A Deformation History-Based Approach for Ultra-Low Cycle Fatigue Damage Evaluation of Steel Structures

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.