Simulating The Behavior of Steel Members Subject To Deterioration

The work described in this report is part of the Phase VI CUREE/Kajima collaborative research project on factors leading to the progressive collapse of structures during earthquakes. Various types of nonlinear behavior are considered. These relate to material inelasticity, low cycle fatigue, and local and global geometric nonlinearities. The effects of sudden onset, quasi-brittle fracture are not considered herein. The class of structures serving as the focus of this work is steel braced frames. For such structures, the braces, columns, beams, and connections are subjected to significant axial loads, as well as bending moments and shear. Under these complexloading conditions, a wide variety of behavior mechanisms and failure modes can be postulated for each type member and connection. Thus, numerical models intended to assess the initiation and propagation of failure need to account for multi-axial states of material nonlinearity, local and global buckling, and the exhaustion of the ability of the material to deform inelastically due to the consequences of ultra low cycle fatigue.

As a part of these studies, component failures are modeled, focusing on physical theory (fiber) and finite element models. Compared to phenomenological models, these types of models require more computational effort, but incorporate more realistic physical representations of members and materials, including the initiation and evolution of damage through complete failure. In addition to examining the inelastic behavior and failure of traditional steel beam-to-column connections, members and connections in concentrically braced frames are emphasized due to the prevalence of global and local buckling. Beams, columns, braces and connections, and subassemblies comprised of these components are analyzed.