Large Scale Tests and Micromechanics-Based Models to Characterize Ultra Low Cycle Fatigue in Welded Structural Details

Fracture and fatigue-induced failure in welded structural details is an important limitstate in earthquake resistant design. Despite its significance, fundamental, physics-based models to simulate Ultra Low Cycle Fatigue (ULCF) in base and weld metals are not readily available, and many of the popular approaches predict ULCF in an empirical manner without considering the complex interactions of stress and strain histories responsible for it. While convenient, these empirical methods may not be reliably transferable to untested details or connections. In this paper, newly developed physicsbased models that aim to simulate ULCF at a continuum level (and apply them through finite element analyses) are introduced. Preliminary results from experiments on six column base plate specimens are presented. These tests, part of a NEESR project, seek to validate these physics-based models. From a practical standpoint, these experiments provide important insights into modes and hierarchies of failure of column base plate details, especially fracture originating in the welds and heat affected zone. The parameters considered include variations in cyclic loading histories and in weld details similar to configurations commonly used in engineering practice.