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

本课题的主要目的是（1）研究钢筋在塑性屈曲区承受大轴向强迫变形的重复荷载作用下的力学行为，得到可用于有限元分析的钢筋滞回模型。（2）研究了在这种加载条件下钢筋的破坏准则。与（1）相关的是，基于有限变形理论，采用纤维模型对钢筋的力学性能进行了有限元分析。在此基础上，建立了一个实用的、精确的应力-应变关系的滞后模型。与（2）相关的是，在液压夹具疲劳试验机上对近百根D19变形钢筋进行了重复加载试验。受迫轴向变形范围从拉伸屈服区到压缩塑性屈曲区。将试件固定长度分别改变为18 d、12 d和6d（d为试件直径），强迫变形幅值改变为23种情况，统计分析了加载重复次数与固定长度、平均压应变和平均拉应变的关系。

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.