Development of analysis system to assess ultimate seismic behavior of steel piers accompanying fracture due to strain localization

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The major damages observed for thin-walled steel piers in the Great Kobe Earthquake are the fracture as well as the local bucklins of plate elements. Since the Kobe Earthquake, intensive cyclic loading tests on steel piers have been carried out to examine the ductility deterioration due the local buckling of plate elements. Furthermore, it is shown that the ultimate local buckling behavior of steel piers under cyclic loading can be accurately analyzed by the geometrically and materially nonlinear FEM analysis based on shell elements if some adequate cyclic plasticity model is used for the constitutive relation of steel. In contrast, the fracture observed in the Kobe Earthquake did not similarly occur in the cyclic loading tests and, hence, it is still a controversial issue how and why this fracture happened. The only fact obtained by the detailed observation on the fractured section of the damaged steel piers is that the brittle fracture initiated from a small ductile fracture. This im … More plies that the occurrence of the small ductile fracture is a necessary requirement for the occurrence of the brittle fracture. Therefore, the investigation into the ductile fracture of steel piers will make it possible to explain the cause of the fracture observed in the Kobe Earthquake.Herein, we present a numerical analysis method to predict the fracture of steel piers under cyclic loading and examine the applicability of this method by cyclic loading test on steel piers. In the analysis, the Gurson constitutive model is modified in order takes into account the cyclic behavior of steel and is implemented in the 3-dimentional solid element. The Gurson model is the most widely used plasticity model that can consider the nucleation and growth of micro voids closely related to the ductile fracture. In order to investigate the validity of the modified Gurson model, the initiation of ductile fracture is observed by conducting a cyclic loading test on thin-walled steel piers with circular cross section. From the comparison between the numerical analysis and the test results, it is shown that the locations of the ductile fracture in the steel piers can be qualitatively predicted by the modified Gurson model. However, regarding the deformation at the initiation of ductile cracks, some difference is observed between the analysis and the experiment. There still remains a difficult problem how to identify the initiation of the ductile cracks in experiment. This problem must be further examined in the future. Less