Ultra-low cycle fatigue (ULCF) damage is one of the main failure modes of steel structures when subjected to intense earthquake action, such as near-field action. However, existing ULCF evaluation methods are based on the plastic strain history of structures, which requires fine numerical simulation and causes high calculation cost. In order to improve and simplify the ULCF evaluation process for steel structures, a new damage index based on the structure deformation history was proposed in this paper, with the application of structure life curve and Miner’s rule. Two types of steel components, notched round steel bar and steel pier, were employed as the research objectives to verify the accuracy of proposed damage index. The predicted ULCF life was compared with the results of tests and finite element simulations, which showed that the application of damage index was of acceptable accuracy. Compared with the traditional plastic strain history-based ULCF evaluation methods, the advantage of proposed damage index is that ULCF life of a given steel structure can be determined quickly according to the loading condition once its life curve is realized, thus eliminating the cumbersome numerical simulation process.

中文翻译：

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基于变形历史的钢结构超低周疲劳评估

超低周疲劳（ULCF）损坏是钢结构在遭受强烈地震作用（例如近场作用）时的主要破坏模式之一。然而，现有的ULCF评估方法是基于结构的塑性应变历史，因此需要精细的数值模拟并导致较高的计算成本。为了改善和简化钢结构的ULCF评估过程，结合结构寿命曲线和Miner法则，提出了一种基于结构变形历史的损伤指标。研究的目的是采用两种类型的钢构件（带缺口的圆钢和钢墩）来验证所提出的损伤指标的准确性。将预测的ULCF寿命与测试和有限元模拟的结果进行了比较，这表明损伤指数的应用具有可接受的准确性。与传统的基于塑性应变历史的ULCF评估方法相比，提出的损伤指数的优势在于，一旦实现了寿命曲线，就可以根据载荷条件快速确定给定钢结构的ULCF寿命，从而消除了繁琐的数值模拟处理。