Cyclic response of plate steels under large inelastic strains

In structures subjected to extreme loading, plate steels are relied upon to plastically deform under large repeated strains. Nevertheless, limited data exists on the hysteretic stress–strain response and low-cycle fatigue life of these steels. In the study described in this paper, axial coupons were tested for five types of plate steel, including conventional and high performance A709 steel as well as specialty low yield point steels, to investigate the material response under repeated inelastic demands of constant amplitude between 1% and 7% strain. Parameters for analytical models were established for cyclic stress–strain and low-cycle fatigue life relationships. Based on this study, it was found that the low-cycle fatigue life of the different types of plate steels was similar and that the effect of increased strain rate was minimal. However, the maximum cyclic stress was found to exceed the yield strength by a factor of 2.0 for the conventional grade steel and up to 4.8 times for the low yield point steels, within just a few reversals in the considered strain ranges. The maximum cyclic stress behavior was not related to the yield strength as much as it was to the manufacturing specifications. This behavior should be considered when using these materials in the limit state design of structures for extreme events such as earthquakes.