Correction of two-surface model for hysteretically loaded structural steels

It becomes important to understand elasto-plastic behaviors of steel structures or members under cyclic loading such as hard earthquakes which cause the stress level exceeding the elastic limit. One of the constitutive models to predict elasto-plastic behaviors of structural steels under uniaxial cyclic loading is Dafalias-Popov's two-surface model. But, this model can not give an accurate prediction of elasto-plastic behaviors for some structural steels under cyclic loading. In this paper, Dafalias-Popov's two-surface model is modified mainly in respect of the movement of bounding lines, the reduction of the elastic range due to increase of strain amplitude and shape parameter expressing the nonlinear stress-plastic strain relation. From analysis of experimental data, it is shown that the proposed model can predict the elasto-plastic behaviors under cyclic loading with better agreement.