Fatigue Assessment of Retrofitted Bridge Welds in the High Cycle Domain

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Recent reports have quantified the significant maintenance costs facing bridge owners, with numbers ranging from $2.2 billion for the Province of Ontario to $140 billion for the entire bridge stock in the US. In order to minimize these costs, new retrofitting methods are being developed for extending the service lives of bridges, including: the use of fatigue performance enhancing post-weld treatments, strengthening with fibre-reinforced polymer (FRP) materials, and deck replacement using lighter materials such as aluminum. In assessing the durability of these retrofitting methods, fatigue remains a central issue. For these methods to be safely implemented on a routine basis, there is a need for further research to: 1) verify their long term performance under in-service variable amplitude (VA) loading conditions, and 2) develop improved predictive models to gain insight regarding behaviour and facilitate optimal retrofit planning and design. To address this need, fundamental research on the fatigue behaviour of retrofitted bridge welds is planned, with projects focusing on each of the above-mentioned retrofitting methods. The research methods to be employed include: rapid fatigue testing (at frequencies up to 100 Hz) of small-scale retrofitted weld specimens, fatigue testing of larger retrofitted joint specimens, crack growth monitoring using advanced techniques (digital imaging, AC potential drop), and nonlinear (strain-based) fracture mechanics analysis. Simplified predictive models will also be developed, based on the results of this fundamental research. The planned research will be original in that it will answer important questions regarding the fatigue behaviour of retrofitted welds under VA loading conditions in the high cycle domain and employ relatively novel and sophisticated testing and analytical methods. The knowledge obtained through this research will lead to significant reductions in the life-cycle costs associated with the maintenance of metal bridges through service life extension, increased structural safety, and reduced retrofit costs. In addition, four graduate students (two Ph.D. and two Master's) will be supported and trained as a result of the requested funds.