Failure of deformed bars subjected to the repeat loading of large deformation in the plastic buckling region

本课题的目的是：(1)研究钢筋在塑性屈曲区受较大轴向强迫变形反复荷载作用下的力学行为，得到钢筋的滞回模型，并可用于有限元分析。(2)研究了这种荷载条件下杆的破坏准则。与(1)相关，基于有限变形理论，采用纤维模型进行有限元分析，研究其力学行为。在此基础上，建立了实用、准确的应力-应变关系迟滞模型。与(2)相关，采用液压握把疲劳试验机对100根左右的D19变形杆进行了重复加载试验。轴向强迫变形范围从拉伸屈服区到压缩塑性屈曲区。将杆样固定长度改变为18d、12d和6d （d为杆径），将强迫变形幅度改变为23例，统计研究加载重复次数与固定长度、平均压缩应变和平均拉伸应变之间的关系。

The aims of this project are (1) examining the mechanical behavior of the reinforcing bars subjected to the repeated loading of very large forced axial deformation in the plastic buckling region, and get the hysteresis model of the bars which can be used for the finite element analysis. And, (2) study the failure criteria of the bars under such loading conditions.Related to (1), mechanical behavior was studied by FEM analysis with fiber model and based on the finite deformation theory. Then, a practical and accurate hysteresis model of the stress-strain relationship was developed based on the analytical results above.Related to (2), repeated loading tests of about a hundred of D19 deformed bars were done using fatigue test machine with hydraulic pressure grips. The range of forced axial deformation was from tensile yield region to compressive plastic buckling region. Changing the fixed length of the bar specimen into 18d, 12d and 6d (d: diameter of the bar), and changing the amplitude of forced deformation into 23 cases, the relationship between the number of repetition of loading and fixed length, average compressive strain and average tensile strain was studied statistically.