Elastoplastic hysteretic behavior and constitutive models of in-service structural steel considering fatigue-induced pre-damages

Fatigue damages are commonly observed in the in-service steel components and progressive deterioration in their mechanical behavior is triggered with increasing service period. Hence the present work aims to investigate the degradation of the mechanical properties of the fatigue-damaged structural steel Q345qD and establish the practical constitutive models. Various fatigue tests before the elastoplastic cyclic loading were conducted to simulate the fatigue-induced pre-damages. The residual mechanical properties of the fatigue-damaged material were investigated and refined versions of the hysteretic constitutive models were proposed. Moreover, the effects of the deterioration in the material properties on the mechanical behavior of the steel components were studied. Experimental results indicate that a prior history of fatigue loading significantly affects the subsequent elastoplastic hysteretic behavior of the in-service material. As the accumulation of the prior fatigue damage, the yield and ultimate strengths of the steel material deteriorate. In particular, the yield plateau disappears when the pre-damage level exceeds 0.5. Both of the strength and ductility of the in-service steel components deteriorate remarkably. This implies that the fatigue damages accumulated in the service history should be included in the seismic design of structures.