Low Cycle Fatigue Propagation in Steel Moment Frames Subjected to Seismic Loads

It has been shown in previous full-scale experiments on steel moment frame connections that fracture initiation is typically not associated with an observable loss of moment carrying capacity. Although low cycle fatigue models have been used to predict fracture initiation, most low cycle fatigue models do not capture fracture propagation. To assess the performance of steel seismic force resisting systems, and in particular steel moment resisting frames as subjected to large earthquakes, it is critical to understand fracture propagation. The damage plasticity model is a local approach to model material failures and has been used in limited studies found in the literature. Finite element models are created using the software LS-DYNA that incorporate the damage plasticity model to capture low cycle fatigue fracture initiation and propagation through element removal. Test data from full-scale moment connection tests conducted previously by the authors are used in this study to evaluate the modeling approach. Observations about the locations of fracture initiation, cycle in which fracture initiated and the evolution of fracture propagation is documented and compared to the experimental results.