Applications of the Extended Finite Element Method (XFEM) for the Analysis of Distortion-Induced Fatigue Cracking in Highway Bridge Girders

Abstract

Fatigue cracking due to distortion-induced stresses is common in web-gap regions of steel bridge girders built prior to the mid-1980s. Various repair techniques have been developed to mitigate this problem, and numerous finite element simulations have been conducted to study the performance of these techniques. The recent implementation of the Extended Finite Element Method (XFEM) within the finite element modeling software Abaqus v.6.10 has created an efficient means for modeling cracks in bridge girders. Simulations with distortion-induced fatigue cracks can subsequently be conducted to further validate the performance of retrofit techniques as well as gain qualitative information about the fatigue cracks themselves. There were several major goals of this thesis. The first goal was to conduct a parametric study to evaluate the performance of the Angles-with-Plate retrofit technique with several different XFEM cracks included in the finite element simulations. Several analysis techniques associated with XFEM cracks were utilized in this study, and their results were compared with experimental observations. These results were found to be sensitive to how the XFEM cracks were simulated along weld-web interfaces, and it was determined that future study is needed to validate the results. The second goal of this thesis was to determine if it was necessary to model fatigue cracks in finite element analyses, and, if it was, to determine the most accurate method of modeling them. Finite element simulations were compared with experimental results, and several methods of modeling cracks with XFEM were utilized. The final goal of this thesis was to utilize XFEM to quantify fatigue crack growth in experimental specimens. Experimental results, finite element simulations, and fracture mechanics principles were employed, and descriptive information about fatigue crack growth was determined.