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

在神户大地震中观察到的薄壁钢桥墩的主要破坏是板件的断裂和局部屈曲。自神户地震以来，对钢桥墩进行了密集的循环加载试验，以研究板件局部屈曲引起的延性劣化。研究还表明，对于钢材的本构关系，只要采用适当的循环塑性模型，基于壳单元的几何和材料非线性有限元分析方法可以较准确地分析钢桥墩在循环荷载作用下的极限局部屈曲行为。相比之下，神户地震中观察到的断裂在循环加载试验中并没有类似的发生，因此，这种断裂是如何以及为什么发生的仍然是一个有争议的问题。通过对受损钢桥墩断口的详细观察，得到的唯一事实是，脆性断裂是从一个小的延性断裂开始的。这个IM…进一步指出，韧性小断裂的出现是脆性断裂发生的必要条件。因此，对钢桥墩延性断裂的研究将有助于解释神户地震中观察到的钢桥墩断裂的原因。本文提出了一种预测钢桥墩在循环荷载作用下断裂的数值分析方法，并通过钢桥墩的循环加载试验验证了该方法的适用性。在分析中，为了考虑钢的循环行为，对Gurson本构模型进行了修正，并在三维实体单元中实现。Gurson模型是目前应用最广泛的塑性模型，它可以考虑与韧性断裂密切相关的微孔洞的形核和长大。为了验证修正的Gurson模型的有效性，通过对圆形截面薄壁钢桥墩进行循环加载试验，观察了其延性断裂的萌生过程。数值分析结果与试验结果的对比表明，修正的Gurson模型可以定性地预测钢桥墩的延性断裂位置。然而，对于延性裂纹萌生时的变形，分析结果与实验结果有一定的差异。如何在实验中识别延性裂纹的萌生仍是一个难题。这个问题必须在未来进一步研究。较少

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