Continuum_Based_Modeling - Physics-Based Continuum Models...

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Physics-Based Continuum Models by ABAQUS to Simulate Fracture and Ultra Low Cycle Fatigue in Steel Structures 1 Authors: Amit M Kanvinde, Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, kanvinde@ucdavis.edu Benjamin V Fell, Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, bvfell@ucdavis.edu Gregory G Deierlein, Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, ggd@stanford.edu A BSTRACT Recent advances in modeling fatigue and fracture in steel structures are outlined. Current approaches to simulate earthquake induced fracture and fatigue in steel structures rely on experimental and semi-empirical methods, or conventional fracture mechanics. While the semi-empirical methods cannot be generalized to a wide range of structural details, conventional fracture mechanics can be reliably used only to simulate brittle fractures similar to those observed during the Northridge earthquake, where large scale yielding is absent. The physics-based micro-models similar to the one described in this paper seek to simulate the fundamental processes of void growth and coalescence and granular cleavage responsible for fracture and ultra low cycle fatigue in structures. These models are relatively free from assumptions regarding behavior and can be used with accuracy to simulate fracture and fatigue in a general sense under a variety of conditions. Either void growth or cleavage can cause sudden crack propagation and strength deterioration at the global structural component scale. Thus, these micro-models, relying on fundamental physics are equally applicable to situations that are regarded as “brittle” or “ductile” at the structural or component level. Examples (including information from a recent Network for Earthquake Engineering Simulation and Research – NEESR project) to illustrate the use of one such model – the Cyclic Void Growth Model (CVGM) to simulate fracture through continuum finite element analyses are presented. Areas for refinement of the models and future work are outlined. I NTRODUCTION Earthquake-induced fracture is an important mode of failure in steel structures, and accurate assessment of this phenomenon is critical to developing fracture-resistant design provisions and for evaluating structural performance. Widespread damage to steel-framed buildings during the 1994 Northridge earthquake highlighted the importance of fracture limit states in structural engineering. The ensuing SAC Joint Venture investigation [9] 1 This paper has been adapted from several conference proceedings, notably Kanvinde and Deierlein (2007 ASCE Structures Congress, Long Beach, CA ) and Kanvinde (2007 Fourth International Conference on Urban Earthquake Engineering, Tokyo, Japan )
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confirmed the significant likelihood of fracture in steel moment frame connections and the sensitivity of response to local effects that are difficult to quantify with conventional structural engineering and fracture mechanics models. The SAC investigation and related
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Continuum_Based_Modeling - Physics-Based Continuum Models...

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