Experimental and constitutive model study of structural steel under cyclic loading

In order to study extremely low cycle fatigue performance of structural steel and find a suitable constitutive relationship under cyclic loading, a total of fifty Q235B and Q345B steel extremely low cycle fatigue experiments have been carried out. The mechanical behavior of Q235B and Q345B structural steel including monotonic loading behavior, hysteresis loading behavior and hysteresis criterion are discussed. With fully recognized cyclic behavior of structural steel, a uniaxial and simplified constitutive relationship of structural steel under cyclic loading is proposed. Then the uniaxial steel constitutive relationship is developed as user-defined material based on the user subroutine interfaces UMAT provided by Finite Element Software ABAQUS. By introducing the fiber beam element method, the steel uniaxial constitutive model can be used for steel structural analysis. With comparison of Q235B and Q345B tests data under various loading systems, the model proposed in this paper is proved correct and can be applied in nonlinear time history analysis of steel frame. Both tests and analysis results show that the response of Q235B and Q345B steel under cyclic loading and monotonic loading are quite different, and the skeleton curve under cycle loading is much higher than monotonic loading after steel yielding. Both cyclic loops and amplitudes seriously affect the fracture ductility of steel material. While the structural steel bearing cyclic loading, the necking and the fracture behavior will occur ahead of time, it means that the cumulative damage makes the ductility of steel reduced. (C) 2011 Elsevier Ltd. All rights reserved.