Experimentation Study Of Low-cycle Plastic Double Failure Mechanism Of Steel Bar Under Axial Load

The structure will bear various loads in its active time, such as strong winds and earthquakes which impact it greatest. In the action of earthquakes and strong winds, the components of structure may enter plastic state repeatedly, and destroyed in a low-cycle plastic form. How to describe the damage criterion of structural members in strong wind or earthquake is a concerned issue in the civil engineering field. Researchers of different countries set up various forms of plastic damage model from different perspectives, to deal with different forms of the structure. Among all of these models, the two-parameter criterion established by Y. J. Park and A. H. S. Ang in 1985 which is expressed by the linear combination of the largest deformation and the plastic energy dissipate capacity was used most widely by the follow-up researchers, since the modified models were mostly based on Park-Ang model. Because Park-Ang model reflects the failure mechanism that the structural damage is due to the deformations of large amplitude and energy dissipation in a certain extent, it is have been generally recognized. However, it is has been discovered that the Park-Ang model was not a perfect model through summarizing and analyzing, it also have some limitations.In order to do some further developments and perfections to the low-cycle plastic damage model, the relationship between the strain ductility coefficients and the energy dissipation capacity was proved to be an approximately exponential relationship base on the low-cycle plastic life equation first. Then with the introduction of an additional energy weighting factor which is concerned with the loading path, a new modified form of Park-Ang model was brought forward in this paper. The combination between the normalized strain ductility coefficients and the normalized plastic strain energy is nonlinear in the modified low-cycle plastic damage model, which considered the effect of the loading path in a certain extent.Finally, a number of steel specimens were tested to get the hysteretic curve under different plastic strain amplitude in order to calculate the plastic strain energy. Then the modified Park-Ang model was verified based on the relationship curve between the plastic strain amplitude and the energy dissipated capacity. It is proved that the modified model can accurately reflect the mechanism of low-cycle plastic damage which was combined by the largest deformation and the plastic strain energy, and has an important theoretical and practical value to the structure members under seismic and strong wind load.