Evaluating Fatigue Cracks in Steel Bridges with Thermoelastic Stress Analysis

Fatigue cracks in bridges are becoming a larger problem for the aging civil infrastructure in the United States due to ever-increasing truck loads and deficient funding for civil infrastructure. A project sponsored by the Center for Transportation Studies is looking at a new approach to evaluate high-risk bridge details. This approach is based on thermoelastic stress analysis (TSA). Much like gases, solids heat up or cool down when they are compressed and expanded, respectively. For solids this is known as the Coulomb Effect. Although the temperature change is small, when stresses are large enough it can be measured with an infrared camera. The project’s goal is to use a relatively inexpensive infrared camera to monitor bridge details and evaluate stress concentrations to detect the presence of fatigue cracks or to predict the likelihood of the formation of a fatigue crack. With that knowledge, steps can be taken to mitigate the effect of the crack or prevent the crack from forming in the first place. This thesis is focused on the “proof of concept” for this project using multi-physics simulation and laboratory testing, as well as a comprehensive literature review of prior work, particularly work which relates to fatigue evaluation and bridges. Understanding the thermoelastic response to random bridge loading is the main technical obstacle in this work. This will be addressed by future work.