BUCKLING BEHAVIOR AND MATERIAL CONSTITUTIVE MODEL OF COMPRESSIVE STEEL BAR WITH DIFFERENT STRENGTH

Slenderness ratio and yield strength are the main parameters affecting the buckling behavior of a compressed reinforcing steel bar; however, previous studies focus on the influence of slenderness ratio, there are few systematic research results related to the effect of yield strength on the strength degradation of buckled reinforcement. The monotonic compression tests considering buckling were thusly conducted on HRB400 and HRB500 reinforcement specimens with slenderness ratio of 4.000, 5.000, 6.000, 6.250, 8.000, 9.000, 9.375, 10.000, 12.000 and 15.000, respectively. The average stress-strain (\overline \sigma _\texts \text- \overline \varepsilon _\texts) curves and mid-span transverse displacements of buckled reinforcement specimens were measured. Combined with the corresponding test results of HRB600 reinforcement implemented by the author, the effects of yield strength, slenderness ratio and buckling direction on the compression strength degradation of buckled steel bars were analyzed. The difference between the \overline \sigma _\texts \text- \overline \varepsilon _\texts curves calculated by D-M model and the buckling behavior of steel bars with different yield strength and slenderness ratio were compared. By analyzing the causes of each kind of error, a modified D-M model was proposed, which can reasonably consider the effects of slenderness ratio and yield strength on buckling. The results show that there are differences in the buckling behavior of specimens with different strength due to the different mechanical properties of steel bar, such as \varepsilon _\textu, \varepsilon _\textsh, f_\texty, f_\textu, and etc. The compressive average stress of steel bar can be further improved after buckling if the slenderness ratio is small, while the buckled reinforcement with bigger slenderness ratio cannot reach the yield strength. The buckling directions of specimens with different slenderness ratio or yield strength are different. The calculation results of D-M model have obvious errors, compared with the experimental results of buckling behavior of specimens with three kinds of strength. The modified D-M model can be directly used for steel bar with different yield strength, and the effects of slenderness ratio and yield strength on the \overline \sigma _\texts \text- \overline \varepsilon _\texts curve of buckled steel bar can be reasonably rendered.