Improvement Of The Hysteretic Constitutive Model For Bridge Structural Steels And Its Application

The FEM analysis accuracy of elasto-plastic seismic response for steel bridge structures always depends on whether the material’s nonlinear hysteretic constitutive model is appropriate. It is currently not yet complete that the selection of steel constitutive model in existing design specification for steel bridges at home and abroad. This problem also has not yet been fully recognized in the research field for seismic performance of steel bridges. Because of the indeterminacy of analysis accuracy that subjected to complex loadings, the application of existing high-accuracy steel constitutive model in the seismic response analysis of complex steel bridges is still limited. Therefore, in this study, combined with the research about the elasto-plastic constitutive model of bridge structural steels in the National Natural Science Foundation of China "Seismic design of complex bridges considered required performance (No.51378460)", modified two-surface hysteretic constitutive model was improved to enable it applicable for complex strain histories such as earthquakes. Based on the improvement, the effect of hysteretic constitutive models on the seismic performance evaluation of steel arch bridges was discussed. The main contents and conclusions of this study include:1. From the two aspects of hysteretic behavior and low-cycle fatigue behavior, the effect of material constitutive models on the ultimate state prediction of steel bridge components was discussed. It shows significant effect of material constitutive models on both hysteretic behavior and low-cycle fatigue fracture prediction. Commonly used bilinear kinematic hardening model could not give accurate analysis results. Using high-accuracy material hysteretic constitutive models is crucial to ensure the veracity of steel bridges’ hysteretic response analysis results.2. Aimed at the hysteresis characteristics of steels subjected to complex strain histories with small strain vibrations, the two-surface model of steels was re-modified by improving the judgment of stress-strain paths. The improving method under uniaxial and multiaxail stress state was given. The accuracy and applicability of the improved method were verified on both material and structural level.3. Aimed at the degradation of tensile capacity under low-cycle fatigue loadings, further improvement of M2SM of steels was made baced on the low-cycle fatigue test results. The improved model can better consider the material’s degradation effect of tensile capacity before the failure stage, which increased the prediction accuracy of stress and hysteretic energy dissipation.4. The two-surface model parameters of the bridge structural steels in China was determined by cyclic loading tests. The hysteretic behavior of Q345 steel was compared with the steel of same grade abroad. The validity of the improved two-surface model proposed in this study was also further verified by the tests.5. Elasto-plastic seismic time-history response analysis was carried out for long-span deck-through and half-through steel arch bridges under strong ground motions. The results obtained by hysteretic constitutive models of improved two-surface model (I2SM) presented in this paper, existing modified two-surface model (M2SM) and bilinear kinematic hardening model (BKHM) were compared. The results show that, although the analysis precision of displacement and axial force responses from different hysteretic constitutive models differs little from each other, the stress-strain responses of the structure are apparently affected. In significantly damaged areas, BKHM gives smaller stress result and obviously different strain response compared with I2SM and M2SM, and tends to overestimate the effect of hysteretic energy dissipation. The difference between the stress-strain responses obtained by I2SM and M2SM cannot be neglected. Moreover, at some position with severe damage, BKHM may underestimate the size of seismic damaged areas. Different hysteretic constitutive models also have influences on structural damage evaluation results based on both deformation behavior and low-cycle fatigue.