Finite element simulation of ultra low cycle fatigue cracking in steel structures

• Fracture in steel members subjected to large amplitude cyclic strains is simulated.
• The method is implemented in conventional nonlinear FEM software.
• The method is validated through analysis of a column-to-base plate connection.
• Simulations predict the locations and number of cycles for crack initiation.
• Crack propagation path and number of cycles to final fracture are predicted.

This paper proposes a new method of simulating ductile fracture in steel structures under large amplitude cyclic straining experienced in earthquakes. The method is developed based on an existing micromechanical model originally proposed for predicting crack initiation in ultra-low cycle fatigue, ULCF. It involves a step-by-step simulation of material degradation within the framework of conventional nonlinear FEM. The method is validated through simulating fracture in a structural detail (column-to-base plate connection) for which several cyclic tests has been previously conducted. It is found that the method can successfully predict the cracking site, its propagation path, the number of cycles corresponding to crack initiation, and also final fracture.