Fatigue life prediction of HTRB630E steel bars based on modified coffin-manson model under pre-strain

High strain low cycle fatigue performance is one of the important indicators for evaluating seismic reinforcement. The earthquake is often accompanied by aftershocks. At this time, the steel bars in the structure are subjected to the low cyclic load under pre-strain. In this article, fatigue life prediction of a new type of HTRB630E (T63E) ultra-high-strength steel bars based on modified Coffin-Manson model under pre-strain is presented. Firstly, the constant amplitude strain low cycle fatigue test for T63E steel bars without and with pre-strain is carried out. The test results indicates that the application of pre-strain causes the fatigue life of T63E steel bars to decrease by 30%-50%, but different pre-strain has the same effect on the fatigue life under the same strain amplitude. Secondly, the Coffin-Manson model is used to simulate the test results using OpenSees software. Thirdly, the modified plastic strain formula is used to predict the fatigue life of T63E steel bars under pre-strain. The simulation results indicate that the modified formula can predict the fatigue life of the steel bar under prestrain more accurately, and the error is reduced from 50% to 10%. Finally, the main factor of the low-cycle fatigue performance of T63E steel bars under strain control is the maximum stress level in the process, which provides new methods and ideas for the later development of complex strain low cycle fatigue life prediction under different paths.