckling starts and the more significant the average stress degradation.The low-cycle fatigue performance of steel bars is mainly affected by the aspect ratio and yield strength.As the aspect ratio or yield strength of the steel bars increases,the more serious the fatigue damage,the worse the low-cycle fatigue performance.This paper has the following innovations.(1)Based on the monotonic compression buckling test results of HRB600,HRB500,and HRB400 steel bars,the influence of length-diameter ratio and yield strength on the monotonic compression buckling performance of domestic steel bars was compared and analyzed.(2)Based on the monotonic compression buckling test results of three kinds of yield strength of domestic steel bars,it is verified that the D-M material model directly used for domestic steel bars has obvious errors,and the model is modified according to the test results.The modified D-M model can describe the domestic steel bars more accurately,and the monotonous compression buckling performance of steel bars.(3)Based on the cyclic loading test data of three kinds of yield strength domestic steel bars,it was verified that the existing fatigue life model could not accurately judge the fatigue failure state of domestic steel bars,and the fatigue model was revised according to the test results.The modified fatigue life model proposed in this paper can reasonably consider the influence of length-diameter ratio and yield strength on the fatigue damage of buckled steel bars,and can more accurately judge the fatigue failure of buckled steel bars. |
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