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

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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.